Interfacially engineered palladium nanoparticle-decorated nickel oxide nanostructured electrocatalysts for high-performance hydrogen evolution reaction

Water splitting has been known as a promising candidate for electrochemical green hydrogen. The hydrogen evolution reaction (HER), which is the half-reaction for water splitting at the cathode, typically requires a high overpotential (η_HER). Transition metal-based nanomaterials (TMBMs) are appealing electrocatalysts for the HER because of their ability to reduce the η_HER. Interfacial engineering is an effective strategy for utilizing TMBMs, wherein noble metals are used to create several active sites on the surfaces of nanostructured TMBMs. This approach simultaneously exploits the advantages of the intrinsically high HER performance of noble metals and the large surface area of TMBM nanostructures. In this study, we synthesized nickel oxide (NiO) nanoplates via an alkali-free hydrothermal approach to produce highly purified electrodes with large surface area, followed by decoration with palladium (Pd) nanoparticles via wet impregnation. Although various combinations of noble metal-decorated TMBMs are available for the HER, Pd and NiO were chosen due to their intrinsically high HER performance and facile processability, respectively. The Pd/NiO electrocatalyst with an ideal compositional threshold of both elements showed outstanding HER performance, affording low η_HER of 59 and 92 mV at high current densities of 50 and 100 mAcm⁻², respectively, and a low Tafel slope of 52 mVdec⁻¹. After 50 h of a stability test, 92 % of the initial performance of the Pd/NiO electrode was maintained. These experimental results have been supported by the Gibbs free energy for Pd/NiO and pristine NiO electrocatalysts estimated in the water dissociation using density functional theory (DFT) calculations. This facile approach of alkali-free hydrothermal synthesis and subsequent wet impregnation to synthesize electrocatalysts based on interface engineering can be further utilized to explore high performance green hydrogen production.