Flower-like NiZnCu composite microstructures assembled by nanosheets as a highly active bifunctional electrocatalyst for urea-assisted energy-saving hydrogen production

Abstract

The urea oxidation reaction (UOR) has a lower overpotential than the oxygen evolution reaction (OER), enabling lower overall energy consumption for water splitting when using UOR instead of OER. However, developing cost-effective and highly active bifunctional electrocatalysts for urea-assisted electrochemical hydrogen production still remains challenging. In this work, a flower-like NiZnCu composite microstructure assembled by nanosheets was electrochemically deposited on nickel foam (labeled as NiZnCu/NF) via a rapid galvanostatic deposition technique at room temperature. The as-deposited NiZnCu flower-like microstructure could serve as a bifunctional electrocatalyst for both hydrogen evolution and urea oxidation. In 1 M KOH solution, the as-obtained NiZnCu/NF electrode required only a low overpotential of ∼25 mV to deliver a current density of −10 mA cm⁻² for HER. Simultaneously, a voltage of 1.33 V was required to achieve a current density of 10 mA cm⁻² for UOR in 1 M KOH + 0.5 M urea media. Even to reach a current density of 100 mA cm⁻² for UOR, only 1.39 V was needed. The metal–metal electronic regulation mechanism is considered to be the main reason for the excellent electrocatalytic performances described above. Employing the as-prepared NiZnCu/NF electrode as the anode and cathode simultaneously, the urea-assisted water electrolysis device (HER‖UOR system) exhibited a voltage reduction of 257 mV compared to the conventional water electrolysis device (HER‖OER system), offering a catalyst option for the HER‖UOR system in practical applications.