Toward Activity Origin of Electrocatalytic Hydrogen Evolution Reaction on Carbon-Rich Crystalline Coordination Polymers

Abstract

The fundamental understanding of electrocatalytic active sites for hydrogen evolution reaction (HER) is significantly important for the development of metal complex involved carbon electrocatalysts with low kinetic barrier. Here, the MSxNy (M = Fe, Co, and Ni, x/y are 2/2, 0/4, and 4/0, respectively) active centers are immobilized into ladder-type, highly crystalline coordination polymers as model carbon-rich electrocatalysts for H2 generation in acid solution. The electrocatalytic HER tests reveal that the coordination of metal, sulfur, and nitrogen synergistically facilitates the hydrogen ad-/desorption on MSxNy catalysts, leading to enhanced HER kinetics. Toward the activity origin of MS2N2, the experimental and theoretical results disclose that the metal atoms are preferentially protonated and then the production of H2 is favored on the MN active sites after a heterocoupling step involving a N-bound proton and a metal-bound hydride. Moreover, the tuning of the metal centers in MS2N2 leads to the HER performance in the order of FeS2N2 > CoS2N2 > NiS2N2. Thus, the understanding of the catalytic active sites provides strategies for the enhancement of the electrocatalytic activity by tailoring the ligands and metal centers to the desired function.