Effect of Polytetrafluoroethylene on Ultra-Low Platinum Loaded Electrospun/Electrosprayed Electrodes in Proton Exchange Membrane Fuel Cells

• Fuel cell electrodes were fabricated using electrospinning/electrospraying (E/E).
• Effect of polytetrafluoroethylene (PTFE) on E/E electrodes was evaluated.
• PTFE increased E/E electrode hydrophobicity and fuel cell performance.
• High power output and ultra-low Pt loadings were achieved with E/E-PTFE electrodes.
• Excellent overall platinum utilization of 0.076 gPt/kW (∼13.2 kW/gPt) was achieved.

In this study, catalyst layers (CLs) were fabricated using a simultaneous electrospinning/electrospraying (E/E) technique to produce unique nanofiber/nanoparticle membrane electrolyte assemblies (E/E MEAs) evidenced by scanning electron microscopy. Specifically, the effect of polytetrafluoroethylene (PTFE) in these E/E MEAs on polymer electrolyte membrane (PEM) fuel cell performance was evaluated. E/E MEAs result in high fuel cell performance at ultra-low platinum (Pt) loadings with higher electrochemical surface areas as evidenced by cyclic voltammetry experiments. Without PTFE, an E/E MEA operated at 172 kPa (25 psi) back pressure results in a maximum power density of 1.090 W/cm2 (H2/O2) and 0.647 W/cm2 (H2/air) with only 0.112 mgPt/cm2 total Pt MEA loading. Introducing PTFE (at only 1 wt%) to the electrospinning process results in an E/E MEA operated at the same back pressure (172 kPa (25 psi)) with an even higher maximum power density of 1.240 W/cm2 (H2/O2) and 0.725 W/cm2 (H2/air) at a lower total Pt MEA loading of 0.094 mgPt/cm2. This corresponds to a significant reduction in Pt loading (16% of control) with only a modest reduction in power density (∼86-87% of control), where the control MEA was produced using a conventional coating method and resulted in maximum power density of 1.420 W/cm2 (H2/O2) and 0.839 W/cm2 (H2/air) at a Pt MEA loading of 0.570 mgPt/cm2 (172 kPa (25 psi)). An excellent total MEA platinum utilization of 0.076 gPt/kW (∼13.2 kW/gPt) was achieved with the E/E MEA with PTFE at only a 0.094 mgPt/cm2 total Pt MEA loading. The improvement in E/E MEA with PTFE was a result of increased hydrophobicity of the nanofibers evidenced by contact angle measurements and improved PEM fuel cell performance at higher limiting current density in the mass transport region.

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