The gas diffusion layer (GDL) is a key component to realize effective gas transport in the electrode of proton exchange membrane fuel cells. To study the effect of different structural parameters on the mass transfer characteristics of the GDL, a developed random reconstruction algorithm is proposed to generate three-dimensional (3D) GDLs with different structures, and the lattice Boltzmann method is used to simulate the flow behavior of reactant gases in the GDL. Through the calculation of the tortuosity and the comparison with the results reported in the references, the accuracy of the model in this paper is demonstrated. The outlet velocity and average velocity of the gas, the gas phase tortuosity, and diffusivity of the GDL are calculated by changing the structural parameters of carbon fiber diameter, porosity, and thickness. It is found that increasing the diameter of the carbon fiber from 7 to 9 μm can increase the reactant gas velocity but has little effect on the improvement of GDL diffusion characteristics. Increasing the porosity from 60 to 80% can significantly increase the reactant gas velocity and improve the diffusion characteristics of the GDL. Increasing the thickness from 112 to 280 μm, the reactant gas velocity is significantly reduced, and the diffusion characteristics of the GDL are weakened, but the change is not obvious. Finally, the influence of GDL structural parameters on electrical conductivity is discussed.

The effect of binder and compression on the transport parameters of the multilayer gas diffusion layer (GDL) is numerically studied by the lattice Boltzmann method. A stochastic algorithm is implemented to generate three multilayer GDLs with a porosity gradient and a uniform GDL, and then, the GDLs are compressed after the binder is added to obtain structures with various binder volume fractions and various compression ratios. The pore size distribution, through-plane (TP) permeability, in-plane (IP) permeability, tortuosity, and electric conductivity of the four structures of GDLs are analyzed. The pore size distributions of GDLs move toward smaller pores due to compression, and the GDL with a larger porosity gradient has a larger maximum pore size. The TP permeability decreases with the increase of compression ratio and binder volume fraction, and the TP permeability of the four GDLs decreases similarly due to compression, but the TP permeability of the multilayer GDL with a larger porosity gradient drops more due to the binder. IP permeability is slightly affected by the compression. Similar to TP permeability, the IP permeability of the multilayer GDL with a large porosity gradient decreases more due to the binder. Multilayer GDL with a small porosity gradient has a smaller tortuosity, more superior pore connectivity, and thus more outstanding gas permeability. The electric conductivity increases with the increase in compression ratio and binder volume fraction.

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Proton exchange membrane fuel cells (PEMFCs) have the advantages of high specific power, good stability, and zero emissions, making them clean and efficient energy conversion devices. Water management is one of the technical challenges limiting the development of PEMFC, with liquid water blocking the pores and increasing the resistance to mass transport. In this paper, a two-dimensional (2D) multiphase lattice Boltzmann (LB) model is developed to obtain the liquid water morphology within the gas diffusion layer (GDL). A 2D multicomponent flow Lattice Boltzmann model considering electrochemical reactions is established to investigate the effects of water saturation, activation overpotential, and pressure difference between the inlet and outlet gas channels on mass transport. At high water saturation, the liquid water forms water films within the GDL preventing reactive gas transport and water vapor are blocked near the catalyst layer making it difficult to remove. The PEMFC can achieve higher current densities at high activation overpotentials, but oxygen starvation will be exacerbated. Increasing the pressure difference between the inlet and outlet gas passages effectively increases the oxygen concentration and reduces the water vapor concentration in the GDL. The present study improves the understanding of the effect of GDL microstructure on mass transport and performance of PEMFC from the mesoscopic scale.

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The gas diffusion layer (GDL) plays a key role in water management. The effects of the structure, wettability, and rib-channel width ratio on liquid water transport in GDL are studied using a multiphase lattice Boltzmann method (LBM) model. It is found that the liquid water in GDL shows capillary fingering behavior. With the increase of carbon fiber diameter or porosity, the water saturation in GDL increases, and the time for liquid water to break through GDL decreases. The porosity has a significant effect on the water saturation in GDL. The water saturation of GDL with a contact angle of 140° is less than that of GDL with a contact angle of 80°. The water saturation in GDL decreases as the rib-channel width ratio increases, while the rib-channel width ratio has little effect on the water saturation in the region of GDL away from the rib. Compared to the rib with a contact angle of 140°, the rib with a contact angle of 60° slightly reduced the water saturation in GDL, and the wettability of the rib has only a small effect on the water saturation in the region of GDL near the rib.

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