Manufacturing of Direct Methanol Fuel Cell Electrodes by Spraying

Spraying is a well-established coating process used to fabricate electrodes for both polymer electrolyte membrane fuel cell (PEMFC) and direct methanol fuel cells (DMFCs), and also for the fabrication of gas-diffusion media (GDM) used in fuel cells. Despite its popularity as a process there is little basic research on how spray parameters and nozzle characteristics affect the droplet sizes of catalyst inks, and how the droplet sizes affect the electrode structure, and eventually the overall membrane-electrode assembly (MEA) performance. We present results from an experimental study to quantify key process parameters in the electrode spraying process, characterizing the spray nozzle, measuring droplet diameters, and investigating the microstructural effects on electrode performance. For this purpose, a spraying apparatus was developed and calibrated, and MEA's were fabricated with fixed electrode loadings but with different droplet sizes. Droplet sizes were controlled by characterizing the spray nozzle and measuring the spray optically by utilizing high-speed photography. It is shown that increasing spraying pressures generally reduces the mean droplet size of the spray, which affects the microstructure of the electrode produced and results in higher MEA performance.