Hydrogen bubble transport of a direct toluene electro-hydrogenation electrolyzer visualized by synchrotron X-ray CT

Toluene/methylcyclohexane stands out as a liquid organic hydride for hydrogen storage and transport at ambient pressure and temperature. Direct toluene electro-hydrogenation electrolyzers, using proton exchange membrane technology, show improved energy efficiency compared to the conventional two-step hydrogenation method. However, challenges persist in understanding the local transport of hydrogen bubbles within the cathode porous transport layer, since these bubbles inhibit toluene transport to reaction sites. This paper investigates the hydrogen bubble transport in an operational direct toluene electro-hydrogenation electrolyzer, for the first time, using synchrotron X-ray technology. Our observations reveal that water permeation and capillary pressure, affected by both current density and operating time, play a significant role in influencing dynamic bubble transport at the cathode, thereby impacting the efficiency of toluene transport to reaction sites.These results offer valuable insights for optimizing this type of electrolyzer design and contribute to advancing hydrogen storage solutions in such devices.