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Photoinduced Absorption Spectroscopy of CoPi on BiVO 4 : The Function of CoPi during Water Oxidation
Author(s) -
Ma Yimeng,
Kafizas Andreas,
Pendlebury Stephanie R.,
Le Formal Florian,
Durrant James R.
Publication year - 2016
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201600711
Subject(s) - copi , materials science , surface photovoltage , photoelectrochemistry , photochemistry , chemical engineering , spectroscopy , electrochemistry , chemistry , electrode , golgi apparatus , biochemistry , physics , quantum mechanics , secretory pathway , engineering , cell
This paper employs photoinduced absorption and electrochemical techniques to analyze the charge carrier dynamics that drive photoelectrochemical water oxidation on bismuth vanadate (BiVO 4 ), both with and without cobalt phosphate (CoPi) co‐catalyst. These results are correlated with spectroelectrochemical measurements of Co II oxidation to Co III in a CoPi/FTO (fluorine doped tin oxide) electrode during dark electrocatalytic water oxidation. Electrocatalytic water oxidation exhibits a non‐linear dependence on Co III density, with a sharp onset at 1 × 10 17 Co III cm −2 . These results are compared quantitatively with the degree of CoPi oxidation observed under conditions of photoinduced water oxidation on CoPi–BiVO 4 photoanodes. For the CoPi–BiVO 4 photoanodes studied herein, ≤5% of water oxidation proceeds from CoPi sites, making the BiVO 4 surface the predominant water oxidation site. This study highlights two key factors that limit the ability of CoPi to improve the catalytic performance of BiVO 4 : 1) the kinetics of hole transfer from the BiVO 4 to the CoPi layer are too slow to effectively compete with direct water oxidation from BiVO 4 ; 2) the slow water oxidation kinetics of CoPi result in a large accumulation of Co III states, causing an increase in recombination. Addressing these factors will be essential for improving the performance of CoPi on photoanodes for solar‐driven water oxidation.