Proton exchange membrane fuel cells (PEMFC) electrochemically combine hydrogen and oxygen to produce electrical energy, heat and water. Therefore, PEMFC offer an alternative to vehicle electrification and reduction of greenhouse gas emissions. However, material limitations under high current density conditions limit the efficiency due to water flooding subsequent mass transport overpotential.

The cathode gas diffusion layer of PEMFC is conventionally a carbon paper material, due to its high electrical conductivity, permeability and mechanical strength. Whereas the porosity and thickness can be controlled, the exact microstructural features are unknown, resulting from the web of randomly orientated fibres. If the microstructural features of the porous layer can be designed, improvements in water flooding and mass transport could be established.

This research talk focuses on the series of studies from concept, simulation and manufacturing of designed microstructures using 3D printing and carbonisation. We investigate the potential improvements to electrical/thermal conductivity, permeability and reduction in the saturation using computational fluid dynamics. Furthermore, the impact of the porous microstructure in a lab scale set up is replicated to understand the effects of under-rib convection and oxygen consumption at the catalyst layer.

With a readily available 3D printing method, prototype materials; resembling those evaluated in the simulation studies are manufactured and carbonised into glassy carbon microstructures. The morphology of carbon was limited by the maximum temperature of the furnace. The resulting structures have in-plane dimensions of 2 cm x 2 cm and through-plane between 400 – 800 µm. They were tested for electrical conductivity with a value of approximately 130 S m^-1.

Through a controlled carbonisation process, structural damage was minimised and the structures were introduced into a membrane electrode assembly (MEA) via spraying and hot pressing. The resulting MEA was tested in a lab cell to understand further considerations that limit the correct implementation of the 3D printed layers. In-homogenous MPL and CL formation along with membrane cracking are hypothesised to be causes of overpotentials.

Figure 1 – Design process of simulation to manufacture, with simulations of (a) electrical potential, (b) water flooding and (c) oxygen distribution in a designed carbon microstructure. (d) and (e) optical microscope images of printed precursor material and final carbonised structures.