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

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/cm(2) (H-2/O-2) and 0.647 W/cm(2) (H-2/air) with only 0.112 mg(pt)/cm(2) 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/cm(2) (H-2/O-2) and 0.725 W/cm(2) (H-2/air) at a lower total Pt MBA loading of 0.094 mg(pt)/cm(2). This corresponds to a significant reduction in Pt loading (16% of control) with only a modest reduction in power density (similar to 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/cm(2) (H-2/O-2) and 0.839 W/cm(2) (H-2/air) at a Pt MEA loading of 0.570 mgpt/cm(2) (172 kPa (25 psi)). An excellent total MEA platinum utilization of 0.076 g(pt)/kW (similar to 13.2 kW/g(pt)) was achieved with the E/E MEA with PTFE at only a 0.094 mg(pt)/cm(2) total Pt MEA loading. The improvement in E/E MBA 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. (C) 2014 Elsevier Ltd. All rights reserved.