Defect engineering with N-doped carbon hybrid cobalt-molybdenum phosphide nanosheets wrapped molybdenum oxide nanorods for alkaline hydrogen evolution reaction.

Regulating the electrocatalytic hydrogen evolution reaction (HER) performance through defect engineering of the surface of the catalysts is an effective pathway. Herein, cobalt-molybdenum phosphide (CoMoP) nanosheets wrapped molybdenum oxide (MoO3) core-shell nanorods (MoO3@CoMoP), as alkaline electrocatalysts with ligand-derived N-doped carbon hybrid and oxygen-vacancies, were synthesized via solvothermal approaches and followed by phosphorization. As expected, the MoO3@MoCoP affords efficient HER with a low overpotential (η) of 84.2 ± 0.4 mV at 10 mA cm-2. After phosphorization, not only the MoCoP active species are incorporated into the catalyst, but also the defects sites are achieved. Impressively, the metal-ligand-derived MoCoP are distributed uniformly in the N-doped carbon hybrid matrix, exhibiting well-exposed active sites. Benefiting from the synergy effect of MoCoP active species and oxygen-vacancy, the MoO3@MoCoP showed increased conductivity and stability, which can deliver a current density of 10 mA cm-2 over 40 h. MoO3@MoCoP exhibits an optimal electronic structure on the surface by charge redistribution at the interface, thereby optimizing the hydrogen adsorption energy and accelerating the hydrogen evolution kinetics. This work paves the way for the design of transition metal electrocatalysts with desirable properties through a promising strategy in the field of energy conversion.

Nitrogen-doped hollow mesoporous carbon spheres for efficient oxygen reduction.

Extensive investigations have been devoted to nitrogen-doped carbon materials as catalysts for the oxygen reduction reaction (ORR) in various conversion technologies. In this study, we introduce nitrogen-doped carbon materials with hollow spherical structures. These materials demonstrate significant potential in ORR activity within alkaline media, showing a half-wave potential of 0.87 V versus the reversible hydrogen electrode (RHE). Nitrogen-doped hollow carbon spheres (N-CHS) exhibit unique characteristics such as a thin carbon shell layer, hollow structure, large surface area, and distinct pore features. These features collectively create an optimal environment for facilitating the diffusion of reactants, thereby enhancing the exposure of active sites and improving catalytic performance. Building upon the promising qualities of N-CHS as a catalyst support, we employ heme chloride (1 wt%) as the source of iron for Fe doping. Through the carbonization process, Fe-N active sites are effectively formed, displaying a half-wave potential of 0.9 V versus RHE. Notably, when implemented as a cathode catalyst in zinc-air batteries, this catalyst exhibits an impressive power density of 162.6 mW cm-2.