Pt nanoparticles loaded onto ultrathin Ni(OH)2 nanosheets for enhanced seawater–urea electro-oxidation and hydrogen evolution at an industrial-grade current density

Abstract

The design of an efficient and corrosion-resistant bifunctional electrocatalyst through coupling the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) in seawater for large-scale hydrogen generation still poses challenges. Herein, Pt/Ni(OH)₂/NF was successfully synthesised via spontaneous galvanic displacement to improve the overall urea water/seawater splitting performance. Pt/Ni(OH)₂/NF showed significantly reduced overpotentials/potentials of 8.5/243 mV and 1.32/1.44 V to achieve a current density of 20/500 mA cm⁻² during the HER and the UOR, which are lower compared to those of commercial Pt/C/NF (41 mV@20 mA cm⁻²) and RuO₂/NF (1.34 V@20 mA cm⁻²). Furthermore, the electrolytic cell voltage of the as-prepared electrode in the alkaline seawater–urea electrolyte was significantly reduced to 1.55 V in comparison with the voltage in commercial Pt/C and RuO₂ systems (1.63 V) at a current density of 100 mA cm⁻². The amorphous Ni(OH)₂ facilitates the adsorption and activation of water, generating a unique Cl⁻ shielding effect, and the Pt nanoparticles promote the formation and desorption of H₂, which synergistically improve the performance and endurance of Pt/Ni(OH)₂. Ultraviolet photoelectron spectroscopy (UPS) showed that Pt/Ni(OH)₂/NF shows a diminished work function, making it easier for electrons to escape and promoting the activation of water molecules. In situ Raman spectroscopy testifies that NiOOH serves as the crucial intermediate in the UOR process over Pt/Ni(OH)₂/NF. This work provides an important reference for efficient hydrogen production in seawater by coupling the thermodynamically more advantageous small molecule oxidation reaction with the HER.