Sonochemical Deposition of a Highly Active NiFe Hydroxide Electrocatalyst for Oxygen Evolution Reaction

This study reports the synthesis of a highly active amorphous NiFe-based electrocatalyst using ultrasound-assisted deposition in an aqueous NiFe nitrate solution. The application of ultrasonic irradiation significantly improved mixing, dispersion, and reaction kinetics, leading to a completely amorphous catalyst with an abundance of highly dispersed active sites. Compared to NiFe layered double hydroxides (LDHs) synthesized via hydrothermal and electrodeposition methods, the ultrasonically deposited catalyst exhibited the highest intrinsic OER activity, as evidenced by normalizing the current density to the electrochemical surface area. Electron diffraction confirmed its unique fully amorphous atomic structure, which is enriched with catalytically active sites. The energetic disordered amorphous phase also promotes enhanced catalytic activity at these sites and therefore exhibits high electrocatalytic activity. To further optimize the performance, a hybrid method combining brief hydrothermal pretreatment with ultrasonic deposition was developed, which integrates the large surface area benefit of hydrothermal synthesis with the high intrinsic activity from sonochemical deposition. The resulting catalyst demonstrated excellent OER performance, achieving low overpotentials of 217 mV and 270 mV at 10 and 100 mA cm–2, respectively, along with a Tafel slope of 35 mV dec–1. This study highlights the effectiveness of sonochemical synthesis, both individually and in hybrid approaches, for the scalable fabrication of efficient noble-metal-free water splitting electrocatalysts.