Mutual promotion of CoP/CNT/Ni2P by heterojunction structural design and intrinsic activity coupling for water splitting

The design of highly stable and active bifunctional catalysts for electrolytic water remains a significant challenge. In this study, self-supported CoP/CNT/Ni₂P bifunctional catalysts with three-phase heterojunction nanostructures were constructed by a multi-step electrodeposition and phosphorylation strategy. X-ray diffraction analysis and transmission electron microscope showed that CoP/CNT/Ni₂P was a three-phase heterojunction nanostructure, and scanning electron microscope results of CoP/CNT/Ni₂P suggested the successful introduction of carbon nanotube (CNT). The X-ray photoelectron spectroscopy results indicate a shift in the elemental binding energy in CoP/CNT/Ni₂P, which is believed to contribute to the electrocatalytic reaction. The incorporation of CNT enhances charge transfer within the multiphase catalyst and maximizes the exposure of catalytically active sites, achieving an increase in catalyst performance. As anticipated, the CoP/CNT/Ni₂P catalyst displays high catalytic activity for both the hydrogen evolution reaction (61 mV at 10 mA cm⁻²) and the oxygen evolution reaction (342 mV at 100 mA cm⁻²), in addition to exhibiting long-term stability at a current density of 10 mA cm⁻² over 40 h. The electrolyzer comprising CoP/CNT/Ni₂P_(+,−) necessitates a modest operating voltage of 1.52 V to attain 10 mA cm⁻² during alkaline water splitting, thereby outperforming the commercial catalyst Pt/C||IrO₂ and earlier reports. This study provides guidance for the development of ultra-high activity and durability catalysts for water splitting.