A hierarchical carbon nanotube forest supported metal phosphide electrode for efficient overall water splitting

Transition metal phosphides (TMPs) have become one type of promising hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalyst in alkaline medium; however, the low amount of metal active sites and the poor electronic conductivity of TMPs have become the limiting factors for achieving high-performance TMP based electrocatalysts. Herein, a hierarchical carbon nanotube (CNT) forest was used to load TMP materials to form self-supported electrodes (NiCoP-CNT@NiCo/CP and NiFeP-CNT@NiCo/CP), guaranteeing catalytic electrodes with a high amount of metal sites and excellent electronic conductivity. As expected, the electrodes display low overpotentials of 82 and 230 mV at a current density of 10 mA cm −2 for the HER and OER in alkaline solutions, respectively. Moreover, the overall water electrolyzer assembled with NiCoP-CNT@NiCo/CP as a cathode and NiFeP-CNT@NiCo/CP as an anode exhibits superior electrolysis performance (1.58 V/10 mA cm −2 ). The remarkable performance is attributed to the unique hierarchical CNT forest architecture of the as-prepared catalytic electrodes and the synergistic effect between TMP nanoparticles and CNTs. Metal phosphides on self-supportive CNT forest materials with a hierarchical branched architecture have abundant active sites and excellent electrical conductivity, providing an effective strategy for preparing efficient OER and HER electrodes.