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Quantum Chemical Study of Hydrogen Evolution during Cobalt Electrodeposition

Abstract

The hydrogen evolution reaction (HER) occurs always as a secondary process during the cobalt electrochemical deposition in an aqueous solution. Thus, the pH at the electrode/electrolyte interface as well as kinetics and mechanism of cobalt electrodeposition can be modified. As a consequence, the growth of deposit may be strongly affected and the formation of porous structure can be obtained. Density Functional Theory (DFT) study has been used to resolve structural issue related to the insitu (electrochemical) X-ray diffraction (XRD) patterns of a well-defined Co electrode surface in aqueous sulphate acid solution. Fundamental concepts postulate that H and H+ cations were the most likely constituents in the compact layer. The adsorption of hydrogen at strained clean Co surfaces has been studied by calculations based on DFT. Both varieties of Co crystallographic structure: hexagonal closed-packed and face centered-cubic were considered, since they have appeared in the XRD results. The calculations were performed for four hkl planes of cubic-Co: (100), (110), (111) and (220) and four hkl planes of hexagonal-Co: (100), (110), (101) and (011). The quantum calculations distinguished more and less stable Co surfaces for the hydrogen adsorption. Considering Eads for each crystallographic plane the formation of Co structure formed during electrochemical processing is discussed.

Agnieszka Franczak, Frédéric Bohr, Alexandra Levesque and Jean-Paul Chopart

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