Hydrogen PEFCs advantages

The primary advantages of the hydrogen PEFC system compared to other fuel cell systems include the following ... 

The DMFC, based on a polymer electrolyte fuel cell (PEFC), uses methanol directly for electric power generation and promises technical advantages for power trains. The fuel can be delivered to the fuel cell in a gaseous or liquid form. The actual power densities of a DMFC are clearly lower than those of a conventional hydrogen-fed polymer electrolyte fuel cell. In addition, methanol permeates through the electrolyte and oxidizes at the cathode. This results in a mixed potential at the cathode (Hohlein et al., 2000). 

When hydrogen is produced by steam reforming of methanol or hydrocarbons, CO is the second-largest byproduct component (about 1 vol %) after CO2- In application to PEFC, to remove CO to a concentration of 100 ppm, CO should be reduced to methane or oxidized to CO2. Oxidation is advantageous because it potentially consumes less hydrogen. 

Fig. 23 Air cathode catalyst mass utilization (A mg-1 Pt) for different types of catalyst layers as developed chronologically for hydrogen/air PEFC. Squares PTFE-bonded Pt black at 4 mg Pt/cm2 circles ionomer-impregnated, PA- type electrodes (0.45 mg Pt/cm2) triangles thin-film Pt/C//ionomer composite (0.13 mg Pt/cm2). The relative advantage of thin-film catalyst layers is seen to increase with cell current density, as expected from the lower transport limitations involved (see Sect. 8.3.7.2.3) [10,11].

Advantages The PEFC has a solid electrolyte which provides excellent resistance to gas crossover. The PEFC s low operating temperature allows rapid start-up and, with the absence of corrosive cell constituents, the use of the exotic materials required in other fuel cell types, both in stack construction and in the BoP is not required. Test results have demonstrated that PEFCs are capable of high current densities of over 2 kW/1 and 2 W/cm. The PEFC lends itself particularly to situations where pure hydrogen can be used as a fuel. 

In general, liquid-fed DMFCs are operated at lower power densities than vapor-fed DMFCs and PEFCs operated on hydrogen. Due to their simpler system design, Uqttid-fed DMFC systems are advantageous, particularly for applications having only a low power demand. 

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