Analytical electrochemistry: theory and instrumentation of dynamic

Dennis C. Johnson. Anal. Chem. , 1980, 52 (5), pp 131–138. DOI: 10.1021/ac50055a018. Publication Date: April 1980. ACS Legacy Archive. Cite this:Ana...
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Anal. Cbern. 1980, 52, 1 3 1 R - 1 3 8 R (395) Hagg, G.; Ersson, N. 0.; Rudenholm, G.; Sellberg, B. J . Appl. Clystallcgr. (Denmark) 1979, 12, 221-224. (396) Berreman, D. W. Phys. Rev. B (USA) 1979, 79, 560-567. (397) Corbett, R. K. Adv. X-ray Anal. (USA) 1979, 22, 201-205. (398) Moss, C.; Wentworth, D. F.; Barnea, 2. J . Appl. Crystallogr. (Denmark) 1979, 72,126. (399) Gruttner, A.; Yvon, K.; Deialoye, M. J , Appl. Crystallogr. (Denmark) 1978, 1 7 , 716. (400) Bichile. G. K.; Kulkarni. R. G. J . Appl. Clystallogr. (Denmark) 1977, 70, 441-443. (401) Freik, D. M.; Rarenko, I. M.; Solonichnyi, Ya. V.; Masiyak, N. T.; Tsidyio, K. V. R i b . Tekh. Eksp. (USSR) 1978, 27, 218-220. (402) Chojnacki, J.; Hodorowicz, S Krist. & Tech. (Germany) 1977, 72, 753-756. (403) Klym, N. M.; Frenchko, V. S.; Petrosian, S. P.; Mudryi, S. I . ; Gal’chak, V. P.; Artym, V. T. F i r . Elektron. ( L v o v ) (USSR) 1977, 7 4 , 87-90. (404) Lisoivan, V. I.; Dikovskaya, R . R.; Sedin, V. I. Prib. Tekh. Eksp. (USSR) 1978. 27, 211-213.

(407) Marquart, R. G.; Katsnelson, I.; Heller, S. R.; Milne, G. W. A. American Chemical Society Meeting, Honolulu. Hawaii, March 1979, Prog. Abstr. CHIF-63 American Chemical Society, Colum‘bus, Ohio. (408) Snyder, R. L.; Johnson, 0.C.; Kahara, E.; Smith, G. S.;Nichols, M. C. Report UCRL-52505 (1978), Energy Res. Abstr. 1978, 3 , Abstr. No. 57266; Chem. Abstr. 1979, 9 0 , 144592a. (409) Calvert, L. D.; Flippen-Anderson, J. L.; Hubbard, C. R.; Johnson, Q .C.; Lenhert, R. G. Nichols, M. C.; Parrish, W.; Smith, D. K.; Smith, G. S.; Snyder, R. L.; Young, R. A. I n “Accuracy in Powder Diffraction”; Block, S., Hubbard, C. R., Ed.; U.S. National Bureau of Standards: Washington, D.C.. 1980, in press. (410) Hubbard, C. R . In “Accuracy in Powder Diffraction”; Block, S., Hubbard, C. R . Ed.: U.S. National Bureau of Standards: Washington, D.C., 1980, in press. (41 1) Hubbard. C. R . Adv. X-ray Anal. (USA), in press. (412) Benedict, U.;Dufour, C. I n “Accuracy in Powder Diffraction”; Block, S., Hubbard. C. R., Ed.; U.S. National Bureau of Standards: Washington, D.C., 1980, in press. (413) Morris. M. C.; McMurdie, H. F.; Evans, E. H.; Paretzkin, B.; de Groot, J. H.: Weeks, B. S.; Newberry. R. J.; Hubbard, C. R . : Carrnel, S. J. Report NBS-MN-25-15, National Bureau of Standards, Washington, D.C., Oct. 1978, 199 pp. (414) Morris, M. C.; McMurdie, H. F.; Evans, E. H.; Paretzkin. B.; de Groot. J. H.: Hubbard, C. R.; Carmel, S. J. Report NBS-MN-25-16, National Bureau of Standards, Washington, D.C., Oct. 1979, in press.

POWDER PAlTERNS-GENERAL

(405) Powder Diffraction File: JCPDS-International Centre for Diffraction Data; 1601 Park Lane, Swarthmore, Pa. 19081. (406) Marquart, R. G.; Katsnelson, I.: Milne, G. W . A,; Heller. S . R.; Johnson. G. G. Jr.; Jenkins, R. J . Appl. Crystallogr. (Denmark), in press.

Analytical Electrochemistry: Theory and Instrumentation of Dynamic Techniques Dennis C. Johnson Department of Chemistry, Iowa State University, Ames, Iowa 500 7 7

First, I wish to applaud David K. Roe whose excellence in the preparation of this review during the past four biennial periods I have only now begun to fully appreciate. I will continue to summarize the literature according to the format used by Professor Roe with six sections. This review is based on literature cited by Chemical Abstracts, Volume 87, No. 23, t o Volume 91, No. 2 2 . Within each section, articles are grouped according to their major thrust. An attempt is made to draw attention to trends in the development of each topic and not t o present a critical review of the literature cited. T h e majority of publications during this review period continue t o pertain to derivations of the current-potentialtime responses of dynamic techniques under various potential or current waveforms and a large assortment of reaction mechanisms. One might speculate now that there is less difficulty in solving the equations of mass transport for a particular kinetic model than in identifying well-behaved electrochemical systems for the experimental verification of the derivations. This reviewer expects that future developments in this area will bring even greater emphasis on computerized procedures of pattern recognition, together with on-line control of the experiment, for identifying the reaction model which matches best the experimental behavior of an unknown reaction. Analytical sensitivity and resolution of voltammetric techniques appear to have been maximized to the satisfaction of most analysts and emphasis on quantitative chemical analysis has turned largely to the matter of efficiency through the use of rapidly scanned waveforms.

(6A)has covered electrode kinetics for the same time period. Dynamic methods of electrochemistry have been extensively applied in research on fuel cells and corrosion, and progress in these areas was reviewed by Kordesch (17A) and Uhlig (30A), respectively. Citations were found for five new advanced texts of which I was able to thoroughly examine only one. Dogonadze and Kuznetsov ( 7 A ) have reviewed developments in the theory of heterogeneous kinetics since 1973, and Brezina ( 4 A ) has treated catalytic processes. Advanced methods of surface electrochemistry were considered by Takamura and Kazawa (27A),and Kaplan (15A) has published on pulsed polarography. Just about all you ever wanted to know about solving boundary-value problems for transient techniques was described in an extensive text by Macdonald (19A). Excellent treatments are included for the general methods of potential-step, controlled-current, linear-sweep and ac voltammetry. New volumes have been added to series which appear on an irregular basis. Volume I1 of “Electroanalytical Chemistry”, edited by Bard, appeared with several chapters related to applications in medicine and pharmacology as well as a chapter on semiconductor electrodes ( 2 A ) . Volume 3 of “Techniques of Electrochemistry”, edited by Yeager and Salkind, treats numerous topics of industrial interest ( 3 4 A ) . After several years of inactivity, Volume 10 was added t o “Advances in Electrochemistry and Electrochemical Engineering” with Gerischer and Tobias as editors (12A). Volume 5 of “Oxides and Oxide Films”, edited by Vijh, contains a chapter on noble-metal oxides (32A). Volume 6 of “Electrochemistry”, edited by Thirsk, contains chapters on electron-transfer reactions ( 2 5 A ) and the use of ac impedance techniques ( I A ) . Venkatesh and Chin (31A) also reviewed ac techniques. Several papers from conferences were published including lectures from the Sixth International Conference on Nonaqueous Solutions by Barthel ( 3 A ) ,Evans and Nelsen (9A), and Miller (22A). Papers published from the 1976 ACS Symposium on the Teaching of Electrochemistry in San Francisco include three by Marcus (20A)on his theories of electron transfer a t electrodes and in solutions. Galus (IOA) reviewed the applications of chronocoulometry a t the 1978

BOOKS AND REVIEWS I t is appropriate that the first citation should be for the text by Selley (26A) which is perfectly suited for a first course in experimental electrochemistry. Electrochemical applications in medical research were reLiewed by Sawyer ( 2 4 A ) with numerous illustrations which will certainly attract the interest of undergraduate and graduate chemists alike. Several articles are also cited for their benefit to the new student of electrochemistry because they review several developments over the last quarter century. Laitinen (18A) has presented a wellorganized and concise report on electroanalysis, and Conway 0003-2700/80/0352-13lR$Ol .OO/O

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1980 American Chemical Society

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Conference on Coulometric Analysis in Warsaw. Additional reviews have been published pertaining to electrode kinetics and the theory of electron-transfer reactions. T h e importance of t h e work function of the electrode was discussed by Trasatti (29A). Various mechanisms for reactions a t electrodes partially or totally covered with films were considered by Dogonadze e t al. ( 8 A ) ,and electrocatalysis was reviewed by McNicol (21A) and Kita ( 1 6 A ) . Gerischer reviewed the electrochemistry of the excited state in his acceptance of the Palladium Medal in 1977. With the increasing concern over the economical aspects of energy conversion, activity is rapidly increasing in photoelectrochemical research. Excellent reviews of this topic were prepared by Nozik (23A) and Wrighton ( 3 3 A ) . T h e increased utility of computational aids for electroanalysis has not gone without notice. Griffiths (13A) has discussed Fourier transform techniques, and Tokuda (28A) has reviewed the use of digital simulation and other numerical methods for solving problems in electrode kinetics. Nomenclature in electrochemistry was the subject of an article by the Analytical Chemistry Division of IUPAC (14il). T h e elimination of IR effects was reviewed extensively by Britz ( S A ) .

MASS TRANSFER Excitement continues over flow-through electrolysis cells with small dead volume for use in flow-injection analysis and liquid chromatography. Further research by Blaedel, who is primarily responsible for the popularity of the tubular geometry, and his co-workers has led to the design of a detector with two tubular electrodes in series for stripping voltammetry with collection ( 4 6 5 ) . Chin and Tsang ( 1 h ' H ) have given a mathematical treatment of the mass transport at an impinging jet electrode and concluded that, under conditions of laminar flow, the electrode surface is uniformly accessible when the electrode radius is less than 'li the diameter of' the nozzle. Shorygin, Kazaryan, and Alirnova ( 4 7 5 ) have tested a microelectrode placed in the channel of a fluid stream. T h e equation of mass transport has not yet been solved rigorously for flow-through amperometric detectors for intermediate values of electrol>.tic efficiency. Weber and Purdy ( 5 7 5 ) are apparently pursuing this goal and, as a first step, have offered an approximate solution to diffusion in thin-layer cells based on a suggestion by Oldhain. Future theoretical treatments of mass transport in flow-through detectors will undoubtedly include considerations of partial kinetic control. It is not expected that a n y unique benefits will arise from this for kinetic studies, in comparison t o other hydrudynaniic techniques such as the rotated disc. because ot' the difficulty in precisely controlling laminar fluid velocities at the electrode over a large dynamic range. T h e steady-state currents for flow-through detectors of low efficiency are predicted to be related to flow rate by the empirical equation is, = k u c , where h is a constant. The value of CY is predicted to be / 3 for electrodes with a cylindrical geometry, e.g., tubular, and ' / %for planar electrodes. This reviewer wishes to dicourage the practice of characterizing the response of detectors by the application of linear least-squares ~ ~ the predicted value of (t analyses to plots of is, vs. L ' using (e.g., 3B, 6 B ) . Slight deviation of the experimental value of N from the predicted value. for whatever reason, will lead to a nonzero intercept for L'~ extrapolated tu zero. T h e observation of these nonzero intercepts has led to conclusions of the existence of an appreciable "end diffusion" even though both positive and negative values of the intercept hove been observed ( 6 B ) . The efficiency of flow-through detectors can approach 100% when the surface area of the electrode is large relative to the dead volume. Reticulated vitreous-carbon electrodes have been found useful for obtaining high efficiencies (713, . 5 0 H ) . Yamada, Okazaki, and Fujiliaga (.58B)have attached t h e name "coulopotentiometry" to the study of' the time-integral of the detector current as a function of' potential. Nam, Feher, Toth, and Pungor (40R) have described an iiidirect coulometric method for electroinactive analytes i n a stream with electrogeneration of a suitable titrant under a triangular current-waveform. Rotated disc (KDE) and ring-disc (IIIII>E:)electrodes continue to be the most popular hydrodynamic electrodes with combined applicability for sensitive quantitative chemical 132R

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analysis and kinetic studies. Several important developmerits have come in the application of hydrodynamically modulated voltammetry (HMV) a t the RDE. Deslouis, Epelboin, Gabrielli, and Tribollet ( 1 75) considered the impedance for the limiting diffusion current a t low modulation frequencies. The theory of HMV has been improved by Tokuda and Bruckenstein (51B)for higher frequencies where the Levich equation does not adequately predict the instantaneous limiting current. T h e theory was tested by Kanzaki and Rruckenstein ( J I B ) for irreversible reactions and the l i - - E curves were shown to be more sensitive to kinetic effects than the conventional i -E curves. Albery, Hillman, and Bruckenstein ( 2 5 )have given a theoretical treatment to the shift of the amplitude and phase of the modulated signals for potentiostatic and galvonostatic experiments at high modulation frequencies; the response was also predicted for a step change in rotation speed. The transient response of disc electrodes rotated at constant speed has been studied. Viswanathan, Farrell Epstein, and Cheh (565) have described a numerical solution for application of pulsed currents based on an earlier diffusion model (13B); and Viswanathan and Cheh (54B) applied the solution to the study of electrochemical kinetics. The authors claim that the technique is especially suited for the study of fast reactions because of the high current densities which can be obtained during the initial portion of the pulse period. Recently, Viswanathan and Cheh (55B) have reported on a general solution for mass transfer a t the KDE under application of periodic currents with pulse, ramp and saw-tooth waveforms. The theory of ac voltammetry a t the RDE has been described by Tokuda and Matsuda for irreversible electrvde reactions (52B) and for the case of coupled first-order chemical reactions (.%'El). Considerations of the application of ac techniques for adsorption phenomena were given by Glarum and hlarshall (24B). The number of papers has risen to 18 in the series o n ring-disc electrodes by Albery and co-workers. T h e latest contribution ( I B ) is a derivation of the equation for collection efficiency when an ac signal of high frequency is applied to the disc electrode. T h e power of ring-disc techniques for the study of complex electrochemical mechanisms was well i l lustrated by Appleby and Savy (4R). Equations were derived to permit evaluation of all rate constants involved i n the reduction of O2 based on experimental results for reduction of O2 and H&. Doerr and Grabner (19H)have applied digital simulation to a RDE surrounded by an optically transparent ring. Hotating mercury-drop (39H) and hemispherical (.Y?B) electrodes have been studied and their voltamrnetric response compared to that of the KDE. An acousto-electrochemicaleffect was noted by Boraay and Yeager ( I I B ) f o r a gold electrode when compressional sound waves a t a frequency of 540 kHz were generated in the vicinity of the electrode surface. The modulated current observed in the absence of electroactive analyte was interpreted as resulting from changes in the ionic distribution of the double layer in reponse to the acoustic effect. The theoretical development of normal pulse and differential pulse polarography appears to have reached a fairly high level of maturity and recent developments pertain essentially to specific applications and refinements. Dillard. O'Dea, and R. Osteryoung ( 1 8 H ) have applied digital simulation to an evaluation of the effects of irreversibility on analytical applications of DPP. Birke ( 5 R ) has presented the theory of' DPP including the effects of electrode expansion and sphericity. Grifone (29H) has discussed the principles of' DPP at slowly dropping electrodes. Dim, Huguet and C'aullet ( I b ' H ) have described differential pulse chronoamperometry i n which execution of the complete diff'erential pulse waveform occurs at a high scan rate near the end of the life-time of a single mercury drop. This technique should be useful for polarographic detection in flow-injection analysis and liquid chromatography for obtaining complete 5 E curves for each detection peak. Application of a double-step potentidl waveform for anodic stripping voltammetry was dewribed by Kankare and Haapakka ( 3 0 H ) with the advantage of more ef't'ectiveelimination of charging current than by conventional diflerential pulse stripping analysis. Saito and Himenu ( 4 5 B ) , and ,J. Osteryoung and Iiirowa-Bisner (42H) have applied the scan-reversal technique f o r pulse polarography suggested b y Oldham and Parry (418)f'or the investigation ( 1 1 irreversible

THEORY AND INSTRUMENTATION OF DYNAMIC TECHNIQUES

Dennis C. Johnson is Professor of Chemistry at Iowa State University, Ames, Iowa. He received a B.A. degree from Bethel College, St. Paul, Minn., in 1963 and the Ph.D. from the University of Minnesota in 1967. After brief appointments as a Temporary Assistant Professor and Postdoctoral Research Fellow at the University of Minnesota, he joined the faculty at Iowa State University in 1968. His research interests include anodic reactions at nobie-metal electrodes, normal and reversed pulse amperometry, underpotentialdeposition, eiectrocatalysis, and applications of flowthrough electrodes as detectors for flow-injection analysis and liquid chromatography.

processes. In this technique, to be called “reverse pulse polarography (RPP)”, the initial potential is chosen a t a value for the faradaic reaction of the analyte and the pulse amplitude is scanned in the direction for the faradaic reaction of the product of the initial reaction. We have successfully applied an amperometric technique based on R P P for chromatographic detection of metal cations without interference from dissolved oxygen (37B). Bond and Grabaric (8E)combined the techniques of normal pulse and ac polarography by use of a waveform which is a linear combination of the two component techniques; and Smith, Bond, and Grabaric (48B)have discussed the theory of the technique. Bond, Grabaric, Jones, and Rumble (9B) have given a theoretical treatment of the combined techniques of the differential-pulse and ac polarography. Advantages of these hybrid techniques include the fact that a wide range of electroanalytical responses a t different time domains can be obtained simultaneously. Several refinements have been made in the application of ac polarography. Bond, O‘Halloran, Ruzic, and Smith (IOB) have applied digital simulation to an evaluation of the maximum scan rate which can be applied. The characteristics of ac polarograms obtained for high scan rates on a single mercury drop have been discussed by Mooring and Kies (38B) who reported that the sweep rate does not affect the peak current for reversible systems except in the case of adsorption. The effect of electrode sphericity on wave shape for amplitude modulated ac polarography was studied by Zheleztosov (59B) and was found to be greater than for the conventional ac technique. Franceschetti and MacDonald (22B) have considered mass transport processes for the small-signal ac technique. Macdonald (35B, 36B) has given a theoretical treatment of the application of small-amplitude cyclic voltammetry for the study of corrosion. T h e origin of the hysteresis in i-E curves was analyzed in terms of the impedance of an equivalent electrical circuit and concluded to result from the nonresistive elements. Some refinements have been made to the application of conventional cyclic and linear sweep voltammetry. Ginzburg ( 2 3 3 ) has proposed a mathematical procedure for improving the estimate of the base line for the reverse sweep. Eggins and Smith (21E) have treated the diffusion-controlled current for linear sweep voltammetry by a least-squares analysis and compared their work with that of Ginzburg. A digital simulation of cyclic voltammetry a t spherical electrodes was described by Spell and Philp (49B) to evaluate the effect of drop size and switchin potential. Factors controllin the effective area of mercury-f r o p electrodes were discussed f ~ Cummings y and Elving ( 1 4 8 , 15E) including shielding by the capillary. Lovric ( 3 4 B ) has given a mathematical treatment of a three-electron polarographic wave for the limiting case of planar diffusion. Gotto, Ishii, and co-workers have continued to develop the new technique of semidifferential electroanalysis with application for stripping voltammetry a t hanging mercury-drop (27B)and mercury-film electrodes (26B). They conclude that the method is nearly comparable in sensitivity to differential pulse stripping voltammetry but is faster to perform. These workers have also investigated the use of a staircase potential ramp in place of a linear ramp for semidifferential and semiintegral electroanalysis and have suggested some advantages of the techniques over pulse polarography. T h e effect of decreasing the concentration of supporting electrolbte has been

considered by Gotto, Grennes, and Oldham ( 2 5 B ) . The distribution of potential and current density have been calculated by Pierini and Newman for rotating ring (43B) and disk electrodes in axisymmetric cells (44B). Doig and Flewitt (20B) have applied a numerical method to calculate the distribution of potential in galvanic corrosion. Evaluations of methods for handling overlapping peaks in square-wave polarography have been presented by Kuhrig (33B),and by Boudreau and Perone (12E). The later authors report that numerical deconvolution by multilinear leastsquares regression is effective for waves separated by as little as 30 mV.

CHARGE TRANSFER A thorough review of the developments in the fundamental theory of electron-transfer is believed to be beyond the scope of this journal. A review of the Marcus theory was mentioned earlier (20A)and three additional citations are noted as points of reference. Christov (2C) has presented a unified theory of charge transfer with consideration of metal oxidation, electrodeposition, redox, and proton-transfer reactions. Considerations of experimental values for the charge-transfer coefficient have been made by Marecek, Samec, and Weber (13C), as well as by Mueller (16C). The theory of the effects of adsorbed ions on reaction kinetics has matured in recent years and current work is concerned with applications of the theory to systematic studies of electrode reactions. Guidelli and Foresti (7C) have studied the reduction of nitromethane in aqueous solutions, as a function of pH, with variation of the potentials of the inner and outer Helmholtz layer made by addition of specifically and nonspecifically adsorbed anions. T h e rate determining step in the reduction mechanism was shown t o change as a function of pH. Papers VI1 and VI11 have appeared in the series coming from the laboratories of Guidelli and co-workers titled “Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes’.. Pezzatini and Moncelli (19C) described their results for reduction of CHBr,COO-, and Piccardi and Guidelli (20C)discussed a study of the Cu(II)-Cu reaction at mercury electrodes. Of particular interest in the later study was evidence for displacement of adsorbed water by specifically adsorbed ions. Simple, one-electron, outer-sphere reactions have been recommended by Anson and Parkinson ( I C ) for use as “kinetic probes” of the ionic structure of the interfacial region. Data obtained for the diffuse-layer potential based on measurements for oxidations of europium(I1) and vanadium(I1) a t mercury were concluded to be more reliable than predictions based on electrocapillary measurements, which are less sensitive to double-layer composition. The reduction of cobalt(I1) ammine has been used by Weaver ( 2 3 2 ) as a kinetic probe. Weaver (24C) has also presented an extensive discussion of intrinsic and thermodynamic factors involved in innersphere and outer-sphere electron-transfer mechanisms as part of a consideration of the role of bridging ligands in electrode reactions. Purity of the supporting electrolyte can be a critical issue when measuring rate constants. Johnson and Resnick ( 8 C ) demonstrated that the reversible reduction of iron(II1) a t platinum electrodes in acidic solutions of commercially available perchloric acid is probably the result of the presence of chloride as a trace impurity. T h e reduction wave is irreversible for solutions prepared from acid which has been redistilled in vacuum. Weber, Samec, and Marecek (25C) have presented results of a more complete study of the effect of anion impurities for the iron(II1)-iron(I1) reaction a t platinum and gold electrodes. Information regarding solvent reorganization in heterogeneous charge-transfer reactions was obtained by Conway and Currie ( 3 C ) through kinetic studies at pressures to 3000 bars. Results were described for cathodic evolution of hydrogen gas and the ferricyanide-ferrocyanide reaction. The prediction is made that the technique is useful for distinguishing between activation associated with long-range polarization and that associated with reorganization of the primary solvation shell or the inner coordination sphere of ions. Effects on electrode kinetics of the adsorption of neutral compounds, e.g., organic surfactants. are less well-understood than the effects of adsorbed ions. Timashev (22C) has summarized calculations of the potential of the reaction plane ANALYTICAL CHEMISTRY, VOL 52, NO 5, APRIL 1980

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resulting from local fields created by formation of donoracceptor complexes between the adsorbate and the electrode surface. T h e field is dependent on the effective amount of charge transferred to t h e metal which is, in turn, controlled by structure of the adsorbate and the polarity of the solvent a t the interface. An expression which simultaneously accounts for changes in double-layer structure, i.e., and blocking was presented by Kiryanov (1OC). Lipkowski and Galus ( 1 l C ) have made a thermodynamic reassessment of the present understanding of the inhibitory effects of organic adsorption, and have described the mechanisms for electrode reactions in which the activated complex is located on the inside or outside of the adsorbed film. Several important derivations and evaluations have appeared for instrumental techniques used in kinetic studies. A general theory of the galvanostatic double-pulse technique for very fast electrode reactions has been presented by Nagy (lac).This is a specific improvement of the theory for treating 7-t traces which are distorted at the end of the prepulse due to instrumental ringing. The technique, together with the new theor , is applicable for measurement of rate constants to 10 cm s- Y for time constants of the double-layer region less than 3 X lO-'s. T h e coulostatic method for fast reactions, which involves application of a small current pulse of very short duration, has been successfully applied by Kanno, Suzuki, and Sato (9C) for evaluation of the rates of metal corrosion. The technique is particularly appropriate because a negligible amount of metal is lost to corrosion and, furthermore, the technique is applicable to solutions of high resistance, e.g., relatively pure water. Recently, Reller and Kirowa-Eisner (21C ) have given analytical derivations for the application of the coulostatic method to multistep reactions where stoichiometric coefficients are not necessarily equal to unity. Nagy ( I 7C) has made a mathematical analysis of the effect of instrumental rise-time on galvanostatic single-pulse and double-pulse methods, and the coulostatic pulse method. The double-pulse method was concluded to be the only method of those considered to yield the correct exchange-current density even for slow pulse generators. Potentiostatic techniques are strongly influenced by the effects of charging current. Elkin, Lentsner, Abaturov, and Kuzmin (6C) have described a technique for measurement of the double-layer and kinetic parameters for application of a single potential step. Miaw and Perone (14C) have applied digital simulation to an analysis of the effects of charging current in potential-step and staircase voltammetry. They determined that serious distortion of the current signals can persist for up to 30 cell-time constants in the case of induced charging. T h e ring-disc electrode was applied by Molodov ( l 5 C ) to studv metal dissolution of the tvDe M + M2+ 2M'. The disc was constructed from the me'tal M and operated at zero current in a solution of M2+;the ring electrode detected loss of M2+ or production of M+. Alternating current methods are frequently applied for corrosion research and many reactions exhibit pseudo-inductance at very low frequencies. This behavior has been concluded to result from relaxation of the coverages of intermediate reaction products on the electrode surface. Macdonald (12C) has described a method of estimating impedance parameters under these circumstances. At the outset of this review, specific mention was made of the great utility which is apparent in the application of computerized techniques of pattern recognition for the investigation of complex reaction mechanisms. That statement was made on the basis of work typified by the publications of DePalma and Perone (5C) describing the technique as applied to potential-sweep voltammetry. Specifically, the procedure involves the determination of kinetic parameters by computerized comparison of the i-E curves with a reference file of theoretical polarograms generated for model mechanisms. Other examples of similar approaches are cited in the remaining sections.

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SURFACE EFFECTS Significant progress has come from efforts to quantitatively describe changes observed in reversible polarographic response (L-E)resulting from adsorption of reactants and products of the electrode reaction. Guidelli and Pezzatini (170) have described a n approximate solution to the corresponding 134R

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boundary-value problem for hanging and dropping mercury electrodes; and Guidelli and Pergola ( 1 6 0 ) extended the solution to adsorption described by Langmuir and Frumkin isotherms. Flanagan, Takahashi, and Anson (130) have extended earlier applications of digital simulation in their laboratory to the case of normal pulse polarography for instances of pre- and post-waves as well as depression of the limiting current resulting from adsorption. T h e treatment of adsorption of electroinactive species in ac polarography has been given by Sluyters-Rehbach, Sluyters, and co-workers (260, 330). More evidence for the applicability of the digital simulation technique for treating complex surface processes has come with additional publications on that topic by AngersteinKozlowska and Conway. In collaboration with Klinger (50), they have treated the case of nucleation and growth mechanisms for formation of two-dimensional surface films. T h e general features of the simulation technique have been described (210) for those wishing more detail. AngersteinKozlowska and Conway ( 4 0 ) have also described very useful procedures for evaluating kinetic parameters for surface processes based on potential-sweep methods. Application is described for electrochemical formation of adsorbed hydrogen and oxygen on platinum electrodes. Indeed, the technique of cyclic voltammetry, which has always been useful as a qualitative tool for investigating surface processes a t solid electrodes, can now provide data for quantitative description of those processes. Under-potential deposition (UPD) of metals on solid electrodes occurs because of highly energetic interaction of the deposited metal with the substrate. Bewick and Thomas ( 8 0 ) have presented data for UPD of thallium and lead on silver which supports the conclusion that the mechanism involves adsorption followed by a two-dimensional nucleation. The UPD of mercury a t gold was studied by Sherwood and Bruckenstein (280) using ring-disc techniques. Evidence is reported that mercury(1) is adsorbed simultaneously with UPD of mercury(0) and the average value of n for the formation of the monolayer in a solution of mercury(I1) is 1.6. The application of coulostatic techniques ( L , , ~ = ~ 0) for study of UPD was described by Untereker, Sherwood, and Bruckenstein ( 3 2 0 ) and experimental results were given for UPD of silver on gold and platinum, and mercury on gold. Metals deposited by UPD have been observed to electrocatalyze certain irreversible processes. This is of interest for energy conversion as well as for development of quantitative, Le., mass-transport limited, voltammetric analysis. Adzic and co-workers ( 1 0 , 20) have studied electrocatalysis of the anodic oxidation of simple organic molecules, including formic acid, on noble-metal electrodes. The electrocatalytic activity of sub-monolayer quantities of deposited metals is believed to result from interference in the mechanism for adsorption of the reaction products which normally foul the electrode surface. Electrocatalysis of the cathodic evolution of hydrogen on gold electrodes has been described by Furuya and Motoo (140).

The promise of great things in quantitative chemical analysis from use of surface-bound redox couples has come closer to fulfillment with improvements in theory and synthetic technique. A comparison of heterogeneous and homogeneous catalysis relevant to modified electrodes has been presented by Andrieux and Saveant (30). A theory of catalytic electrodes was developed by Brown and Anson ( 9 0 ) for application of the coulostatic technique for measurement of electron-transfer rates of bound redox couples. Laviron (220) has discussed application of linear scan and ac voltammetry for investigation of chemically modified surfaces. Noteworthy citations describing the benefit of improvements in synthetic techniques must include the work of Lenhard and Murray ( 2 3 0 ) on ferrocenes. There was increasing application of spectroscopic techniques for examination of the composition and structure of solid electrode surfaces. The matter of transfer of an electrode from the electrolyte solution to the high vacuum chamber of a spectrometer without exposure to the laboratory atmosphere was treated by Ansell, Dickinson, Povey, and Sherwood (60). Clavilier and Chauvineau ( 1 0 0 ) used Auger electron spectroscopy (AES) to measure contamination of platinum surfaces treated by argon glow discharge. Baker, Rand, and Woods ( 7 0 )applied AES in conjunction with cyclic voltammetry to

THEORY AND INSTRUMENTATION OF D Y N A M I C TECHNIQUES

examine the surface composition of platinum-rhodium alloys. X-ray emission spectroscopy was used by Michell, Rand, and Woods (250) to determine the oxygen content of a ruthenium electrode subjected to severe anodic conditions. T h e use of low energy electron diffraction (LEED), which has always been popular for study of solid catalysts in gas phase reactions, has been applied to electrode surfaces. T h e adsorption of hydrogen a t platinum was studied by Hubbard, Ishikawa, and Katekaru ( 1 9 0 )using LEED; and Felter and Hubbard (120) have combined LEED, AES, and cyclic voltammetry to study adsorption of iodine on platinum. T h e influence of surface films on electrode response has received significant attention. In a series of three papers, Gueshi, Tokuda, and Matsuda ( I 5 D , 3 1 0 ) have solved the boundary value problem for the limiting response of a partially blocked electrode for a variety of experiments including cyclic and ac voltammetry. T h e electrode surface was modeled as a hexagonal array of cylindrical spaces terminated a t the electrode surface by concentric active and inactive regions. Convective contribution to mass transport was not considered. Dogonadze and Kuznetsov ( I 1 0 ) have reviewed several possible mechanisms for electron transfer a t electrodes covered by an insulating or semiconducting film. Heusler and Yun (180) have presented experimental data for niobium and titanium electrodes covered by a film of oxide in support of a rate equation based on a model for a n-type semiconducting film. A model has been presented for membrane-covered oxygen electrodes (Clark type) by Jensen, Jacobsen, and Thomsen (200) which is useful for estimating the sensitivity of these electrodes. Malpas, Fredlein, and Bard ( 2 4 0 ) have described an application of the piezoelectric effect to detect adsorption and formation of films as a function of electrode potential.

HOMOGENEOUS REACTIONS T h e facility with which some electrochemists are able to deal with the boundary-value problems corresponding to coupled electrochemical-chemical reactions is truly astounding and it parallels the complexity of new model reactions that are currently of interest. One of the consequences of this progress is an increasing tangle of the associated nomenclature. In an attempt to improve the tools of communication, Mairanovskii (13E) has suggested a system of notation which appears adequate for even the most complex schemes. Examples were also given for 1 2 different reaction mechanisms. T h e case of preceding coupled chemical reactions ( c e ) has received some attention. A step-wise increase of concentration in controlled-potential coulometry was described by Uchiyama, Muto, and Nozaki (21E) for investigation of relatively slow preceding homogeneous redox reactions. The technique was illustrated for the oxidation of the iron(I1)-EDTA complex by H N 0 2 and KBrO?. Galvez, Serna, Molina, and Marin (9E) have rigorously derived an equation for the polarographic i-E curves when the electrochemical process is reversible, and they have discussed the validity of steady-state approximations which were made. T h e case of three parallel charge-transfer reactions coupled by two preceding chemical reactions was described by Nishihara and Matsuda (18E) for the DME assuming linear diffusion. This mechanism was proposed to explain the polarographic reduction of nickel(I1)-glycine complexes for which three waves are observed. The coulostatic study a t a mercury electrode of intermediate products formed by pulse X-ray radiolysis was described by Barrigelletti et al. ( 6 E ) . Mechanisms with following irreversible coupled chemical reactions (ec) are very interesting, particularly when the chemical reactions occur on the same time-scale as the electron-transfer step. Contamin, Levart, and Schuhmann (8E) have described the use of ac techniques with a thin-layer cell for the study of fast homogeneous reactions with rate constants up to 2 X lo4 s-'. Aoyagui has teamed with Matsuda and Mizota (14E, 16E, 17E) to produce three publications describing a coulostatic method based on the application of reversed double-pulses for the study of very fast following reactions. T h e method consists of the application of shortlived current pulses of opposite polarity separated by a variable time period. T h e first pulse generates the unstable compound and the second pulse causes the unreacted product to be converted back t o its original form. The authors have

provided the theory for interpretation of the potential relaxation curves (E-t) and claim the method to be useful for measuring rate constants in the range 103-10fis I . Catalytic mechanisms, that is ec with regeneration of the reactant by homogeneous redox or chemical reactions, continue as the most popular for electroanalytical kineticists. This popularity is probably the result of the facts that many examples of this mechanism are known, the mechanism makes possible the quantitative voltammetric determination of many electroinactive substances, and the electrochemical studies are convenient for probing many homogeneous reaction mechanisms. Andrieux, Dumas-Bouchiat, and Saveant ( 5 E ) have published a very thorough three-part discussion of homogeneous redox catalysis with the purpose of giving quantitative consideration of those factors which govern catalysis. They have also shown that the difficulty of obtaining kinetic and mechanistic information for ec mechanisms with a fast electron transfer and a very fast, irreversible homogeneous reaction can be overcome by an indirect approach which utilizes the homogeneous redox catalysis of the electrochemical reaction t o be considered. Laviron (12E)has discussed regeneration mechanisms for potential-sweep voltammetry in thin-layer cells. Included were considerations of disproportionation as well as catalytic mechanisms. T h e influence of coupled homogeneous redox mechanisms in dc and ac polarography was presented by Matusinovic and Smith (15E) for the homogeneous reduction of cobalt(II1)-pentammine complexes by europium(I1). This reaction was concluded to occur by the Yamaoka mechanism in which an irreversible reductive wave is enhanced by addition of a second, more easily reduced substance. Galvez, Serna, and Fuenta (IOE) have extended their series on pulse polarography with a contribution to the theory of catalytic currents for that technique. Homogeneous chemical catalysis, as opposed to redox catalysis, involves an electrophilic-nucleophilic reaction between the substrate and the product of the electrode reaction. Saveant and Bink (19E) have treated this situation for the case of competing side-reactions which consume the catalyst. The theory was presented for the techniques of polarography, rotating disc electrodes, and controlled potential coulometry. Many electrochemical organic reactions occur by e r e mechanisms. When the second electron-transfer reaction occurs more easily than the first, disproportionation can occur. Amatore and Saveant have added to their series on ece mechanisms for the case of disproportionation studied by linear sweep voltammetry (2E)and potential-step chronoamperometry (3E). In the latter case. the effectiveness of single-step techniques for discriminating between the limiting reaction mechanisms is discussed. Perhaps the least familiar of coupled reaction mechanisms is the case of electrochemically induced reactions in which acid-base or electrophile-nucleophile reactions become faster following addition (or removal) of an electron to the chemical system. T h e electron is then removed (or added) from the system after reaction. Examples include ligand substitution in chromium complexes and cis-trans isomerization of functional olefins. Amatore, Saveant, and Thiebault ( 4 E ) have considered the competing kinetic mechanisms of ece and disproportionation reactions which can lower the efficiency of induced reactions. The use of digital computers to assist in the characterization of coupled mechanisms is becoming more attractive as the complexity increases for the reactions of interest. These methods include both simulation to assist in the visualization of kinetic effects, simulation t o generate working curves for evaluation of kinetic parameters, and routines for matching experimental results to an assortment of possible mechanisms. Speiser and Rieker (20E) have performed simulation with a collocation technique for several reactions including ec mechanisms. Amatore, Nadjo, and Saveant ( I E ) have described their use of finite-difference analysis and convolution of the faradaic signal for the study of fast ec mechanisms by large amplitude techniques, e.g., cyclic voltammetry. T h e technique amounts to the fitting of experimental data with the formal kinetics of the assumed mechanism. Cheng and McCreery ( 7 E ) applied simplex optimization procedures for curve fitting in the determination of both the reversible E I l 2 and the rate constant of the homogeneous reaction for potential-step chronoamperometry. Hanafey, Scott, Ridgway, ANALYTICAL CHEMISTRY, VOL. 52, NO. 5, APRIL 1980

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and Reilley ( I I E )applied an explicit finite difference program to generate response ratios for 2 2 reaction mechanisms in chronoamperometric and chronocoulometric analysis. The authors also demonstrated the ability of double-step methods t o differentiate between possible mechanisms.

INSTRUMENTATION Publication of the journal Chemical Instrumentation, which was discontinued with Volume 8 in 1977, was revived in 1979 under the title Chemical, Biomedical a n d Enuironmental Instrumentation. Detailed descriptions of complete digital systems are rare and references to digital hardware pertain mainly to descriptions of inexpensive gadgetry for dedicated functions. Yeakel, Burrows, and Hughes (31F)have described a digital signal generator for differential pulse voltammetry under rapid scan. Carlsson, Lindstrom, and Pulkkis (SF) have constructed a square-root-of-timemarker for chronocoulometry. Sawatari, Imanishi, Umezawa, and Fujiwara (21F) have designed an analog-to-digital converter with high precision and immunity to noise. Engstrom and Blaedel ( 1 4 F ) have interfaced a programmable desk-top computer to a rot,ated disc system for automatic pulsed-rotation voltammetry. Edmonds (13F)and Danielson, Brown, Appellof, and Kowalski ( I O F ) have also described an automated electroanalytical system using a small computer for experimental control and data processing. Garreau, Saveant, and Tessier (16F) described a computational approach utilizing a shifting-amplification method for the study of electrode reactions by a high-frequency ac technique. T h e most significant progress in electroanalytical instrumentation is being made in the area of digital software. The review by Griffiths on the applications of Fourier transformation in electrochemistry has already been cited (13A). DeLevie, Sarangapani, and Czekaj (1IF) have applied Fourier transformation for numerical differentiation and d a t a smoothing. Applications of filter algorithms were described by O'Haver (I9F) and by Seelig and Blount (23F). Ichise, Yamagishi, and Kojima (18F) have used a Hadamard transform for pattern recognition in qualitative analysis. Tryk and Park (27F) have described an algorithm for computing decay rates for first-order coupled reactions; and Yamada et al. (30F) have presented a description of programs for information retrieval and file management in electrochemical kinetic studies. A description of a theory of errors and the treatment of i-t data for an on-line system applied to controlled-potential electrolysis was given by Shia and Meites (24F). A description of software for a computerized Kalousek polarograph was given, along with a brief review of the theory, by Bos ( 2 F ) . Several citations are given to indicate the techniques benefiting most from computerization. On-line techniques have been beneficial for facilitating ac measurements (5F, 15F, 2 2 0 b u t the most popular applications have been for pulse and differential-pulse polarographic techniques (3F, 4F, 6F, 12F, 25F, 28F). Tanaka and Tamada (26F) have given several examples of the applications of real-time analysis to electrochemical measurements and simulation. Analog software has apparently been exploited to the fullest, judging from the small number of publications in this area. Three note-worthy exceptions include descriptions of a lowcost, triangular-wave generator (29F); a circuit for powerof-time chronopotentiometry (9F);and the use of a multiplier circuit for simultaneous measurement of the in-phase and phase-angle components in ac polarography ( I F ) . Small but useful aids included a thin-layer cell for routine analysis ( 7 F ) , a cell for use under vacuum-line conditions (17F),and a high-precision speed controller for use with rotating electrodes (2OF). LITERATURE CITED BOOKS AND REVIEWS

(1A) Armstrong, R. D.; Mell, M. F.; Metcalfe, A. A. "Specialist Periodical Report Electrochemistry", Volume 6; Thirsk, H. R., Ed.; The Chemical Society: London, 1978; Chapter 3. (2A) Bard, A. J., Ed. "Electroanalytical Chemistry", Volume 11: Marcel Dekker: New York, 1979. (3A) Barthel, J. Pure Appl. Chem. 1979, 5 7 . 2093-2124. (4A) Brezina, M.; et al. "Catalytic Processes in Electrochemistry"; Academia: Prague, 1978. C . A . 1979, 9 0 , 129472. (5A) Britz, D. J . Electroanal. Chem. Interfacial Electrochem. 1978, 88, 309-353. (6A) Conway, B. E. J . Electrochem. SOC. 1977, 124. 41OC-421C.

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(7A) Dogonadze, R. R.; Kuznetsov, A. M. "Kinetics of Heterogeneous Chemical Reactions in Solutions", VINITI: Moscow, 1978. Reviewed by Ulstrup, J. J . Elecfroanal. Chem. Interfacial Electrochem. 1979, 103, 299-300. (8A) Dogonadze, R . R.; Kuznetsov, A. M.; Ulstrup, J. Electrochim. Acta 1977, 22, 967-975. (9A) Evans, D. H.; Nelsen, S . F. "Characterization of Solutes in Non-aqueous Solvents", Mamantov, G., Ed.; Plenum: New York, 1978; pp 131-154. (10A) Galus, 2. "Coulometric Analysis, Conference 1978". Pungor, E., Ed.; Akademia Kiado: Budapest, 1979. C . A . 1979, 9 1 , 165410a. (11A) Gerischer, H. J . Electrochem. SOC. 1978, 125, 218C-226C. (12A) Gerischer, H.; Tobias, C. W., Eds. "Advances in Electrochemistry and Electrochemical Engineering", Volume 10: Wiley: New York, 1977. (13A) Griffiths, P. R. "Transform Technipues in Chemistry", Griffiths, P. R., Ed.; Plenum: New York, 1978; pp 355-378. (14A) IUPAC Analytical Chemistry Division Pure Appl. Chem. 1979, 51. 1159-1 174. (15A) Kaplan. 8.Ya. "Pulsed Polarography": Khimiya: Moscow, 1978. C . A . 1979, 9 0 , 45971s. (16A) Kita, H. KagakuKcgyo1977, 28, 1167-1171. C . A . 1978, 88, 1123144. (17A) Kordesch, K . V. J . Electrochem. SOC.1978, 725, 77C-91C. (18A) Laitinen, H. A. J , Electrochem. SOC.1978, 125, 25OC-254C. (19A) Macdonald, D. D. "Transient Techniques in Electrochemistry"; Plenum: New York, 1977. Reviewed by Parsons, R. J . Electroanal. Chem. Interfacial Electrochem. 1979, 9 5 , 250. (20A) Marcus, R . A. "Special Topics in Electrochemistry"; Rock, P. A,, Ed.; Elsevier: Amsterdam, 1977; pp 180-209. Reviewed by Appleby, A . J. J . Electroanal. Chem. Interfacial Electrochem. 1978, 9 1 , 147. (21A) McNicol. 8. D. "Specialist Periodical Report: Catalysis", Volume 2, Dowden, D. A.; Kemball, C., Eds.; The Chemical Society: London, 1978, Chapter 10. (22A) Miller, L. L. Pure Appl. Chem. 1979, 51, 2125-2129. (23A) Nozik, A. J. Ann. Rev. Phys. Chem. 1978, 2 9 , 189-222. (24A) Sawyer, P. N. J . Electrochem. SOC. 1979, 725, 419C-436C. (25A) Schmidt, P. P. "Specialist Periodical Report: Electrochemistry", Volume 6, Thirsk, H. R., Ed.: The Chemical Society: London, 1978; Chapter 4. (26A) Selley, N. J. "Experimental Approach to Electrochemistry"; Edward Arnold: London, 1977. Reviewed by Parsons, R. J . Electroanal. Chem. Interfacial Electrochem. 1978, 8 7 , 443. (27A) Takamura, T., Kozawa, A,, Eds. "Surface Electrochemistry-Advanced Methods and Concepts"; Japan Scientific Societies Press: Tokyo, 1978. Reviewed by Parsons, R. J , Electroanal. Chem. Interfacial Electrochem. 1979, 9 9 , 400-401. (28A) Tokuda, K.: Matsuda, H. Denki Kagaku Oyobi Kogyo Butsuri Kagoku 1978. 46, 374-382. C . A . 1978, 8 9 , 1 8 7 8 1 6 ~ . (29A) Trasatti, S. "Advances in Electrochemistry and Elec!rochemical Engineering", Volume 10; Gerischer, H., Tobias, C. W.. Eds.; Wiiey: New York, 1977; pp 213-321. (30A) Uhlig, H. H. J . Electrochem. SOC.1978, 125, 58C-61C. (31A) Venkatesh, S.:Chin, D.-T. I s r . J . Chem. 1979, 78, 56-64 (32A) Vijh, A. K., Ed. "Oxides and Oxide Films", Volume 5; Marcel Dekker: New York, 1977. (33A) Wrighton, M. S. Acc. Chem. Res. 1979, 72, 303-310. (34A) Yeager, E.:Salkind, A. J., Eds. "Techniques of Electrochemistry", Volume 3: Wiley: New York, 1978. MASS TRANSFER

(1B) Albery, W. J.; Compton, R. G.; Hillman, A. R. J , Chem. Soc. faraday Trans. 1 1978. 74. 1007-1019. (2B) Albery, W. J.; Hillman, A. R.; Bruckenstein, S. J . Electroanal. Chem. Interfacial Electrochem. 1979, 100, 687-709. (38) Aoki, K.; Matsuda, H. J . Electroanal. Chem. Interfacial Electrochem. 1978, 9 4 , 157-163. (48) Appleby, A. J.; Savy, M. J . Electroanal. Chem. Inferfacial Electrochem. 1978, 9 2 , 15-30. (58) Birke. R. L. Anal. Chem. 1978, 5 0 , 1489-1496. (66) Blaedei, W. J.; Iverson, D. G. Anal. Chem. 1977, 49, 1563-1566. (78) Blaedel, W . J.; Wang, J. Anal. Chem. 1979, 57, 799-802. (86) Bond, A. M.; Grabaric. B. S. J . Electroanal. Chem. Interfacial Electrochem. 1978, 87, 251-260. (9B) Bond, A. M.; Grabaric, B. S.;Jones, R. D.; Rumble, N. W. J . Electroanal. Chem. Inferfacial Electrochem. 1979, 100, 625-640. (10B) Bond, A. M.; O'Halloran, R . J.: Ruzic, I.; Smith, D. E. J . Electroanal. Chem. Interfacial Electrochem. 1978, 9 0 , 381-388. ( 1 l B ) Borsay, F.; Yeager, E. Trans. SOC.Adv. Electrochem. Sci. Techno/. 1977, 12, 179-185. C . A . 1979, 9 0 , 1 7 7 1 0 4 ~ . (128) Boudreau, P. A.; Perone, S. P. Anal. Chem. 1979, 5 7 , 811-817. (138) Chin, D.-T.; Tsang, C.-H. J . Electrochem. SOC.1978, 725, 1461-1470. (148) Cummings, T. E.; Elving, P. J. Anal. Chem. 1978, 50, 480-488. (158) Cummings, T. E.; Elving, P. J. Anal. Chem. 1978. 5 0 , 1980-1988. (168) Dian. G.: Huguet, J.; Caullet. C. J , Electroanal. Chem. Interfacial Electrochem. 1978, 88, 277-284. (178) Deslouis, C.; Epelboin, I.; Gabrielli, C.; Tribollet, B. J . Ekctroanal. Chem. Interfacial Electrochem. 1977, 82, 251-269. (186) Dillard, J. W.; O'Dea. J. J.; Osteryoung, R. A. Anal. Chem. 1979, 5 7 , 115-1 19. (198) Doerr, R.; Grabner, E. W. Ber. Bunsenges. Phys. Chem. 1978, 8 2 , 164- 168. (208) Doig, P.: Flewitt. P. E. J. J . Electrochem. SOC.1979, 726. 2057-2063. (218) Eggins, B. R.; Smith, N. H. Anal. Chem. 1979, 5 1 , 2282-2283. (228) Franceschetti, D. R.; MacDonald, J. R. J . Electroanal. Chem. Interfacial Electrochem. 1979, 107, 307-316. (238) Ginzburg, G. Anal. Chem. 1978, 5 0 , 376-377. (248) Ghrum, S. H.; Marshall, J. H. J. Electrochem. SOC.1979, 126, 424-430. (258) Goto, M.; Grennes. M.; Oldham, K. 8. J . Electrochem. SOC.1979, 126, 50-54. (26B) Goto, M.; Kazuhiko, I.; Ishii, D. Anal. Chem. 1979, 5 7 , 110-1 15

THEORY A N D INSTRUMENTATION OF D Y N A M I C TECHNIQUES (278) Goto, M.; Ikenoya. K.; Kajihara. M ; Ishii, D. Anal. Chim. Acta 1978, 101. 131-138 (2881 Goto. M.; Ishii, D. J . Elecfroanal. Chem. Interfacial flectrochem. 1979, 102. 49-58. (298) Grifone. L. Cion. Chim. 1977. 54, 13-17. C . A . 1978. 89. 990151 (308) Kankare. J J.; Haapakka, K. E Anal. Chim. Acta 1979, 1 1 7 , 79-87. (318) Kanzaki. Y., Bruckenstetn. S. J . Electrochem. SOC 1979, 126, 437-441. (328) Kim. J. T.; Jorne. J. J. J . Electrochem. SOC. 1979, 726. 1937-1938. (338) Kuhrig, 8. 2 . Chem. 1978. 18. 415-417. C . A . 1979, 90. 94363d. (348) LLovric. M.J . Electroanal. Chem. Interfacial Electrochem. 1979, 702, 143- 153. 358) Macdonald. D. D. J . flectrochem. SOC. 1978. 125, 1443-1449. 368) Macdonald, D. D. J . Electrochem. SOC.1979, 725, 1977-1981. 378) Maitoza. P.; Johnson, D. C. Submitted to Anal. Chem. 388) Mooring, C. I.; Kies, H. L. Anal. Chim. Acta 1977, 94, 135-147. 398) Mortko. H. J.; Cover, R . E. Anal. Chem 1979, 5 1 . 1144-1149 408) Nagy, G.; Feher. Z s . ; Toth, K.; Pungor, E Anal. Chim Acta 1978. 100, 181-191. (418) Oldharn. K. 6.; Parry, E. P. Ana;. Chem. 1970, 42. 229-233 (428) Osteryoung, J.; Kirowa-Etsner, E . Anal. Chem. 1980, 5 2 , 62-66. (438) Pierini. P.; Newman. J. J . Electrochem. Soc. 1979, 125, 79-84. (448) Pierini, P.; Newman, J. J . Electrochem. Soc. 1979, 126, 1348-1352. (458) Saito, A,; Himeno, S. J . Electroanal. Chem. Interfacial Electrochem. 1979, 707, 257-262. (468) Schieffer, G. W.; Blaedel, W J. Anal. Chem. 1978, 5 0 , 99-102. (478) Shorygin, A. P.; Kazatyan. E. V ; Alimova. R Z . Elektrokhim. 1977, 73, 1572-1575. (488) Smith, D. E.; Bond, A. M.; Grabaric, 8 S. J . Electronanal. Chem. Interfacial Electrochem. 1979. 95. 237-240. (498) Spell, J E.; Philp, R . H., Jr Anal. Chem. 1979. 5 1 , 2287-2288. (508) Strohl. A. N.; Curran, D. J Anal. Chem. 1979, 51. 1045-1049 (516) Tokuda, K.; Bruckenstein. S. J . Electrochem. Soc. 1979, 126. 431-436. (528) Tokuda. K.; Matsuda. H. J . flectroanal. Chem. Interfacial Electrochem. 1978, 90 149-163 (538) Tokuda, K , Matsuda, H J flectroanal Chem Interfacial Electrochem 1979 95 147-157 (548) Viswanathan; K.: Cheh. H. Y. J . Electrochem. SOC. 1979, 125, 1616-161 8. (556) Viswanathan. K.; Cheh. H. Y . J . Electrochem. Soc. 1979. 126. 3 - -~- + .4- n. .i (566) Viswanathan, K.; Farrell Epstein. M. A,; Cheh. H. Y. J . Electrochem. Soc. 1978. 125. 1772-1776. (578) Weber,'S. G,'; Purdy, W. C Anal. Chim Acta 1978, 99. 77-88. (588) Yamada, T.; Okazaki, S.; Fujinaga, T. Bull. Inst. Chem. Res.. Kyoto Univ. 1978, 56, 151-169. C . A . 1978. 8 9 , 208436s. (598) Zheleztsov. A. V. Zh. Anal. Khim. 1978. 3 3 , 2089-2095. CHARGE TRANSFER

(1C) Anson, F. C.; Parkinson, B. A. J . Electroanal. Chem. Interfacial Elecfrochem. 1977, 8 5 , 317-328 (2C) Christov, S. G. J . Electroanal. Chem. Interfacial Electrochem. 1979, 100, 513-532. (3C) Conway, B. E.; Currie. J. C. J , Electrochem. Soc. 1978, 125, 252-257. 257-264. (4C) Darnaskin, B.; Kuznetsova. L.; Palm, U.; Vaartnou. M.; Salve, M. J . Electroanal. Chem. Interfacial Electrochem. 1979, 700, 365-377. (5C) DePalma. R . A.; Perone, S. P. Anal. Chem. 1979, 51, 825-828, 829-832. (6C) Elkin, V. V.; Lentsner. B. 1.: Abaturov, M. A.; Kuzmin, V. G. J . Electroanal. Chem. Interfacial Electrochem. 1979, 96, 149-157. (7C) Guidelli, R.; Foresti, M. L. J . flectroanal. Chem. Interfacial Electrochem. 1978, 88, 65-77. (8C) Johnson, D. C.; Resnick, E. W. Anal. Chem. 1977, 49, 1918-1924. (9C) Kanno, K.-I.; Suzuki, M.; Sato, Y. J . Electrochem. Soc. 1978. 125, 1389- 1393. (1OC) Kiryanov, V. A. Elektrokhim. 1979, 15, 1401-1405. (1 1C) Lipkowski, J.; Galus, 2 . J . Electroanal. Chem. Interfacial Electrochem. 1979, 98, 91-104. (12C) Macdonald, D. D. J . Electrochem. Soc. 1978, 725, 2062-2064. (13C) Marecek, V.; Sarnec, Z.;Weber, J. J . Electroanal. Chem. Interfacial flectrochem. 1978, 94, 169-185. (14C) Miaw, L.-H. L.; Perone, S. P. Anal. Chem. 1979, 5 1 , 1645-1650. (15C) Molodov, A. I.; Elektrokhim. 1977, 73, 1625-1630. (16C) Mueller, L. 2. Phys. Chem. (Leipzig) 1979, 260, 995-998. (17C) Nagy, Z . J . Electrochem. Soc. 1979, 725, 1809-1811. (18C) Nagy, Z . J . Electrochem. Soc. 1979, 126, 1148-1155. (19C) Pezzatini, G.; Moncelli. M. R . J . Electroanal. Chem. Interfacial Electrochem. 1978, 9 0 , 165-171. (20C) Piccardi, G.; Guidelli, R. J . flectroanal. Chem. Interfacial Electrochem. 1978, 90, 173-183. (21C) Reller, H.: Kirowa-Eisner, E. J . Nectroanal. Chem. Interfacial Elecfrochem. 1979, 103, 335-346. (22C) Timashev. S. F. Elektrokhim. 1979, 75, 333-338. (23C) Weaver, M. J. J . Electroanal. Chem. Interfacial Electrochem. 1978, 93, 231-246. (24C) Weaver, M. J. Inorg. Chem. 1979, 78,402-408. (25C) Weber, J.; Samec, Z.;Marecek, V. J . Electroanal. Chem. Interfacial Electrochem. 1978, 89, 271-288. SURFACE EFFECTS

(1D) Adzic, R . R.; Spasojevic. M. D.; Despic. A. R. J , Elechoanal. Chem. Interfacial Electrochem. 1978. 9 2 . 31-43. (2D) Adzic, R. R.; Tripkovic, A. V. J . Nectroanal. Chem. Interfacialflectrochem. 1979, 99, 43-53.

(3D) Andrieux, C. P.: Saveant. J. M. J . Electroanal. Chem. InterfacialElectrochem. 1978. 9 3 , 163-168. (4D) Angerstein-Kozlowska. H.; Conway. 8 . E. J flectroanal. Chem. Interfacial Electrochem. 1979, 9 5 , 1-28. (5D) Angerstein-Kozlowska. H.; Conway. 8 . E.; Klinger. J. J . Electroanal. Chem. Interfacial Electrochem. 1978. 8 7 , 301-320, 321-337. (6D) Ansell, R . O., Dickinson, T.: Povey, A. F.: Sherwood. P. M. A. J , Electroanal. Chem. Interfacial Electrochem. 1979, 9 8 , 69-77, 79-89. (7D) Baker, B G.. Rand. D. A. J.; Woods, R. J . Nectroanal Chem. Interfacial Electrochem. 1979, 97, 189-198. (8D) Bewick. A.; Thomas, 8 . J . flectroanal. Chem. Interfacial Electrochem. 1977. 8 5 . 329-337 (9D) Brown, A P Anson F C J Electroanal Chem InterfaclalElecfrochem 1978, 92. 133-145 (10D) Clavilier, J , Chauvineau. J P J Electroanal. Chem InterfacialElectrochem. 1979, 100, 461-472. (11D) Dogonadze, R. R ; Kuznetsov, A. M. Electrochim. Acta 1977, 22, 967-975. (12D) Felter, T. E.; Hubbard, A. T. J . Electroanal. Chem. Interfacial Electrochem. 1979, 100, 473-491. (13D) Flanagan, J. 8 . ; Takahashi. K.; Anson, F. C. J . flectroanal. Chem. Interfacial Electrochem. 1977, 8 5 , 257-266. (14D) Furuya. N.: Motoo, S. J . Electroanal. Chem. Interfacial Electrochem. 1978, 88, 151-160. (15D) Gueshi. T.; Tokuda, K.: Matsuda, H. J . flectroanal. Chem. Interfacial Electrochem. 1978, 89, 247-60; ibid., 1979, 101, 129-138. (16D) Guidelli, R ; Pergola. F. J . flecfroanal. Chem. Interfacial Electrochem. 1977, 8 4 , 255-270. (17D) Guidelli. R.; Pezzatini. G. J . flecfroanal. Chem. Interfacial Electrochem. 1977, 84, 211-234. (18D) Heusler, K. E.; Yun, K. S. Hectrochim. Acta 1977, 22, 977-986. (19D) Hubbard. A.; Ishikawa. R. M.; Katekaru, J. J . Electroanal. Chem. Interfacial Electrochem. 1978. 86. 271-288. (20D) Jensen, 0. J.; Jacobsen, T.; Thornsen. K. J . Electroanal. Chem. Interfacial Electrochem. 1978, 8 7 , 203-21 1 (21D) Klinger, J ; Conway, B. E.: Angerstein-Kozlowska, H. Comput. Chem. 1978, 2 . 117-129. (22D) Laviron, E. J , flectroanal. Chem. Interfacial Electrochem. 1979, 100, 263-270; ibid., 1979, 101, 19-28. (23D) Lenhard, J. R.; Murray, R. W. J . A m . Chem. Soc. 1978. 100, 7870-7875. (24D) Malpas, R . E.; Fredlein, R. A.; Bard, A J. J . Electroanal. Chem. Interfacial Electrochem. 1979, 98, 171-180. (25D) Michell, D ; Rand, D. A. J.; Woods, R . J . flectroanal. Chem. Interfacial Elecfrochem. 1978, 89, 11-27. (26D) Mooring, C. I.; Sluyters-Rehbach, M.; Sluyters, J. H. J . Electroanal. Chem. Interfacial Electrochem. 1978, 8 7 , 1-16. (27D) Ross, P. N., Jr. J Electrochem. SOC.1979, 726, 67-77. (280) Sherwood, W. G.; Bruckenstein. S. J . Electrochem. Soc. 1978, 725, 1098-1102. (29D) Sherwood, W. G.; Untereker, D. F., Bruckenstein, S. J . Electrochem. Soc. 1978, 725, 384-389. (30D) Smith. D. F.; Willman. K.; Kuo, K.: Murray, R. W. J . Electroanal. Chem. Interfacial Electrochem. 1979, 95, 217-227. (31D) Tokuda, K.; Gueshi, T.; Matsuda, H J . Electroanal. Chem. Interfacial Electrochem. 1979. 102, 41-48. (32D) Untereker, D. F.; Sherwood. W. G.. Bruckenstein, S. J . Electrochem. S O C . 1978, 125, 380-384. (33D) Wijnhorst, C. A.: Sluyters-Rehbach, M.; Sluyters, J. H. J . Elecfroanal. Chem. Interfacial Electrochem. 1978. 8 7 , 17-29. HOMOGENEOUS REACTIONS

(1E) Amatore. C.; Nadjo, L.; Saveant, J. M. J . Elecfroanal. Chem. Interfacial Electrochem. 1978, 90, 321-331. (2E) Amatore. C.; Saveant, J. M. J . Electroanal. Chem. Interfacial Electrochem. 1977, 85,27-46. (3E) Amatore, C.; Saveant. J. M. J . Nectroanal. Chem. Interfacial Electrochem. 1979. 702. 21-40. (4E) Amatore. C.: Saveant, J. M.; Thiebault, A J . Electroanal. Chem. Inferfacial Electrochem. 1979, 103, 303-320. (5E) Andrieux. C P.; Dumas-Bouchiat, J. M.; Saveant, J. M. J . flectroanal. Chem. Interfacial Electrochem. 1978, 8 7 , 39-53; ibid.. 1978, 87, 55-65; ;bid.. 1978, 88, 43-48. (6E) Barrigelletti, F.; Busi, F.; Ciano, M.; Comcialini, V.; Tubertini, 0.; Barker. G. C.; J . Hectroanal. Chem. Interfacialflecfrochem. 1979, 97, 127-133. (7E) Cheng, H.-Y.; McCreery. R. L. Anal. Chem. 1978, 5 0 , 645-648. Levart, E.; Schuhmann, D. J . flectroanal. Chem. Interfacial (8E) Contamin, 0.; Electrochem. 1978. 88, 49-56. (9E) Galvez, J.; Serna. A.; Molina, A.; Marin, D. J . Electroanal. Chem. Interfacial Elecfrochem. 1979, 102, 277-288. (10E) Galvez, J.; Serna, A.; Fuenta, T. J . Electroanal. Chem. Interfacial Electrochem. 1979, 96, 1-6. (11E) Hanafey, M. K.; Scott, R. L.; Ridgway, T. H.; Reilley. C. N. Anal. Chem. 1978. 5 0 , 116-137. (12E) Laviron, E. J . Electroanal. Chem. Interfacial Electrochem. 1978, 87, 31-37. (13E) Mairanovskii, V. G. J. Electroanal. Chem. Interfacbl Electrochem. 1979, 97, 103-105. (14E) Matsuda, H.: Aoyagui, A. J . Electroanal. Chem. Interfacial €lecb.ochem. 1978, 87, 155-163. I15E) Matusinovic. T.; Smith. D. J. Elecfroanal. Chem. Interfacial Electrochem. 1979, 98, 133-139. (16E) Mizota, H.; Aoyagui. S. J , Electroanal. Chem. Interfacial Electrochem. 1978 ., 8 7 , 165-172 ~. (17E) Mizota, H.; Aoyagui, S.; Matsuda, H. J . Electroanal. Chem. Znterfacial Electrochem. 1978. 87, 173-179. ~

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Anal. Chem. 1980, 52. 138R-151 R (18E) Nishihara, C.; Matsuda, H. J . Electroanal. Chem. Interfacial Electrochem. 1977, 8 5 , 17-26. (19E) Saveant, J. M.; Bink, S. K . J . Electroanal. Chem. Interfacial Electrochem. 1978, 9 7 , 35-45. (20E) Speiser, B.; Rieker, A. J . Electroanal. Chem. Interfacial Electrochem. 1979, 702, 1-20. (21E) Uchiyama, S.; Muto, G.; Nozaki, .K. J . Electroanal. Chem. Interfacial Electrochem. 1978, 97, 301-308.

(14F) Engstrom, R. C.; Biaedel, W. J. Chem., Biomed.. Environ. Instrum. 1979, 9 , 61-69. (15F) Fleming, A. N.; Harrison, J. A. J. Electroanal. Chem. 1978, 87, 339-345. (16F) Garreau. D.; Saveant, J. M.; Tessier, D.J . Electroanal. Chem. Interfacial Electrochem. 1979, 703, 321-333. (17F) Holloway, J. D. L.; Senfileber, F. C.; Geiger, W. E., Jr. Anal. Chem. 1978, 5 0 , 1010-1013. (18F) Ichise, M.: Yamagishi, H.: Kojima, T. J . Electroanal. Chem. Interfacial Electrochem. 1978, 94, 187-199. (19F) O’Haver, T. C. Anal. Chem. 1978, 5 0 , 676-679. (20F) Paul, R . L. Electrochim. Acta 1978, 2 3 , 991-994. (21F) Sawatari. K.; Imanishi, Y.; Umezawa. Y.; Fujiwara, S. Bunseki Kagaku 1978, 2 7 , 180-183. C . A . 1978, 8 9 , 99008f. (22F) Schwall, R. J.; Bond, A. M.; Smkh, D.E. J . Electroanal. Chem. Interfacial Electrochem. 1977, 8 5 , 217-229. (23F) Seelig, P. F.; Blount, H. N.; Anal. Chem. 1979, 51, 327-337. (24F) Shia, G. A.; Meites, L. J . Electroanal. Chem. Interfacial Electrochem. 1978, 8 7 , 369-380. (25F) Sierra Alcazer, H. 8.: Fleming, A. N.; Harrison, J. A. Surf. Techno/. 1977,

INSTRUMENTATION

( I F ) Blutstein. H.; Bond, A. M.; Norris, A. J . Electroanal. Chem. Interfacial Electrochem. 1978, 8 9 , 75-81. (2F) BOS, M. Anal. Chim. Acta 1978, 703, 367-378. (3F) Bond, A . M.; Grabaric, B. S. Anal. Chem. 1979, 51, 126-128. (4F) Bond, A. M.; Grabaric, B. S. Anal. Chem. 1979, 51, 337-341. (5F) Bond, A. M.; Schwall, R. J.: Smith, D. E. J . Electroanal. Chem. Interfacial Electrochem. 1977, 8 5 , 231-247. (6F) Brown, S. D.; Kowalski, B. R. Anal. Chim. Acta 1979, 707, 13-27. (7F) Caja, J.; Czerwinski, A.; Mark, H. B., Jr. Anal. Chem. 1979, 57, 1328-1329. (8F) Carlsson, C.; Lindstrom, M.; Pulkkis, G. Chem., Biomed., Environ. Instrum. 1979, 9 ,21 1-218. (9F) Chow, L. H.; Ewing, G. W. Anal. Chem. 1979, 57, 322-327. (1OF) Danielson, J. D. S.; Brown, S. D.; Appellof, C. J.; Kowalski, B. R. Chem., Biomed., Environ. Instrum. 1979, 9 , 29-47. (11F) DeLevie, R.; Sarangapani, S.; Czekaj, P. Anal. Chem. 1978, 50, 110-1 15. (12F) Drake, K . F.; VanDuyne, R. P.; Bond, A. M. J . Electroanal. Chem. Interfacial Electrochem. 1978, 8 9 , 231-246. (13F) Edmonds, T. E. Anal. Chim. Acta 1979, 708, 155-160.

6 - , 61-67 -

(26F) Tanaka. N.; Tarnada, A. Kagaku, Zokan(Kyot0) 1978, 78, 47-62. C . A . 1979. 9 0 . 158895. (27F) Tryk, D. A.; Park, S . - M . Anal. Chem. 1979, 57, 585-586. (28F) Van Bennekom, W. P. Anal. Chim. Acta 1978, 707, 283-307. (29F) Woodward, W. S.; Rocklin, R . D., Murray, R . W. Chem., Biomed., Environ. Instrum. 1979, 9 , 95-105. (30F) Yamada, A.; Kato, Y.; Doi, I.; Saito, K.; Tanaka, Y.: Tanaka, N. Sci. Rep. Tohoku Univ., Ser. 11977, 50, 41-73. C . A . 1978, 8 8 , 135901. (31F) Yeakel, B. D.; Burrows, K. C.; Hughes, M. C. Chem., Biomed., Environ. Instrum. 1979, 9 , 239-259.

Analytical Electrochemistry: Methodology and Applications of Dynamic Techniques William R. Heineman Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 4522 1

Peter T. Kissinger” Department of Chemistry, Purdue University, West Lafayetfe, Indiana 47907

As for previous editions of this review, we have endeavored to report on developments involving the more experimental aspects of finite current analytical electrochemistry. Representative references have been selected from a vast number of publications which for the most part appeared in print from January 1978 through December 1979. Our intent here has been t o convey what we judge to be the most novel developments which promise to have a long term impact on the field. Any selection of this sort is a matter of personal preference and due to limitations of time and space many excellent papers have not been cited. For those wishing exhaustive coverage of this area we strongly recommend that they subscribe to the Chemical Abstracts section on Analytical Electrochemistry which is available through the American Chemical Society “CA Selects” program.

ming suggests that there are three major advantages of semiconductors when compared to metal electrodes: “[l]In a semiconductor well-defined energy bands exist, their energy separation depending on the type of semiconductor; [2] t h e carrier density can be varied by doping over many orders of magnitude; [3] the occupation of energy levels by electrons or holes can be increased by optical excitation.” While these features have yet to realize important analytical results, the possibilities in this field are substantial and should be given more attention. Semiconductor electrodes are proving to be useful for the direct conversion of light into electricity and also for the photocatalytic generation of fuels and other useful chemicals. These areas have been recently reviewed by Wrighton (2A)and by Bard (3A). In order to briefly cover this very extensive area of research, we have selected some of the publications from several of the more active research groups. These citations will serve as an excellent entry to other recent work in this field. The Bard group in Texas has been extremely enthusiastic about semiconductor electrodes having published a t least 22 papers on this subject in the last few years. They have reported on electroluminescence at single crystals of n-type T i 0 2 ( 4 A ) ;aqueous photoelectrochemical cells with mixed polycrystalline n-type CdS-CdSe ( 5 A ) ;photoelectrochemistry of n- and p-GaAs ( 6 A ) and n- and p-InP in acetonitrile ( 7 A ) ; n-GaAs photovoltaic cells in acetonitrile ( 8 A ) ;electron spectroscopy of S/Se substitution in CdSe and CdS single crystals (9A); photogeneration of solvated electrons from p-GaAs in liquid ammonia (10A);characterization of n-Fe203in acetonitrile ( 1I A ) , and (finally) electrochromism and photoelectrochemistry of W 0 3 films prepared in various ways (12A).

ELECTRODE MATERIALS Semiconductors a n d O t h e r U n u s u a l Electrode Materials. Analytical chemists first became interested in semiconductor electrodes in the middle 1960’s because of their apparent value as optically transparent electrodes. At t h a t time the fact that the materials were semiconductors was of no interest per se and was normally considered to be a disadvantage. In the early 1970s physical electrochemical studies of the interface between semiconductors and electrolyte solutions gained tremendous momentum as it became clear that semiconductor electrodes had great potential for photoelectrochemistry and as substrates for covalently modified electrodes (see next section). In a n excellent recent review Memming discusses the known characteristics of charge transfer processes a t semiconductor electrodes ( 1 A ) . Mem138 R

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