Effect of clamping pressure on liquid-cooled PEMFC stack performance considering inhomogeneous gas diffusion layer compression

Gas diffusion layer (GDL) is a critical component of fuel cells, since it directly determines the transfer rate of mass, charge and heat that in turn affects the cell performance and stability. Within a fuel cell stack, assembled by over hundreds of single cells, GDL plays a more dominant role since the GDL deformation caused by assembly pressure would result in significant changes in its thermal, electrical and transport properties, thus impacting the uniformity, consistency and overall performance of the stack. Here, a numerical study is performed to investigate the effect of clamping pressure on the performance of liquid-cooled PEMFC stacks, which can be utilized as a guidance for stack assembly process in practical application. In particular, inhomogeneous compression as well as nonlinear strain-stress behavior of GDL are taken into consideration in the fuel-cell stack model, thus the GDL at under-rib and under-channel regions owns different physical properties, i.e., thickness, porosity, effective diffusivity, permeability, thermal conductivity, electrical conductivity, and contact resistance. It is found that the stack power output can be maximized when clamping pressure ranging from 1.5 MPa and 3.5 MPa owing to the balanced mass transport and contact resistance, meanwhile, 1.5 MPa enables the lowest voltage difference among different single cells that is beneficial in cell-to-cell consistency. Moreover, the inhomogeneous compression of GDL is found to be capable of facilitating water removal via enhanced convection at both in-plane and through-plane directions, and avoiding local hotspots with the increased in-plane thermal conductivity.