Heteroatom Doping of Molybdenum Carbide Boosts pH-Universal\nHydrogen Evolution Reaction

Abstract

Tuning electronic\nstructures through heteroatom doping to weaken\nthe Mo–H binding strength and constructing larger specific\nsurface areas are considered an effective strategy to improve the\nhydrogen evolution reaction (HER) activity on β-Mo₂C in full pH range. In this report, a CH₄ (10%)/H₂ inducing universal method for the formation of heteroatom-doped\n(F, N, S, or B) β-Mo₂C nanoparticles (NPs) with nanosized\nand clean surface supported on reduced graphene oxide (rGO) (Mo₂E<i>_x</i>C_1–<i>x</i>/rGO, E = F, N, S, or B) is proposed. Doping with different\nheteroatoms introduced different promoting effects on Mo₂C toward HER in the full pH range. The Mo₂F<i>_x</i>C_1–<i>x</i>/rGO electrocatalysts\nshow the best activity for HER in acidic, alkaline, and neutral media,\nwith the onset overpotentials of 37, 45, and 105 mV, respectively,\nwhich achieve 10 mA cm^–2 at overpotentials of only\n95 mV in 1 M HClO₄. More noteworthy is the fact that the\nMo₂F<i>_x</i>C_1–<i>x</i>/rGO electrocatalysts only require 232 and 397 mV\nof overpotentials to reach 400 mA cm^–2 in acidic\nand alkaline solutions, respectively. Besides, the Mo₂F<i>_x</i>C_1–<i>x</i>/rGO\nelectrocatalysts only need 480 mV of overpotential to reach 200 mA\ncm^–2 in neutral conditions. Meanwhile, larger specific\nsurface areas with nanosized and clean surfaces also contribute to\nimproving the performance of HER, especially Mo₂F<i>_x</i>C_1–<i>x</i>/rGO.\nHowever, the promoting effect of HER by tuning the electronic structures\nthrough doping of B and S into Mo₂C is very limited. Moreover,\ndoped Mo₂C-based electrocatalysts in this work show superior\nstabilities for HER in the full pH range.