Influence of Membrane Cathode Assembly Composition and Fabrication Methods on Proton Exchange Membrane Electrolyzers for Electrochemical Toluene Hydrogenation

As the world shifts towards renewable energy, efficient storage solutions for intermittent power sources have become essential. Although green hydrogen is promising, it is difficult to store physically owing to its small molecular size and light weight. One chemical method for storing green hydrogen involves the use of liquid organic hydrogen carriers such as methylcyclohexane (MCH). This study investigates the electrochemical hydrogenation of toluene to MCH in a proton exchange membrane electrolyzer, focusing on the effects of catalyst loading, ionomer content, fabrication method, and microporous layer (MPL) in a membrane cathode assembly (MCA). The optimal ionomer content, which varies with the catalyst loading, enhances the current density by facilitating proton transport, while excessive ionomers obstruct the active sites and electron pathways. Overpotential breakdown analysis revealed that incorporating an MPL improves electrical contact and catalyst utilization, reducing both the ohmic and kinetic overpotentials. The catalyst-coated substrate (CCS) method outperformed the catalyst-coated membrane method in mass transport. Consequently, the MCA fabricated using the CCS method with the MPL demonstrated the highest current efficiency for toluene hydrogenation. These findings offer insights into the optimization of cathode design for efficient electrochemical toluene hydrogenation, advancing the development of MCH-based electrochemical hydrogen storage systems.