Hydrogen production via electrolysis is an efficient way to store excess energy from renewable energy plants, but electrolysis must be made more applicable. Conventional water electrolysis is complicated by a gas distribution and management system to prevent the mixing of H2 and O2 gases, which creates significant safety hazards. The use of membranes and diaphragms solves the gas mixing problem but reduces efficiency and directly affects the cost of hydrogen production. Here we show decoupled water electrolysis concept, where hydrogen evolution and oxygen evolution are spatially and temporally separated using a WO3 charge storage electrode as a red-ox mediator. Electrolysis is realized in two steps, where in the first step the oxygen evolution reaction (OER) and intercalation of H+ in the WO3 material take place. In the second step, the deintercalation of H+ from the WO3 material and the reduction of H+ to H at the other electrode takes place. In the electrolysis process H2 and O2 gasses are produced with purity >99.9%. The overall efficiency of the electrolyzer is 65%.