Resolving Water-Oxidation Kinetics by Combining Operando Spectroscopy with O2 Evolution Rates over Seven Orders of Magnitude
5 affiliations
- 1Department of Materials
- 2Imperial College London
- 3Department of Chemistry
- 4University of Oxford
- 5University of Copenhagen
Abstract
Electrocatalytic water oxidation is central to renewable energy conversion, yet the origin of its potential–current response remains challenging to define. Classical electrode kinetics attributes the empirical exponential increase in current with potential to the linearly lowering of the activation barrier with applied potential, as described by Butler–Volmer formalisms, while potential-dependent coverage of active surface states has also been considered as an important factor in electrocatalytic kinetics. However, direct quantitative experimental links between the state evolution, activation-energy changes, and the macroscopic potential-current response remain limited. Here, by combining temperature-dependent electrochemistry with operando optical spectroscopy, we show that the apparent activation energy decreases approximately linearly with the coverage of electrophilic *O active states on iridium oxide catalysts. Potential-current data across more than 7 orders of magnitude, obtained from microelectrode and electrochemical mass spectrometry, reveal a continuously evolving Tafel slope from ~20 to 160 mV dec-1, which is not captured by the simplest version of Butler-Volmer equation. In contrast, a second-order coverage-dependent barrier model, employing *O active state densities determined from optical spectroscopy, is found to give a good fit to the global potential-current response, with the coverage dependence of the activation barrier being in good agreement with that measured directly from temperature-dependent data. More complex models are also discussed. These results link water oxidation kinetics to the accumulation and interaction of active states, providing a framework for understanding kinetics of multistep electrocatalytic reactions.
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BibTeX
@misc{liang2026resolving,
title = {{Resolving Water-Oxidation Kinetics by Combining Operando Spectroscopy with O2 Evolution Rates over Seven Orders of Magnitude}},
author = {Caiwu Liang and Jack Kirk Pedersen and Reshma Rao and Jan Rossmeisl and Ifan E.L. Stephens and Soren B. Scott and James R. Durrant},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15009952/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009952/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Resolving Water-Oxidation Kinetics by Combining Operando Spectroscopy with O2 Evolution Rates over Seven Orders of Magnitude
AU - Caiwu Liang
AU - Jack Kirk Pedersen
AU - Reshma Rao
AU - Jan Rossmeisl
AU - Ifan E.L. Stephens
AU - Soren B. Scott
AU - James R. Durrant
PY - 2026
DA - 2026/10/05
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009952/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009952/v1
AB - Electrocatalytic water oxidation is central to renewable energy conversion, yet the origin of its potential–current response remains challenging to define. Classical electrode kinetics attributes the empirical exponential increase in current with potential to the linearly lowering of the activation barrier with applied potential, as described by Butler–Volmer formalisms, while potential-dependent coverage of active surface states has also been considered as an important factor in electrocatalytic kinetics. However, direct quantitative experimental links between the state evolution, activation-energy changes, and the macroscopic potential-current response remain limited. Here, by combining temperature-dependent electrochemistry with operando optical spectroscopy, we show that the apparent activation energy decreases approximately linearly with the coverage of electrophilic *O active states on iridium oxide catalysts. Potential-current data across more than 7 orders of magnitude, obtained from microelectrode and electrochemical mass spectrometry, reveal a continuously evolving Tafel slope from ~20 to 160 mV dec-1, which is not captured by the simplest version of Butler-Volmer equation. In contrast, a second-order coverage-dependent barrier model, employing *O active state densities determined from optical spectroscopy, is found to give a good fit to the global potential-current response, with the coverage dependence of the activation barrier being in good agreement with that measured directly from temperature-dependent data. More complex models are also discussed. These results link water oxidation kinetics to the accumulation and interaction of active states, providing a framework for understanding kinetics of multistep electrocatalytic reactions.
ER -