Catalysts for Polymer Membrane Fuel Cells

Low-temperature fuel cells with a polymer membrane electrolyte are at an exciting time in their development [...

Fabrication of High Performing Pemfc Catalyst-Coated Membranes with a Low Cost Air-Assisted Cylindrical Liquid Jets Spraying System

In this work, a low cost air-assisted cylindrical liquid jets spraying (ACLJS) system was developed to prepare high-performance catalyst-coated membranes (CCMs) for proton exchange membrane fuel cells (PEMFCs). The catalyst ink was flowed from a cylindrical orifice and was atomized by an air stream fed from a coaxial slit and sprayed directly onto the membrane, which was suctioned to a heated aluminum vacuum plate. The CCM pore architecture including size, distribution and volume can be controlled using various flow parameters, and the impact of spraying conditions on electrode structure and PEMFC performance was investigated. CCMs fabricated in the fiber-type break-up regime by ACLJS achieved very high performance during PEMFC testing, with the top-performing cells having a current density greater than 1900 mA/cm2 at 0.7 V under H2/O2 flows and 700 mA/cm2 under H2/Air at 1.5 bar(absolute) pressure and 60% gas RH, and 80°C cell temperature

Application of a Coated Film Catalyst Layer Model to a High Temperature Polymer Electrolyte Membrane Fuel Cell with Low Catalyst Loading Produced by Reactive Spray Deposition Technology

In this study, a semi-empirical model is presented that correlates to previously obtained experimental overpotential data for a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC). The goal is to reinforce the understanding of the performance of the cell from a modeling perspective. The HT-PEMFC membrane electrode assemblies (MEAs) were constructed utilizing an 85 wt. % phosphoric acid doped Advent TPS® membranes for the electrolyte and gas diffusion electrodes (GDEs) manufactured by Reactive Spray Deposition Technology (RSDT). MEAs with varying ratios of PTFE binder to carbon support material (I/C ratio) were manufactured and their performance at various operating temperatures was recorded. The semi-empirical model derivation was based on the coated film catalyst layer approach and was calibrated to the experimental data by a least squares method. The behavior of important physical parameters as a function of I/C ratio and operating temperature were explored

Preparation of Radiation-grafted Powders for use as Anion Exchange Ionomers in Alkaline Polymer Electrolyte Fuel Cells

A novel alkaline exchange ionomer (AEI) was prepared from the radiation-grafting of vinylbenzyl chloride (VBC) onto poly(ethylene-co-tetrafluoroethylene) [ETFE] powders with powder particle sizes of less than 100 μm diameter. Quaternisation of the VBC grafted ETFE powders with trimethylamine resulted in AEIs that were chemically the same as the ETFE-based radiation-grafted alkaline anion exchange membranes (AAEM) that had been previously developed for use in low temperature alkaline polymer electrolyte fuel cells (APEFC). The integration of the AEI powders into the catalyst layers (CL) of both electrodes resulted in a H2/O2 fuel cell peak power density of 240 mW cm−2 at 50 °C (compared to 180 mW cm−2 with a benchmark membrane electrode assembly containing identical components apart from the use of a previous generation AEI). This result is promising considering the wholly un-optimised nature of the AEI inclusion into the catalyst layers

Inflammatory Cytokine Gene Expression in Mesenteric Adipose Tissue during Acute Experimental Colitis

BACKGROUND: Production of inflammatory cytokines by mesenteric adipose tissue (MAT) has been implicated in the pathogenesis of inflammatory bowel disease (IBD). Animal models of colitis have demonstrated inflammatory changes within MAT, but it is unclear if these changes occur in isolation or as part of a systemic adipose tissue response. It is also unknown what cell types are responsible for cytokine production within MAT. The present study was designed to determine whether cytokine production by MAT during experimental colitis is depot-specific, and also to identify the source of cytokine production within MAT. METHODS: Experimental colitis was induced in 6-month-old C57BL/6 mice by administration of dextran sulfate sodium (2% in drinking water) for up to 5 days. The induction of cytokine mRNA within various adipose tissues, including mesenteric, epididymal, and subcutaneous, was analyzed by qRT-PCR. These adipose tissues were also examined for histological evidence of inflammation. The level of cytokine mRNA during acute colitis was compared between mature mesenteric adipocytes, mesenteric stromal vascular fraction (SVF), and mesenteric lymph nodes. RESULTS: During acute colitis, MAT exhibited an increased presence of infiltrating mononuclear cells and fibrotic structures, as well as decreased adipocyte size. The mRNA levels of TNF-α, IL-1β, and IL-6 were significantly increased in MAT but not other adipose tissue depots. Within the MAT, induction of these cytokines was observed mainly in the SVF. CONCLUSIONS: Acute experimental colitis causes a strong site-specific inflammatory response within MAT, which is mediated by cells of the SVF, rather than mature adipocytes or mesenteric lymph nodes

Addressing the Challenge of Electrochemical Ionomer Oxidation in Future Anion Exchange Membrane Water Electrolyzers

Hydrogen production through anion-exchange membrane water electrolyzers (AEMWEs) offers cost advantages over proton-exchange membrane counterparts, mainly due to the good oxygen evolution reaction (OER) activity of platinum-group-metal-free catalysts in alkaline environments. However, the electrochemical oxidation of ionomers at the OER catalyst interface can decrease the local electrode pH, which limits AEMWE performance. Various strategies at the single-cell-level have been explored to address this issue. This work reviews the current understanding of electrochemical ionomer oxidation and strategies to mitigate it, providing our perspective on each approach. Our analysis highlights the competitive adsorption strategy as particularly promising for mitigating ionomer oxidation. This Perspective also outlines future directions for advancing high-performance alkaline AEMWEs and other energy devices using hydrocarbon ionomers

Highly Conductive In-SnO2/RGO Nano-Heterostructures with Improved Lithium-Ion Battery Performance

The increasing demand of emerging technologies for high energy density electrochemical storage has led many researchers to look for alternative anode materials to graphite. The most promising conversion and alloying materials do not yet possess acceptable cycle life or rate capability. In this work, we use tin oxide, SnO2, as a representative anode material to explore the influence of graphene incorporation and In-doping to increase the electronic conductivity and concomitantly improve capacity retention and cycle life. It was found that the incorporation of In into SnO2 reduces the charge transfer resistance during cycling, prolonging life. It is also hypothesized that the increased conductivity allows the tin oxide conversion and alloying reactions to both be reversible, leading to very high capacity near 1200 mAh/g. Finally, the electrodes show excellent rate capability with a capacity of over 200 mAh/g at 10C

High Performance FeNC and Mn-oxide/FeNC Layers for AEMFC Cathodes

While the Anion Exchange Membrane Fuel Cell (AEMFC) is gaining interest due to high power performance recently achieved with platinum-group-metal (PGM) catalysts, its implementation will require high-performing PGM-free cathodes. FeNC catalysts have shown high activity and stability for the Oxygen Reduction Reaction (ORR) in alkaline electrolyte; however, the production of hydrogen peroxide during ORR can lead to premature degradation of FeNC and ionomer. In order to minimize the amount of peroxide formed on FeNC, α-MnO2, β-MnO2, δ-MnO2 and α-Mn2O3 were investigated as co-catalysts, with the aim of increasing the apparent activity of FeNC-based cathodes for the hydrogen peroxide reduction reaction (HPRR). The specific activity of α-Mn2O3 for the HPRR was distinctly superior to the other Mn-oxides. The four Mn-oxides were mixed with a FeNC catalyst comprising atomically-dispersed FeNx sites, showing higher HPRR activity and higher four-electron ORR selectivity than FeNC alone. The stability of α-Mn2O3/FeNC was studied operando by on-line inductively-coupled plasma mass spectrometry, to evaluate the potential and time dependent leaching of Mn and Fe. Finally, FeNC and α-Mn2O3/FeNC were applied at the cathode of AEMFCs, both achieving similar or higher current density at 0.9 V than a Pt/C commercial cathode, and peak power densities of ca. 1 W·cm−2

Electrochemical Methane Activation and Conversion to Oxygenates at Room Temperature

Methane was electrochemically activated at room temperature to CH3OH, HCHO, CO and HCOO− and other low molecular weight oxygenates at room temperature using CO32− as an oxygen-donating species over a NiO-ZrO2 bifunctional electrocatalyst. Products were identified using Mass Spectrometry and 1H-Nuclear Magnetic Resonance Spectroscopy. O2 and CO2 were also observed as products resulting from carbonate electrolysis and/or the oxygen evolution reaction. Methane was adsorbed and activated by NiO while CO32− was adsorbed onto non-conducting ZrO2. Oxygen was then abstracted and donated from CO32− to electrocatalytically active sites to form new C-O or O-H bonds. This proposed low temperature electrochemical partial oxidation of methane may provide a new pathway for the synthesis of complex oxygenates and long chain hydrocarbons