Tuning Catalytic Activity of Ni-Co Nanoparticles Synthesized by Gamma-Radiolytic Reduction of Acetate Aqueous Solutions

Transition metal-based catalysts show great potential to replace Pt-based material in energy conversion devices thanks to their low cost, reasonable intrinsic activity, thermodynamic stability, and corrosion resistance. The electrochemical performance of such catalysts is sensitive to their composition and structure. Here, it is demonstrated that homogeneous alloy nanoparticles with varying Ni-to-Co ratio and controlled structure can be synthesized from aqueous Ni(Co) acetate solutions using a facile gamma-radiolytic reduction method. The obtained samples are found to possess defects that are ordered to form polytypes structures. The concentration of these defects depends on the Ni-to-Co ratio, as supported by the results of ab initio calculations. It is found that structural defects may influence the activity of catalysts toward the oxygen evolution reaction, while this effect is less pronounced with respect to the oxygen reduction reaction. At the same time, the activity of Ni-Co catalysts in the hydrogen evolution reaction is affected by formation of Ni-OH bonds on the surface rather than by the presence of structural defects. This study demonstrates that the composition of Ni-Co nanoparticles is an essential factor affecting their structure, and both composition and structure can be tuned to optimize electrochemical performance with respect to various catalytic reactions.