Hydrogen-fuelled PEMFC

DMFCs have potential near-term applications mainly in the portable power source market, as they are smaller, lighter, simpler, and cleaner than conventional batteries. Liquid methanol is consumed directly in a DMFC, which implies a higher energy density of the fuel cell system. But the power densities achievable with state-of-the-art DMFCs are still very small in comparison to hydrogen-fuelled PEMFCs. One of the major problems lies in the use of liquid methanol solution on the anode of the DMFC, which, on the one hand, keeps the ionomeric membrane water saturated (and thus no humidification is needed) but, on the other hand, does not keep fuel (methanol or any other organic fuel, e.g., formic acid, ethanol) and water from permeating to the cathode side, since the basic PFSA membranes are permeable to both methanol and water. - The fuel and water crossover from anode to cathode hampers the performance of the air cathode. 

It is generally recognized that the development of Pt-based alloys is one feasible strategy for Pt load reduction and activity enhancement in fuel cells, including both hydrogen-fuelled PEMFCs and DMFCs. In this chapter, we introduce the research and development of Pt-based alloy catalysts for both the ORR and the MOR. The alloying effect and corresponding mechanism as well as the stability of Pt-based alloy catalysts towards the ORR and MOR will be described in detail. The topics of CO- and methanol-tolerant Pt-based alloy catalysts will not be discussed in this chapter (please see instead Chapter 16, CO-Tolerant Catalysts ). 

The result of both these problems is that the performance of the DMFC is markedly worse than other types, such as a hydrogen-fuelled proton exchange membrane fuel cell (PEMFC). Figure 6.1 shows the performance of a state-of-the-art DMFC in 2002, compared with the Yjl graph for a hydrogen-fuelled PEMFC. The shape of the graph is broadly similar, but the voltages and current densities are considerably lower. 

---