Abstract
Hydrogen evolution reaction(HER)and oxygen evolution/reduction reaction(OER/ORR)relying on high-performance and low-cost single-atom catalysts(SACs)driven by renewable energy sources offer a sus-tainable route to carbon-neutral chemicals and fuels.Herein,first-principles calculations were performed to investigate the catalytic HER/OER/ORR activity of a novel graphitic carbon nitride monolayer(g-C7N3)supported single transition metal(TM@g-C7N3).High stability as well as positively charged active site(TM-site)and desirable electrical conductivity lay the foundation for TM@g-C7N3 acting as efficient HER/OER/ORR electrocatalysts.We screened out the non-noble-metal Rh@g-C7N3 SAC exhibiting great po-tential as the trifunctional electrocatalysts for water splitting(ηHER=0.06 V and ηOER=0.46 V)and a metal-air battery(ηORR=0.28 V)on both kinetic and thermodynamic scales,whereas the Ni@g-C7N3 can be served as a bifunctional OER/ORR catalyst with a low overpotential of 0.33 V/0.31 V,for both of which the high thermodynamic stability and oxidation barrier guarantee their outstanding performances at ambient conditions.The mechanism analysis indicates the filling of d-orbital electrons of TM-atom can play an important role in determining the value of an energy descriptor(△GOH·),and the suitable△GOH.values make for the TM@g-C7N3 candidates to possess favorable OER/ORR overpotential.Particu-larly,the Rh-d orbital of Rh@g-C7N3 is evidently hybridized with the OH*-p orbital,resulting in the lone electrons initially distributed in the antibonding orbital pairing up and occupying the downward bonding orbital,ensuring OH*can be adsorbed on Rh@g-C7N3 appropriately.Moreover,multiple-level descriptors including d-band center,COHP,Nd,and φ are used to reveal the origin of the electrocatalytic activity.
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