Diffusion media materials and characterisation

Abstract Gas‐diffusion media (also known as gas diffusers and gas‐diffusion backings) are required in most polymer electrolyte fuel cell (PEFC) designs. Their function is to provide uniform reactant (H 2 , O 2 , and electrons) access to and product (H 2 O) removal from the electrodes, efficient heat removal from the membrane electrode assembly (MEA), and mechanical support to the MEA. The vast majority of gas‐diffusion media are based on carbon‐fiber materials; a variety of forms are used, with carbon‐fiber paper and carbon cloth receiving widest application. This chapter describes the production and properties of currently available and emerging materials. Commonly employed treatments and coatings used to tailor the wicking and hydrophobic properties of diffusion media for efficient water removal are discussed. Finally, ex‐situ and in‐situ methods for characterizing diffusion media are described.