Efficient overall water splitting catalyzed by robust FeNi3N nanoparticles with hollow interiors

Abstract

The structure and morphology tuning of nitrides is urgently desired to boost their intrinsic activity for electrochemical reactions. Herein, we demonstrate hollow structured FeNi₃N nanoparticles with largely improved intrinsic activity synthesized via combining facile oxygen-etching with thermal nitridation as efficient bifunctional catalysts for overall water splitting. Facile structure and morphology tuning is realized without involving a conductive support or complicated fabrication procedures, and this catalyst shows many good catalytic characteristics including high catalytic activity, excellent stability, and accelerated catalytic kinetics. To our delight, this facile approach endows FeNi₃N nanoparticles with largely improved activity for the oxygen evolution reaction (OER) and meanwhile without performance loss for the hydrogen evolution reaction (HER). In specific, overpotentials required for 10 mA cm⁻² are only 185 and 210 mV for the HER and OER, respectively, much lower than those of bulk FeNi₃N (235 and 280 mV @ 10 mA cm⁻² for the HER and OER), accompanying appreciated long-term stability. A low cell voltage of 1.63 V is realized in water electrolysis to offer a current density of 10 mA cm⁻², about 130 mV lower compared to that of a bulk state FeNi₃N catalyst. The structural evolution of metal (oxy)hydroxide is observed from the in situ Raman spectrum, and the significance of metal (oxy)hydroxides is revealed for both the electrodes of the HER and OER. The promotion effect compared with pristine FeNi₃ and bulk FeNi₃N is studied with the help of thorough physical characterization and electrochemical measurements. The largely improved performance is affirmatively attributed to the metallic characteristic FeNi₃N phases, high active site exposure, and boosted intrinsic activity. The current findings are helpful for designing subsequent transition metal-based catalysts applied for the water electrolysis technique.