Toluene permeation through solid polymer electrolyte during toluene direct electro-hydrogenation for energy carrier synthesis

For the transportation and storage of hydrogen energy by toluene-methylcyclohexane organic hydride systems, the performance of toluene direct electro-hydrogenation electrolyzers using solid polymer electrolytes (SPE) for the membrane and ionomers must be improved. In this study, we investigate the effect of the equivalent weight (EW) and the side-chain length of the SPE on toluene permeability and electrochemical performance. The SPE membrane with a lower EW and a shorter side chain shows a lower toluene permeability. The lower EW, with higher acidity, decreases toluene solubility by salting-out in the hydrophilic mass transport path. The shorter side chain, which lowers the water uptake, suppresses toluene permeation by decreasing the cross-sectional area of the mass transport path. In the electrochemical measurement using the electrolyzer, the combination of SPEs with long side chain and high EW for both the membrane and ionomer shows the best performance. For long-term anode deactivation by membrane-permeated toluene, the membrane should be designed to reduce toluene permeability. Meanwhile, the ionomer has the advantage of higher EW and long side chain.