Water Management in A PEMFC: Water Transport Mechanism and Material Degradation in Gas Diffusion Layers

Polymer electrolyte membrane fuel cells (PEMFCs) directly convert the chemical energy of the reactants into electrical energy and usually consist of a proton exchange membrane (PEM) sandwiched between two catalyst layers (CLs), two porous gas diffusion layers (GDLs) often coated with a microporous layer (MPL) on the CL side, and two bipolar plates with embedded gas channels. Protons and electrons produced by a hydrogen oxidation reaction in the anode CL flow through the membrane and the external circuit, respectively, and participate in the oxygen reduction reaction in the cathode CL producing water and waste heat. Despite considerable progress in the overall cell performance made in the past decade, a pivotal performance, and durability limitation centers on the water management of the PEMFC, namely the transport of product water (both liquid and vapor) and the resulting drying and/or flooding in the constituent components. In current PEMFC technologies, water content of the membrane determines the membrane performance and its durability. Although sufficient water content is required to maintain high proton conductivity of the membrane, excessive liquid water in the fuel cell can flood, and block the pores of the CLs, GDLs, and gas channels. Both a dry membrane and flooded electrode hinder the performance and lead to an accelerated degradation of the fuel cell.