Electrochemical study of formate oxidation at the nickel electrode

Ni-based nanoparticles (NPs) were synthesized, deposited on a carbon support, and comprehensively characterised by TGA, (HR)TEM, XRD and XPS. The material comprises of core-shell NPs with a metallic Ni core and a sub-stoichiometric oxygenated Ni shell, with total size ranging between 5 and 30 nm, dispersed onto Vulcan XC72 carbon support (Ni@Ni(O x H y )/C). Electrochemical studies at different scan rates and formate concentrations indicate that formate is oxidized from ca. 1.30 V vs. RHE and that formate oxidation is a diffusion-limited reaction in the studied conditions. Results from EIS, in situ Raman and in situ infrared spectroscopy evidence the underpotential formate adsorption on Ni(OH) 2 and NiOOH. The reaction is selective to carbon dioxide, which converts into carbonate ions because of the alkaline electrolyte. Moreover, formate oxidation seems to occur through a different pathway depending on the phase of nickel oxyhydroxide. The phase formed at lower potentials (γ-NiOOH) oxidises formate through a purely electrochemical pathway while the one (β-NiOOH) formed at higher potentials oxidises it through a catalytic electrochemical-chemical pathway, redox-mediated by the Ni(OH) 2 /NiOOH couple. Based on these findings, a reaction pathway is proposed for both phases.