Single transition-metal atoms anchored on a novel Dirac-dispersive π-π conjugated holey graphitic carbon nitride substrate: computational screening toward efficient bifunctional OER/ORR electrocatalysts

Nonprecious-metal-group single-metal-atom catalysts with bifunctional catalytic capabilities toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are highly sought after in energy-conversion and storage technology. However, producing renewable and sustainable energy sources remains challenging. Currently, single-transition metal atoms anchored on pi-pi conjugated two-dimensional (2D) graphitic carbon nitride substrates form pi-d conjugated conductive channels that enhance the overall electrocatalytic activity. Herein, first-principles calculations were carried out to design and demonstrate a novel macropore graphitic carbon nitride (g-C10N3) as a promising 2D electrocatalyst substrate to support single-transition metal (TM, from Sc to Au). The "donation-acceptance" charge interaction in the TM-N-2 moiety effectively balances the adsorption strength of oxygenated intermediates in Ni@g-C10N3 and Rh@g-C10N3, making them effective bifunctional OER/ORR electrocatalysts with IrO2/Pt-beyond overpotentials being as low as 0.39/0.38 V and 0.54/0.44 V, respectively. Additionally, they possess high stability and conductivity and are less susceptible to oxidation and corrosion under working conditions. This guarantees high activity under ambient conditions. Then, the origin of the OER/ORR activity of TM@g-C10N3 is explained using multilevel descriptors: intrinsic phi, Bader charge, integral crystal orbital Hamilton population (ICOHP), bond length, and d-band center (epsilon d). In particular, for optimal Ni@g-C10N3, the clear hybridization between the Ni-d orbital and surface O-p orbital causes the paired electrons to occupy the bonding orbitals. This enables OH* to be adsorbed on the Ni@g-C10N3, thereby achieving the highest catalytic performance.