TY - JOUR

T1 - Spectroelectrochemical Analysis of the Water Oxidation Mechanism on Doped Nickel Oxides

AU - Rao, Reshma R.

AU - Corby, Sacha

AU - Bucci, Alberto

AU - García-Tecedor, Miguel

AU - Mesa, Camilo A.

AU - Rossmeisl, Jan

AU - Giménez, Sixto

AU - Lloret-Fillol, Julio

AU - Stephens, Ifan E.L.

AU - Durrant, James R.

N1 - Funding Information: The authors would like to acknowledge funding from the EU FET programme (A-LEAF 732840). S.C. would like to thank Imperial College for a Schrodinger Scholarship. I.E.L.S. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 866402). R.R.R., J.R.D., and I.E.L.S. 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. S.G. acknowledges the financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain through projects ENE2017-85087-C3-1- R and PID2020-116093RB-C41, and S.G. and C.A.M. acknowledge the Generalitat Valeniana for grant APOSTD (APOSTD/2021/251) and University Jaume I, for postdoc fellowship POSDOC/2019/20 and project UJI-B2020-50. Publisher Copyright: © 2022 American Chemical Society. All rights reserved.

PY - 2022/5/4

Y1 - 2022/5/4

N2 - Metal oxides and oxyhydroxides exhibit state-of-the-art activity for the oxygen evolution reaction (OER); however, their reaction mechanism, particularly the relationship between charging of the oxide and OER kinetics, remains elusive. Here, we investigate a series of Mn-, Co-, Fe-, and Zn-doped nickel oxides using operando UV-vis spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry. The Ni2+/Ni3+redox peak potential is found to shift anodically from Mn- < Co- < Fe- < Zn-doped samples, suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped samples. At OER-relevant potentials, using optical absorption spectroscopy, we quantitatively detect the subsequent oxidation of these redox centers. The OER kinetics was found to have a second-order dependence on the density of these oxidized species, suggesting a chemical rate-determining step involving coupling of two oxo species. The intrinsic turnover frequency per oxidized species exhibits a volcano trend with the binding energy of oxygen on the Ni site, having a maximum activity of ∼0.05 s-1at 300 mV overpotential for the Fe-doped sample. Consequently, we propose that for Ni centers that bind oxygen too strongly (Mn- and Co-doped oxides), OER kinetics is limited by O-O coupling and oxygen desorption, while for Ni centers that bind oxygen too weakly (Zn-doped oxides), OER kinetics is limited by the formation of oxo groups. This study not only experimentally demonstrates the relation between electroadsorption free energy and intrinsic kinetics for OER on this class of materials but also highlights the critical role of oxidized species in facilitating OER kinetics.

AB - Metal oxides and oxyhydroxides exhibit state-of-the-art activity for the oxygen evolution reaction (OER); however, their reaction mechanism, particularly the relationship between charging of the oxide and OER kinetics, remains elusive. Here, we investigate a series of Mn-, Co-, Fe-, and Zn-doped nickel oxides using operando UV-vis spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry. The Ni2+/Ni3+redox peak potential is found to shift anodically from Mn- < Co- < Fe- < Zn-doped samples, suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped samples. At OER-relevant potentials, using optical absorption spectroscopy, we quantitatively detect the subsequent oxidation of these redox centers. The OER kinetics was found to have a second-order dependence on the density of these oxidized species, suggesting a chemical rate-determining step involving coupling of two oxo species. The intrinsic turnover frequency per oxidized species exhibits a volcano trend with the binding energy of oxygen on the Ni site, having a maximum activity of ∼0.05 s-1at 300 mV overpotential for the Fe-doped sample. Consequently, we propose that for Ni centers that bind oxygen too strongly (Mn- and Co-doped oxides), OER kinetics is limited by O-O coupling and oxygen desorption, while for Ni centers that bind oxygen too weakly (Zn-doped oxides), OER kinetics is limited by the formation of oxo groups. This study not only experimentally demonstrates the relation between electroadsorption free energy and intrinsic kinetics for OER on this class of materials but also highlights the critical role of oxidized species in facilitating OER kinetics.

U2 - 10.1021/jacs.1c08152

DO - 10.1021/jacs.1c08152

M3 - Journal article

C2 - 35442661

AN - SCOPUS:85129228710

VL - 144

SP - 7622

EP - 7633

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 17

ER -