Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
DOI: https://doi.org/10.29363/nanoge.nfm.2022.185
Publication date: 11th July 2022
Iridium oxide is the state-of-the-art electrocatalyst for water oxidation in polymer electrolyte membrane (PEM) electrolysers for green hydrogen production. Amorphous iridium oxides (IrOx) show far higher activity than the rutile crystalline iridium oxides (IrO2), but the underlying origin behind the discrepancy in activity for IrOx and IrO2 remains poorly understood. Density functional theory (DFT) calculations are usually used to explain the kinetic difference based on the thermodynamic barrier for forming *OH, *O, and *OOH intermediates on a single Ir site of well-defined model catalysts.[1, 2] However, unambiguously correlating the theoretical free energy with experimentally observed kinetic is very challenging, especially for disordered and non-well defined nano-particle systems, such as amorphous IrOx. In addition, the ambiguities in measuring the number of active states for determining the intrinsic activity per states has further rendered it difficult to understanding the correlation between activity and the observed physical/chemical discrepancies on IrOx and IrO2.
In this talk, I will present our results on using time-resolved UV-vis absorption spectroscopy to experimentally probe the energetics of intermediate states and correlating them with water oxidation kinetics on rutile and amorphous iridium oxides. We have identified the same oxidised species for both IrOx and IrO2 and quantified their concentrations as a function of potential. By comparing the concentration of oxidised states to water oxidation reaction rates, we can directly measure turnover frequency (TOF) for IrOx and IrO2 and correlated them with the experimentally measured energetics of the states. Therefore, this study shines insights into the origin of activity difference between amorphous and rutile iridium oxides.
The authors would like to acknowledge the funding support from BP through the BP International Centre for Advanced Materials (bp-ICAM), and Imperial College-Chinese Scholarship Council Studentship, which made this research possible.
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