Differences in N species induced by pyrolysis temperature: D-band center adjustment over the biomass carbon-supported CoP for boosting hydrogen evolution reaction

Nitrogen (N) species in biomass-based carbon can be adjusted through pyrolysis at different temperatures, optimizing the valence band structure of supported metal nanoparticles through electronic metal-support interactions (EMSIs). Herein, ginkgo leaves-based carbon supported cobalt phosphide (CoP@NSPC-T, T = 850, 900 and 950 °C) was obtained via carbothermal reduction method at different pyrolysis temperature. Pyridinic N and pyrrolic N in carbon lattice were dramatically decreased with pyrolysis temperature raised, whereas the graphitic N showed the opposite trend. The change in N species (pyridinic N, pyrrolic N and graphitic N) reconfigured the valence band structure of CoP@NSPC-T, inducing the enhancement of work function and the upshift of d-band center. A relationship between the ratio of (pyridinic N + pyrrolic N)/graphitic N, work function, d-band center, and HER activity (η10) of catalysts was established. CoP@NSPC-900 with a moderate work function value and d-band center tend to achieve a balance for Volmer process and Heyrovsky process, exhibiting the lowest η10 value activity among the resulted catalysts as the ratio of (pyridinic N + pyrrolic N)/graphitic N is 1.33.