Polybenzimidazole-coated carbon felts for vanadium redox flow batteries

Abstract

Several researchers integrated thin polybenzimidazole (PBI) layers into membranes to block vanadium transport. In this work, we follow an orthogonal approach, and bond a thin PBI layer to carbon felt (CF). This shifts the vanadium blocking function from the membrane to the electrode, and reduces the role of the membrane to sealing the cell and acting as spacer between anode and cathode, for the case that a carbon fiber pokes through the thin PBI layers. Using PBI-CF electrodes, we assemble cells with cheap non-fluorinated membranes, which are not optimized for the use in vanadium redox flow batteries. A commercial anion exchange membrane (DABCO-SEBS), sulfonated polystyrene (sPS56), and sulfonated Radel (sPES) show lower resistance than Nafion 212. When assembled with PBI-CF electrodes and a gasket, the cells with sPES and sPS56 show an energy efficiency of 82.6% and 83.3%, respectively, at 150 mA cm−2, higher than that of a cell using CF and Nafion 212 (78.8%). One set of PBI-CF is tested for 3000 charge/discharge cycles without failure.