Ultrasonic‐Assisted Synthesis of Amorphous Polyelemental Hollow Nanoparticles as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

Large‐scale electrolysis of water for hydrogen generation requires efficient, stable, and low‐cost electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Highly active and stable electrocatalysts can be achieved by amorphous materials with tunable polyelemental compositions, and further enhanced with proper nanostructures. Herein, the ultrasonic‐assisted template‐free synthesis of amorphous polyelemental (Co, Ni, Fe, W, B, P) hollow nanoparticles (PE‐HNP) is reported as an efficient and stable electrocatalyst for both OER and HER. For HER, as‐prepared PE‐HNP attains 1200 mA cm−2 current density at a low overpotential of 195 mV. For OER, PE‐HNP is in situ oxidized to form PEO‐HNP, which attains 1200 mA cm−2 current density at a low overpotential of 309 mV. The activities of PE‐HNP and PEO‐HNP remain unaffected after 20 h HER or OER test at high current densities, showing higher activity and stability than the benchmark electrocatalysts Pt/C and IrO2, respectively. The PEO‐HNP║PE‐HNP electrolyzer needs a 1.85 V cell voltage to drive a high current density of 400 mA cm−2, which is much better than the IrO2║Pt/C electrolyzer (2.15 V for 400 mA cm−2). The strategy provides a cost‐effective and convenient method to synthesize amorphous polyelemental materials with designed hollow nanostructures for the development of high‐performance electrocatalysts.