The Hybrid Bi-Cell Approach for Reducing Active Water Management in the Direct Methanol Fuel Cell

Direct methanol fuel cells (DMFCs) provide an avenue for developing high (specific) energy density, portable power sources. While the overall energy efficiencies that have been reported for DFMCs are rather modest (e.g., approximately 15-20%), interest in the technology stems from the specific energy methanol (6.1 kWhr/kg) which still enables very large system energy densities to be achieved (1, 2). Despite this key benefit, the size and cost of the DMFC technology remain key technical hurdles.

To date, many if not most efforts to develop DMFC technologies have used membrane electrolyte assemblies (MEAs) which utilize proton exchange membrane (PEM) electrolyte materials. These acidic PEM materials tend to be quite robust ; however, their use has relegated the DMFC systems to use of relatively large balance of plant (BoP) components for active water/fuel management (3, 4) and expensive platinum based catalyst materials (5).  

In this talk, we review an approach which is intended to address the size of the BoP required for active water/fuel management as well as enable the removal of some of the platinum based catalysts. This approach uses a bi-cell, or pseudo-bipolar, configuration which has been previously shown to be well suited to portable power applications (6). The novelty of this approach is the combination of a first acidic MEA using PEM electrolyte materials and a second alkaline MEA using anion exchange membrane (AEM) electrolyte materials. This configuration naturally balances the water stoichiometry of the methanol oxidation and oxygen reduction reactions between the adjacent acid and alkaline MEAs, significantly improving the water balance within the system. The integration of alkaline AEM materials has the additional benefit of opening doors for alternatives to platinum based catalysts.

A multi-phase, multi-component transport model is used as the basis of this work, which is intended to demonstrate the technical feasibility of the approach for miniaturizing portable DMFC system. A previous study by Kim et al. has shown the compatibility of the materials (7). In this talk, focus will be placed on comparing standard and hybrid configurations and the relative water/fuel management requirements. Additional attention will be placed on the treatment of direct oxidation of methanol in an alkaline MEA and the effect of MEA properties. 

1.         D. Chu and R. Jiang, Electrochim Acta 51(26), 5829 (2006).

2.         R. Jiang, C. Rong and D. Chu, J Power Sources 126(1-2), 119 (2004).

3.         R. Jiang and D. Chu, J Electrochem Soc 155(8), B798 (2008).

4.         R. Jiang and D. Chu, J Electrochem Soc 155(8), B804 (2008).

5.         S. Wasmus and A. Kuver, J Electroanal Chem 461(1-2), 14 (1999).

6.         R. Jiang and D. Chu, J Power Sources 93(1-2), 25 (2001).

7.         H. Kim, M. Unlu, J. F. Zhou, I. Anestis-Richard and P. A. Kohl, J Power Sources 195(21), 7289 (2010).