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.
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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