Strain Engineering of Ru–Co₂Ni Nanoalloy Encapsulated with Carbon Nanotubes for Efficient Anion and Proton Exchange Membrane Water Electrolysis

Alloying atomically dispersed noble metals with earth-abundant transition metal nanoparticles (NPs) presents a promising approach to enhance the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water electrolysis. However, the challenge remains of reducing the size of the NPs without sacrificing high activity and durability. In this study, Ru–Co₂Ni nanoalloy particles (NAPs) encapsulated in nitrogen-doped carbon nanotubes (NCNTs) are introduced, forming a core-shell electrocatalyst (Ru–Co₂Ni@NCNT). This design leverages Ru site optimization, CNT density control, strain engineering, efficient water dissociation, and outstanding bubble release dynamics within the core-shell structure. These factors significantly improve catalytic performance with low overpotentials of 35 and 57 mV overpotential in 1.0 m KOH and 0.5 m H₂SO₄ solutions, respectively, at a current density of 10 mA cm⁻². Density functional theory (DFT) calculations reveal that while Ru sites serve as active sites, they also modify the electronic structure of Co and Ni, optimizing their hydrogen adsorption energies and improving HER efficiency. The Ru–Co₂Ni@NCNT catalyst is successfully integrated into both anion exchange membrane (AEM) and proton exchange membrane (PEM) electrolyzers, demonstrating stable operation at 0.5 A cm⁻² for 500 h, underscoring its potential for efficient and durable hydrogen production.