Hydroquinone Couple by a

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Catalytic Interconversion of the Quinone/Hydroquinone Couple by a Surface-Bound Os(III/II) Polypyridyl Couple Prateek Dongare, Ying Wang, Dean M Bass, and Thomas J. Meyer J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b04920 • Publication Date (Web): 20 Jun 2018 Downloaded from http://pubs.acs.org on June 26, 2018

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The Journal of Physical Chemistry

Catalytic Interconversion of the Quinone/Hydroquinone Couple by a Surface-Bound Os(III/II) Polypyridyl Couple Prateek Dongare, Ying Wang, Dean M Bass and Thomas J. Meyer* Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 275993290, United States [email protected]

Supporting Information Placeholder

ABSTRACT: Surface catalytic interconversion of hydroquinone (H2Q) and 1,4-benzoquinone (Q) occur at a fluorine-doped tin oxide electrode (FTO) modified by the addition of the surface-bound couple, [Os(bpy)2((4,4’-PO3H2)2bpy)]3+/2+ (OsP2+, bpy = bipyridine and 4,4’-(PO3H2)2 = 4,4’-phosphonato2,2’-bipyridine). Significant rate enhancements are observed with the added solution buffers - phosphate, acetate, and citrate - and a surface-bound, pyridine base. Analysis of cyclic voltammograms for the 2e/2H+ couple, by use of the Butler-Volmer equation, point to the importance of acid-base effects and Hbonding in enhancing the reaction rate at the electrode. INTRODUCTION The quinone/hydroquinone (Q/H2Q) couple is ubiquitous in nature and widely studied.1 In photosystem II, reduction of plastoquinone to plastoquinol by proton-coupled electron transfer (PCET)2-4 is a key step with ubiquinone and plastoquinone acting as mobile electron-proton carriers. As a couple, Q/H2Q also provides an inexpensive approach to storing energy in aqueous redox-flow batteries.5-7 8-9 In the reactivity of Q/H2Q couples, hydrogen bonding can play a critical role. It enables pathways in which electron and proton transfer occur simultaneously to avoid high-energy electron transfer intermediates. 10-14 The accessibility of H-bonding, and pathways involving proton-coupled electron transfer (PCET), can dictate reactivity by the use of pathways in which simultaneous electron and proton transfer avoid highenergy electron transfer intermediates. In previous studies, Ru(III) based polypyridyl complexes have been shown to be excellent catalytic

oxidants (E0 = 1.27 V vs NHE) toward a variety of organic and inorganic substrates.8 Compared to related Ru(III) complexes, Os(III) complexes are weaker oxidants with E0 = 0.80 V vs NHE for the Os(bpy)33+/2+ couple in pH 6.5 phosphate buffer and 0.5 M at 25 oC. A potential that more closely overlaps with the Q/H2Q couple in a coordination environment that minimizes electron transfer barriers.15 The Q/H2Q couple undergoes a reversible twoelectron interconversion in a half reaction that is rapid in protic solvents in contrast to aprotic solvents.16 The chemistry is complicated by the 2e- irreversible nature of the couple. At pH 7, under standard conditions, the redox potentials for the two half reactions are shown in eq 1 (potentials in V vs NHE, pH 7, 25°C, I = 0.1 M). Based on the experimental data, semi-quinone (HQ●) is unstable toward disproportionation into Q and H2Q (2HQ● → H2Q + Q) by ∆G0 = -0.70 eV and, as a reaction intermediate, can be a significant contributor to the reaction barrier for the couple. Q + e- + H+ → HQ●

(1a); E0՛ = 0.34 V

HQ● + e- ⇄ HQ−

(1b); E0՛ = 0.46 V

HQ− + H+ ⇄ H2Q

(1c); pKa = 9.85

In an earlier study, we reported on the kinetics of oxidation of hydroquinone to benzoquinone by [Os(dmb)3]3+ in the reaction, 2[Os(dmb)3]3+ + H2Q → 2[Os(dmb)3]2+ + Q + 2H+.17 The reaction was monitored by stopped flow kinetics in aqueous solutions. The results of a detailed kinetic analysis revealed contributions from 7 distinct pathways for the reaction over a variety of conditions with significant variations in rate behavior depending on experimental conditions.2, 17 The overall reaction occurs with ∆G° = 0 at pH = 1.2. Below this pH,

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reduction of Q to H2Q by [Os(dmb)3]2+ occurs and, above it, oxidation of H2Q to Q by [Os(dmb)3]3+. A potential-pKa diagram for the Q/H2Q couple under standard conditions at pH = 0 is shown in Figure S1.

OH

The appearance of multiple pathways in the mechanism for Q/H2Q interconversion arises from the intervention of concerted electron-proton transfer (EPT) pathways and the use of conjugate acid/base couples such as H2PO4-/HPO42- and acetic acid/acetate (HAc/Ac-) as proton acceptors. Kinetic evidence was obtained for the acid-assisted reduction, [Os(dmb)3]2+, Q---H3PO4 → [Os(dmb)3]3+ + HQ● + H2PO4-, and for EPT oxidation with acetate acting as the proton acceptor base, [Os(dmb)3]3+, Ac---H2Q → [Os(dmb)3]2+ + HQ● + HAc. Given the importance of transferring solution-based reactivity to electrode surfaces for fuel cell, battery, and photoelectrochemical applications, we have extended the earlier work in solution to an electrode surface.17-18 In the experiments described, here we return to the surface oxidation of H2Q, but by the phosphonate-modified catalyst shown in Figure 1 on planar fluorine-doped tin oxide (FTO) electrode surfaces. The use of the transparent conducting oxide electrode utilizes this n-type metal oxide semiconductor which has proven to be highly versatile in a variety of device applications.8, 19-22 With their transparency and conductivity properties they provide an important tool for controlling surface potential in electrochemical and related applications.22 In this manuscript, we explore the role of the Os(III) form of the surface-bound electron transfer mediator couple, [Os(bpy)2((4,4’-PO3H2)2bpy)]3+/2+ (FTOOsP2+) on the oxidation of H2Q to Q. The experiments provide an opportunity to explore the relationship between solution and surface reactivity and for the possible role of bases in controlling reactivity on electrode surfaces. This is an extension of earlier experiments on tyrosine oxidation23 by the surfacebound couples, [M(4,4ʹ-CH2PO3H2bpy)(bpy)2]3+/2+ (M = Ru, Os). The goal of the current experiments was to exploit proton-coupled electron transfer pathways to minimize overall reaction barriers in the interconversion between Q and H2Q at electrode surfaces for possible applications in Dye Sensitized Photoelectrochemical Cells (DSPEC), redox-flow batteries, and related applications.

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OH

Hydroquinone

Figure 1. Structures of the catalyst OsP2+ and the phosphonated, butoxy-pyridine base, NBuOP (pKa(HNBuOP+) = 6.5)24 in solution and on a FTO fluorine-doped tin oxide electrode. EXPERIMENTAL SECTION Reagents and Materials. All commercial chemical reagents were used as received except as noted. Os(bpy)2(4,4′-(HO)2P(O)CH2)2bpy) (OsP) complex was prepared according to literature procedures.25 The synthesis of NBuOP was reported elsewhere.26 All solutions were freshly prepared with deionized water provided by a MilliQ purification system (Synthesis A10). H2Q was purified by sublimation to give bright white crystals and purity was checked by 1H NMR. Methods. Electrochemical measurements were performed with a CH Instruments (CHI) model 601D potentiostat at room temperature (22 ± 1 °C). A threeelectrode configuration was applied in a threecompartment cell with a fluorine-doped tin oxide electrode (FTO, 1 cm2) purchased from Delta Technologies (Stillwater, MN) as working electrode, Ag/AgCl (3 M KCl, 0.17 V vs NHE) reference electrode, and graphite counter electrode with the

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conversion of Ag/AgCl to NHE by adding 0.17 V. The ionic strength (I) was adjusted to 0.5 M with added NaCl. FTO slides were loaded with OsP2+ and the base NBuOP by immersion in 0.1 mM solutions of the complex in methanol for 2 hrs followed by 6 hrs in 0.1 M solutions of the base to give the surfacederivatized electrodes FTO-OsP2+. The surface area of the FTO-Os2+ electrodes was 1 cm2 with the electrodes formed by immersion into a 1 cm2 area of the FTO slides in OsP2+ methanol solutions. This ensures that only the required area is covered with the OsP2+ catalyst. The slides were removed, rinsed with methanol, water, and dried under a stream of nitrogen. The maximum surface coverage for FTO bound OsP2+ was calculated to be Γ = 1.2 × 10-10 mol/cm2 (see SI and ref 23 for details). For the co-loading experiments, CV experiments showed that the surface was ~50% covered with OsP2+ and the ratio of FTOOsP2+ and NBuOP was estimated by XPS measurements as ~1:1.26 (see SI and ref 26 for details) UV−visible spectra were recorded on an Agilent Technologies model 8453 diode-array spectrophotometer with ChemStation software. RESULTS 2+

The complex, [Os(bpy)2((4,4’-PO3H2)2bpy)] (OsP2+), was loaded on planar FTO glass electrodes (see above). The overall loading of the catalyst on the electrode was controlled by varying the soaking time.27 The surface-bound OsP3+/2+ couple, E1/2 = 0.80 V vs. NHE (figure 2), is pH independent and stable on the electrode surface.17 Eo for the Q/H2Q, 2e‒/2H+ couple, is pH-dependent with typical Nernstian behavior, shifting 59 mV/pH unit at 25 ºC below pK1 for the hydroquinone.16, 28 Based on the redox potentials for the OsP3+/2+ couple, oxidation of H2Q occurs at ∆Go’ = 0 at pH =1.2 (eq 2).17 H2Q + 2FTO-OsP3+→ Q + 2H+ + 2FTO-OsP2+ (2) Figure 2 shows a CV scan of OsP2+ loaded on an FTO surface (Γ = 1.2 × 10-10 mol/cm2)23 in phosphate buffer at pH = 5, I = 0.5 M NaCl at a scan rate of 100 mVs-1 at 295 ± 3 K. A chemically reversible wave for the OsP3+/2+ couple is evident at E0 = 0.80 V vs NHE. The high stability of the OsP3+/2+ couple at controlled pH values, below 7.0, provided a basis for its use as a catalyst couple. In a series of multiple scans (50 scans at 100 mV/s), the OsP3+/2+ reversible wave remains the same suggesting there was no sign of catalyst decomposition from the surface (Fig S7). However, a ~35% decrease in faradic current is observed after 50 scans suggesting some catalyst desorption with extended scans. CV’s were also acquired at pH 3, 4,

and 5 to establish the stability of the couple on the surface with no evidence for decomposition or significant loss from the surface between runs in CVs with the phosphonate surface binding unaffected (Figure S7). In a series of repetitive experiments, a single FTO-OsP2+ electrode was used multiple times without change.

Figure 2. Cyclic voltammogram (CV) of surfacebound OsP2+ (Γ = 1.2 × 10-10 mol/cm2) on an FTO electrode in a phosphate buffer at pH = 6.5 in 0.5 M NaCl at a scan rate of 100 mVs-1 at 295 ± 3 K. Substantial current enhancements were observed for the oxidation of H2Q with the added buffers citric acid/citrate (H3C6H5O7/H2C6H5O7‒) at pH 3, acetic acid/acetate (HAc/Ac‒) at pH 4, and H2PO4-/HPO42‒ at pH 6.5. Enhancements were also observed with the surface-loaded HNBuOP+/NBuOP base with pKa = 6.47.24 The collective data are shown in figures 3 and S2-S5. The plots of Ip vs (υ)1/2 are indicative of a diffusional process for an electrochemically irreversible process consistent with the RandlesSevcik equation.29 As in solution, catalysis is initiated by electron transfer from FTO-OsP2+ to FTO-OsP3+ (eq 3.1) followed by the oxidation of H2Q at the surfacebound catalyst (eq 3.2). In the solution mechanism in eq 2, reduction to H2Q is followed by proton loss and further reduction to give Q.

FTO-Os 2+

FTO-Os 3+ + e

FTO-OsP3+ + H2Q → FTO-OsP2+ + H2Q+●

H2Q

(3.1) (3.2)

Q + 2H+ + e- (3.3) 3

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The impact of the added FTO-OsP3+/2+ couple on the surface electrochemistry is profound. As shown in Figure S5, from -0.19 to 1.34 V with 1 mM of H2Q on the bare FTO. Cyclic voltammograms with added base, Figure 3, show that the response at the modified electrode depends on the added base and the thermodynamic barrier between the surface-bound catalyst and Eo’ for the Q/H2Q couple. The impact of the added phosphate buffer H2PO4-/HPO42- and the surface-bound NBuOP base can be seen by the peak current comparisons (Ip) in Figure 3 at a scan rate of 100 mVs-1. The peak currents for the anodic peak vary from 0.49 mA in 500 mM phosphate buffer to 0.28 mA with co-loaded NBuOP, because of the decrease in surface concentration of complex. The peak current fell to 0.1 mA in unbuffered water. There was a difference of 0.21 mA between peak current values in the HPO42buffered and unbuffered solutions and of 0.18 mA between the electrode with added NBuOP and unbuffered water. The oxidative current for the co-loaded assembly was diminished compared to the FTO-Os3+-phosphonate wave by nearly half (Figure 3). The decrease is due to the fact that half of the FTO surface sites are covered by the NBuOP catalyst, decreasing the number of Os3+ outer-sphere oxidant sites available for H2Q to react, note the details of XPS analysis in ref 26. Regardless of the choice of buffer used, catalysis was rapid compared to aqueous solutions (Table-1). As shown by the data Figure 3 at the scan rate of 100 mV/sec, with high concentrations of the added solution buffers, the peak-to-peak separation between peak currents for ∆Ep, the peak-to-peak potential difference for the H2Q/Q couple, is constant. It varies, with the pH of the external buffer from 6.5 for H2PO44-/HPO42- to citrate at pH 3.0 with no changes in ∆E1/2 for the pH independent OsP3+/2+ couple.

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Figure 3. Overlaid cyclic voltammograms for FTOOsP2+ (Γ = 1.2 × 10-10 mol/cm2) with H2Q (1.0 mM) in 500 mM buffers with phosphate (blue, H2PO44/HPO42, pKa 7.2 at pH 6.5), acetate (red, HAc/Ac, pKa 4.7 at pH 4.0), or citrate (black, H3C6H5O7/H2C6H5O7‒, pKa 6.4 at pH 3.0), co-loaded with NBuOP (cyan, pKa = 6.5). All data were acquired in 0.5 M NaCl at a scan rate of 100 mVs-1 at 295 ± 3 K. Arrows depict the direction of the scans. The catalytic waves were scan rate dependent with Ep values that shift systematically to higher potentials as the scan rate is increased. For example, for the phosphate buffer, Ep = 0.83 V at a scan rate of 10 mV s-1. The latter shifts to Ep = 0.9 V at 200 mVs-1 (figure S1-3) similar to results obtained earlier on the oxidation of tyrosine23 by diffusional electron transfer to the electrode and chemical oxidation at surfacebound OsP2+ sites.23 The rate constant (k) for H2Q oxidation to Q was evaluated by a cyclic voltammetry procedure described below with more details in the SI.29 For a surface diffusional process, application of the ButlerVolmer equation gives limiting peak currents, , as shown in eq 4.29-30 0.227 exp

(4)

In eq 4, Ip is the peak current of the electrode area; F is the faradaic constant, 96,485 C/mol; A is the electrode surface area, cm2; n is the number of electrons transferred, taken to be 2 for hydroquinone oxidation to quinone; C is the concentration of hydroquinone, mol/cm3; is the transfer coefficient; Ep is the peak potential, V; is the apparent formal potential for the electrochemical process,30 f = F/RT, F is the faradaic constant, R is the gas constant, 8.314 J/(K/Mol), T is the temperature in K; ko is the diffusional electron transfer rate constant in cm/s. Analysis of the CV data by using eq 4, and plots of lnIp vs Ep-E0f, are shown in fig S6 of the SI along with kinetic fits. Rate constants obtained from the fits are presented in Table 1. Table 1. List of rate constants obtained by use of eq. 4. Base/solvent pH k×10-6 (cm s-1)(a) Citrate 3.0 6.71 Acetate 4.0 3.29 Phosphate 7.2 4.77


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NBuOP Unbuffered H2O

~7.0 ~7.0

3.62 1.53

Data were acquired with FTO-OsP2+ 1 mM of H2Q, 500 mM of buffer with a constant I = 0.5 M NaCl as a supporting electrolyte at 295±2 0C.

Figure 4. Illustrating surface assemblies with: (a) a NBuOP base co-loaded with the Os(III) catalyst, (b) the Os(III) catalyst with an added acceptor base, B.

a

DISCUSSION In 1.0 mM solutions of H2Q in 0.5 M NaCl, an electrochemically irreversible wave for the Q/H2Q couple is observed on FTO electrodes that are surface modified by the addition of OsP2+. The origin of the wave was first discussed by Laviron in his pioneering study on the Q/H2Q couple.31 Under our conditions, on chemically modified OsP2+ electrodes, electron transfer involving the Q/H2Q couple is initiated by addition of the complex to the surface. Given the kinetics data with added bases, and the results in Figure 3, the chemistry at the surface includes pathways for H2Q oxidation that are catalyzed by added bases.32 The appearance of these pathways is consistent with earlier results on interconversion between Q/H2Q by proton-coupled electron transfer, where electron transfer occurred to OsP2+ and proton transfer to the acid form of the base.14,33 For the base-derivatized surface, with both OsP2+ and the pyridyl base surface bound, electron and proton transfer occur to adjacent electron and proton acceptor sites on the surface, Figure 4a.

(a)

The ability of the electrode to catalyze the oxidation of H2Q from pH 6.5 to 3.0 with added bases with the OsP3+/2+ couple at E1/2 = 0.80 V vs. NHE is impressive. At pH 3 with the buffer ‒ H3C6H5O7/H2C6H5O7 , the reaction is initiated by oxidation of –OsP2+ to OsP3+ followed by proton transfer to the base H2C6H5O7‒ in a reaction that is disfavored by 0.3 V (Scheme 1). Scheme 1 -OsP2+ - e- → -OsP3+ -OsP3+ + HO-C6H4-OH---H2C6H5O7‒ → -OsP2+ + HO-C6H4-O● + H2C6H5O7-H (RDS) -OsP3+ + HO-C6H4-O● → -OsP2+ + O=C6H4=O + H+ The mechanistic details at the derivatized electrodes in the absence of added buffer at pH 7 are less clear. However, the current was significantly decreased compared to solutions with the added H2PO4-/HPO42buffer. With no added base and water as the proton acceptor, with pKa(H3O+) ≤ 0, the mechanism may involve a direct outer-sphere oxidation at the electrode,34 Scheme 2, followed by loss of a second electron and proton equilibration. Scheme 2 -OsP2+ - e- → -OsP3+ -OsP3+ + HO-C6H4-OH → -OsP2+ + HO-C6H4-OH●+

(b)

-OsP3+ + HO-C6H4-OH● → -OsP2+ + O=C6H4=O + 2H+ CONCLUSIONS The results described here are directly relevant for applications involving solution-based Q/H2Q couples in battery, Dye Sensitized Photoelectrochemical Cells (DSPEC), or related applications. Our results provide direct insight into the importance of surface catalysis by an OsP3+/2+ couple with added rate control by added buffers with enhancements based on protoncoupled electron transfer. Variations with added bases



are consistent with the acid-base properties of the buffer with a rate enhancement of up to a factor of ~6 in 500 mM H3C6H5O7/H2C6H5O7‒. It is also notable that minimum base is required for the surface enhancement effect with added NBuOP with both catalyst and base added to the electrode surface. ASSOCIATED CONTENT Supporting Information. Experimental details and figures. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author [email protected] ACKNOWLEDGMENT This work is solely supported as part of the UNC EFRC: Center for Solar Fuels, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001011. The XPS analysis was performed at the Chapel Hill Analytical and Nanofabrication Laboratory CHANL, a member of the North Carolina Research Triangle Nanotechnology Network, RTNN, which is supported by the National Science Foundation, Grant ECCS1542015, as part of the National Nanotechnology Coordinated Infrastructure, NNCI. References 1. Gagliardi, C. J.; Westlake, B. C.; Kent, C. A.; Paul, J. J.; Papanikolas, J. M.; Meyer, T. J., Integrating Proton Coupled Electron Transfer (PCET) and Excited States. Coord. Chem. Rev. 2010, 254, 2459-2471. 2. Weinberg, D. R.; Gagliardi, C. J.; Hull, J. F.; Murphy, C. F.; Kent, C. A.; Westlake, B. C.; Paul, A.; Ess, D. H.; McCafferty, D. G.; Meyer, T. J., ProtonCoupled Electron Transfer. Chem. Rev. 2012, 112, 4016-93. 3. Dongare, P.; Maji, S.; Hammarström, L., Direct Evidence of a Tryptophan Analogue Radical Formed in a Concerted Electron−Proton Transfer Reaction in Water. J. Am. Chem. Soc. 2016, 138, 2194-2199. 4. Soetbeer, J.; Dongare, P.; Hammarstrom, L., Marcus-Type Driving Force Correlations Reveal the Mechanism of Proton-Coupled Electron Transfer for

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Phenols and [Ru(bpy)3]3+ in Water at Low pH. Chem. Sci. 2016, 7, 4607-4612. 5. Rugolo, J.; Aziz, M. J., Electricity Storage for Intermittent Renewable Sources. Energy Environ. Sci. 2012, 5, 7151-7160. 6. Son, E. J.; Kim, J. H.; Kim, K.; Park, C. B., Quinone and Its Derivatives for Energy Harvesting and Storage Materials. J Mater Chem A 2016, 4, 11179-11202. 7. Soloveichik, G. L., Flow Batteries: Current Status and Trends. Chem. Rev. 2015, 115, 1153311558. 8. Ashford, D. L.; Gish, M. K.; Vannucci, A. K.; Brennaman, M. K.; Templeton, J. L.; Papanikolas, J. M.; Meyer, T. J., Molecular Chromophore–Catalyst Assemblies for Solar Fuel Applications. Chem. Rev. 2015, 115, 13006-13049. 9. Brennaman, M. K.; Dillon, R. J.; Alibabaei, L.; Gish, M. K.; Dares, C. J.; Ashford, D. L.; House, R. L.; Meyer, G. J.; Papanikolas, J. M.; Meyer, T. J., Finding the Way to Solar Fuels with Dye-Sensitized Photoelectrosynthesis Cells. J. Am. Chem. Soc. 2016, 138, 13085-13102. 10. Gupta, N.; Linschitz, H., Hydrogen-Bonding and Protonation Effects in Electrochemistry of Quinones in Aprotic Solvents. J. Am. Chem. Soc. 1997, 119, 6384-6391. 11. Alligrant, T. M.; Alvarez, J. C., The Role of Intermolecular Hydrogen Bonding and Proton Transfer in Proton-Coupled Electron Transfer. J. Phys. Chem. C 2011, 115, 10797-10805. 12. Medina-Ramos, J.; Alligrant, T. M.; Clingenpeel, A.; Alvarez, J. C., Comparing the Hydrogen-Bonding Effect of Brönsted Bases in Solution and When They Are Covalently Bound to the Surface of Glassy Carbon Electrodes in the Electrochemical Behavior of Hydroquinone. J. Phys. Chem. C 2012, 116, 20447-20457. 13. Clare, L. A.; Pham, A. T.; Magdaleno, F.; Acosta, J.; Woods, J. E.; Cooksy, A. L.; Smith, D. K., Electrochemical Evidence for Intermolecular ProtonCoupled Electron Transfer through a Hydrogen Bond Complex in a P-Phenylenediamine-Based Urea. Introduction of the “Wedge Scheme” as a Useful Means to Describe Reactions of This Type. J. Am. Chem. Soc. 2013, 135, 18930-18941. 14. Gamboa-Valero, N.; Astudillo, P. D.; González-Fuentes, M. A.; Leyva, M. A.; Rosales-Hoz, M. d. J.; González, F. J., Hydrogen Bonding Complexes in the Quinone-Hydroquinone System and the Transition to a Reversible Two-Electron Transfer Mechanism. Electrochim. Acta 2016, 188, 602-610. 15. Dongare, P.; Myron, B. D. B.; Wang, L.; Thompson, D. W.; Meyer, T. J., [Ru(bpy)3]2+∗


Page 7 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Revisited. Is It Localized or Delocalized? How Does It Decay? Coord. Chem. Rev. 2017, 345, 86-107. 16. Ji, X.; Banks, C. E.; Silvester, D. S.; Wain, A. J.; Compton, R. G., Electrode Kinetic Studies of the Hydroquinone−Benzoquinone System and the Reaction between Hydroquinone and Ammonia in Propylene Carbonate: Application to the Indirect Electroanalytical Sensing of Ammonia. J. Phys. Chem. C 2007, 111, 1496-1504. 17. Song, N.; Gagliardi, C. J.; Binstead, R. A.; Zhang, M. T.; Thorp, H.; Meyer, T. J., Role of ProtonCoupled Electron Transfer in the Redox Interconversion between Benzoquinone and Hydroquinone. J. Am. Chem. Soc. 2012, 134, 1853841. 18. Song, N.; Zhang, M.-T.; Binstead, R. A.; Fang, Z.; Meyer, T. J., Multiple Pathways in the Oxidation of a Nadh Analogue. Inorg. Chem. 2014, 53, 4100-4105. 19. Kelvin, H. L. Z.; Kai, X.; Mark, G. B.; Russell, G. E., P -Type Transparent Conducting Oxides. J. Phys.: Condens. Matter 2016, 28, 383002. 20. Liu, H.; Avrutin, V.; Izyumskaya, N.; Özgür, Ü.; Morkoç, H., Transparent Conducting Oxides for Electrode Applications in Light Emitting and Absorbing Devices. Superlattices Microstruct. 2010, 48, 458-484. 21. Dixon, S. C.; Scanlon, D. O.; Carmalt, C. J.; Parkin, I. P., N-Type Doped Transparent Conducting Binary Oxides: An Overview. J Mater Chem C 2016, 4, 6946-6961. 22. Moholkar, A. V.; Pawar, S. M.; Rajpure, K. Y.; Bhosale, C. H.; Kim, J. H., Effect of Fluorine Doping on Highly Transparent Conductive Spray Deposited Nanocrystalline Tin Oxide Thin Films. Appl. Surf. Sci. 2009, 255, 9358-9364. 23. Gagliardi, C. J.; Jurss, J. W.; Thorp, H. H.; Meyer, T. J., Surface Activation of Electrocatalysis at Oxide Electrodes. Concerted Electron−Proton Transfer. Inorg. Chem. 2011, 50, 2076-2078. 24. Galano, A., et al., Empirically Fitted Parameters for Calculating Pka Values with Small Deviations from Experiments Using a Simple Computational Strategy. J Chem Inform Model 2016, 56, 1714-1724. 25. Gillaizeau-Gauthier, I.; Odobel, F.; Alebbi, M.; Argazzi, R.; Costa, E.; Bignozzi, C. A.; Qu, P.; Meyer, G. J., Phosphonate-Based Bipyridine Dyes for Stable Photovoltaic Devices. Inorg. Chem. 2001, 40, 6073-6079. 26. Wang, D.; Marquard, S. L.; Troian-Gautier, L.; Sheridan, M. V.; Sherman, B. D.; Wang, Y.; Eberhart, M. S.; Farnum, B. H.; Dares, C. J.; Meyer, T. J., Interfacial Deposition of Ru(II) BipyridineDicarboxylate Complexes by Ligand Substitution for

Applications in Water Oxidation Catalysis. J. Am. Chem. Soc. 2018, 140, 719-726. 27. Hyde, J. T.; Hanson, K.; Vannucci, A. K.; Lapides, A. M.; Alibabaei, L.; Norris, M. R.; Meyer, T. J.; Harrison, D. P., Electrochemical Instability of Phosphonate-Derivatized, Ruthenium(III) Polypyridyl Complexes on Metal Oxide Surfaces. ACS Appl. Mater. Interfaces 2015, 7, 9554-9562. 28. Quan, M.; Sanchez, D.; Wasylkiw, M. F.; Smith, D. K., Voltammetry of Quinones in Unbuffered Aqueous Solution: Reassessing the Roles of Proton Transfer and Hydrogen Bonding in the Aqueous Electrochemistry of Quinones. J. Am. Chem. Soc. 2007, 129, 12847-12856. 29. Bard, A. J.; Faulkner, L. R., Electrochemical Methods: Fundamentals and Applications, 2 ed.; John Wiley & Sons, Inc: New York, 2001. 30. Wanga, Y.; Hasebe, Y., Methylene BlueInduced Stabilization Effect of Adsorbed Glucose Oxidase on a Carbon-Felt Surface for Bioelectrocatalytic Activity. J electrochem soc 2012, 159, F110-F118 31. Laviron, E., Electrochemical Reactions with Protonations at Equilibrium. J Electroanal Chem Interface Electrochem 1984, 169, 29-46. 32. Song, N.; Concepcion, J. J.; Binstead, R. A.; Rudd, J. A.; Vannucci, A. K.; Dares, C. J.; Coggins, M. K.; Meyer, T. J., Base-Enhanced Catalytic Water Oxidation by a Carboxylate–Bipyridine Ru(II) Complex. Proc. Natl. Acad. Sci. 2015, 112, 49354940. 33. Song, N.; Dares, C. J.; Sheridan, M. V.; Meyer, T. J., Proton-Coupled Electron Transfer Reduction of a Quinone by an Oxide-Bound Riboflavin Derivative. J. Phys. Chem. C 2016, 120, 23984-23988. 34. Rees, N. V.; Clegg, A. D.; Klymenko, O. V.; Coles, B. A.; Compton, R. G., Marcus Theory for Outer-Sphere Heterogeneous Electron Transfer: Predicting Electron-Transfer Rates for Quinones. J. Phys. Chem. B 2004, 108, 13047-13051.



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Hydroquinone Couple by a

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