In contrast to alkaline water electrolysis, acidic water electrolysis remains an elusive goal due to the lack of earth-abundant, efficient, and acid-stable water oxidation electrocatalysts. Here, we show that materials with intrinsically poor electrocatalytic activity can be turned into active electrocatalysts that drive the acidic oxygen evolution reaction (OER) effectively. This development is achieved through ultrafast plasma sputtering, which introduces abundant oxygen vacancies that reconstruct the surface electronic structures, and thus, regulated the surface interactions of electrocatalysts and the OER intermediates. Using tungsten oxide (WO3) as an example, we present a broad spectrum of theoretical and experimental characterizations that show an improved energetics of OER originating from surface oxygen vacancies and resulting in a significantly boosted OER performance, compared with pristine WO3. Our result suggests the efficacy of using defect chemistry to modify electronic properties and hence to improve the OER performance of known materials with poor activity, providing a new direction for the discovery of acid-stable OER catalysts.