Construction of MnX (X = P, O, S) nanoparticles embedded in porous carbon/graphene nanocomposite fibers as efficient bifunctional oxygen electrocatalyst for Zn–air batteries

Porous carbon coated manganese compounds nanoparticles (MnX, X = P, O or S) is a kind of potential catalysts for oxygen electrocatalysis due to the controllable d-band center, while the complex mechanism and performance difference is yet to reveal due to the lack of catalyst platform. Herein, the ORR catalytic activity and difference reason between manganese phosphide, oxide, and sulfide are tested and discussed via manganese compounds contained carbon-based catalyst platforms synthesis and Density functional theory (DFT). Manganese compounds nanoparticles active sites are uniformly distributed in porous carbon fibers/graphene composite, which guarantees the high mass transfer ability and conductive ability. Experiment results show that catalyst with Mn₂P active sites exhibits best bifunctional catalytic activity for ORR/OER, which only need 0.89 V (vs. RHE) to achieve a half-wave potential (E_1/2) in ORR and 1.58 V (vs. RHE) to reach the overpotential at 10 mA cm^-2 (E₁₀) in OER. Theoretical analysis shows that the d-band center of Mn in Mn₂P is much closer to the Fermi level than MnS and MnO. The rate-determining process of Mn₂P has the smallest energy barrier of 0.56 eV, indicating the best ORR activity. This work provides paves a solid way for the synthesis of carbon-based catalysts with manganese compounds active sites.