A Redox Flow Battery-Integrated Rechargeable H 2 /O 2 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 NO 3 - /NO-Br 2 /Br - and H 4 SiW 12 O 40 /H 5 SiW 12 O 40 whose redox potentials are as close as possible to those of O 2 /H 2 O and H 2 /H 2 O, 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.