Optimization of Direct Methanol Fuel Cell Systems and Their Mode of Operation

The merits of the DMFC as the technology of choice for micro-fuel cell power systems in hand held consumer electronics devices have been described in the Introductory Technical Remarks for this School. The DMFC scheme in Figure 1 reveals it is important key feature: direct and complete conversion of methanol fuel to CO₂ in a methanol/air cell operating at a temperature well under 100°C. With neat liquid methanol having a heating value of near 5 Wh/CC — i.e. theoretical energy content in one CC of liquid methanol equal to that of a relatively large cell phone battery – and with the simple nature of a “direct” fuel cell that can use this energy-rich liquid fuel directly, one might expect easy reduction to practice of a DMFC power pack (fuel + fuel cell + auxiliaries) of energy density higher than that of a Li-ion battery. In reality, however, three main barriers to the reduction to practice of DMFC systems of superior energy density, have been: (i) high methanol permeability of mainstream ionomeric membranes used in polymer electrolyte fuel cells, (ii) the water management challenge posed by water product generated on the cathode side of the DMFC while being required for the cell process on the anode side, and (iii) the moderate power density of DMFC stacks (compared with hydrogen fueled stacks), defined by the modest rate of the anodic oxidation of methanol. This chapter describes innovative approaches developed during the last decade for the resolution of the first two barriers and, in the context of the third challenge, describes briefly the state-of-the-art of electrocatalyst research and development for polymer electrolyte DMFCs.