An H-2-Fe3+ recombination method is being developed for all-iron flow batteries. Working principles are described and a proof-of-concept in-tank reactor is demonstrated. A membrane-less galvanic reactor is characterized using potential, polarization and impedance measurements at hydrogen partial pressures ranging from 0.3 to 11.3 psig. Through a vertical reactor geometry, hydrogen recombination rates of up to 60 mA cm(-2) were measured at P-H2 = 4.5 psig for a reactor with a platinum loading of 3.2 mg cm(-2), based on the geometric catalyzed area. This is equivalent to over 375 mA cm(-2) with respect to the cross sectional area of the reactor at the waterline. This rate is sufficient that the reactor will readily fit inside the positive reservoir of a flow battery. The reactor was found to be resistant to degradation by flooding or catalyst loss. (C) 2016 Elsevier B.V. All rights reserved.