NiFe₂O₄ Nanoparticles/NiFe Layered Double-Hydroxide Nanosheet Heterostructure Array for Efficient Overall Water Splitting at Large Current Densities

Constructing catalysts with new and optimizational chemical components and structures, which can operate well for both the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER) at large current densities, is of primary importance in practical water splitting technology. Herein, the NiFe₂O₄ nanoparticles/NiFe layered double hydroxide (LDH) nanosheet heterostructure array on Ni foam was prepared via a simple one-step solvothermal approach. The as-prepared heterostructure array displays high catalytic activity toward the OER with a small overpotential of 213 mV at 100 mA cm^–2 and can afford a current density of 500 mA cm^–2 at an overpotential of 242 mV and 1000 mA cm^–2 at 265 mV. Moreover, it also presents outstanding HER activity, only needing a small overpotential of 101 mV at 10 mA cm^–2, and can drive large current densities of 500 and 750 mA cm^–2 at individual overpotentials of 297 and 314 mV. A two-electrode electrolyzer using NiFe₂O₄ nanoparticles/NiFe LDH nanosheets as both the anode and the cathode implements active overall water splitting, demanding a low voltage of 1.535 V to drive 10 mA cm^–2, and can deliver 500 mA cm^–2 at 1.932 V. The NiFe₂O₄ nanoparticles/NiFe LDH nanosheet array electrodes also show excellent stability against OER, HER, and overall water splitting at large current densities. Significantly, the overall water splitting with NiFe₂O₄ nanoparticles/NiFe LDH nanosheets as both the anode and the cathode can be continuously driven by a battery of only 1.5 V. The intrinsic advantages and strong coupling effects of NiFe₂O₄ nanoparticles and NiFe LDH nanosheets make NiFe₂O₄ nanoparticles/NiFe LDH nanosheet heterostructure array abundant catalytically active sites, high electronic conductivity, and high catalytic reactivity, which remarkably contributed to the catalytic activities for OER, HER, and overall water splitting. Our work can inspire the optimal design of the NiFe bimetallic heterostructure electrocatalyst for application in practical water electrolysis.