Electrospinning deposition of poly(acrylic acid): platinum/carbon catalyst ink to enhance polymer electrolyte membrane fuel cell performance

Abstract

Abstract

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Polymer–Particle Interactions and Spinnability

“…The results demonstrate that PAA concentration significantly impacts the fiber morphologies, consistent with previous findings . Uniform fibers were obtained at an intermediate PAA concentration suggesting an optimal viscoelasticity of the inks.…”

“…Increasing PAA concentration beyond 1.64 wt % resulted in an overall increase in the average diameter of the fibers, which were found to be ∼400 nm at 1.64 wt % PAA, increasing up to 2.3 μm at 3.62 wt % PAA, as shown in Figure . The observed fiber morphological transitions, from only beads to uniform fibers, and variation of the fiber diameter with increasing the PAA concentration is similar to several previous studies. − , At PAA concentrations >1.64 wt %, defectsintermittent clumps of nondispersed ink materialsbegin to appear along the fibers (Figure e,g). Beyond 3.62 wt %, we begin to experience pumping difficulties where large chunks of catalyst are ejected intermittently (Figure h).…”

“…The typical perfluorosulfonic acid ionomer that is used in the catalyst ink formulation is relatively low in molecular weight (Mw ≈ 200,000 g/mol) and does not impart sufficient elasticity to enable fiber formation. , To enable nanofiber formation, high molecular weight (Mw) polymer additives (e.g., polyacrylic acid, polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile), referred to as carrier polymers, are commonly added to the catalyst inks. ,− ,− To fabricate uniform fibers, the concentration of the carrier polymer must be high enough that it provides sufficient elasticity to fabricate uniform fibers but not so much that it results in defective fibers due to flow instabilities caused by a significant increase in the viscoelasticity of the inks. , Most importantly from a performance perspective, excess carrier polymers can negatively affect fuel cell performance. Interaction of the carrier polymer with the particles (catalyst/carbon) and the ionomer may reduce the three-phase (catalyst–ionomer–carbon) interface and inhibit full utilization of the catalyst. ,, Furthermore, excessive carrier polymers in the fiber may also reduce the overall porosity and hinder mass transport in the catalyst layer …”

“…Polyacrylic acid (PAA) is one of the commonly used carrier polymers for the fabrication of nanofiber fuel-cell catalyst layers for a variety of catalyst systems. ,,, Previous studies have identified the optimal concentration of PAA in the inks to produce uniform fiber morphologies . Researchers have also reported on the impact of PAA on performance, though at limited PAA concentrations (10–15 wt % PAA with respect to (w.r.t) total solids, i.e., Nafion, PAA, and particles). , Excessive PAA was found to reduce fuel cell performance by decreasing the ionic and electronic conductivity of the electrode. , However, systematic studies investigating how the concentration of PAA affects both the evolution of the fiber morphologies and the performance are scarce.…”

Effect of Dispersion Solvents and Ionomers on the Rheology of Catalyst Inks and Catalyst Layer Structure for Proton Exchange Membrane Fuel Cells

“…The catalyst ink is first deposited on the substrate via solution deposition techniques, including ultrasonic spraying, 10 slot-die coating, 11 inkjet printing, 12 electrostatic spraying, 13 and gravure coating, 14 then evaporated, and dried to fabricate a CL. The deposition process of catalyst inks regulates the structure of the CL, including the three-phase interface, 12 pores, 14 Pt utilization rate, 13 and ionomer distribution, 15 thereby affecting the performance of MEAs. As such, the formation of CLs is closely related to several factors including ink formulation, substrate, deposition technique, and ink rheology.…”