In situ construction of surface defects of carbon-doped ternary cobalt-nickel-iron phosphide nanocubes for efficient overall water splitting

The ternary cobalt-nickel-iron phosphide nanocubes (P-Co0.9Ni0.9Fe1.2 NCs) with high intrinsic activity, conductivity, defect concentration and optimized ratio have been realized through a facile phosphorization treatment using ternary cobalt-nickel-iron nanocubes of Prussian blue analogs (PBA) as a precursor. The scanning electron microscopy and transmission electron microscopy results show that the P-Co0.9Ni0.9Fe1.2 NCs maintain a cubic structure with a rough surface, implying the rich surface defects as exposed active sites. The thermal phosphorization of the ternary PBA precursor not only provids carbon doping but also leads to the in situ construction of surface defects on the NCs. The carbon doping from the PBA precursor lowers the charge transfer resistance and optimizes the electronic transformation. The synergistic effect among the ternary metal ions and rich defects contributes to the enhanced electrocatalytic performance. The P-Co0.9Ni0.9Fe1.2 NCs achieve low overpotentials of -200.7 and 273.1 mV at a current density of 10 mA cm(-2) for the hydrogen evolution reaction and the oxygen evolution reaction, respectively. The potential of overall water splitting reaches 1.52 V at a current density of 10 mA cm(-2). The long-term stability of the electrocatalysts was also evaluated. This work provides a facile method to design efficient transition-metal-based bifunctional electrocatalysts for overall water splitting.