(255g) Exploration of Nanofiber-Nanoparticle Electrodes Fabricated Via Simultaneous Electrospinning/Electrospraying for Ultra-Low Platinum Fuel Cells

Recently, in our laboratory, a new simultaneous electrospinning and electrospraying (E/E) process was developed to produce unique nanofiber-nanoparticle electrodes for polymer electrolyte membrane (PEM) fuel cells and resulted in high power densities at ultra-low platinum (Pt) loadings. These results demonstrated the impact of electrode morphology on Pt loading. Although promising, these previous results did not explore the impact of all of the electrode morphology parameters (e.g., fiber/catalyst content, fiber size, fiber/catalyst structure, porosity, etc.) on fuel cell performance (kW), Pt loading (mg), and subsequently Pt utilization (kW/mg). In this study, E/E electrodes were systematically fabricated to fundamentally investigate the impact of various parameters (nanoparticle aggregate size and distribution, nanofiber size and distribution, electrode porosity, nanofiber purity (ratio of conductive polymer Nafion to carrier polymer), nanoparticle purity (with and without Nafion)) on PEM fuel cell performance and Pt utilization. Results show that electrodes with low nanofiber purity using a conductive carrier polymer have similar Pt utilization to those with high nanofiber purity using a neutral carrier polymer. Electrodes with conductive carrier polymer nanofibers have higher Pt utilization with higher nanoparticle purity, while those with neutral carrier polymer nanofibers have higher Pt utilization with lower nanoparticle purity. At lower Pt loadings, electrodes with an average nanofiber size less than 100 nm have higher Pt utilization and those with an average nanofiber size greater than 100 nm have lower Pt utilization. Nanoparticle purity had no significant effect on nanoparticle aggregate size or electrode porosity, but changes in Pt utilization were observed due to the sole effect of mass transfer resistance from Nafion surrounding the nanoparticle. To our knowledge, previous studies have not been able to independently study mass transfer resistances, charge transfer resistances, and porosities of the catalyst layer on fuel cell performance, because of their coupled effects within the layer. Utilizing the E/E process, we can investigate the morphology in the catalyst layer and its effect on mass transfer and charge transfer resistances separately, which will highly impact the design of and elucidate various transport phenomena effects in the catalyst layer for ultra-low Pt loadings.