Synergistically Tuning Electronic Structure of Porous β‐Mo₂C Spheres by Co Doping and Mo‐Vacancies Defect Engineering for Optimizing Hydrogen Evolution Reaction Activity

The development of novel non‐noble electrocatalysts with controlled structure and surface composition is critical for efficient electrochemical hydrogen evolution reaction (HER). Herein, the rational design of porous molybdenum carbide (β‐Mo 2 C) spheres with different surface engineered structures (Co doping, Mo vacancies generation, and coexistence of Co doping and Mo vacancies) is performed to enhance the HER performance over the β‐Mo 2 C‐based catalyst surface. Density functional theory calculations and experimental results reveal that the synergistic effect of Co doping with Mo vacancies increases the electron density around the Fermi‐level and modulates the d band center of β‐Mo 2 C so that the strength of the MoH bond is reasonably optimized, thus leading to an enhanced HER kinetics. As expected, the optimized Co 50 ‐Mo 2 C‐12 with porous structure displays a low overpotential (η 10 = 125 mV), low‐onset overpotential (η onset = 27 mV), and high exchange current density ( j 0 = 0.178 mA cm −2 ). Furthermore, this strategy is also successfully extended to develop other effective metal (e.g., Fe and Ni) doped β‐Mo 2 C electrocatalyst, indicating that it is a universal strategy for the rational design of highly efficient metal carbide‐based HER catalysts and beyond.