Conventional water electrolyzer simultaneously generates H-2 and O-2 in neighboring electrode compartments which raises various issues by gas mixing. Thus, decoupled water electrolysis is desired to avoid the problems. Motivated by the above, spatially decoupled hydrogen evolution reaction (HER) is demonstrated in this work, leveraging a redox targeting-based flow battery employing iron triethanolamine (Fe(III)TEA)-K2MnO4 couple. This system spatially separates HER from the electrode compartment. Sustained hydrogen is achieved by reaction between regenerated Fe(II)TEA and water in the negative electrolyte storage tank. The Faradaic efficiency of the decoupled HER is 70% and keeps stable upon prolonged operation. The onset overpotential of HER is 24 mV which is lower than previous studies. We anticipate the approach presented in this work would offer an alternative solution to water electrolysis for scalable and safe hydrogen production with improved gas purity. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.