The dissociation of water is the rate-determining step of several energy-relating reactions due to high energy barrier in homolysis of H-O bond. Herein, engineering vacancy-atom ensembles via injecting oxygen vacancy (V_O) into single facet-exposed TiO₂-Pd catalyst to form V_O-Pd ensemble is proposed and implemented. The outstanding activity of as-prepared catalyst, 1.5-PdTV_O, toward water dissociation is established with a turnover frequency of 240 min⁻¹ in ammonia borane hydrolysis at 298 K. Density functional theory simulation suggests that the V_O-Pd ensemble is responsible for the high intrinsic catalytic activity. Water molecules tend to be dissociated on V_O sites and ammonia borane molecules on Pd atoms. Those H atoms from water dissociation on V_O combine with H atoms from ammonia borane on Pd atoms to generate H₂. This insights into engineering vacancy-atom ensembles catalysis provide a new avenue to design catalytic materials for important energy chemical reactions.