Mixed Reactant Low Temperature Fuel Cells: The Swiss-Roll Cell Design and Selective Electrocatalysts

Eliminating the proton exchange membrane (PEM) together with the platinum-based anode and cathode catalysts and replacing the bulky bipolar plates with lighter and flexible alternatives, would significantly improve the economic outlook of low temperature fuel cells operated with liquid fuels. To address the afore-mentioned issues of PEM fuel cells, at the University of British Columbia we have developed a novel mixed reactant fuel cell design referred to as the Swiss-roll cell, fed with a two-phase mixture of liquid fuel and air (or oxygen) [1-5]. Here, a research progress review is presented related to both selective electrocatalysis and Swiss-roll cell engineering applied to two alkaline fuel cell systems: sodium borohydride – oxygen and sodium borohydride – nitrous oxide, respectively. On the anode, the borohydride electro-oxidation reaction is a complex, up to eight electron transfer process, with possibly competing hydrogen evolution generated by either faradaic (i.e., electrocatalytic) or non-faradaic (i.e., thermocatalytic) pathways.  Experimental results correlated with density functional theory modelling predictions are discussed focused on the borohdyride electro-oxidation mechanism on catalysts such as: Pt, Au and Os. On the cathode side, in case of the oxygen reduction reaction (ORR) in alkaline media the comparative performance of gas diffusion electrodes with electrocatalysts such as MnO₂, Ag and Fe-aminoantypyrine (Fe-AAPyr) is presented. For nitrous oxide reduction, the electrode kinetics on Pd and Pt electrocatalysts are compared. It is shown that the selective electrocatalyst discovery combined with cell electrochemical engineering innovations enables significant improvements in the power output, reaching 250 mW/cm² for the membrane-free Swiss-roll mixed-reactant direct borohdyride fuel cell operated at 50 ⁰C and near atmospheric pressure using non-platinum anode and cathode catalysts.  

References:

1. A. Aziznia, C. Oloman and E.L. Gyenge, J.Power Sources, 212, 154-160 (2012).
2. A. Aziznia, C. Oloman and E.L. Gyenge, ChemSusChem, 6, 847-855 (2013).
3. A. Serov, A. Aziznia, P. H. Benhangi, K. Artyushkova, P. Atanassov and E. Gyenge,  J. Mat. Chem. A, 1, 14384-14391, (2013).
4. A. Aziznia, C. Oloman and E.L. Gyenge, J.Power Sources, 265, 201-213 (2014).
5. C. W. Oloman, British Patent GB 2474202, 2012.