Structural and compositional optimization of bimetallic NiCo alloy for of alkaline evolution reaction

Abstract

Alkaline hydrogen evolution reaction (HER) is highly desired due to its economic utility as well as its basic significance in the study of all electrocatalytic processes taking place on cathode electrodes. Herein, we report the nickel and cobalt-based bimetallic alloy nanoparticles embedded in nitrogen-doped carbon (NixCoy@NC) starting from novel metal-organic complexes. Among the synthesized alloy nanoparticle catalysts, Ni1Co3@NC exhibits the best performance for HER, reaching a current density of 10 mA/cm2 merely at an overpotential of 28 +/- 0.5 mV, outperforming state-of-the-art noble Pt-based, as well as non-noble metal-based catalysts. Remarkably, this catalyst displays a high turnover frequency (TOF) of 0.328 s-1 and even long-term durability at higher current density (50 mA/cm2) up to 175 h with negligible decay. A series of advanced characterizations reveal that Ni1Co3@NC undergoes minimal near-surface restructuring, majorly retaining its structure during longer operations. In order to comprehend the interaction between the inherent HER activity and the metal effect, we conducted further experiments for several bimetallic alloy nanoparticles by alloying Co nanoparticles with Mn, Fe, and Zn. Density functional theory (DFT) calculations demonstrate that the proper choice of alloying elements and their concentrations in encapsulated metallic Co clusters facilitates the HER activity by providing favorable H absorption adsorption sites on their surface. In particular, alloying with Ni significantly improve localized electronic states around the Fermi level leading to a favorable H absorption adsorption and lower HER activation barrier than those in the monometallic nanoclusters. This work sheds important light on the structure-function link for bimetallic alloy nanoparticles made of non-noble metals that exhibit electrocatalytic HER activity in an alkaline medium.