In situ imaging of liquid water and ice formation in an operating PEFC during cold start

A transparent polymer-electrolyte fuel cell (PEFC) was developed to study liquid water and ice formation during startup from subzero temperatures. A silver mesh was used as the cathode gas diffusion layer to allow direct observation of phase transition and water transport on the surface of the catalyst layer (CL). It was found that at a current density of 0.02 A/cm ² and startup temperature of-5°C, water exists in the cathode CL in solid and gas phases. At startup temperatures higher than -3°C, however, water droplets are found on the CL surface and the cold-start operation is significantly prolonged. It is therefore suggested that the freezing-point depression of water in the cathode CL is no greater than 2°C and plays a negligible role in cold-start theory and practice.