Titanate Intercalation

Mar 30, 2009 - Present study provides a low cost and simply controlled test-bed for fundamental study on electrochemical preparation of a new class of...
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J. Phys. Chem. C 2009, 113, 6832–6838

Electrochemical Preparation of Copper-Based/Titanate Intercalation Electrode Material Shengfu Tong, Wen Wang, Xin Li, Yaohua Xu, and Wenbo Song* College of Chemistry, Jilin UniVersity, Changchun 130012, People’s Republic of China ReceiVed: December 3, 2008

This work demonstrated for the first time the feasibility of electrochemical preparation of copper-based/ titanate intercalation electrode material. Cupric ion was first intercalated into the layered titanate host by ion exchange and subsequently reduced by electrochemical methods, resulting in the copper-based/titanate intercalation electrode materials. The successful formation of copper-based/titanate (Cu-TO) intercalation materials by electrochemical reduction following ion exchange (Cu(II)-TO) were characterized by X-ray diffraction, scanning electron microscopy, and conventional electrochemical techniques. The effects of experimental conditions, i.e., dispersant for ion exchange, electroreductive medium, and methods, on activities of the resulting electrode materials toward glucose electrooxidition were investigated in detail. Results revealed that both the stability and the electrooxidative activity to glucose of Cu-TO intercalation electrode materials were largely improved compared with that of Cu(II)-TO, indicating the necessity and superiority of the electrochemical reduction step carried out following ion exchange. The potential applications of this new class of copper-based/titanate materials in electrocatalysis and electroanalysis were demonstrated. Present study provides a low cost and simply controlled test-bed for fundamental study on electrochemical preparation of a new class of metallic/metal-based titanate intercalation materials for electrocatalysis, electroanalysis, and relevant fields. Introduction Inorganic nanosized materials with mesoporous/layered structures have attracted extensive research interest during the past decades due to their good physical stability, chemical inactivity, availability, high surface area, and environmental benign properties.1 Among these, titanate has been extensively investigated in the fields of photocatalysis, photoluminescence, and photoelectrochemistry after the layered structure was demonstrated by Andersson and Wadsley, especially since the discovery of electrochemical photolysis of water at TiO2 in 1972.2-4 The structures of layered titanate can be described as stacked polyanion sheets of interconnected TiO6 octahedral with intercalated cations in the interlayer region. The negatively charged metal oxide sheet exhibits strong intrasheet covalent bonds, while those between the sheets are actually relatively weak.5,6 Other cations or positively charged particles are easily exchanged with the intercalated cations within the interlayer of titanate. So far, lots of articles about the ion exchange properties of titanates are reported, for example, the swelling behavior of organosilyated lithium potassium titanate prepared by cation exchange was investigated by Ogawa;7 the ion exchange capacities of titanate for Co2+, Ni2+, Cu2+, and Zn2+ and the influence of organic reagents were evaluated by Nunes8 and ElNaggar,9 respectively. Application of layered titanate nanofibers as adsorbents to remove toxic radioactive and heavy metal ions from water based on the ion exchange property was demonstrated recently by Zhu.10 On the basis of the ion exchange and swelling properties of the layered titanates, the modification and functionalization of titanates could be achieved by insertion of various inorganic/ organic cations or biomolecules.5,11 The chemical and physical properties of the resulting functionalized titanates drastically * To whom correspondence should be addressed: e-mail, wbsong@ jlu.edu.cn; tel, +86-431-85168352; fax, +86-431-85167420.

depend on the intercalated materials.2 For example, Domen and co-workers12 successfully inserted Ru(bpy)32+ into layered titanante by ion exchange, and the product exhibited photocurrent generation under visible-light irradiation. Similar works were also carried out by other groups;2,13 Ogawa immobilized alkyl and phenyl groups in the interlayer space of titanate to specifically adsorb 4-nonylphenol;14 Zhang et al. fabricated a titanate electrode with lithium intercalation into H-titanate nanotubes and investigated its electrochemical properties as a lithium battery electrode material.15 Besides these, titanates are also introduced into the magnetic and optical fields by being functionalized with different transition-metal ions.16 Though the titanates are widely studied in many fields, only a few reports emerged recently concerning the applications of functionalized titanates in electroanalysis,11,17,18 for example, myoglobin was intercalated into the layered titanate nanosheets for determination of H2O2.11 Inorganic materials, especially the transition-metal-based materials, exhibit excellent activity and high stability in electrocatalysis for small organic molecules. The layered titanates functionalized with transition-metal-based particles are promising novel materials with potential applications in electrocatalysis, electroanalysis, and other relevant fields. To our best knowledge, most studies for functionalization of titanate with inorganic particles are based on the ion exchange property of titanates, and the resulting functionalized materials normally suffer from the drawbacks of lack of stability due to the reversibility of ion exchange process. To improve the stability of the functionalized titanates, additional treatments are required.19 Thermal treatments, electrophoresis, and chemical reduction methods are commonly employed to improve the combination of the intercalated composite with the Ti-O host layers.2 For instance, Teng et al. distributed CuO over titanate by calcinations,20 Matsumoto et al. prepared functional titanate electrode by electrophoresis,2 Li et al. investigated the ion exchangeable

10.1021/jp8106342 CCC: $40.75  2009 American Chemical Society Published on Web 03/30/2009

Copper-Based/Titanate Intercalation Electrode Material

J. Phys. Chem. C, Vol. 113, No. 16, 2009 6833

SCHEME 1: The Flow Chart of Synthetic Steps for KTO

titanate nanotubes and reduced [Ag(NH3)2]+ into Ag(0) with chemical reagent,16 and Wiley and co-workers converted the Cu(II) to Cu(0) as a byproduct with n-butyllithium following ion exchange in the fabrication of (LixCl)LaNb2O7.21b Though these treatments are effective, they hold drawbacks of being time-consuming, requiring high temperature and high potential, and are not easy to control, which limit their extensive applications. It is important to exploit convenient, controllable, and low cost methods to functionalize titanates.19 Electrochemical routes exhibit lots of superiorities contrary to the above-mentioned methods, such as low cost, versatility, controllability for almost all metals, and avoidance of complicated separation procedures.22,23 Electrochemical methods have recently demonstrated powerful and convenient routes to obtain diversely nanostructured metal films by rational selection of the supports,22 and the quantity of the products could be readily controlled by monitoring the potential applied and the coulombs consumed.23 Matsumoto et al. found occasionally the irreversible electrochemical reduction of the interlayer silver complex molecules [Ag(NH3)2]+ to Ag metal without deintercalation during the photoelectrochemical measurements;2b however, detailed electrochemical reduction of the intercalated metal complex ions to metal was not investigated. We are inspired by this finding and demonstrate in this work the feasibility of preparation of the metal/titanate intercalation materials by direct electrochemical reduction of the intercalated metallic ion in titanate. We are especially interested in functional metal-based electrode materials because of their interesting aspects in catalysis for small organic molecules. Copper-based (including Cu, Cu2O, and CuO) materials are industrially important and can be widely used in magnetic storage media, solar energy transformation, electronics, batteries, and catalysis.21 Nanosized copper-based electrode materials, overcoming the drawbacks of an enzyme-based glucose sensor (instability, interference from oxygen, and difficulties in miniaturization, poor reproducibility, etc.), are outstanding candidates in enzymeless glucose sensor fields;24,25 Sato et al. prepared Cu2+-doped layered hydrogen titanate and investigated its photochemical properties;24c CuO/ titanate composite was prepared by Teng et al. with calcinations and exhibited high catalytic activity in selective reduction of NO to NH3.20 In our present study, cupric ion was first intercalated into a typical layered titanate by ion exchange, and the intercalated cupric ion was subsequently reduced by electrochemical methods resulting in a novel copper-based/titanate (Cu-TO) intercalation electrode material. Formation of Cu-TO intercalation materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and conventional electrochemical techniques. Effects of experimental conditions, i.e., dispersant for ion exchange (including water, acetone, and n-propylamine), electroreductive medium, and methods (such as cyclic potential scan (CPS), potentiostat (POS), and dualpulse (DP)), on the properties of the resulting copper-based electrode materials toward glucose oxidation were studied in detail. In this work, the layered structure of titanate was selected to confine the copper clusters growth and protect them from

conglomeration. By this way, a novel Cu-TO intercalation electrode material with prolonged lifetime and good performance was expected. This work provides a low cost and simply controlled test-bed for fundamental study of electrochemical preparation of a novel class of metal-based titanate intercalation electrode materials for electrocatalysis and electroanalysis. Experimental Section 1. Reagents and Instrumentation. All chemicals in the experiment were analytical grade and used as received. Electrochemical experiments were performed with a CHI660B electrochemical station in a conventional three-electrode cell under nitrogen atmosphere at room temperature. Bare or modified indium tin oxide (ITO), platinum (Pt) wire, and saturated calomel electrode (SCE) were used as the working (WE), counter (CE), and reference (RE) electrodes, respectively. X-ray diffraction (XRD) patterns of the samples were recorded on a XRD-6000 (Shimadzu, Japan) powder diffractometer equipped with Cu KR radiation (λ ) 1.5418 Å). The morphologies of the materials were observed by scanning electron microscopy (SEM) (SSX-550, Shimadzu, Japan). 2. Synthesis of the Layered Titanate. The procedures for schematic synthesis of the layered titanate were according with Sasaki’s method,5 and the procedure could be described as shown in Scheme 1. Briefly, K2CO3, Li2CO3, and TiO2 were mixed intimately in molar ratio. The mixture was then heated at 700 °C for 2 h for decarbonation. The decarbonated powder was ground and calcined subsequently at 1100 °C for 24 h. After cooling, the white crystal of layered titanate with molecular formula K0.81Li0.27Ti1.73O4 (referred as KTO) was obtained. 3. Cu(II) Intercalation by Homogeneous Ion Exchange. Homogeneous ion exchange was carried out by stirring 50 mg of KTO in (a) 5 mL of 0.15 M CuCl2 (aqueous solution), (b) 5 mL of 0.15 M CuCl2 (acetone-water solution, Vactone ) 60%), and (c) 5 mL of 0.15 M CuCl2 (n-propylamine solution, referred as C3N-water solution obtained by dropping C3N into CuCl2 until the solution was pellucid) at room temperature for 12 h. The white KTO powder turned to light green or blue, and the sediment was separated by filtration, rinsed with enormous ultrapure water to remove excess reagents, and dried for use. The resulting intercalation materials are denoted as Cu(II)-TOa, Cu(II)-TOb, and Cu(II)-TOc, respectively. 4. Electrochemical Reduction of Cu(II) Intercalated in Titanate and Electrochemical Test of the Electrodes. Ten milligrams of Cu(II)-TOa (referred as Cu(II)-TO in the following text without emphasis) was mixed with 2 mL of ethanol under sonication for 25 min. A suitable amount of the prepared suspension was spin-coated onto an ITO electrode surface (0.25 cm2), resulting the Cu(II)-TO films electrode. Electrochemical reduction of the Cu(II) intercalated in titanate films was performed in electrolytes of different pH value (including 0.1 M H2SO4, 0.1 M K2SO4, and 0.1 M NaOH) by using cyclic potential scan (CPS), potentiostat (POS), and dualpulse (DP) methods, respectively. The resulting copper-based/ titanate films were denoted as Cu-TO, and 0.1 M NaOH was used as the reaction medium for electrochemical test of the electrodes and for glucose electrooxidation.

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Figure 1. XRD patterns of KTO before (a) and after (b) Cu(II) intercalation by ion exchange.

SCHEME 2: Schematic Representation of Homogeneous Ion Exchange of Titanate with Cu(II)

Results and Discussion Intercalation of Cu(II) into the Layered Titanate by Ion Exchange. Several works on ion exchange of titanate with cupric cation demonstrated that titanate in alkali metallic forms have higher ion exchange capacity to cupric cation (Cu(II)) than its acidic state8,9 and the cation uptake decreased with increasing acidity due to either high energy requirement for cation dehydration or high competing effect of H+ ions with the exchange sites in a higher acidic medium.26 On the basis of the above considerations, KTO was employed as the preceding material for ion exchange. The formal layered structures of the titanate were demonstrated by XRD analysis (Figure 1a). The distance of the interlayer (d) was 7.60 Å, which was in good agreement with the results of Sasaki.5 Cu(II) exchange was carried out in CuCl2 solution (a, b and c mentioned above). The replacement of K+ and the intercalation of Cu(II) were described by eq (1): two K+ were replaced by one Cu(II) diffused into the titanate interlayer to maintain a charge balance,8a where the intercalated Cu(II) could be [Cu(H2O)4]2+ or [Cu(C3H9N)n]2+. Homogeneous ion exchange processes of titanate with Cu(II) are schematically represented in Scheme 2.

KTO + Cu(II) f K+ + Cu(II) - TO

(1)

Figure 1b illustrates the formal layered structures of the sample obtained by homogeneous ion exchange. The intercalation of cupric ion in other two mixed mediums showed the same tendency and are not shown in the figure. The interlayer distance (d) was 9.16 Å, 1.56 Å larger than that of its parent KTO (Figure 1a). The expansion of the interlayer distance of titanate after ion exchange demonstrated a successful replacement of K+ by Cu(II) in the interlayers, as implied by previous reports.13 a This phenomenon is also found after Cu2+, Ni2+, etc., were intercalated without destroying the structure of titanate.8,9,27 Since there was no evidence for any structure changes for Cu(II) ion exchange in various media, Cu(II)-TO prepared in aqueous medium was selected as a protocol in the following study. The successful Cu(II) intercalation into titanate by ion exchange was also demonstrated by conventional electrochemi-

Figure 2. The CVs of KTO (a) and Cu(II)-TO (b) film electrodes in 0.1 M NaOH at 50 mV s-1, and the solution behavior of Cu(II) (inset) on a bare ITO surface.

cal characterization. Figure 2 illustrates the compared cyclic voltammograms (CVs) of KTO and Cu(II)-TO film electrodes in 0.1 M NaOH aqueous solution in the potential range from -1.0 to +0.8 V. The KTO film electrode (curve a) was stable and exhibited a wide potential window during the successive potential scanning in alkaline solution. On the contrary, intercalation of Cu(II) (curves b) resulted in a dramatic change in the voltammetric behavior. For example, the reductive current on Cu(II)-TO film electrodes increased dramatically from about -0.30 V and reached a maximum around -0.52 V, while during the positive scanning, the oxidative peak appeared at about -0.03 V and the anodic current enhanced greatly when the potential reached +0.65 V. These electrochemical characteristics are very similar with that of a solution behavior of Cu(II) on a bare ITO surface (inset of Figure 2), where the cathode and anode currents were ascribed to the redox processes of Cu(II)/ Cu(I) pair and Cu(II)/Cu(III) pair, respectively.24b,28 The presence of Cu(II) in the layered titanate revealed by electrochemical measurement and XRD evaluation demonstrated that homogeneous ion exchanges of Cu(II) were accomplished successfully in various media. Electrochemical Reduction of Cu(II) Intercalated Titanate. To exploit a novel route for preparation of metal-based titanate intercalation electrode materials, we demonstrated here for the first time the feasibility of electrochemical preparation of copper-based titanate intercalation electrode materials by electroreduction following the cupric ion exchange in titanate. The interlayer distance of titanate was utilized to confine the copper clusters’ growth and protected them from conglomeration. Effects of experimental conditions, i.e., electroreductive medium and methods (such as CPS, POS and DP), on properties of the resulting electrode materials were investigated in detail. The novel Cu-TO intercalation electrode materials were expected exhibiting high activity, prolonged lifetime, and excellent performances for glucose oxidation compared with the easily accessed copper particles.24 The Morphologies of the Resulting Materials. The morphologies of the modified titanate films on the ITO substrate before and after electrochemical reduction were observed by SEM. From Figure 3, both Cu(II)-TO (Figure 3a) and Cu-TO (Figure 3b) films exhibited homogeneous representations with uniform sizes around 30 µm. The structures of our titanate films were similar to the results reported previously.2 Simultaneously, the observed individual particles of Cu(II)KTO and Cu-TO obtained by ion exchange and additional electroreduction are similar to their parent KTO. This phenomenon indicates that the ion exchange process and the subsequent electroreduction procedure did not destroy the structures of titanate, which is in good agreement with the XRD results in the present work (Figure 5) and the reports published.2,27 No

Copper-Based/Titanate Intercalation Electrode Material

Figure 3. The SEM micrographs of the titanate films before and after electroreduction following ion exchange in CuCl2 aqueous solution: (a) Cu(II)-TO; (b) Cu-TO.

significant changes in the morphology of Cu-TO were observed after the additional electroreduction step, suggesting the high stability of the structures of titanates.2 The Effect of Electrolyte on Electrochemical Reduction of Cu(II). The effect of electrolyte on reduction of the intercalated Cu(II) was studied. NaOH (0.1 M), H2SO4 (0.1 M), and K2SO4 (0.1 M) were used as electrolytes in CPS electroreduction. The successive electrochemical reduction of Cu(II)-TO films in 0.1 M NaOH solution is shown in Figure 4A. With successive potential scanning, the original reductive peak around -0.52V shifted negatively to -0.55 V, new reductive peaks and new oxidative peaks appeared at -0.80 and -0.95, -0.35, and -0.10 V, respectively. Meanwhile, both anodic and cathodic currents increased obviously, the -0.55 V peak current became steady fleetly while the fifth cycle processed; however, the peak current at -0.8 V increased evidently with the increasing cyclic potential scan and tended to be steady as the eighth cycle performed. The electrochemical behavior of the stable copperbased titanate films in 0.1 M NaOH was similar to that of the bulk metallic copper electrode (inset in Figure 4A), and the corresponding redox peaks were attributed to the transform of Cu(0)/Cu(I), Cu(I)/Cu(II), and Cu(II)/Cu(III).24b,28 Figure 5 shows XRD patterns of Cu(II)-TO intercalation materials before (a) and after (b) electroreduction. The layered structures did not change after electroreduction as revealed by the similarity of the two XRD profiles, in accordance to the SEM results.

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Figure 4. Successive electroreduction of Cu(II)-TOaq films by cyclic potential scan in 0.1 M NaOH (A), 0.1 M H2SO4 (B), and 0.1 M K2SO4 (C) at 50 mV s-1. The potential scan cycles are given in the figures. Inset of part A shows CV of bulk Cu electrode 0.1 M NaOH at 50 mV s-1.

Figure 5. XRD patterns of Cu(II)-TO films before (a) and after (b) electroreduction.

The successive CPS reductions of Cu(II)-TO films in 0.1 M H2SO4 and K2SO4 are shown in Figure 4B and Figure 4C. In acidic electrolyte, the reductive peak was positively shifted and the oxidative one was negatively shifted. The positive shift was much more pronounced than the negative one, for example, the reductive peak shifted 200 mV positively and the oxidative one shifted 40 mV negatively when the second cycle performed. Moreover, in contrast to the basic condition, both anodic and cathodic currents declined rapidly with repeated potential scan. The redox current tended to be steady after the third cycle. The trend of the current declining is similar to that with the bulk copper electrode under same conditions. The electrochemical reduction under neutral condition was similar with that of the acidic electrolyte. The electrochemical characteristics of the

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Figure 6. Net oxidation currents of 0.2 mM glucose on Cu-TO films obtained by CPS in 0.1 M NaOH (a), 0.1 M H2SO4 (b), and 0.1 M K2SO4 (c).

resulting copper-based titanate films obtained in 0.1 M H2SO4 or K2SO4 were analogous to that obtained in 0.1 M NaOH. Glucose oxidation reaction was used to evaluate the activity of the copper-based/titanate intercalation electrode materials obtained by CPS reduction in various electrolytes. Figure 6 illustrates the net oxidation currents of glucose (0.2 mM) in 0.1 M NaOH on Cu-TO films obtained by CPS in various electrolytes. On the films electroreduced in neutral (curve c) and basic (curve a) electrolytes, glucose oxidation was much more obvious compared with Cu-TO obtained in acidic solution (curve b). Additionally, the net oxidation currents at Cu-TOs were much larger than that of Cu(II)-TOs (not shown in the figure), suggesting the effective electroreduction of the intercalated Cu(II) in basic and neutral electrolytes. At all potentials more positive than +0.55 V, the net glucose oxidative currents on films reduced in 0.1 M K2SO4 were much larger than those prepared in 0.1 M NaOH. Therefore, 0.1 M K2SO4 was selected as electrolyte for Cu(II)-TO electroreduction. The Effect of Electrochemical Techniques on the Reduction of Cu(II). In comparison with CPS, POS and DP methods have been demonstrated to be effective routes for fabrication of metallic films materials because of their controllable processes in electrodeposition. Controllable reduction of the intercalated Cu(II) in titanate by POS and DP in the selected electrolyte was expected to tune the size and dispersion of the metal-based particles, and thus modify the activity of the resulting electrode materials. Figure 7 shows the compared electrochemical characteristics of Cu-TO films reduced in the selected electrolyte by various electrochemical techniques in 0.1 M NaOH without (A) and with (B) 0.2 mM glucose. In Figure 6A, the copper redox peaks aroused by the transformation between the different valent of copper in 0.1 M NaOH were all obviously on Cu-TO films reduced by various electrochemical techniques, indicating the successful reduction of the intercalated Cu(II) following ion exchange by various electrochemical techniques. The peak currents of Cu-TO films prepared by DP were larger than those of the other two. The glucose activities at the copper-based functionalized titanate films reduced by POS and DP in the selected electrolyte were evaluated and compared with that of CPS, as shown in Figure 6B. In the potential range of +0.3 to +0.8 V, the net glucose oxidative currents on the three films reduced by various electrochemical routes were in the sequence of DP > POS > CPS. For example, the +0.6 V glucose oxidative currents on films reduced by POS and DP were almost 4 and 7 times larger than that of CPS. The onset potentials, peak potentials, and net peak currents density of 0.2 mM glucose in 0.1 M NaOH on Cu-TO films reduced by various electrochemical techniques in 0.1 M K2SO4 electrolyte are compared in Table 1. On Cu-TO films reduced by POS and DP, the onset potentials and peak

Figure 7. Compared electrochemical characteristics of Cu-TO films reduced by various electrochemical techniques in 0.1 M NaOH without (A) and with (B) 0.2 mM glucose: (a) CPS; (b) POS; (c) DP.

TABLE 1: Compared Data for Glucose Oxidation (0.2 mM Glucose in 0.1M NaOH) on Cu-TO Films Reduced by Various Electrochemical Techniques in 0.1 M K2SO4 Electrolyte electrochemical techniques cyclic potential scan constant potential dual pulse

onset peak net peak current potential (V) potential (V) density (µA · cm-2) 0.60 0.45 0.43

0.70 0.62 0.61

54.0 84.4 114.8

potentials of glucose were 160 and 85 mV negatively shifted compared to CPS, and their net peak currents were 60-110% enhanced compared with the CPS result. From Figure 6 and Table 1, it could be seen that the onset potentials and peak potentials of glucose oxidation on films reduced by DP were more negative, and the glucose oxidation current on the same films were more pronounced than those of the others. The glucose peak potential on the electrode obtained by DP method was 50 mV more negative than that of the copper nanoparticle film electrode, and the corresponding oxidative current was almost 100% enhanced compared with Zhu’s result.24b This could be ascribed to the effective electrochemical reduction of the intercalated Cu(II) in titanate by the DP method. The dependences of electrochemical reduction parameters of DP (nucleation potential, step time, growth potential, and growth time) on glucose activity were investigated, and the corresponding data are given in Table 2. From Table 2, the optimum parameters of nucleation potential, step time, growth potential, and growth time for DP reduction of Cu(II) in titanate were -0.6 V, 0.2 s, -0.1 V, and 120 s, respectively. On the basis of the above results, Cu-TOb and Cu-TOc films were fabricated (reduced by DP in 0.1 M K2SO4) and their electrooxidative behaviors to glucose were exploited. The oxidative current of glucose (0.2 mM) at Cu-TOb and Cu-TOc films are 1.26 times and 1.16 times that at Cu-TOa, respectively. It is reasonable to explain that the ion exchange capacity of titanate is influenced by dispersant used for ion exchange, as demonstrated by ElNaggar.9 The electrochemical stabilities of Cu-TO films (ion exchanged in CuCl2-water and reduced by DP in 0.1 M K2SO4)

Copper-Based/Titanate Intercalation Electrode Material

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TABLE 2: The Responses of 0.2 mM Glucose in 0.1 M NaOH on Cu-TO Films Reduced by Dual-Pulse Method at Various Electrochemical Parameters nucleation potential (V) nucleation time (s) growth potential (V) growth time (s) onset potential (V) peak potential (V) -0.4 -0.4 -0.4 -0.6 -0.6 -0.8 -0.6

0.1 0.2 0.2 0.2 0.2 0.2 1

-0.1 -0.1 -0.1 -0.1 -0.2 -0.2 -0.03

in 0.1 M NaOH without and with glucose were investigated in this work. The current response of Cu-TO films in 0.1 M NaOH without and with 0.2 mM glucose at +0.55 V decayed by 1.12% and 3.25% after 100 continuous potential cycles in the potential range of +0.30 to +0.70 V at a scan rate of 50 mV s-1. The current response of the same electrode decayed only 6.72% after 2 months of storage at room temperature. These results demonstrated that the electrochemical stability of the intercalated Cu within KTO films are improved compared with that of the more easily accessed Cu or CuO.25d To verify the necessity of the additional electroreduction step, the electrochemical behaviors of Cu(II)-TO and Cu-TO films after soaking in 0.1 M K2SO4 for 6 h were compared. It was interesting to find that after soaking in 0.1 M K2SO4, neither electrochemical behavior of Cu(II) nor electrooxidative current of glucose was observed at the Cu(II)-TO film electrode, while, Cu-TO kept the electrochemical characterization of Cu and the electrooxidation activity to glucose as well. This can be ascribed to the intercalated Cu(II) deintercalated from Cu(II)-TO,19 and additional electroreduction step is required by considering the superiority of greatly enhanced stability of the intercalated materials. In another approach, a comparison of the electrooxidative currents of glucose generated at different film electrodes, including bare KTO films in electrolyte containing Cu(II), Cu(II)-TO, and Cu-TO films was also carried out. It was found that the electrooxidative current of glucose (+0.6 V vs SCE) at the Cu(II)-TO film was nearly the same as that of the bare KTO film in the electrolyte containing 0.1 mM Cu(II). However, the electrooxidative current of glucose at the Cu-TO film (+0.6 V vs SCE) was 2.4 times of that of Cu(II)-TO. Obviously, above results demonstrated that the combination between the intercalated composite and the Ti-O host layers of the materials experienced electrochemical reduction was largely improved.8,9 Moreover, the Cu-TO exhibited much higher electrochemical activity to glucose than Cu(II)-TO. In summary, this electrochemical-assisted method is more convenient, controllable, and easier to operate in preparation of metalfunctionalized titanate intercalation materials compared with the widely adopted calcinations reported previously.20 Conclusions Copper-based/titanate intercalation electrode materials were electrochemically accomplished for the first time. Reduction of the cupric ions intercalated in titanate by ion exchange was performed in eletrolytes with different pH values by various electrochemical techniques. The XRD and SEM characterizations revealed that featured and regular layered structures of titanate remained after experiencing ion exchange and subsequent electrochemical reduction. Electrochemical studies demonstrated that the combination between the intercalated composite and the Ti-O host layers of the materials experienced

60 60 120 120 120 120 360

0.57 0.55 0.57 0.45 0.47 0.50 0.55

0.67 0.60 0.61 0.57 0.60 0.62 0.63

net peak current (µA · cm-2) 66.7 36.7 1.5 121.1 60.2 82.8 14.9

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