Prussian-Blue-Analogue-Derived Ultrathin Co₂P-Fe₂P Nanosheets for Universal-pH Overall Water Splitting

The great interest in large-scale electrochemical water splitting toward clean hydrogen has spurred large numbers of studies on developing cost-efficient and high-performance bifunctional electrocatalysts. Here, a Prussian-blue-analogue-derived method is proposed to prepare honeycomb-like ultrathin and heterogeneous Co₂P-Fe₂P nanosheets on nickel foam, showing low overpotentials of 0.080, 0.088, and 0.109 V for the hydrogen evolution reaction (HER) at 10 mA cm^-2 as well as 0.290, 0.370, and 0.730 V for the oxygen evolution reaction (OER) at 50 mA cm^-2 in alkaline, acidic, and neutral electrolytes, respectively. When directly applied for universal-pH water electrolysis, excellent performances are achieved especially at ultralow voltages of 1.45 V at 10 mA cm^-2, 1.66 V at 100 mA cm^-2, and 1.79 V at 500 mA cm^-2 under alkaline conditions. In situ Raman spectroscopy measurements demonstrate that the excellent HER performance can be attributed to heterogeneous Co₂P-Fe₂P while the ultrahigh alkaline OER performance originates from reconstruction-induced oxyhydroxides.