Issue 8, 2016

Kinetic analysis of photoelectrochemical water oxidation by mesostructured Co-Pi/α-Fe2O3 photoanodes

Abstract

Solar water splitting using catalyst-modified semiconductor photoelectrodes is a promising approach to harvesting and storing solar energy. Prior studies have demonstrated that modification of α-Fe2O3 photoanodes with the water-oxidation electrocatalyst Co-Pi enhances photon-to-current conversion efficiencies, particularly at less positive potentials, but the mechanism underlying this enhancement remains poorly understood. Different experimental techniques have suggested very different interpretations of the microscopic origins of this improvement. Here, we report results from photoelectrochemical and impedance measurements aimed at understanding the Co-Pi/α-Fe2O3 interface of mesostructured composite photoanodes. Contrary to expectations, these measurements reveal that α-Fe2O3 water-oxidation kinetics actually slow upon deposition of Co-Pi, but electron–hole recombination slows even more, resulting in a net enhancement of water-oxidation quantum efficiency. The negative shift in the JV curve caused by Co-Pi deposition is found to result from the introduction of an alternative pathway for water oxidation catalyzed by Co-Pi, which allows the composite photoanode to avoid positive charge accumulation at the α-Fe2O3 surface. We detail the role of Co-Pi thickness optimization in balancing the slower recombination against the slower water oxidation kinetics to achieve the lowest water-oxidation onset potential. These results provide new insights into the microscopic properties of the catalyst/semiconductor interface in Co-Pi/α-Fe2O3 composite solar water-splitting photoanodes.

Graphical abstract: Kinetic analysis of photoelectrochemical water oxidation by mesostructured Co-Pi/α-Fe2O3 photoanodes

Supplementary files

Article information

Article type
Paper
Submitted
03 ሴፕቴ 2015
Accepted
16 ኦክቶ 2015
First published
16 ኦክቶ 2015

J. Mater. Chem. A, 2016,4, 2986-2994

Author version available

Kinetic analysis of photoelectrochemical water oxidation by mesostructured Co-Pi/α-Fe2O3 photoanodes

G. M. Carroll and D. R. Gamelin, J. Mater. Chem. A, 2016, 4, 2986 DOI: 10.1039/C5TA06978E

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