Towards an organic thermally regenerative fuel cell for truck engines

A thermally regenerative fuel cell (TRFC) on board a long-haul truck would convert waste heat from the engine or exhaust into electrical energy. We propose a TRFC in which waste-heat drives the endothermic dehydrogenation of a secondary benzylic alcohol to the corresponding ketone in a catalytic reaction chamber adjacent to the engine. 1-Phenyl-1-propanol has been identified as a suitable alcohol. In a fully functioning TRFC, the H 2 produced from the dehydrogenation will be sent to the fuel cell's anode, while the ketone, propiophenone, will be sent to the cathode to serve as an oxidant, together producing electricity to charge a battery that could power auxiliary vehicle components. The electrochemical reduction of the ketone back to the original benzylic alcohol would take place at the cathode. For such a system to be viable, both reactions must be very selective and rapid. Herein, the initial development of this system and the implications of catalyst and benzylic alcohol choice on the performance of both of these reactions are discussed. For the dehydrogenation of 1-phenyl-1-propanol, Pd/SiO 2 offers the highest selectivity (99.65%) at 200 °C. For the re-hydrogenation of the analogous ketone, propiophenone, palladium catalysts offer the highest selectivity, although the highest rates are observed for platinum immobilized on Vulcan XC-72 carbon support; surface modification of commercial catalysts with n-butyl tin also affects the selectivity and rate in a manner that depends on the choice of catalyst support. It has also been shown that the electronic and steric properties of the phenyl ring substituents and the identity of the alkyl chain affect the rate and selectivity. Highly selective, reversible and heterogeneously catalyzed benzylic alcohol dehydrogenation equilibria are investigated with applications to a proposed thermally regenerative fuel cell system to convert engine waste heat into electricity.