Electrochemical data and surface analyses are presented for RuOx ‐ and Pt‐modified surfaces of indium tin oxide (ITO) electrodes. The goal of this study was to combine the excellent optical transparency of this material with good catalytic activity. Spray pyrolysis was used to develop RuOx islands on the ITO electrode surface. Platinum was deposited by spray pyrolysis and electrodeposition. Unlike the ring‐like morphology obtained with RuOx , both methods yielded dense Pt clusters on the ITO surface. In all these cases, the good optical transparency of ITO was not compromised even at relatively high catalyst loads. For example, even at the maximal catalyst loadings in these experiments, the electrodes showed ∼50% light transparency. Detailed surface characterizations were carried out on these catalyst‐modified ITO surfaces using scanning electron microscopy, profilometry, scanning Auger microscopy, Auger electron spectroscopy, and x‐ray photoelectron spectroscopy. Electrochemical data for RuOx ‐ and Pt‐modified ITO electrodes are presented for the oxygen evolution, hydrogen evolution, and bromide oxidation reactions and compared with the behavior of the virgin material. Finally, an electrochemical method is described for assaying the Ru content of the ITO surface. This method yields results with an approximately one‐to‐one correspondence with the Ru content estimated from the Auger electron spectroscopy data.

Cyclic voltammetry (CV) is shown to be a useful technique for the evaluation of the performance of heterojunction photoelectrodes in photoelectrochemical systems. The Si/Sn‐doped indium oxide (ITO) heterojunction was used as a model system. Photoelectrochemical interfaces were constructed and analyzed, using this heterojunction in series with an aqueous redox electrolyte, comprising normalFefalse(CN)64−/3− or Fe2+/3+ redox couples. Both p‐type as well as n‐type Si substrates were utilized for this purpose. The photovoltage generated at the Si/ITO heterojunction is shown to be modified by overpotential losses at the ITO/redox electrolyte interface. Such losses are minimal for the normalFefalse(CN)64−/3− redox couple (a fast redox system) and appreciable for the Fe2+/3+ system, which is kinetically sluggish even in the presence of Cl− catalyst. The photoresponses of the Si/ITO/redox electrolyte interfaces were analyzed by CV as a function of three variables; namely, redox concentration, light flux, and applied potential. A simple equivalent‐circuit representation is finally presented for a heterojunction photoelectrode.

021ChemInform Abstract (by Ru and Pt).

Conductive and transparent oxide thin films such as Sb-doped tin oxide and Sn-doped indium oxide (ITO) generally display sluggish electrochemical behavior towards multi-electron redox systems. As a critical step towards the construction of a photoelectrolysis device based on Si/ITO heterojunctions, we describe herein our success with the design and optimization of catalytic charge-storage centers on the ITO electrode surface. The key feature of our approach is the control of catalyst morphology such that the excellent optical transparency of the ITO layer is not compromised to any significant extent. This is accomplished by a two-stage spray pyrolysis method which will be described in detail elsewhere (I). Aside from solar energy storage possibilities, the results described here may have relevance to other applications which require a combination of optical transparency and electrocatalytic property for the electrode material.The important finding of this study is that in the case of Ru, our catalytic modification approach results in the formation of a ring-like island morphology on the parent ITO surface. Representative photomicrographs are contained in Fig. I. This figure also illustrates the gradual overlap of the catalyst rings with increased loading (spray duration). Auger electron maps of the surface revealed the peripheral portions of the rings to be predominantly Ru with the center regions comprising mainly ITO. Consistent with the expectation that these catalyst islands are mainly localized on the surface, Auger depth profiles reveal a precipitous decline in the Ru levels a few X into the ITO layers. Detailed surface analyses of these catalytically-modified ITO layers will be presented in a forthcoming paper (i). Good optical transparency was maintained for these layers even at relatively high Ru loading (cf. Fig. Id). For example, transmittance measurements yielded values of 72% and 64% at 500 nm for samples shown in Fig. Ib and d, respectively. These values should be compared with the reference level of 80% recorded for bare ITO, cf. Fig. la. *Electrochemical Society Student Member, **Electrochemical Society Active Member.Platinization of the ITO surface results in a different island morphology relative to~e Ru case described above. Contrasting the ring-like structure noted with Ru, clusters form in this case, the distribution of which again is dependent on the spray-duration. Electrodeposited Pt yielded a similar morphology. Similar to the Ru case, the optical transparency of these platinized ITO layers was excellent.Representative polarization curves for Ru-and Pt-modified ITO electrodes are contained in Figs. 2-4. Curves for bare ITO are also shown for comparison. Details on ITO electrode fabrication have been given previously (2). The electrochemical data in Figs. 2-4 demonstrate the efficacy of catalytically-modified ITO layers for driving the 02 evolution, bromide oxidation, and proton reduction reactions. The modified electrodes show no deterioration in performance over many cycles of operation....

The kinetic facility of charge transfer was studied by cyclic voltammetry (CV) at Smdoped indium oxide (ITO) electrode/acetonitrile interfaces for 18 one-electron outer-sphere redox systems. The results were compared with Pt, and the relative trends in redoxkinetics were analyzed from a phenomenological viewpoint. The strong dependency of redox kinetics at the ITO surface on the location of electrolyte energy levels (redox potential) argues against the complete transparency of the space-charge layer in ITO to electron tunneling processes. The new results seem to be consistent with a model proposed by previous authors, which considers mediation of electron tunneling by deep-lying donor states in the space-charge region. For positive-lying redox systems, this mediation step is rate determining. For redox systems lying at potentials negative enough to overlap with the ITO conduction bandedge, a direct and facile charge transfer process seems to prevail. The implications of these kinetics trends in the use of ITO electrodes as a corrosion-resistant coating for n-Si and p-Si photoelectrode surfaces are next analyzed using CV and steady-state voltammetry. Correlations of the photopotentials measured at n-Si/ITO and p-Si/ITO for selected nonaqueous redox systems with redox potentials and kinetics parameters are finally presented, and the trends compared with "naked" Si surfaces. It is shown that CV is a more sensitive probe of kinetics effects than the steady-state scanning mode. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-04-13 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-04-13 to IP