Electrodeposition of α-Ni/β-Co composite coatings on the carbon felt: Structural features and electrochemical performance

Efficient hydrogen production by electrolysis of aqueous and aqueous-alcohol solutions is based on the use of electrode materials with a low overpotential of hydrogen evolution reaction (HER). Apart from materials containing noble metals (Pt, Pd, etc.), coatings consisting of the iron triad metals (Fe, Ni, Co) obtained by electroplating method on the substrate surface (nickel foam, carbon fibers) are used. However, there is a problem with the crystallites size and the coating degree of the substrate. The use of simple (non-complex) electrolytes doesn't solve them. This article is devoted to the preparation of composite Ni-Co coatings from a complex citrate electrolyte by electrodeposition on carbon felt and their testing in an aqueous-alcoholic solution of KOH. The pH effect of the electrolyte on the morphology, structure, and electrochemical properties has been studied. The morphology and structure of synthesized coatings have been investigated using SEM and PXRD methods. The chemical composition of the samples has been determined by EDX spectroscopy. The electrochemical performance of the coatings has been evaluated by cyclic voltammetry and chronopotentiometry methods. The synthesized samples are carbon filaments with a submicron coating (300 nm) of the alpha-Ni/beta-Co composite. The crystallite sizes are 15 +/- 5 nm and depend on the pH value of the electrolyte used. It has been found that the use of nanocomposites reduced the overpotential of HER to -196 mV while maintaining their stability. Thus, the study shows that the use of a complex electrolyte based on citric acid allows obtaining nanoscale composite coatings of alpha-Ni/beta-Co on a carbon substrate. Changing the pH of the electrolyte makes it possible to vary the coating degree of the substrate and the Ni:Co ratio in the composite. A more detailed study of the observed overpotential shift to the anodic side remains an interesting issue. (C) 2020 Elsevier B.V. All rights reserved.