Abstract: Designing highly active and stable noble-metal-free electrocatalysts for water splitting over a wide pH range is critical yet remains significantly challenging. In this work, Mo-doped CoP nanoparticles (Mo-CoP) supported and enwrapped by porous single-atomic-Co doped carbon framework (Co-N-C) were designed and prepared by a simple one-pot pyrolysis method. The Mo-CoP/Co-N-C electrocatalyst exhibits superior performance with low overpotentials of only 45 mV for hydrogen evolution reaction (HER) and 201 mV for oxygen evolution reaction (OER) in 1 M KOH at 10 mA cm ^-2 current density. Such excellent catalytic activity can be ascribed to enhanced intrinsic activity, large surface area, and highly exposed active sites. Meanwhile, an extremely small overpotential of only 250 mV is required for a large current density of 500 mA cm ^-2 in HER, which exceeds the performance of benchmark 10% Pt/C. Besides, Mo-CoP/Co-N-C also exhibits superior HER performance in acidic and neutral mediums, with overpotentials of only 41 and 98 mV in 0.5 M H₂SO₄, and 1 M PBS, respectively, thus achieving efficient water splitting at a wide pH range. The long-term stabilities are guaranteed with no significant decline of catalytic activities for more than 24 h in all electrolytes, which can be ascribed to the carbon layer encapsulation structure. Addition-ally, in overall water splitting, the electrocatalytic cell consisting of the as-synthesized Mo-CoP/Co-N-C only requires a cell voltage of 1.611 V at 100 mA cm ^-2 with excellent stability, exceeding that of the benchmark Pt/C||RuO2 couple (1.645 V at 100 mA cm ^-2 ). This work not only presents a highly efficient electrocatalyst for pH-universal water splitting but also provides a new perspective for the design and construction of transition metal catalysts with excellent stability

Key words: Cobalt phosphide, Mo doping, Single atomic catalyst, Water splitting, pH-universal