Tuning A‐Site Cation Deficiency in Pr0.5La0.5BaCo2O5+δ Perovskite to Realize Large‐Scale Hydrogen Evolution at 2000 mA cm−2

Abstract Industrial‐level hydrogen production from the water electrolysis requires reducing the overpotential ( η ) as much as possible at high current density, which is closely related to intrinsic activity of the electrocatalysts. Herein, A‐site cation deficiency engineering is proposed to screen high‐performance catalysts, demonstrating effective Pr 0.5‐ x La 0.5 BaCo 2 O 5+ δ (P 0.5‐ x LBC) perovskites toward alkaline hydrogen evolution reaction (HER). Among all perovskite compositions, Pr 0.4 La 0.5 BaCo 2 O 5+ δ (P0.4LBC) exhibits superior HER performance along with unique operating stability at large current densities ( J = 500–2000 mA cm−2 geo). The overpotential of ≈636 mV is achieved in P0.4LBC at 2000 mA cm−2 geo, which outperforms commercial Pt/C benchmark (≈974 mV). Furthermore, the Tafel slope of P0.4LBC (34.1 mV dec −1 ) is close to that of Pt/C (35.6 mV dec −1 ), reflecting fast HER kinetics on the P0.4LBC catalyst. Combined with experimental and theoretical results, such catalytic activity may benefit from enhanced electrical conductivity, enlarged Co‐O covalency, and decreased desorption energy of H * species. This results highlight effective A‐site cation‐deficient strategy for promoting electrochemical properties of perovskites, highlighting potential water electrolysis at ampere‐level current density.