Single-atom nickel on defective g-C4N3 as a promising bifunctional electrocatalyst for the OER and ORR: a first-principles analysis

Abstract

Searching for inexpensive and highly active materials to replace noble metals for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is an important challenge. The two-dimensional semi-metallic carbon nitride g-C4N3 is an excellent candidate for electrochemical reactions owing to its eminent conductivity and stability. Here, using density functional theory (DFT) a series of low-budget non-noble transition metal single-atom (SAC) loaded on the g-C4N3 (named as TM@C4N3, TM = Cr, Mn, Fe, Co, Ni, Cu) were investigated as electrocatalysts for OER and ORR. Ni@C4N3 shows an enormous application potential as electrode material, with OER and ORR overpotentials of 0.59 V and 0.23 V, respectively. The second lowest binding energy between Ni and support g-C4N3 indicates that Ni@C4N3 possesses good overall stability. The d-band center as well as metal valence as the descriptor exhibit good agreement with the adsorption energy of the intermediate. A linear relationship exists among the adsorption energies of the three intermediates O, OH, and OOH, given the similarity that they are all bonded to the metal through one oxygen atom. By adjusting the adsorption energy of these intermediates, the catalytic activity of electrocatalysts can be tuned for OER and ORR. This study confirmed that Ni@C4N3 is a good bifunctional catalyst and provides important guidance for the design of bifunctional electrocatalysts for OER and ORR.