Imperial College London
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Dr Samuel Hillman

Faculty of Natural Sciences, Department of Chemistry

Research Associate
 
 
 
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Contact

 

s.hillman16

 
 
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Location

 

G22Molecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Citation

BibTex format

@article{Bozal-Ginesta:2021:10.1021/acscatal.1c03290,
author = {Bozal-Ginesta, C and Rao, RR and Mesa, CA and Liu, X and Hillman, SAJ and Stephens, IEL and Durrant, JR},
doi = {10.1021/acscatal.1c03290},
journal = {ACS Catalysis},
pages = {15013--15025},
title = {Redox-state kinetics in water-oxidation IrOx electrocatalysts measured by operando spectroelectrochemistry},
url = {http://dx.doi.org/10.1021/acscatal.1c03290},
volume = {11},
year = {2021}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - Hydrous iridium oxides (IrOx) are the best oxygen evolution electrocatalysts available for operation in acidic environments. In this study, we employ time-resolved operando spectroelectrochemistry to investigate the redox-state kinetics of IrOx electrocatalyst films for both water and hydrogen peroxide oxidation. Three different redox species involving Ir3+, Ir3.x+, Ir4+, and Ir4.y+ are identified spectroscopically, and their concentrations are quantified as a function of applied potential. The generation of Ir4.y+ states is found to be the potential-determining step for catalytic water oxidation, while H2O2 oxidation is observed to be driven by the generation of Ir4+ states. The reaction kinetics for water oxidation, determined from the optical signal decays at open circuit, accelerates from ∼20 to <0.5 s with increasing applied potential above 1.3 V versus reversible hydrogen electrode [i.e., turnover frequencies (TOFs) per active Ir state increasing from 0.05 to 2 s–1]. In contrast, the reaction kinetics for H2O2 is found to be almost independent of the applied potential (increasing from 0.1 to 0.3 s–1 over a wider potential window), indicative of a first-order reaction mechanism. These spectroelectrochemical data quantify the increase of both the density of active Ir4.y+ states and the TOFs of these states with applied positive potential, resulting in the observed sharp turn on of catalytic water oxidation current. We reconcile these data with the broader literature while providing a unique kinetic insight into IrOx electrocatalytic reaction mechanisms, indicating a first-order reaction mechanism for H2O2 oxidation driven by Ir4+ states and a higher-order reaction mechanism involving the cooperative interaction of multiple Ir4.y+ states for water oxidation.
AU  - Bozal-Ginesta,C
AU  - Rao,RR
AU  - Mesa,CA
AU  - Liu,X
AU  - Hillman,SAJ
AU  - Stephens,IEL
AU  - Durrant,JR
DO  - 10.1021/acscatal.1c03290
EP  - 15025
PY  - 2021///
SN  - 2155-5435
SP  - 15013
TI  - Redox-state kinetics in water-oxidation IrOx electrocatalysts measured by operando spectroelectrochemistry
T2  - ACS Catalysis
UR  - http://dx.doi.org/10.1021/acscatal.1c03290
UR  - https://pubs.acs.org/doi/abs/10.1021/acscatal.1c03290
UR  - http://hdl.handle.net/10044/1/93069
VL  - 11
ER  -
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