Abstract: Widespread deployment of proton exchange membrane water electrolyzers (PEMWE) relies on acid-stable oxygen evolution reaction (OER) catalysts capable of operating at high current densities. Inspired by the robust chemistry of lead-acid batteries, we introduce lead (Pb) into ruthenium-iridium mixed oxide (RuIrO_x) through a facile sol-gel method. The as-prepared RuIrPbO_x nanoparticulate catalysts with the optimal composition (Ru_0.5Ir_0.4Pb_0.1O_x) achieve an overpotential of 241 mV at 10 mA cm^-2 and exceptional stability of 1000 h at a high current density of 100 mA cm^-2 without degradation. In situ differential electrochemical mass spectrometry indicates that doping RuIrO_x with an appropriate amount of Pb helps to suppress the participation of lattice oxygen during OER, contributing to structural preservation and long-term stability. Density functional theory calculations reveal that Pb doping effectively regulates the electronic structure of the Ru sites, reducing Ru-O covalency, which in turn increases the Ru dissolution energy and therefore prevents Ru leaching—a key degradation pathway for Ru-containing OER catalysts. When integrated into a membrane electrode assembly, the PEMWE cell can operate at a large current density of 3.0 A cm^-2 under 1.96 V (at 60 °C) for 400 h with minimal performance degradation, demonstrating the significant potential of the Ru_0.5Ir_0.4Pb_0.1O_x as an efficient and durable OER catalyst for practical applications under demanding conditions.