Sparkling Synergy:\nEnhancing Hydrogen Evolution with\na Mesoporous CoP/FeP Interface

The reaction kinetics is predominantly determined by\nthe surface\nand interface engineering of electrocatalysts. Herein, we demonstrate\nthe growth of cobalt monophosphide and iron monophosphide (CoP/FeP)\nwith an effective solid interface. The surface of CoP/FeP is mesoporous,\nwhich is obtained by phosphidizing mesoporous CoFe<sub>2</sub>O<sub>4</sub>. The CoP/FeP electrode exhibits substantially superior hydrogen\nevolution reaction (HER) performance compared to CoP and FeP. The\noverpotentials (η) required to generate 10 mA cm<sup>–2</sup> are determined to be around 98 mV<sub>RHE</sub> (CoP/FeP), 220 mV<sub>RHE</sub> (FeP), and 265 mV<sub>RHE</sub> (CoP) in an acidic electrolyte.\nThe exchange current density and Tafel slopes suggest that CoP/FeP\nhas better redox properties and kinetic abilities compared to FeP\nand CoP. Furthermore, the CoP/FeP electrode exhibits reduced electrochemical\nimpedance and superior surface charge transport characteristics in\ncomparison to both the CoP and FeP electrodes. In addition to having\na greater number of catalytically active sites, the turnover frequency\nof CoP/FeP is approximately 2 and 5 times higher than that of FeP\nand CoP, respectively. The CoP/FeP electrode maintains a consistent\ncurrent density of around 25 mA cm<sup>–2</sup> for a continuous\nperiod of 24 h during the HER, attesting to the excellent durability\nof the CoP/FeP electrode. In addition, a relationship between differential\nhydrogen adsorption energy (Δ<i>E</i><sub>H</sub>),\nthe corresponding Gibbs free energy change (Δ<i>G</i><sub>H</sub>), and the hydrogen coverage on distinct surfaces, namely,\nCoP, FeP, and CoP/FeP, is established. The calculation findings show\nthat the CoP/FeP surface, which is predominantly exposed with CoP,\nexhibits the highest catalytic potential for the HER. The estimation\nof the specific HER activity of the electrodes, normalized to the\nelectrochemically active surface area, corroborates the calculation\nfindings.