CeO2-enhanced surface reconstruction of Ni3S2 nanosheets for improved urea-assisted water splitting performance†

Abstract

Urea-assisted water splitting represents a prospective approach for sustainable hydrogen (H₂) production. However, the challenge of designing highly efficient, durable, and economically viable bifunctional electrocatalysts hampers the practical implementation of this technology. In this work, we design a Ni₃S₂–CeO₂ heterostructure catalyst on nickel foam, tailored to upgrade the efficiency and cost-effectiveness of urea-assisted electrolysis. The catalyst features a unique interconnected nanosheet architecture, which boosts its activity, obtaining 100 mA cm⁻² for the urea oxidation reaction (UOR) with an overpotential of just 146 mV, and only 56 mV at 10 mA cm⁻² for the hydrogen evolution reaction (HER). When employed at both electrodes in a urea electrolysis electrolyzer, the Ni₃S₂–CeO₂/NF catalyst reaches a high current density of 500 mA cm⁻² at 1.734 V. Experimental results and DFT calculations demonstrate that the Ni₃S₂–CeO₂/NF heterogeneous interface facilitates electron redistribution and increases electronic density at the Fermi level, thereby enhancing the conductivity. The incorporation of CeO₂ facilitates Ni₃S₂ surface reconstruction, forming NiOOH active species with abundant oxygen vacancies (O_V) that optimize urea adsorption and improve UOR kinetics. Additionally, CeO₂ reduces the hydrogen adsorption energy (ΔG_H*), accelerating the HER process. These synergistic effects allow the Ni₃S₂–CeO₂/NF catalyst to achieve outstanding bifunctional activity in the UOR and HER, underscoring its potential for efficient urea-assisted electrolysis with low overpotentials at high current densities. This investigation provides guidance for creating effective bifunctional catalysts for sustainable hydrogen production.