Theoretical investigation on the bifunctional hydrogen/oxygen electrode catalysis in Cd–N–C-doped graphene systems regulated by the active center configuration

Abstract

Clean energy devices such as fuel cells and metal-air batteries can effectively solve the problems of environmental pollution and energy shortage. The common electrochemical reactions on hydrogen electrode (oxidation as HOR and evolution as HER) and oxygen electrode (reduction as ORR and evolution as OER) are important reaction in the conversion process of chemical energy and electric energy. However, the electrochemical conversion of these reactions is relatively low, with high overpotential (ƞ) even on Pt and Ru based catalysts, respectively, in addition to the high cost, which hinder the successful commercialization. Therefore, it is of great important to develop novel catalysts with acceptable ƞ at the same time cost effective. Here, the novel Cd–N–C-doped graphene catalyst systems with active center configuration (ACC) formed by low-boiling point non-precious metals Cd with a carbon and nitrogen coexist coordination environment are reported through a detailed study of density functional theory (DFT). The stability of catalyst was proved by energy calculations and dynamic simulations. Based on Gibbs free energy change (ΔG), ƞ and mechanisms of catalytic reactions were studied. Cd–N1C3-gra is a high efficiency HER and HOR catalyst with ƞ as low as 0.01 V. Cd–N2C2-o-gra is an efficient ORR and OER bifunctional catalyst with ƞOER = 0.48 V and ƞORR = 0.64 V. Based on the comparison of the free energy variation of principal and secondary reactions, their negligible yield of hydrogen peroxide was confirmed. Our research has further promoted the development of low-boiling point non-precious metals in electrocatalysis.