Electrocatalytic carbon dioxide reduction on graphene-supported Ni cluster and its hydride: Insight from first-principles calculations

We present an analysis of the trends of CO2 reduction reaction on graphene-supported nickel and nickel hydride clusters based on density functional theory calculations. It is observed that the generation of nickel hydride clusters on graphene endows the catalyst with active positive Ni and negative H sites, which enhances CO2 adsorption and facilitates electrochemical reactions. On the clean Ni10-gra model, chemisorption of CO2 predominates and governs the selectivity of the COOH* pathway, as evidenced by a notable adsorption free energy (ΔGads) of −0.85 eV for the CO2* intermediate. However, the adsorption energy experiences a substantial reduction to −0.24 eV on the 7HNi10-gra model, which in turn results in the observation of the CO2 desorption phenomenon in models characterized by higher nH* ratios. In addition, the energy reduction and stabilization associated with HCOO* formation in the presence of an increasing number of H* atoms are not substantial, thereby facilitating an alternative electrocatalytic route that leads to the generation of formic acid, methanol and methane. Our computational study presents an all-encompassing mechanism describing CO2 adsorption and subsequent conversion to various products on diverse nH*-Ni10-gra models, which significantly advances the understanding of the influence of metal hydrides in the electrochemical environment.