Speaker: Reshma R Rao, lmperial College London

Time: 20:00 p.m., June 13, 2023, GMT+8

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Abstract:

One of the most remarkable catalytic reactions observed in nature is the oxidation of water at Photosystem II, which harnesses energy from sunlight. The mechanism for water oxidation involves the accumulation of multiple oxidizing equivalents in close proximity, which triggers the crucial O-O bond formation step. Such a mechanism, relying on ‘redox levelling’ of neighbouring centres has been increasingly shown to be at play on a number of photo- and electrocatalysts. In this talk, I will present developments in time-resolved optical spectroscopy to identify the density of different oxidized species as a function of potential and establish how this controls the reaction kinetics. As an example, monolayers of molecular iridium dimers and heterogeneous amorphous iridium oxides will be compared for the water oxidation reaction. For the catalysts investigated, three redox transitions can be observed. Although similar oxidized species are found to accumulate at water oxidation potentials, the correlation between the density of oxidized species and water oxidation kinetics is very different. On molecular catalysts, there is limited interaction between isolated iridium centres, and thus the intrinsic activity per oxidized site is invariant with potential. On the contrary, for heterogeneous oxide catalysts, a high degree of cooperative effects results in faster kinetics with increasing accumulation of oxidized species on the surface. Therefore, through this work, I will highlight the power of operando time-resolved spectroscopy in unravelling the critical role of oxidized species in facilitating water oxidation kinetics and the implications of this on catalyst design.

Biography:

Reshma obtained her PhD in 2019 from the Massachusetts Institute of Technology, where she worked with Professor Yang Shao-Horn on understanding the fundamental processes that occur at oxide-water interfaces under electrochemical conditions that are relevant for water splitting. In January 2020, she moved to Imperial College London, as a Research Associate in Professor James Durrant's group in the Department of Chemistry; from 2021 she was also co-advised by Dr. Ifan Stephens in the Department of Materials. Since October 2022, Reshma holds a Royal Academy of Engineering research fellowship at the Department of Materials, Imperial College London. Her research interests include understanding (electro)chemical reactivity at solid-gas and solid-liquid interfaces using operando spectroscopic techniques.

Source: iCANX