Oxygen Reduction Reaction at Multi-Copper Complexes Investigated by Modified Electrode and In Situ XAFS
Recently, Gewirth and co-workers have achieved a preparation of binuclear copper complex, Cu2(Hdatrz)2, as an electrocatalyst for ORR[4-6]. Although the catalyst shows relatively large overpotential for ORR in acidic solution, the activity in alkaline solution is quite high. The active site for ORR in the catalyst has been proved to be bi-copper centers [6-7] and the investigation of ORR mechanism at the catalyst seems to be valuable.
In the present study, we have adopted in situ X-ray absorption fine structure (XAFS) spectroscopy to monitor the electronic structure of Cu centers during ORR and to determine the molecular structure of Cu2(Hdatrz)2 complexes on electrodes. In situ XANES measurement has shown that the ORR at the Cu centers requires the formation of CuI species and the rate-determining step for ORR is dependent on pH.
For further development of metal complex catalysts by replacing Cu centers to other metal ions, a easy preparation of model complex electrode should be required. Chemically modified model electrodes are also constructed on gold surface to investigate ORR at multi-metal complex using electrochemistry and spectroscopic methods.
This work was supported by New Energy, Industrial Technology Development Organization (NEDO). XAFS experiments were performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2010G200 and 2013G173)
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