The effect of thickness and wetproof level of the gas diffusion layer on electrode flooding and cell performance was investigated. Three types of gas diffusion media were tested: SGL SIGRACET carbon papers, with and without a microporous layer, and Toray TGPH carbon paper without a microporous layer. Overall, it was found that SGL carbon paper with the microporous layer gave the best fuel cell performance even at low air stoichiometries. It was also found that adding poly(tetrafluoroethylene) (PTFE) to the gas diffusion layer could enhance gas transport and water transport when a cell operates under flooding condition, but excessive PTFE loading could lead to a high flooding level in the catalyst layer. It is our opinion that a combination of hydrophobic pores for gas transport and hydrophilic pores for liquid water transport within the macroporous layer is needed. It is also our opinion that the optimal ratio of hydrophobic and hydrophilic pores depends on the pore size and its distribution. Finally, it was observed that without the microporous layer, thinner gas diffusion materials were more sensitive to liquid water accumulation than the thicker ones.

Modeling of liquid water distribution in polymer electrolyte membrane fuel cells (PEMFCs) is challenged by uncertainties in characterizing the two-phase transport properties of the porous transport layer (PTL) and the catalyst layer (CL). Capillary pressure, representing both pore structures and wetting features of the porous media, is a key factor in controlling liquid water transport and distribution in the porous electrode of PEMFCs. By incorporating experimentally measured capillary pressure functions, a single-domain, three-dimensional, and two-phase transport model was developed to predict liquid water saturation in the PTL and CL of a PEMFC with long straight channels, where the two-phase flow complications were minimized at practical stoichiometry. In the cathode CL, the liquid water saturation was found to be higher under the channel than that under the ribs at high current densities. In the cathode PTL, however, the liquid water saturation level was observed to be lower under the channel than that under the ribs. At high current densities, the average water saturation levels are insensitive to current density and fall in the range of 0.4–0.5 in the CL and 0.2–0.3 in the PTL. Finally, the effects of liquid water on oxygen transport and cell performance were investigated.

Renewable energy sources including wind and solar require reliable electrical energy storage systems because of their intermittent nature. Electrochemical energy storage devices such as batteries, fuel cells and flow batteries, and electrochemical capacitors are among the leading energy storage systems because of their scalability, versatility, and ability to provide the energy densities needed for large-scale electrical energy storage. Redox flow batteries consist of two separate electrolytes, one storing the electroactive materials for the negative electrode reactions and the other for the positive electrode reactions. An ion-selective membrane is often used to prevent mixing or crossover of the electroactive species, which can result in the chemical short-circuit. Only the common counter ion carrier is allowed to cross the membrane.

A two-dimensional, two-phase, steady-state, isothermal model was developed for a fuel cell region consisting of the catalyst and gas diffusion layers bonded to a proton exchange membrane (PEM). This model extends the previously published one-dimensional model of the gas diffusion and catalyst layers to two dimensions in order to account for the effects of the shoulder of the gas distributor and the electronic conductivity of the solid phase. The new model was validated with experimental results and then used to investigate the effect of the relative dimensions of the shoulders and channels on the cell performance. The effects of the in-plane liquid water permeability and electronic conductivity of the gas diffusion layer on cell performance were also examined. It was found that more channels, smaller shoulder widths on the gas distributor, and higher in-plane water permeability of the gas diffusion layer can enhance the transport of liquid water and oxygen, leading to better cell performance. The in-plane electronic conductivity of the gas diffusion layer was found to have minimal effect on the cell performance. However, a highly nonuniform distribution of electronic current was formed within the gas diffusion and catalyst layers when the in-plane electronic conductivity was low.

A two-phase model was developed to study the impact of the capillary property of the gas diffusion (GDL) and catalyst layers (CL) and the saturation-level jump condition at the interface between these two dissimilar materials on the liquid water transport rate and the liquid water saturation levels in these porous layers and the performance of the cathode of a proton exchange membrane fuel cell (PEMFC). The study involves adjusting various aspects of the capillary curves of these porous layers and studying how these changes affect the cathode electrochemical performance to identify the most sensitive aspects. The simulated results show that fuel cell performance and the liquid water saturation levels in the CL and GDL depend on both the individual two-phase properties of these components and their interactions at the GDL/CL interface. The boundary condition at the GDL/channel interface for saturated air operation constrains the transport phenomenon in the GDL and CL to the hydrophobic regions of the capillary pressure curves. It was also found that capillary properties of the GDL had a more significant effect on the fuel cell performance than those of the CL, and better fuel cell performance was obtained with GDL and CL with high capillary diffusion capability and low hydrophilic porosity.