The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. The production of hydrogen through water splitting seems a promising and appealing solution. We found that a robust nanoparticulate electrocatalytic material, H2–CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer. This material consists of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte and mediates H2 evolution from neutral aqueous buffer at modest overpotentials. Remarkably, it can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O2–CoCat or CoPi) catalysing O2 evolution. The switch between the two catalytic forms is fully reversible and corresponds to a local interconversion between two morphologies and compositions at the surface of the electrode. After deposition, the noble-metal-free coating thus functions as a robust, bifunctional and switchable catalyst.
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The authors thank P. Jegou for XPS measurements, B. Sartor for the design and construction of a specific electrochemical cell allowing working with FTO-coated glass electrodes, P. Chernev, K. Klingan, M. Risch and I. Zaharieva (FU Berlin) as co-workers during the XAS measurements at the KMC-1 beamline of the BESSY synchrotron (Helmholtz Zentrum Berlin, HZB) which were technically supported by F. Schäfers and M. Mertin (HZB). Financial support by the Nanosciences Program of CEA (Grant Nanocat’ O2), the UniCat cluster of excellence (Unifying Concepts in Catalysis, Berlin) and the European Commission (7th Framework Programme, SOLAR-H2, grant # 212508) is gratefully acknowledged.
A European patent application (EP-12352001) has been filed for the preparation, characterization and properties of H2-CoCat.
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Cobo, S., Heidkamp, J., Jacques, PA. et al. A Janus cobalt-based catalytic material for electro-splitting of water. Nature Mater 11, 802–807 (2012). https://doi.org/10.1038/nmat3385
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