Effect of Clamping Compression on the Mechanical Performance of a Carbon Paper Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells

Abstract

During all the assembly stages of a polymer electrolyte membrane fuel cell (PEMFC) stack, gas diffusion layers (GDLs) endure clamping loads in the through-plane direction several times. Under such complicated assembly conditions, GDLs have to deform with the changes in structure, surface roughness, pore size, etc. A comprehensive understanding of the compressive performance of GDLs at different clamping phases is crucial to the assembly process improvement of PEMFCs. Two typical clamping compression was designed and performed to get close to the actual assembly conditions of PEMFCs. The results indicate that the initial clamping compression and the magnitude of the maximum clamping load have great impacts on the segmented compressive properties of GDLs. The nonlinear compressive performance of the GDL is mainly attributed to the unique microstructural information. The rough surface morphology contributes to the initial compressive characteristics where the big strain along with the small stress occurs, and the irreversible failures such as carbon fiber breakages and adhesive failures between fibers and binders account for the hysteresis between different compression stages. Importantly, it is found that the clamping compression hardly influences the small pore distribution below 175 μm but affects the large pore distribution over 200 μm.

Mechanical response of carbon paper gas diffusion layer under patterned compression

“…Another interpretation would be the influence of fiber rearrangement and damages in the GDL bulk rather than around the rib edge, such as cross-link breakage that has been observed in the literature on similar GDL materials [10,33]. These bonds can be ensured either by the binder incorporated during the papermaking process [5], or by the PTFE impregnated afterwards, which is mainly located at the fiber junctions [63,64].…”

“…It has been proposed that the nonlinearity of the macroscopic response could be explained by the apparition of new contact points between the fibers subjected to a bending under compression at the microscale [23,30,32]. Moreover, the GDL strain is not fully reversible and presents a residual deformation after loading [10,31,33,34] A number of models have been already proposed in the literature to represent this original behavior. Some of them assume a linear elastic behavior with a strain-dependent Young modulus, for which the parameters were identified with a polynomial fit [23,30].…”

Materials, components, assembly and performance of flexible polymer electrolyte membrane fuel cell: A review

“…It is worth being pointed that the physical properties of GDL inside PEMFCs often differ from that outside PEMFCs, e.g., porosity or permeability, as the GDL in PEMFCs bears compression stress under assembly force and bending stress in bending. Under compression and bending stress, the GDL's pore structure or porosity will be changed to a certain extent [64][65][66][67]. The carbon paper-based GDL's structure could be destroyed due to the irreversible fracture occurs in low bending stress or small bending angle, resulting in the decrease of performance, such as decreased electron conductivity.…”

In situ investigation of ion exchange membranes reveals that ion transfer in hybrid liquid/gas electrolyzers is mediated by diffusion, not electromigration

“…Properties such as conductivity and permeability of membranes, mechanical stability, as well as current/potential characteristics of polymer electrolyte membrane (PEM) fuel cells, are strongly inuenced by the clamping pressure. 48,49 The reproducibility of the applied clamping pressure was ensured by using ISO M3 HELICOIL® threaded inserts (Böllhoff, stainless steel 304) in the PEEK cell body, calibrated for torques up to 0.10 N m. The use of metallic bolts and threaded inserts also ensures a higher resistance against wearing compared to polymer-based materials, which is also an important source of non-reproducibility over time of the clamping pressure. The calibration of the torque was performed using a torque wrench (Wiha, ESD Tor-queVario®-S, 0.04-0.46 N m), setting the applied torque (M) to 0.04 N m. It is possible to determine the total force (and therefore pressure) applied to the membrane as follows.…”