Hydrogen crossover fuel efficiency

In general, hydrogen crossover has a negative impact on fuel cells this includes reduced fuel efficiency, decreased fuel cell OCV [11], and accelerated degradation of the membrane and the CLs [81,83],... 

In addition, if some hydrogen is lost due to hydrogen crossover or diffusion out of the fuel cell, the fuel cell efficiency will be further reduced. If we assume that the current generated by hydrogen loss is /loss and the actual current of the fuel cell is /ceii, then the electrical energy efficiency of a fuel cell can be further modified as in Eqn (1.75) ... 

This chapter mainly deals with the fundamentals of H2/air PEM fuel cells, including fuel cell reaction thermodynamics and kinetics, as well as a brief introduction to the single fuel cell and the fuel cell stack. The electrochemistry and reaction mechanisms of H2/air fuel cell reactions, including the anode HOR and the cathode ORR, are discussed in depth. Several concepts related to PEM fuel cell performance, such as fuel cell polarization curves, OCV, hydrogen crossover, and fuel cell efficiencies, are also introduced. With respect to fuel cell stmctures and components, the material properties and effects on fuel cell performance are also discussed. In addition, several important conditions for fuel cell operation, including temperature, pressure, RH, and gas stoichiometries and flow rates, and their effects on fuel cell operation, are also briefly presented. This chapter provides the requisite baseline knowledge for the remaining chapters. 

Besides affecting the proton conductivity, the temperature can also influence the hydrogen crossover of PEM fuel cell membranes. During hydrogen crossover, hydrogen diffuses across the membrane from the anode to the cathode, leading to a lower fuel cell efficiency and degradation of the... 

H2 crossover is the phenomenon of hydrogen crossing from the anode to the cathode through the PEM in a PEM fuel cell. This is an inevitable but undesirable phenomenon in operating PEM fuel cells. As discussed in Chapter 6, H2 crossover not only decreases fuel efficiency but it also leads to membrane decay and even fuel cell failure. Hydrogen that crosses over from the anode will be oxidized electrochemically on the cathode this reaction can be expressed using Reaction (l.I) in Chapter 1. Similar to Pt oxidation on the cathode, this... 

Although Figure 3-21 shows that fuel cell efficiency above 60% may be possible, albeit at very low current and power densities, in practice that is rarely the case. At very low current densities, hydrogen crossover and internal current losses, although very small, become important, and the efficiency-power curve flattens. For the particular case, a maximum efficiency of -55% is reached (Figure 3-22). 

FIGURE 3-22. Fuel cell efficiency vs power density curve solid line with and dashed line without internal current and/or hydrogen crossover losses. 

A particular version of the PEFC is the direct methanol fuel cell (DMFC). As the name implies, an aqueous solution of methanol is used as fuel instead of the hydrogen-rich gas, eliminating the need for reformers and shift reactors. The major challenge for the DMFC is the crossover of methanol from the anode compartment into the cathode compartment through the membrane that poisons the electrodes by CO. Consequently, the cell potentials and hence the system efficiencies are still low. Nevertheless, the DMFC offers the prospect of replacing batteries in consumer electronics and has attracted the interest of this industry. 

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