Developing efficient and stable oxygen evolution reaction (OER) electrocatalysts that can work stably in acidic conditions is crucial for advancing proton-exchange membrane water electrolysers commercialization. Here, we prepared a heterostructure-based OER electrocatalyst by in-situ growing RuO₂ nanoparticles on metal-organic-framework-derived Co₃O₄ nanoaggregates that can operate stably in acidic electrolytes. The interface of RuO₂/Co₃O₄ heterostructure, as well as their effect on electronic structure, were examined by various advanced characterizations. The optimized RuO₂/Co₃O₄ electrocatalyst reveals an ultra-low overpotential of 206 and 320 mV at 10 and 100 mA·cm⁻², respectively. X-ray photoelectron spectroscopy, differential electrochemical mass spectroscopy measurements and theoretical calculations indicate that the as-constructed RuO₂/Co₃O₄ interfaces could reduce the metal-oxygen covalence and energy barriers of rate-determining step, thereby decreasing the participation of lattice oxygen and preventing excessive oxidation of Ru sites during OER. In practical PEMWE systems, RuO₂/Co₃O₄ achieves 1.63 V at 1 A·cm⁻², and maintains remarkable stability for over 500 h with a very small voltage degradation rate of 0.2 mV·h⁻¹. This study provides a promising avenue for developing cost-effective OER electrocatalysts with superior activity and stability for advanced energy conversion.