Binary nickel iron phosphide composites with oxidized surface groups as efficient electrocatalysts for oxygen evolution reaction
Electrocatalytic water splitting becomes an effective approach to produce hydrogen as a clean energy source. Developing electrocatalysts for oxygen evolution reaction (OER) with high efficiency and low cost is crucial for the entire hydrogen energy systems due to the sluggish kinetics of OER. Herein, we have synthesized the binary NiFeOH, NiFeO and NiFeP two-dimensional (2D) nanosheets on carbon cloth (CC) via a facile hydrothermal method combined with phosphorization and oxidation treatment. The porous binary NiFeP nanosheets indicated an OER overpotential of 281 mV to achieve 20 mA·cm-2 and a small Tafel slope of 74 mV·dec-1, which were lower than those of the NiFeO (336 mV and 81 mV·dec-1). After the continuous OER operation for 50 h, the NiFeP-32/CC exhibit small degradation of the current density (88 % remain). The results have indicated that there were larger amounts of NiO and NiOOH phases formed on the NiFeP nanosheets during the OER process. The electrocatalytic activity for oxidized NiFeP with NiO and NiOOH phases were higher than the pure NiFeO and NiFeOH, indicating that the synergistic effects among the NiFeP, NiO and NiOOH phases could improve the OER activity.