The rational design of efficient bifunctional single-atom electrocatalysts for industrial water splitting and the comprehensive understanding of its complex catalytic mechanisms remain challenging. Here, we report a Ni single atoms supported on oxygen-incorporated Mo₂C via Ni-O-Mo bridge bonds, that gives high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) bifunctional activity. By ex situ synchrotron X-ray absorption spectroscopy and electron microscopy, we found that after HER, the coordination number and bond lengths of Ni-O and Ni-Mo (Ni-O-Mo) were all altered, yet the Ni species still remain atomically dispersed. In contrast, after OER, the atomically dispersed Ni were agglomerated into very small clusters with new Ni-Ni (Ni-O-Ni) bonds appeared. Combining experimental results and DFT calculations, we infer the oxidation degree of Mo₂C and the configuration of single-atom Ni are both vital for HER or OER. This study provides both a feasible strategy and model to rational design highly efficient electrocatalysts for water electrolysis.

用于工业水分解的高效双功能单原子电催化剂的合理设计以及对其复杂催化机制的全面理解仍然具有挑战性。在这里，我们报道了通过Ni-O-Mo桥键负载在掺氧Mo ₂ C上的Ni单原子，它具有高析氧反应（OER）和析氢反应（HER）双功能活性。通过异位同步加速器X射线吸收光谱和电子显微镜，我们发现经过HER后，Ni-O和Ni-Mo（Ni-O-Mo）的配位数和键长都发生了改变，但Ni物种仍然存在原子分散。相比之下，OER 后，原子分散的 Ni 聚集成非常小的簇，并出现新的 Ni-Ni (Ni-O-Ni) 键。结合实验结果和DFT计算，我们推断Mo ₂ C的氧化程度和单原子Ni的构型对于HER或OER都至关重要。这项研究为合理设计高效水电解电催化剂提供了可行的策略和模型。