A Redox Flow Battery-Integrated Rechargeable H₂/O₂ Fuel Cell

The practical application of the H-2/O-2 proton-exchange membrane fuel cell (PEMFC) is being greatly limited by the use of high-cost Pt as electrode catalysts. Furthermore, the H-2/O-2 PEMFC is nonrechargeable and thus precludes kinetics energy recovery when equipped on electric vehicles and peak power regulation when combined to power grids. Here, we demonstrate a rechargeable H-2/O-2 PEMFC through embedding a redox flow battery into a conventional H-2/O-2 PEMFC. This flow battery employs H-2/O-2 reactive redox pairs such as NO3-/NO-Br-2/Br- and H4SiW12O40/H5SiW12O40 whose redox potentials are as close as possible to those of O-2/H2O and H-2/H2O, respectively, so that the chemical potential losses during their reactions with O-2 at the cathode and H-2 at the anode were minimized. More importantly, the electrochemical reversibility allows the H-2/O-2 reacted redox pairs to be easily regenerated through fuel cell discharging on catalyst-free carbon electrodes at a low overpotential and brings in the fuel cell both chemical and electrical rechargeability, thereby realizing integrated functions of electricity generation- storage as well as efficient operation (achieving an open-circuit potential of 0.96 V and a peak power density of 0.57 W/cm(2), which are comparable to a conventional H-2/air PEMFC) with catalyst-free carbon electrodes.