期刊
CATALYSTS
卷 9, 期 11, 页码 -出版社
MDPI
DOI: 10.3390/catal9110926
关键词
water oxidation; cobalt oxides; in situ spectroscopy; EPR; spectroelectrochemistry
资金
- Deutsche Forschungsgemeinschaft (DFG) Cluster of Excellence RESOLV [EXC1069]
- Australian Research Council [FT140100834]
- Australian Research Council [FT140100834] Funding Source: Australian Research Council
Here we report an in situ electron paramagnetic resonance (EPR) study of a low-cost, high-stability cobalt oxide electrodeposited material (Co-Pi) that oxidizes water at neutral pH and low over-potential, representing a promising system for future large-scale water splitting applications. Using CW X-band EPR we can follow the film formation from a Co(NO3)(2) solution in phosphate buffer and quantify Co uptake into the catalytic film. As deposited, the film shows predominantly a Co(II) EPR signal, which converts into a Co(IV) signal as the electrode potential is increased. A purpose-built spectroelectrochemical cell allowed us to quantify the extent of Co(II) to Co(IV) conversion as a function of potential bias under operating conditions. Consistent with its role as an intermediate, Co(IV) is formed at potentials commensurate with electrocatalytic O-2 evolution (+1.2 V, vs. SHE). The EPR resonance position of the Co(IV) species shifts to higher fields as the potential is increased above 1.2 V. Such a shift of the Co(IV) signal may be assigned to changes in the local Co structure, displaying a more distorted ligand field or more ligand radical character, suggesting it is this subset of sites that represents the catalytically 'active' component. The described spectroelectrochemical approach provides new information on catalyst function and reaction pathways of water oxidation.
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