Amorphous iron-nickel phosphide nanocone arrays as efficient bifunctional electrodes for overall water splitting

The synthesis of low-cost and highly active electrodes for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is very important for water splitting. In this work, the novel amorphous iron-nickel phosphide (FeP-Ni) nanocone arrays as efficient bifunctional electrodes for overall water splitting have been in-situ assembled on conductive three-dimensional (3D) Ni foam via a facile and mild liquid deposition process. It is found that the FeP-Ni electrode demonstrates highly efficient electrocatalytic performance toward overall water splitting. In 1 M KOH electrolyte, the optimal FeP-Ni electrode drives a current density of 10 mA cm^-2 at overpotential of 218 mV for the OER and 120 mV for the HER, and can attain such current density for 25 h without performance regression. Moreover, a two-electrode electrolyzer comprising the FeP-Ni electrodes can afford 10 mA cm^-2 electrolysis current at a low cell voltage of 1.62 V and maintain long-term stability, as well as superior to that of the coupled RuO₂/NF‖Pt/C/NF cell. Detailed characterizations confirm that the excellent electrocatalytic performances for water splitting are attributed to the unique 3D morphology of nanocone arrays, which could expose more surface active sites, facilitate electrolyte diffusion, and benefit charge transfer and also favorable bubble detachment behavior. Our work presents a facile and cost-effective pathway to design and develop active self-supported electrodes with novel 3D morphology for water electrolysis.