Abstract
Direct methanol fuel cells (DMFC) have several advantages for a broad spectrum of energy density demanding applications, ranging from portable devices to stationary backup power. DMFCs deliver power at high efficiencies compared to internal combustion technologies and uses high energy density methanol as the fuel. However, DMFCs face several challenges, including methanol crossover at the cathode and slow methanol oxidation reaction (MOR) kinetics at the anode that impede its DMFC performance relative to hydrogen polymer electrolyte fuel cells (PEFCs). Since the the anode is a much bigger source of overpotentials than the H2 PEFC, we must carefully consider it's characteristics in designing the membrane electrode assembly (MEA) and it requires extensive experimental and modeling studies to investigate these hindrances and mitigate their impacts on performance. It is widely known that vapor-fed DMFCs suffer less from methanol crossover. However, a complete understanding of the vapor-fed MOR kinetics in porous electrodes is lacking. When modeling DMFCs it is a common practice to assume that the reaction order of the MOR is zero. However previous studies have shown that the liquid-fed MOR on PtRu/C catalysts has areaction order of 0.5 [1, 2]. However, we found that the reaction order of the vapor-fed MOR can differ from that value. We also investigated the effect of different catalyst loading and the effect of methanol crossover on reaction order.
This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under Award Number DE-EE0008440.
References
S.Lj. Gojkovic´ et al., Electrochimica Acta 48 (2003) 3607/3614
D. Chu, S. Gilman, J. Electrochem. Soc. 143 (1996) 1685.