Transport mechanisms analysis of large-size proton exchange membrane fuel cells with novel integrated structure under ultra-high current densities

For proton exchange membrane fuel cells, augmenting power density is of utmost importance and designing novel structures to diminish volume represents a vital approach. Metal foam presents a promising substitute for conventional flow fields to obviate the need for gas diffusion layers, though the microstructural discrepancies with electrodes pose difficulties, especially in large-scale fuel cells. In this research, an integrated fuel cell structure combining nickel metal foam and a carbon nano fiber film (CNFF) is designed, trimming the single cell thickness from 1.275 mm to 0.885 mm. The CNFF facilitates the gas transport from metal foam to catalyst layers. A three-dimensional plus one-dimensional numerical model is constructed to elucidate the internal mechanisms. In a 1 cm² fuel cell, a thinner CNFF leads to membrane electrode assembly (MEA) dehydration and higher porosity hinders heat dissipation. When scaling up to 300 cm² and contrasting with a conventional parallel channel-rib fuel cell, the integrated fuel cell shows inferior performance at low and medium current densities due to elevated ionic ohmic loss. However, it surpasses the conventional one at high current densities, with the output voltage rising from 0.552 V to 0.593 V at 4.1 A cm⁻² due to diminished concentration loss. Additionally, temperature and relative humidity are pivotal parameters influencing the equilibrium between membrane water content and transport resistance. This research contributes to the design of integrated fuel cells with enhanced volume power density, providing valuable insights for their large-scale implementation.