Ultraeven Mo-Doped CoP Nanocrystals as Bifunctional Electrocatalyst for Efficient Overall Water Splitting

To develop precious-metal-free bifunctional catalysts for overall water splitting, ultraeven Mo-doped CoP composites (Mo-CoP) have been fabricated by an in situ phosphorization protocol using CoMo-layered double hydroxide (CoMo-LDH) as the precursor. The ordered arrangement of cations in the CoMo-LDH could be easily phosphored and generate the ultraevenly dispersed Mo element within the CoP structure, resulting in the excellent bifunctional catalyst for overall water splitting. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activities of the composites present an increase first and then a decreasing tendency with increased Mo doping content. Among all the Mo-doped CoP materials, the composite with a Mo/Co mole ratio of 1/2.3 presents the highest HER activity and stability in acidic conditions. At the current density of -10 mA·cm^-2 in 0.5 M H₂SO₄, the overpotential is only 116 mV. In addition, the composite also presents excellent HER and OER performance under alkaline conditions. The overpotential is 118 mV for HER and 317 mV for OER at 10 mA cm^-2 in 1 M KOH. It requires a cell voltage of 1.7 V to achieve a current density of 10 mA·cm^-2 and maintains a stable water-splitting current for at least 24 h, which is superior to most reported alkaline media. This simple and efficient synthetic approach could also be used for ultraeven doping between other transition metal ions.