The participation of lattice oxygen in the oxygen evolution reaction (OER) process has been proved to be faster in kinetics than the mechanisms where only metal is involved, although activating the lattice oxygen in the traditional rigid structures remains a big challenge. In this work, efforts are devoted to exploring a new flexible structure that is competent in providing large amounts of oxygen vacancies as well as offering the freedom to manipulate the electronic structure of metal cations. This is demonstrated by anchoring low valence state Co at high valence state Nb sites in the tetragonal tungsten bronze (TTB)-structured Sr0.5Ba0.5Nb2-xCoxO6-δ, with different ratios of Co to Nb to optimize the Co substitution proportion. It is found that the occupation of Co in the Nb5+ sites gives rise to the generation of massive surface oxygen vacancies (Ovac), while Co itself is stabilized in Co2+ by adjacent Ovac. The coexistence of Ovac and LS Co2+ enables an oxygen intercalation mechanism in the optimal SBNC45 with specific activity at 1.7 V versus reversible hydrogen electrode that is 20 times higher than for the commercial IrO2. This work illuminates an entirely new avenue to rationally design OER electrocatalysts with ultrafast kinetics.