Carbon Dots-Mediated 0D/2D Interface Engineering in Ni₃S₂ Nanosheets for Efficient Electrocatalytic Urea Oxidation Coupled with Hydrogen Evolution

The urea oxidation reaction (UOR) has gained significant attention as an alternative to the oxygen evolution reaction (OER) for reducing energy consumption during simultaneous hydrogen production and degradation of urea. However, developing efficient electrocatalysts for UOR remains challenging due to the sluggish intrinsic kinetics involved in the six-electron process. In this study, we report the use of carbon-dot-modified ultrathin Ni 3 S 2 nanosheets on nickel foam (Ni 3 S 2 –CDs@NF) with a quasi-parallel structure for urea-assisted electrocatalytic hydrogen evolution reaction (HER). The zero-dimensional/two-dimensional (0D/2D) Ni 3 S 2 –CDs@NF catalyst exhibit high bifunctional catalytic activities with a potential of 88 mV for HER and 1.35 V (vs RHE) for UOR at a current density of 10 mA cm –2 . By incorporating Ni 3 S 2 –CDs@NF into a symmetrical electrolytic cell, low cell voltages of 1.67 and 1.81 V were acquired at the current densities of 50 and 100 mA cm –2 for HER||UOR, which are 110 and 280 mV lower than those of the nonreal HER||OER system, respectively. Further electrochemical tests demonstrated that the 0D/2D heterointerface between CDs and Ni 3 S 2 maximized the exposure of surface-active sites while enhancing the electron transfer rates and reaction kinetics. This study not only offers insights into efficient carbon-dot-based electrocatalysts for urea electrolysis, but also holds significant potential for applications in electrochemical energy conversion and wastewater treatment.