Flower-like NiZnCu Composite Microstructures Assembled by Nanosheets as a Highly Active Bifunctional Electrocat alyst for Urea-assisted Energy-saving Hydrogen Productio n

Abstract

The urea oxidation reaction (UOR) has a lower overpotential than the oxygen evolution reaction (OER), enabling a 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 flowerlike 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 flowerlike 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 merely required a low overpotential of ~25 mV to deliver a current density of -10 mA cm -2 for HER. Simultaneously, 1.33 V of voltage was demanded 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 of voltage was needed. The metal-metal electronic regulation mechanism is considered to be the main reason for the above excellent electrocatalytic performances. 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), which offers a catalyst selection for the HER||UOR in practical applications.