Large-scale production of hydrogen fuels via electrochemical water splitting requires efficient and cost-effective electrocatalysts. Molybdenum carbide (Mo₂C), as a promising substitute for expensive Pt-based catalysts, exhibits outstanding electrocatalytic performance toward hydrogen evolution reaction (HER). Herein, by combining theoretical studies and experimental measurements, we systematically investigate the surface stability and HER activity of Mo₂C. We demonstrate that the Mo₂C(1 0 0) surface is oxidized under HER turnover condition, and the HER activity shows a positive correlation with the oxidation degrees of this surface. The Mo₂C(1 0 0) surface covered by a monolayer of oxygen atoms is verified as the most stable surface structure, which derives the optimum HER activity, and thus the surface chemisorbed oxygen atoms are identified as the active sites. This study provides new insights into developing efficient electrocatalysts for HER based on Mo₂C.

通过电化学水分解大规模生产氢燃料需要高效且具有成本效益的电催化剂。碳化钼（Mo ₂ C）作为昂贵的基于Pt的催化剂的有前途的替代品，对氢气析出反应（HER）表现出出色的电催化性能。本文中，通过理论研究和实验测量相结合，我们系统地研究了Mo ₂ C的表面稳定性和HER活性。我们证明Mo ₂ C（1 0 0）表面在HER周转条件下被氧化，并且HER活性显示出与该表面的氧化度呈正相关。莫₂氧原子单层覆盖的C（1 0 0）表面被证实是最稳定的表面结构，可产生最佳的HER活性，因此化学吸附的表面氧原子被识别为活性位点。这项研究为开发基于Mo ₂ C的HER高效电催化剂提供了新见解。