Effect of the cathode catalyst loading on mass transfer in toluene direct electrohydrogenation

Abstract

Toluene (TL)-methylcyclohexane (MCH) organic hydride is one of the most promising carrier candidates for the large-scale transport and storage of hydrogen. TL Direct electrohydrogenation electrolyzers based on solid polymer electrolyte membrane technology exhibit significant advantages in terms of energy efficiency compared with the conventional TL hydrogenation method. Mass transfer in the catalyst layer is a crucial aspect of the performance of these electrochemical devices. In this study, experiments were conducted using catalyst-coated membranes with various thicknesses to control the catalyst loading (carbon-supported platinum/ruthenium alloy) and investigate its influence on the mass transfer properties and electrolytic performance of a TL direct electrohydrogenation electrolyzers. The current efficiency was also evaluated for TL concentrations between 1% and 100% in the cathode reactant. The results indicated than an optimum thickness of the cathode catalyst layer corresponding to catalyst loadings of 1.4–1.6 mg cm−2 could maximize the current efficiency of the electrolyzer. The presence of hydrogen gas generated as a side reaction in the high-TL concentration range and high MCH concentrations in the low-TL concentration range are the main factors contributing to a decrease in current efficiency.