Fabrication of Platinum Group Metal-Free Catalyst Layer with Enhanced Mass Transport Characteristics Via an Electrospraying Technique

The performance of platinum group metal-free (PGM-free) catalyst layers suffers from mass transport limitations owing to the thickness required to achieve sufficiently high loading to match the performance of the Pt-based electrodes. A more detailed understanding of the PGM-free electrode structure is of a great importance to further improve their performance, but the nanoscale structure presents a challenge. In the present study, a non-PGM catalyst was synthesized by the sacrificial support method, and the electrospraying technique was used to fabricate catalyst layer electrodes. Electrodes with substantially different structural properties were obtained by varying the electrospraying parameters such as ink flow rate and the distance between the needle and the substrate. A wide range of structural properties of these non-PGM electrodes were experimentally measured, including thickness, porosity, pore size distribution, specific surface area, and the mass transport characteristics in the form of tortuosity. In general, the non-PGM catalyst layers fabricated by the electrospraying technique had much lower tortuosity than conventional catalyst layers due to a combination of highly porous structure and larger interagglomerate pores reducing the impact of the Knudsen effect. Geometric tortuosity was also obtained by adjusting the measured effective diffusivity values to remove the Knudsen effect, and it was found that electrosprayed and conventional layers follow a similar trend with porosity.