Stabilizing active sites of non-iridium-based oxygen evolution reaction (OER) electrocatalysts is crucial, but remains a big challenge for hydrogen production by acidic water splitting. Here, we report that non-stoichiometric Ti oxides (TiO x ) can safeguard the Ru sites through structural-confinement and charge-redistribution, thereby extending the catalyst lifetime in acid by 10 orders of magnitude longer compared to that of the stoichiometric one (Ru/TiO 2 ). By exploiting the redox interaction-engaged strategy, the in situ growth of TiO x on Ti foam and the loading of Ru nanoparticles are realized in one step. The as-synthesized binder-free Ru/TiO x catalyst exhibits low OER overpotentials of 174 and 265 mV at 10 and 500 mA cm -2 , respectively. Experimental characterizations and theoretical calculations confirm that TiO x stabilizes the Ru active center, enabling operation at 10 mA cm -2 for over 37 days. This work opens an avenue of using non-stoichiometric compounds as stable and active materials for energy technologies.