Degradation Characteristics of Electrospun Gas Diffusion Layers with Custom Pore Structures for Polymer Electrolyte Membrane Fuel Cells

Abstract

Electrospinning has been demonstrated to be a versatile technique for producing hydrophobic gas diffusion layers (GDLs) with customized pore structures for the enhanced performance of polymer electrolyte membrane (PEM) fuel cells. However, the degradation characteristics of custom hydrophobic electrospun GDLs (eGDLs) have not yet been explored. Here, for the first time, we investigate the degradation characteristics of custom hydrophobic eGDLs via an ex situ accelerated degradation protocol using H2O2. The surface contact angle of degraded eGDLs (44 ± 12°) was lower than that of pristine eGDLs (137 ± 6°). The loss of hydrophobicity was attributed to the degradation (via hydrolysis) of the fluorinated monolayers (formed via a direct fluorination treatment) on the electrospun carbon fiber surfaces as evidenced by the reduction in surface fluorine content. Degradation of the surface monolayers affected fuel cell performance under multiple operating conditions. At 100% relative humidity (RH), the loss of monolayers led to higher liquid water content and lower cell voltages compared to the pristine eGDL. At 50% RH, the degraded eGDL led to lower cell voltages due to the lower electrical conductivity of the degraded materials. The lower electrical conductivity was attributed to the oxidation of carbon fibers upon loss of the monolayers. Our results indicate the importance of designing robust hydrophobic surface treatments for the advancement of customized GDLs for effective long-term fuel cell operation.

A Super Uniform Hydrophobic Gas Diffusion Layer for a Proton Exchange Membrane Fuel Cell

“…However, this part of the signal was significantly increased in the GDL modified with HFTS, which was caused by the introduction of hydroxyl groups during nitrification . A binding energy of >290 eV is the signal belonging to C–F Figure b shows the fluorine signals of carbon paper modified with PTFE and HFTS.…”

“…29 A binding energy of >290 eV is the signal belonging to C−F. 15 Figure 2b shows the fluorine signals of carbon paper modified with PTFE and HFTS. Only one fluorine signal appears in both samples, which indicates that no other impurities are formed in this liquid phase reaction.…”

“…Regardless of the method used to infiltrate PTFE, the presence of hydrophilic zones is unavoidable due to the limitations of PTFE ductility. Although some researchers have used organic agents to treat GDL, achieving uniform hydrophobicity, , there is a need for a cost-effective and easily scalable method for achieving uniform hydrophobic treatment that can make GDLs have uniform hydrophobicity without increasing electrical and thermal resistance.…”

Alternative architectures and materials for PEMFC gas diffusion layers: A review and outlook

“…However, electrochemical and polarisation curves were not performed and as such the full conclusion of the capability of the e-GDL in a PEMFC has yet to be confirmed. Certain challenges need to be overcome to improve e-GDL durability as Balakrishnan et al [26] reported a notable drop in contact angle (from 136 • to 44 • ) after accelerated stress tests in hydrogen peroxide due to a degradation of the fluorinated monolayers. Polarisation curves indicated that the degraded electrospun GDL suffered higher levels of liquid water accumulation and mass transport losses than the pristine with a significant potential drop voltage following the 0.5 A cm − 2 .…”

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

“…Using highly oriented sulfonated PI nanofibers, Tamura and Kawakami produced proton exchange membranes for fuel cells with high chemical and mechanical stability as well as high proton conductivity parallel to the nanofibers [ 239 ]. Electrospun nanofibers mats with pore size gradients were suggested by Balakrishan et al for polymer-electrolyte membrane fuel cells [ 240 ], who also studied degradation of such electrospun gas diffusion layers [ 241 ], while Kallem et al highlight some possible strategies for nanofiber-based proton exchange membranes with aligned nanofiber mats [ 242 ].…”