Proceedings of nanoGe Spring Meeting 2022 (NSM22)
DOI: https://doi.org/10.29363/nanoge.nsm.2022.150
Publication date: 7th February 2022
Hydrogen plays a critical role in the energy transformation to a sustainable future, due to its widespread applications as a fuel for transport, feedstock to chemical industries and a heat source for buildings. Low temperature water electrolysis can enable hydrogen production renewably and at scale, but device efficiencies are currently limited by poor kinetics of water oxidation at the anode [1]. The low operating pH and high oxidizing conditions experienced at the anode in proton exchange membrane water electrolyzers limits the choice of materials to catalyse the oxygen evolution reaction to oxides of iridium, which is highly scarce [1],[2]. Mechanistic understanding of the water oxidation reaction on iridium oxides can enable rational development of more active catalysts with lesser precious metal loading.
Iridium oxides exhibit complex redox chemistry, which cannot be understood using electrochemical measurements alone. Particularly, the redox transitions on iridium oxides can exhibit non-Nernstian behavior, resulting in the redox transitions being dependent on pH and cations present in the electrolyte. In this talk, I will demonstrate the power of optical spectroscopy to track potential-dependent electroabsorption changes as a function of electrolyte pH from 1 to 13 on iridium based oxides. These measurements enable a direct comparison of the nature of redox active species in acidic and alkaline solution and also provide insights about the electrolyte environment on the redox potential, and consequently binding energetics of oxygenated species on IrOx. Using complementary stepped potential spectroelectrochemical measurements, the density of these redox active sites can also be computed as a function of potential [3] and the kinetics of water oxidation in acid and base can be linked directly to the density of oxidized species [4], [5]. Furthermore, in addition to quantitative detection of redox states, measurements of the kinetics of charge accumulation in natural and deuterated electrolyte provides insights into the role of ion transport within the oxide and the degree of bulk iridium redox. Therefore, based on our spectroscopic results on iridium-based oxides, we can experimentally probe the effect of interfacial pH and ions on charge accumulation and its impact on water oxidation kinetics.
The authors would also like to acknowledge the funding and technical support from BP through the BP International Centre for Advanced Materials (bp-ICAM), which made this research possible.
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