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Water management becomes a more critical issue as the power performance of polymer electrolyte membrane fuel cells (PEMFC) is progressively improved. Herein, we present a ditch-structured microporous layer (MPL) that can prevent water flooding in PEMFCs. In-plane ditch structures are carved on an MPL using a nanosecond-pulse laser ablation technique while preserving the surface porosity of the MPL. When the direction of the ditches is aligned perpendicular to the flow field direction, the power performance is significantly enhanced due to the facilitated mass transport under the rib area. The i–V polarizations and limiting current analysis suggest that not gas transport but water transport is responsible for the power performance enhancement. Compared with a perforated MPL prepared by the same technique, the ditch-structured MPL is more effective in mitigating water flooding. Diagonal and radial ditches exemplify the efficacy in making complex ditch patterns. The delicate structural engineering of the MPL enabled by laser ablation can offer a novel design platform for advanced fuel cells.

Ionomer films even only a few nanometers thick in the catalyst layer of a polymer electrolyte membrane fuel cell are detrimental to the power performance at low Pt loadings due to their large oxygen transport resistance. Therefore, removing the ionomer films on the Pt surface for oxygen transport while preserving them on the carbon surface for proton transport can be an ideal ionomer distribution. Herein, we achieve ionomer-lean Pt surfaces by masking the Pt nanoparticles of the Pt/C catalyst with an alkanethiol. Due to the weakening of the ionomer/Pt interaction by the molecular mask, a low population of ionomers on the Pt surface is achieved while preserving the fast proton transport in the catalyst layer. The alkanethiol is then electrochemically removed from the catalyst layer, recovering the catalytic activity of the Pt. Electrochemical analyses showed a reduced oxygen transport resistance through the ionomer film and a consequent enhancement of the power performance. This molecular masking strategy marks the beginning of the nano-scale control of ionomer distribution in the development of advanced fuel cells.

Although, the use of hydrocarbon membranes is one of the ways to reduce the cost of polymer electrolyte membrane fuel cells, it cannot be practically adopted due to its low mechanical durability under a dynamic wet/dry operation. Here, we present an externally-reinforced hydrocarbon membrane achieved by a three dimensional interlocking interfacial layer which forms a strong interfacial bonding between the hydrocarbon membrane and the catalyst layers. Although a conventional hydrocarbon membrane is easily delaminated from gas diffusion electrodes, the use of the three dimensional interlocking interfacial layer, prepared with a polystyrene nanoparticle template method, enhances the interfacial adhesion by 207 times. The hydrocarbon membrane, tightly connected to the gas diffusion electrodes by the three dimensional interlocking interfacial layers, has a humidity cycling durability that is 1.9 times higher in the membrane electrode assembly level by restricting the dimensional change of the membrane. Furthermore, due to the proton conducting property of the three dimensional interlocking interfacial layer, the external reinforcement does not cause any power performance losses.

With the demands for better performance of polymer electrolyte membrane fuel cells, studies on controlling the distribution of ionomers have recently gained interest. Here, we present a tunable ionomer distribution in the catalyst layer (CL) with dipropylene glycol (DPG) and water mixtures as the ionomer dispersion medium. Dynamic light scattering and molecular dynamics simulation demonstrate that, by increasing the DPG content in the dispersion, the size of the ionomer aggregates in the dispersion is exponentially reduced because of the higher affinity of DPG for Nafion ionomers. The ionomer distribution of the resulting CLs dictates the dimensional feature of the ionomer dispersion. Although the ionomer distribution becomes more uniform with increasing the DPG content, an optimal power performance is obtained at a DPG content of 50 wt % regardless of feed humidity because of balanced proton and mass transports. As a guide for tuning the ionomer distribution, we suggest that the ionomer aggregates in the dispersion with a size close to that of the Pt/C aggregates form a highly connected ionomer network and maintain a porosity in the catalyst/ionomer aggregate, resulting in high power performance.

In this study, a new rugged catalyst layer (CL) structure is derived from a Nafion fiber mat to enhance the mass transport properties of polymer electrolyte membrane fuel cell. Nafion fiber mat is fabricated on a membrane surface by electrospinning technique and then a catalyst ink is sprayed on the fiber-coated membranes. With the Nafion fiber mat with 3.0 μm fiber diameter, a rugged CL supported on the fiber mat is formed, dictating the structural feature of the Nafion fiber mat. The resulting CL, which features an expanded outer CL surface, exhibits 21% improved power performance at 0.4 V under high humidity operation due to the increase of gas and water transport properties. These results demonstrate that Nafion fiber mat can be as an effective and scalable scaffold for the development of advanced CL.

H3PO4-doped polybenzimidazole (PBI) membranes have been employed for high temperature polymer electrolyte membrane fuel cell (HT-PEMFC). Although a thinner PBI membrane is beneficial in enhancing power performance, the use of thin PBI membrane has been hindered by its poor mechanical property and consequent difficulty in membrane handling during membrane electrode assembly (MEA) fabrication. Here, novel fabrication route to realize a thin PBI membrane (∼35 μm)-based HT-MEA is presented. The key feature of the process is to fabricate thin blend membrane of PBI and poly(ethylene glycol) (PEG) and laminate the blend membrane to anode gas diffusion electrode (GDE) followed by H3PO4 doping. The introduction of PEG to PBI film enables the tight bonding of the membrane to the GDE at a mild lamination temperature and mitigates the membrane expansion with the doping, preserving the tight interfacial bonding. Due to the lowered membrane thickness, the corresponding MEA exhibits a high power density of 264 mW cm-2 at 0.6 V. Therefore, the new fabrication strategy based on the blend of PBI/PEG is highly effective in improving both process and power performance of HT-MEA.

Protecting low coordinated sites (LCS) of Pt nanoparticles, which are vulnerable to dissolution, may be an ideal solution for enhancing the durability of polymer electrolyte fuel cells (PEMFCs). However, the selective protection of LCSs without deactivating the other sites presents a key challenge. Herein, we report the preferential protection of LCSs with a thiol derivative having a silane functional group, (3-mercaptopropyl) triethoxysilane (MPTES). MPTES preferentially adsorbs on the LCSs and is converted to a silica framework, providing robust masking of the LCSs. With the preferential protection, the initial oxygen reduction reaction (ORR) activity is marginally reduced by 8% in spite of the initial electrochemical surface area (ECSA) loss of 30%. The protected Pt/C catalyst shows an ECSA loss of 5.6% and an ORR half-wave potential loss of 5 mV after 30,000 voltage cycles between 0.6 and 1.0 V, corresponding to a 6.7- and 2.6-fold durability improvement compared to unprotected Pt/C, respectively. The preferential protection of the vulnerable LCSs provides a practical solution for PEMFC stability due to its simplicity and high efficacy.

Ce-based materials have been widely used as a radical scavenger to improve the chemical durability of the membrane in polymer electrolyte fuel cells; however, any negative effects from Ce ions on power performance have not been reported as an issue before except for ionomer contamination by Ce3+. Herein, we propose and experimentally demonstrate the detrimental effect of Ce4+ on the Pt/C catalyst. Due to the strong oxidation power of Ce4+, Pt and carbon are subjected to oxidative decomposition under contact with Ce4+. Based on the electrochemical and spectroscopic analyses of the Pt/C stored in Ce3+ and Ce4+ electrolyte, Pt2+ dissolution and carbon corrosion by Ce4+ are verified. As a result, the active surface area and oxygen reduction reaction activity of Pt/C are considerably reduced after storage in the Ce4+ electrolyte. Additionally, at the membrane electrode assembly level, it is demonstrated that the Ce4+ leached out from the CeO2 causes a significant power performance decay along with the loss of the active surface area and an increase in the charge transfer resistance. The newly-found detrimental effect of Ce4+ on the Pt/C catalyst emphasizes the importance of preventing Ce4+ dissolution to improve the membrane durability by Ce-containing radical scavengers.

In this study, we examined the influence of the dispersion solvent in three dipropylene-glycol/water (DPG/water) mixtures, with DPG contents of 0, 50, and 100 wt%, on ionomer morphology and distribution, using dynamic light scattering (DLS) and molecular-dynamics (MD) simulation techniques. The DLS results reveal that Nafion-ionomer aggregation increases with decreasing DPG content of the solvent. Increasing the proportion of water in the solvent also led to a gradual decrease in the radius of gyration (Rg) of the Nafion ionomer due to its strong backbone hydrophobicity. Correspondingly, MD simulations predict Nafion-ionomer solvation energies of −147 ± 9 kcal/mol in water, −216 ± 21 kcal/mol in the DPG/water mixture, and −444 ± 9 kcal/mol in DPG. These results suggest that higher water contents in mixed DPG/water solvents result in increased Nafion-ionomer aggregation and the subsequent deterioration of its uniform dispersion in the solvent. Moreover, radial distribution functions (RDFs) reveal that the (-CF2CF2-) backbones of the Nafion ionomer are primarily enclosed by DPG molecules, whereas the sulfonate groups (SO3−) of its side chains mostly interact with water molecules.

In this study, we present a novel catalyst layer (CL) with in-plane flow channels to enhance the mass transports in polymer electrolyte membrane fuel cells. The CL with in-plane channels on its surface is fabricated by coating a CL slurry onto a surface-treated substrate with the inverse line pattern and transferring the dried CL from the substrate to a membrane. The membrane electrode assembly with the in-plane channel-patterned CL has superior power performances in high current densities compared with an unpatterned, flat CL, demonstrating a significant enhancement of the mass-transport property by the in-plane channels carved in the CL. The performance gain is more pronounced when the channel direction is perpendicular to the flow field direction, indicating that the in-plane channels increase the utilization of the CL under the rib area. An oxygen-transport resistance analysis shows that both molecular and Knudsen diffusion can be facilitated with the introduction of the in-plane channels. The direct CL patterning technique provides a platform for the fabrication of advanced CL structures with a high structural fidelity and design flexibility and a rational guideline for designing high-performance CLs.

A scalable nanofastener featuring a 3D interlocked interfacial structure between the hydrocarbon membrane and perfluorinated sulfonic acid based catalyst layer is presented to overcome the interfacial issue of hydrocarbon membrane based polymer electrolyte membrane fuel cells. The nanofastener-introduced membrane electrode assembly (MEA) withstands more than 3000 humidity cycles, which is 20 times higher durability than that of MEA without nanofastener.