Coupling alloying and doping strategies to improve and stabilize Pd-based catalysts for acidic hydrogen evolution

Palladium (Pd) is regarded as a promising electrocatalyst material for the hydrogen evolution reaction (HER) due to its similar hydrogen binding energy to Pt and excellent acid resistance. However, two challenges that must be urgently addressed are the relatively low HER activity stemming from the slightly stronger hydrogen adsorption strength and the insufficient durability caused by the propensity for PdH_x formation. Herein, we propose a strategy that combines alloying and doping effects to enhance both the HER activity and durability of Pd-based materials. The as-obtained Ni-doped Pd₄S hollow nanoparticles (Ni-Pd₄S HNPs) exhibit excellent HER performance, requiring only an overpotential of 51 mV to achieve a current density of 10 mA cm^-2, thereby surpassing previously reported Pd-based nanomaterials. Furthermore, Ni-Pd₄S HNPs exhibit superior HER stability compared to Pd/C and Pt/C electrocatalysts. Density functional theory (DFT) calculation results show that the enhanced performance of Ni-Pd₄S HNPs arises from alterations in the electronic structure of the Pd active sites due to Ni doping and S alloying, which consequently drive the Gibbs free energy of hydrogen adsorption towards zero.