9 These show that an increase of the ionomer content within the cathode catalyst layer leads to higher anodic hydrogen volume fractions. 3– 5, 9, 10, 13– 15 Further investigations on structural effects were carried out by Trinke et al. In summary, these studies found that increases in cell temperature, in cathode pressure, and in current density result in increased hydrogen crossover. There are various existing studies dealing with the influence of external operation conditions on hydrogen crossover. 4, 5, 9 Hence, the loss of hydrogen leads to reduced faradaic efficiencies and triggers safety issues, which have to be solved for future system designs. 6– 8 However, thin membranes also lead to higher concentration gradients of the produced gases across the membrane, which results in enhanced gas crossover. For instance, thin membranes are required for the reduction of undesired ohmic voltage losses. 1– 5 Furthermore, the voltage loss mechanisms in the electrochemical polarisation behaviour of PEM water electrolysers are not fully resolved yet and offer possibilities for improvement. The results indicate that the cell voltage should not be the only criterion for optimizing the system design, but that the material design has to be considered for the reduction of hydrogen crossover in PEM water electrolysis.įor the development of next generation polymer electrolyte membrane (PEM) water electrolysers, the generation of a comprehensive understanding of gas crossover phenomena is necessary. Moreover, increases in cathode pressure are amplifying the compression effect on hydrogen crossover and mass transport losses. The mass transport limitations also become visible in enhanced anodic hydrogen contents with increasing compression at high current densities. It is shown that a higher compression leads to increased mass transport overpotentials, although the overall cell performance is improved due to the decreased ohmic losses. In this study, we provide an analysis of the effect of elevated cathode pressures (up to 15 bar) in addition to increased compression of the membrane electrode assembly on hydrogen crossover and the cell performance, using thin Nafion 212 membranes and current densities up to 3.6 A cm −2.
Besides the impact of external operating conditions, the structural properties of the materials also influence the mass transport within the cell. Hydrogen crossover poses a crucial issue for polymer electrolyte membrane (PEM) water electrolysers in terms of safe operation and efficiency losses, especially at increased hydrogen pressures.
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