Owing to the scarcity of Pt, low-cost, stable, and efficient nonprecious metal-based electrocatalysts that can be applied in a wide pH range for the hydrogen evolution reaction (HER) are urgently required. Herein, a highly efficient and robust HER catalyst that is applicable at all pH values is fabricated, containing isolated Co-single atomic sites anchored in the self-supported WO3arrays grown on Cu foam. At a current density of 10 mA cm–2, the HER overpotentials are 117, 105, and 149 mV at pH values of 0, 7, and 14, respectively, which are significantly lower than those of the undoped WO3, suggesting superior electrocatalytic H2-evolution activity at all pH values. The catalyst also exhibits long-term stability over a wide pH range, particularly in an acidic medium over 24 h, owing to the excellent anticorrosion properties of WO3. Density functional theory calculations prove that the enhanced HER activity is attributed to the isolated Co sites because these optimize the adsorption energy of H* species on WO3. Moreover, the high electrical conductivity of Co-doped WO3and the three-dimensional array structure supported on the porous metal support afford a catalyst with suitable HER kinetics to enhance the catalytic performance.