Hydrogen is a potential candidate for energy carrier role with high gravimetric energy density of 33kWh/kg. However, owing to its low volumetric energy density, 0.003kWh/l at STP, which is very small compared to common fuels, it poses logistical barriers in its widespread use. Conventional methods of hydrogen storage and transportation include compression up to pressures near ~80MPa or liquefaction by cooling down to temperatures below -253˚C. Another promising method of hydrogen storage is to chemically store in the form of organic hydrides. One such organic hydride is methyl-cyclo hexane (MCH), which is liquid at standard temperature and pressure and can be reversibly hydrogenated and de-hydrogenated for storage and extraction of hydrogen, respectively.

Extraction of hydrogen from MCH through dehydrogenation is an endothermic process (ΔH=204.8kJ/mol), so to favor hydrogen production the reaction is carried out at high temperatures. Conventionally, this is carried out in chemical plant sized reactors at temperatures near ~350˚C [1]. Maintaining such a high temperature in small scale energy devices increases the cost and complexity. Hence it is difficult to carry out dehydrogenation locally within the energy devices which utilize the thus extracted hydrogen. A low temperature (<120˚C) and low pressure (~1atm) dehydrogenation process able to be carried out in small scale devices can herald widespread use of MCH as a hydrogen carrier. This will promote hydrogen as a viable option to conventional fuels.

In this study, we have demonstrated the dehydrogenation of MCH at room temperature and pressure using polymer electrolyte membrane (PEM) based electrochemical cell. By applying a potential across the membrane electrode assembly (MEA), consisting of carbon supported catalyst electrode as anode and cathode, hydrogen evolution was observed at cathode side with the supply of MCH at the anode. Quinones have been used as reaction mediator to lower the electrode potential required for the dehydrogenation of liquid MCH to below the water electrolysis potential (1.23V). Formation of toluene as a dehydrogenation by-product at anode was also confirmed using gas chromatography mass spectrometry (GC-MS) analysis. Effect of temperature variation and anode reactant flow rate has been investigated.

References

1. F. Buonomo, D. Sanfilippo, F. Trifirò, in: G. Ertl, H. Knözinger, J. Weitkamp (Eds.), Handbook of Heterogeneous Catalysis, vol. 5, VCH, Weinheim, 1997, p. 2140