Electrochemical Characterization of Pre‐conditioning Process of Electrospun Nanofiber Electrodes in Polymer Electrolyte Fuel Cells

Abstract

Structure innovation and optimization of polymer electrolyte fuel cell (PEFC) catalyst layers is instrumental in improving catalyst utilization and effectiveness. Electrospinning technique has been recently used to fabricate nanofiber electrodes for PEFCs with improved performance compared to electrosprayed electrodes. However, the origins for the performance improvement are yet poorly understood. This study examined the evolution of the electrochemically active surface area (ECSA) and electrochemical impedance spectroscopy (EIS) during the pre‐conditioning process, and compared the performance of electrospun nanofiber electrodes with electrosprayed electrodes within a wide range of operating conditions. ECSA increases, and both mass transfer resistance and charge transfer resistance decrease monotonically during the pre‐conditioning process of electrospun nanofiber electrodes. Such effects are attributed to the dissolution of poly(acrylic acid) (PAA) and the ensuing change of the interface between Pt and the ionomer. After pre‐conditioning, the electrospun nanofiber electrodes outperformed the electrosprayed electrodes with the same Pt‐loadings at 80 °C, whereas the electrosprayed electrodes have higher cell voltages at high current densities at 60 °C and 70 °C in high relative humidity (RH) range. The change in the relative performance of the two types of electrodes is attributed to the competing effects of electrode thickness and pore sizes on cathode gas transport.

Towards ultralow platinum loading proton exchange membrane fuel cells

“…58 Moreover, experiments demonstrated a higher ECSA and performance for the layered fiber arrangement CL than the random particle stacking CL, especially at ultralow Pt loading. [60][61][62][63] For example, the MEA with the former showed approximately 20% larger power density than that with the latter at a low Pt loading of 0.1 mg Pt cm À2 . 60 The pores in the layered fiber arrangement CL can be divided into two types: one is formed by the catalyst/support agglomerations inside the fibers and the other is formed by the fibers that cross each other.…”

“…58 Moreover, experiments demonstrated a higher ECSA and performance for the layered fiber arrangement CL than the random particle stacking CL, especially at ultralow Pt loading. 60–63 For example, the MEA with the former showed approximately 20% larger power density than that with the latter at a low Pt loading of 0.1 mg Pt cm −2 . 60…”

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

“…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.…”

“…2 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. 7,21,26,27 Previous studies have identified the optimal concentration of PAA in the inks to produce uniform fiber morphologies. 25 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).…”

Determination Method of Dimensionless Moduli for Estimation of PEFC Performance

“…To improve polymer electrolyte fuel cell (PEFC) performance and increase durability, the catalysts and membranes have been developed (1,2,3) and the CCL structures have been investigated (4,5,6). There are a lot of operating conditions which control the PEFC performance as well.…”