Boosting Acidic Hydrogen Evolution Kinetics Induced by Weak Strain Effect in PdPt Alloy for Proton Exchange Membrane Water Electrolyzers

Strain engineering is an effective strategy for manipulating the electronic structure of active sites and altering the binding strength toward adsorbates during the hydrogen evolution reaction (HER). However, the effects of weak and strong strain engineering on the HER catalytic activity have not been fully explored. Herein, the core-shell PdPt alloys with two-layer Pt shells (PdPt_2L) and multi-layer Pt shells (PdPt_ML) is constructed, which exhibit distinct lattice strains. Notably, PdPt_2L with weak strain effect just requires a low overpotential of 18 mV to reach 10 mA cm^-2 for the HER and shows the superior long-term stability for 510 h with negligible activity degradation in 0.5 M H₂SO₄. The intrinsic activity of PdPt_2L is 6.2 and 24.5 times higher than that of PdPt_ML and commercial Pt/C, respectively. Furthermore, PdPt_2L||IrO₂ exhibits superior activity over Pt/C||IrO₂ in proton exchange membrane water electrolyzers and maintains stable operation for 100 h at large current density of 500 mA cm^-2. In situ/operando measurements verify that PdPt_2L exhibits lower apparent activation energy and accelerated ad-/desorption kinetics, benefiting from the weak strain effect. Density functional theory calculations also reveal that PdPt_2L displays weaker H^* adsorption energy compared to PdPt_ML, favoring for H^* desorption and promoting H₂ generation.