3 years ago

Observing the Electrochemical Oxidation of Co Metal at the Solid/Liquid Interface Using Ambient Pressure X-ray Photoelectron Spectroscopy

Observing the Electrochemical Oxidation of Co Metal at the Solid/Liquid Interface Using Ambient Pressure X-ray Photoelectron Spectroscopy
Stephanus Axnanda, Yong Han, Zhi Liu, Philip N. Ross, Yimin Li, Zahid Hussain, Baohua Mao, Ethan J. Crumlin, Rui Chang
Recent advances of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) have enabled the chemical composition and the electrical potential profile at a liquid/electrode interface under electrochemical reaction conditions to be directly probed. In this work, we apply this operando technique to study the surface chemical composition evolution on a Co metal electrode in 0.1 M KOH aqueous solution under various electrical biases. It is found that an ∼12.2 nm-thick layer of Co(OH)2 forms at a potential of about −0.4 VAg/AgCl, and upon increasing the anodic potential to about +0.4 VAg/AgCl, this layer is partially oxidized into cobalt oxyhydroxide (CoOOH). A CoOOH/Co(OH)2 mixture layer is formed on the top of the electrode surface. Finally, the oxidized surface layer can be reduced to Co0 at a cathodic potential of −1.35 VAg/Cl. These observations indicate that the ultrathin layer containing cobalt oxyhydroxide is the active phase for oxygen evolution reaction (OER) on a Co electrode in an alkaline electrolyte, consistent with previous studies.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcb.7b05982

DOI: 10.1021/acs.jpcb.7b05982

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