Improvement of Current Efficiency of a Membrane Electrolyzer for Electrohydrogenation of Toluene As Hydrogen Carrier Synthesis

Introduction In order to reduce carbon dioxide emissions, a significant number of renewable energies that are uneven distribution with fluctuation must be introduced. Therefore, to increase renewable energies, energy carrier technology is needed for storage and transportation. Toluene-methylcyclohexane organic chemical hydride system is one of promising technologies as hydrogen storage and transportation. Electrohydrogenation of toluene with water splitting has higher theoretical energy conversion efficiency compare to a series process of water electrolysis and hydrogenation. Cathode side is a cathode membrane assembly with PtRu/C, which is applied PEFC technology. Anode is a dimensionally stable electrode for oxygen evolution reaction in acidic electrolyte using industrial electrolysis technology. In our previous study, we demonstrated good performance of the electrolyzer with hydrophilized membrane; however, hydrogen generated with low concentration of toluene feed, which should be improved (1). In this study, the effect of the design of toluene feed flow field on the cell voltage and the current efficiency has been investigated to increase conversion ratio from toluene to methylcyclohexane without hydrogen generation. Experimental A single cell electrolyzer made of titanium with 100 cm 2 of projected electrode area was used to determine the performance. Figure 1 shows the schematic drawing of flow field for the cathode. A parallel flow, which is usual for industrial electrolysis and liquid electrolyte fuel cells, a serpentine flow, which is conventional for polymer electrolyte fuel cells, and an interdigitated flow have been investigated to improve the performance of the electrolyzer. The anode flow field was parallel. A cathode was a carbon paper (35BC, SGL) coated 0.5 mgcm -2 of PtRu (TEC61E54, TKK) with Nafion dispersion. The cathode was pressed on a perfluoroethylene sulfuric acid (PFSA) membrane (Nafion ® 117, DuPont) for a cathode membrane assembly. The membrane of the cathode side was mechanically hydrophilized. A DSE ® anode with IrO 2 based electrocatalyst is used for oxygen evolution. Backing of the anode was titanium felt. The anode was uniformlypressed on the membrane by elastic force of the titanium felt. 10 cm 3 min -1 of toluene or 50% toluene-methylcyclohexane mixture and 1M (=moldm -3 ) of H 2 SO 4 were supplied to the cathode and anode for hydrogenation of toluene, respectively. Cell voltage was determined with 4 mVs -1 of voltage sw