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Cerium oxide-containing interlocking interfacial layer improved mechanical adhesion and chemical stability of the interface. For the first time as a hydrocarbon-based membrane, it operated stably for more than 500 hours.

The durability of the membrane electrode assembly (MEA) is one of the important requirements for the successful commercialization of anion exchange membrane fuel cells (AEMFCs). While chemical stabilities of the components (the catalyst, membrane, and ionomer) have been assessed by ex situ tests, the degradation mode of the components in a single-cell is still not fully understood. Herein, the degradation of a MEA based on an ionomer having a polycarbazole main chain and a trimethyl ammonium side group was systematically investigated for a single-cell level under constant current conditions. The degradations of the catalyst, membrane, and ionomer were compared by in situ electrochemical and ex situ post-mortem analyses. The catalyst and ionomer in the cathode showed significant degradation, whereas the membrane was relatively durable, suggesting that the formation of a strong alkaline environment in the cathode catalyst layer is a major cause of the performance fade. The use of an alkaline-stable ionomer with an N,N-dimethylhexylamine group, which is designed based on density functional theory (DFT) calculations, in the cathode catalyst layer leads to 87% durability improvement. This work enhances the understanding of the key factors affecting the durability of AEMFCs under real operation and suggests practical strategies toward higher durability.

Proton exchange membranes with high through-plane proton conductivity are a critical component of high-performance fuel cells, electrolyzers, and batteries. However, isotropically distributed proto...

In this study, molecular dynamics simulations were used to understand the effects of the surface properties of the catalyst on ionomer film morphology by switching the nature of the catalyst surfac...

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.

Background Succinate dehydrogenase inhibitors (SDHIs) have been widely used to manage plant diseases caused by phytopathogenic fungi. Although attention to and use of SDHI fungicides has recently increased, molecular responses of fungal pathogens to SDHIs have often not been investigated. A SDHI fungicide, fluopyram, has been used as a soybean seed treatment and has displayed effective control of Fusarium virguliforme, one of the causal agents of soybean sudden death syndrome. To examine genome-wide gene expression of F. virguliforme to fluopyram, RNA-seq analysis was conducted on two field strains of F. virguliforme with differing SDHI fungicide sensitivity in the absence and presence of fluopyram. Results The analysis indicated that several xenobiotic detoxification related genes, such as those of deoxygenase, transferases, and transporters, were highly induced by fluopyram. Among the genes, four ATP-binding cassette (ABC) transporters were characterized by the yeast expression system. The results revealed that expressions of three ABC-G transporters were involved in reduced sensitivity to multiple fungicides including fluopyram. Additionally, heterologous expression of a major facilitator superfamily (MFS) transporter that was highly expressed in the fluopyram insensitive F. virguliforme strain in the yeast system conferred decreased sensitivity to fluopyram. Conclusion This study demonstrated that xenobiotic detoxification related genes were highly up-regulated in response to fluopyram and expression of ABC or MFS transporter genes was associated with reduced sensitivity to the SDHI fungicide. This is the first transcriptomic analysis of the fungal species response to fluopyram and the finding will help elucidate the molecular mechanisms of SDHI resistance. This article is protected by copyright. All rights reserved.

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.

During a survey of diseased plants on Wando Island, Korea from May to June 2020, a severe leaf spot disease was observed in the upper leaves of Japanese bay tree (Machilus thunbergii). Early symptoms were light blackish spots on the leaf surface and enlargement of older spots. Dry leaf spots surrounded with deep black margins were common throughout the plants. Symptomatic leaf samples were collected, and the causal pathogen was isolated on potato dextrose agar (PDA). Three fungal isolates (CMML20-1, CMML20-3, and CMML20-4) were cultured on PDA for morphological characterization at 25 °C in the darkness. Fungal colonies were circular, fast-growing, olivaceous to dark grey, and with abundant aerial mycelium. Sporulation was induced in 14 h-10 h light-dark conditions, and the conidia were single-celled, thin-walled with a smooth surface, ellipsoid with round apices, and measuring 17.5–20.5 (avg. 17.5) μm × 7.5–10.0 (7.9) μm. The morphological characteristics resembled those typical for Neofusicoccum parvum. Molecular identification was confirmed by partially sequencing the internal transcribed spacer (ITS) region and the translation elongation factor 1-α (EF1-α) genes. Pathogenicity tests were conducted on detached leaves and whole plants of M. thunbergii. High disease prevalence was observed, and Koch postulates were fulfilled. This is the first worldwide report of N. parvum causing leaf spots on Machilus thunbergii.

The development of anion exchange membranes and ionomers plays a critical role in performance of anion exchange membrane fuel cells. However, the optimal design of catalyst layer structures still remains unexplored despite its significance. Herein, the rational design guide is presented for cathode and anode catalyst layers using m-TPN1 ionomer by controlling the size of ionomer aggregates in dispersion and comparing various catalyst layer structures. The size of m-TPN1 aggregates decreases, creating a more uniform ionomer distribution and a larger triple-phase-boundary. As ionomer distribution of the cathode catalyst layer becomes more uniform, the power density of membrane-electrode-assembly is enhanced. Also, the power density at fully humidified condition strongly correlates with the porosity of anode catalyst layer due to the limitation of hydrogen transport at anode by water flooding.

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.

Misfiring in spark ignition engines should be avoided, otherwise unburned fuel and oxygen are brought into the catalyst, and subsequent combustion greatly increases the temperature, possibly resulting in immediate damage to the catalyst. As a new concept of misfire detection method, the signal fluctuation of a wide-range oxygen sensor has been introduced to monitor the fluctuation of the oxygen concentration at the exhaust manifold confluence point. The current research aims to develop a tool that is capable of predicting the variation in oxygen concentration at the exhaust manifold confluence point, and to investigate the flow characteristics of the misfired gas in the exhaust manifold under misfiring conditions in a cylinder. The oxygen concentration at the confluence point could be predicted by comparing the gas flowrate from the misfiring cylinder with the total exhaust gas flowrate. The gas flowrates from each of the cylinders were calculated using a one-dimensional engine cycle simulation including a gas dynamic model of the intake and exhaust systems. The variation in oxygen concentration was also determined experimentally using a fast-response hydrocarbon analyser. The trend of the oxygen concentration fluctuation calculated by the analytical model was compared with the experimental results. The analytical model could duplicate the measured trend of the fluctuation of oxygen concentration at the confluence point, which was characterized by twin peaks for one misfiring. The twin peaks are mainly caused by the mixing of the misfired gas with the burned gas from normally operating cylinders. The effects of engine load and speed on the characteristics of the variation in oxygen concentration were also investigated analytically and experimentally.

Operating polymer electrolyte membrane fuel cell(PEMFC) at high temperatures (HT, 100oC~200oC) is beneficial owing to fast kinetics for electrochemical reactions and high tolerance to carbon monoxide(CO) poisoning. Also, the HT operation allows a simpler system design by eliminating water management and PROX. However, current HT-PEMFCs still suffer from insufficient power performance partly originating from large membrane resistance. Typically, HT-PEMFC employs the phosphoric acid-doped PBI membrane and its proton conductivity depends on the acid doping level. Therefore, increasing the doping level is prerequisite for high power performance of HT-PEMFC. However, phosphoric acid doping level is practically limited by a decreased mechanical stability of the membrane with acid doping. To mitigate the problems caused by the loss of low mechanical strength with the acid doping, a thick PBI membrane (>100um) is conventionally employed although its large membrane resistance and consequent negative influence on power performance. Against this backdrop, in this study, we present a novel approach for addressing the trade-off between proton conduction and mechanical robustness of PBI based HT membrane. For fabricating an reinforced PBI membrane coupled with a porous PTFE membrane, PBI filling in a porous PTFE membrane is highly challenging due to low compatibility between hydrophobic PTFE and hydrophilic PBI. In this work, to make the PTFE surface hydrophilic, a porous PTFE membrane is treated with dopamine which is as known nature-inspired adhesive and self-polymerized into polydopamine via a pH-induced oxidation. A polydopamine layer can be formed on the PTFE surface by simply immersing the porous PTFE membrane in the aqueous buffered dopamine solution at room temperature. Compared to the pristine PTFE membrane, the polydopamine-treated PTFE membrane is more densely filled with PBI after the impregnation of PBI solution, indicating an effective intrusion of the PBI solution into the modified hydrophilic pores. The reinforced membrane shows a higher mechanical strength after phosphoric acid doping process even at a thin membrane thickness(~50um) in comparison with a 100 micron thick un-reinforced PBI membrane. The second feature of this approach is the introduction of plasticizer in the PBI matrix for increasing the acid doping level for the reinforced PBI/PTFE membrane. In general, mechanical supports suppress swelling of the PBI matrix with phosphoric acid solution, resulting in a lower acid doping level compared to that of pristine PBI membrane. However, poly(ethylene glycol) (PEG), which can be exchanged with phosphoric acid, provides an additional space for accommodating phosphoric acid in the PBI matrix when incorporated in the PBI matrix. PEG and PBI forms a miscible blend and PEG can be extracted out during the acid doping process, being exchanged with phosphoric acid as confirmed by DSC and FT-IR analysis. The PEG/PBI blend exhibits a higher mechanical stability owing to its lower expansion but a higher proton conductivity owing to its high acid doping level after the acid doping, clearly demonstrating the benefit of the approach. When the PEG-plasticized PBI matrix and polydopamine-treated PTFE support are combined, the mechanical stability can be significantly improved compared with the PEG-plasticized PBI membrane and the proton conductivity be enhanced compared with the PTFE-reinforced PBI membrane. The power performance of an in-house membrane electrode assembly (MEA) employing the novel reinforced membrane is comparable to that of a commercial HT-MEA. Therefore, the combined strategy can overcome the trade-off between mechanical stability and proton conductivity in the design of HT-PBI membranes.

Polymer electrolyte membrane fuel cell (PEMFC) technology faces considerable demands of cost competitiveness for mass commercialization of fuel cell electric vehicle. A significant challenge to the cost reduction is the reduction of Pt loading for membrane electrode assembly (MEA). Besides a lowered catalytic activity, low Pt-loaded catalyst layer (CL) suffers from large mass transports resistance, resulting in low power performance at high current densities. Such larger mass transport resistance at a lowered Pt loading can be attributed to a larger oxygen transport resistance from the ionomer film covering catalysts and more significant water flooding due to a lower amount of the pore volume in cathode CL. For conventional CL structure, gaseous oxygen and liquid water share the same network of meso-pores (< 50 nm) inside a flat CL for their transport, therefore, the water condensation in the pores inevitably causes a blocking of oxygen transport. In order to address this issue, an ionomer fiber-induced macro-porous CL is presented. It is fabricated via electrospinning of ionomer fibers onto the membrane, followed by spray-coating catalyst ink on the ionomer fiber-decorated membrane. The ionomer fiber deposition on the membrane induce a roughening of the membrane surface, which allows the formation of a CL, morphology of which dictates that of the ionomer fibers, and of micron-scale pores between the CL and gas diffusion layer. The new CL structure dramatically improves power performances at high current densities owing to an effective oxygen and water transport through the micron-scale mass transport pathway. From polarization curve and oxygen transport resistance analysis, and stability under constant current operation for various feeds, the efficacy of the unique CL morphology in enhancing power performances is demonstrated and understood. Also, the relationship between the macro-pore in CL and mass transport resistance is investigated with systematically varying the pore size and porosity.

For decades, in polymer electrolyte membrane fuel cell (PEMFC) field, hydrocarbon (HC) membranes have been constantly studied to replace perfluorinated sulfonic acid membranes owing to their low cost and high fuel efficiency. However, adopting HC membranes to practical PEMFCs has been not successful due to their poor mechanical stability which causes a mechanical failure with generating pin-hole under repeated volume expansion/shrinkage during cell operation. Conventionally, the problem has been addressed by inserting a porous mechanical supporter in HC membrane which is denoted as ‘internal reinforcement’. However, the introduction of the inert support decreases proton conduction and increases membrane cost. Here we present an external reinforcement of HC membrane as a new strategy to enhance mechanical durability of HC membrane. It features the incorporation of mechanically tough porous fibrous network into catalyst layers and the strong connection of HC membrane and the toughened catalyst layers with introducing an interlocking interface. The mechanically toughened catalyst layers and interfaces can effectively mitigate the volume change of HC membrane, lowing the membrane failure. Under an accelerated humidity cycling test, the externally reinforced HC membrane exhibits an enhanced durability compared to un-reinforced counterpart. Furthermore, contrary to the internal reinforcement, the external reinforcement strategy does not cause any loss of proton conductivity of HC membrane. Therefore, the external reinforcement coupled with toughed catalyst layers and interfaces can provide an effective way to enhance durability with preserving the proton conductivity of pristine HC membrane.