Molybdenum phosphide (MoP) has been recognized as a promising family of non-noble metal electrocatalysts for hydrogen evolution reaction (HER) by water splitting, but their electrocatalytic HER activities are still far from desirable and the active sites of MoP-based electrocatalysts have rarely been explored. Herein, we demonstrate a novel hybrid nanostructure composed of carbon encapsulating ultra-low Co/Ni-doped MoP nanoparticles, which can be adopted as highly active and stable HER catalysts in pH-universal electrolytes. The optimized carbon-encapsulated MoP nanoparticles with a Ni/Mo molar ratio of 0.02 achieve a low overpotential of 102 mV at 10 mA cm^-2 and a small Tafel slope of 58.1 mV dec^-1 in 0.5 M H₂SO₄ solution, outperforming most of previously reported MoP-based electrocatalysts. More importantly, density functional theory based calculations reveal that the △G_H* of Ni/Co doped MoP at the Mo site is lower than that at the P site, and the lowest △G_H* of the doping form of Ni and Co at Mo site was interstitial and substitutional+interstitial, respectively. Higher catalytic performance is observed on doped Mo-terminated surface especially in the presence of non-stoichiometric Ni and Co defects. The lowest free energy of Ni-doping implies that Ni-doped MoP hybrid nanostructures possess weak hydrogen adsorption energy and excellent HER catalytic activity in a wide pH range. The combined experimental and theoretical study paves the way for the identification of the active sites in MoP-based hybrid electrocatalysts toward high-performance HER.

磷化钼（MoP）已被公认为是有前景的通过水分解产生氢气发生反应（HER）的非贵金属电催化剂家族，但它们的电催化HER活性仍远未令人满意，基于MoP的电催化剂的活性位点很少被探索了。在本文中，我们展示了一种新型的杂化纳米结构，该结构由碳包封的超低Co / Ni掺杂MoP纳米颗粒组成，可在pH通用型电解质中用作高活性和稳定的HER催化剂。Ni / Mo摩尔比为0.02的优化碳封装的MoP纳米颗粒在10 mA cm ^-2时具有102 mV的低过电势，在0.5 MH ₂ SO _4中的Tafel斜率小，为58.1 mV dec ^-1解决方案，胜过大多数以前报道的基于MoP的电催化剂。更重要的是，基于密度泛函理论的计算表明，Ni / Co掺杂的MoP的Mo的△G _{H *}低于P的位置，△G _{H *}最低Ni和Co在Mo位点的掺杂形式分别为间隙和置换+间隙。在掺杂的Mo端接的表面上观察到更高的催化性能，尤其是在存在非化学计量的Ni和Co缺陷的情况下。Ni掺杂的最低自由能表明Ni掺杂的MoP杂化纳米结构在较宽的pH范围内具有较弱的氢吸附能和出色的HER催化活性。结合实验和理论研究为基于MoP的杂化电催化剂中的活性位点识别为高性能HER铺平了道路。