Synthesis of Hydrogen Peroxide in Neutral Media by an Iron-Doped Nickel Phosphide Catalyst

The two-electron oxygen reduction reaction (2e^- ORR) for electrochemical hydrogen peroxide (H₂O₂) synthesis has drawn much attention due to its eco-friendly, cost-effective, and highly efficient properties. Developing catalysts with excellent H₂O₂ production rates and selectivity is still a big challenge. In this work, an iron-doped nickel phosphide (Fe-Ni-P) catalyst was synthesized by a solvent thermal method. The synthesis temperature of 180 °C could obtain the best 2e^- ORR catalyst, i.e., Fe-Ni-P-180, since the crystallization of metal phosphide under this temperature was promoted. In addition, Fe-Ni-P-180 had a high catalytic activity, high electron transfer rate, and low electrochemical resistance. The H₂O₂ production rate constant of Fe-Ni-P-180 was 9.99 ± 0.63 μM/(min cm²) and the Faradaic efficiency was 94.38 ± 4.68% at 0.25 V vs RHE, which increased by 57.9 and 15.4% compared with Ni-P, respectively. Fe-Ni-P-180 could work in a wide pH range of 5-9 with the optimized pH of 7, and it exhibited low specific energy consumption and great reusability. The elemental state analysis demonstrated that Ni^δ+, Fe^δ+, and P^δ- are all active species, and the doping of Fe increases the crystallization of metal phosphide.