PEMFC MEA and System Design Considerations

Proton exchange membrane fuel cells (PEMFCs) are being developed and sold commercially for multiple near term markets. Ballard Power Systems is focused on the near term markets of backup power, distributed generation, materials handling, and buses. Significant advances have been made in cost and durability of fuel cell products. Improved tolerance to a wide range of system operation and environmental noises will enable increased viability across a broad range of applications. In order to apply the most effective membrane electrode assembly (MEA) design for each market, the system requirements and associated MEA failures must be well understood. The failure modes associated with the electrodes and membrane degradation are discussed with respect to associated system operation and mitigating approaches. A few key system considerations that influence MEA design include expected fuel quality, balance-of-plant materials, time under idle or open circuit operation, and start-up and shut-down conditions

SARS-CoV-2 B.1.617.2 Delta variant replication and immune evasion

Abstract: The B.1.617.2 (Delta) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in the state of Maharashtra in late 2020 and spread throughout India, outcompeting pre-existing lineages including B.1.617.1 (Kappa) and B.1.1.7 (Alpha)1. In vitro, B.1.617.2 is sixfold less sensitive to serum neutralizing antibodies from recovered individuals, and eightfold less sensitive to vaccine-elicited antibodies, compared with wild-type Wuhan-1 bearing D614G. Serum neutralizing titres against B.1.617.2 were lower in ChAdOx1 vaccinees than in BNT162b2 vaccinees. B.1.617.2 spike pseudotyped viruses exhibited compromised sensitivity to monoclonal antibodies to the receptor-binding domain and the amino-terminal domain. B.1.617.2 demonstrated higher replication efficiency than B.1.1.7 in both airway organoid and human airway epithelial systems, associated with B.1.617.2 spike being in a predominantly cleaved state compared with B.1.1.7 spike. The B.1.617.2 spike protein was able to mediate highly efficient syncytium formation that was less sensitive to inhibition by neutralizing antibody, compared with that of wild-type spike. We also observed that B.1.617.2 had higher replication and spike-mediated entry than B.1.617.1, potentially explaining the B.1.617.2 dominance. In an analysis of more than 130 SARS-CoV-2-infected health care workers across three centres in India during a period of mixed lineage circulation, we observed reduced ChAdOx1 vaccine effectiveness against B.1.617.2 relative to non-B.1.617.2, with the caveat of possible residual confounding. Compromised vaccine efficacy against the highly fit and immune-evasive B.1.617.2 Delta variant warrants continued infection control measures in the post-vaccination era

PEMFC MEA and System Design Considerations

Proton exchange membrane fuel cells (PEMFCs) are being developed and sold commercially for multiple near term markets. Ballard Power Systems is focused on the near term markets of backup power, distributed generation, materials handling, and buses. Significant advances have been made in cost and durability of fuel cell products. Improved tolerance to a wide range of system operation and environmental noises will enable increased viability across a broad range of applications. In order to apply the most effective membrane electrode assembly (MEA) design for each market, the system requirements and associated MEA failures must be well understood. The failure modes associated with the electrodes and membrane degradation are discussed with respect to associated system operation and mitigating approaches. A few key system considerations that influence MEA design include expected fuel quality, balance-of-plant materials, time under idle or open circuit operation, and start-up and shut-down conditions

Ti4O7 supported Ru@Pt core-shell catalyst for CO-tolerance in PEM fuel cell hydrogen oxidation reaction

A new method is developed for synthesizing Ti4O7 supported Ru@Pt core-shell catalyst (Ru@Pt/Ti4O7) through pyrolysis followed by microwave irradiation. The purpose is to improve the Ru durability of PtRu from core-shell structure and strong bonding to Ti4O7 oxide. In this method, the first step is to co-reduce the mixture of ruthenium precursor and TiO2 in a H2 reducing atmosphere under heat-treatment to obtain a Ru core on Ti4O7 support, and the second step is to create a shell of platinum via microwave irradiation. Energy dispersive X-ray spectrometry, X-ray Diffraction, High-resolution Scanning Transmission Electron Microscopy with the high-angle annular dark-field method and Electron Energy-Loss Spectroscopy are used to demonstrate that this catalyst with larger particles has a core-shell structure with a Ru core and a Pt shell. Electrochemical measurements show Ru@Pt/Ti4O7 catalyst has a higher CO-tolerance capability than that of PtRu/C alloy catalyst.Peer reviewed: YesNRC publication: Ye

Carbon-Doped TiO2 and Carbon, Tungsten-Codoped TiO2 through Sol-Gel Processes in the Presence of Melamine Borate: Reflections through Photocatalysis

A series of C-doped, W-doped, and C,W-codoped TiO2 samples have been prepared using modified sol-gel techniques. Reproducible inexpensive C-doping arises from the presence of melamine borate in a sol-gel mixture, whereas W-doping is from the addition of tungstic acid to the sol. The materials have been characterized using elemental analysis, N-2 physisorption (BET), thermogravimetric analysis, X-ray diffraction, Raman, X-ray photoelectron, UV-vis spectroscopies, and photocatalytic activity measurements. Doping C and W independently results in an increased absorbance in the visible region of the spectrum with a synergistic effect in increased absorbance when both elements are codoped. The increased visible-light absorbance of the W-doped or codoped materials is not reflected in photocatalytic activity. Visible-light-induced photocatalytic activity of C-doped material was superior to that of an undoped catalyst, paving the way for its application under only visible-light irradiation conditions. A significant fraction of the spectral red shift commonly observed with doped catalysts might be due to the formation of color centers as a result of defects associated with oxygen vacancies, and bandgap-related narrowing or intragap localization of dopant levels are not the only factors responsible for enhanced visible-light absorption in doped photocatalysts. Furthermore, bandgap narrowing through increases in the energy of the valence band may actually decrease photo-oxidation activity through a curtailment of one route of oxidation.LP

Materials for polymer electrolyte fuel cells

The commercial success of the polymer electrolyte fuel cell (PEFC) will to a large extent be determined by the nature, properties, functionality, and cost of the electrochemical sub-components used in the membrane electrode assembly (MEA). Materials research activities in Switzerland for the PEFC are being pursued at the Paul Scherrer Institut (Villigen AG) and the Swiss Federal Institute of Technology in Lausanne with different objectives. The radiation grafted proton exchange membrane developed at the Paul Scherrer Institut (PSI) has been brought to a near-product-like quality level with encouraging performance close to state-of-the-art materials and a life-time of several thousand hours. Furthermore, the membrane shows low methanol crossover in the direct methanol fuel cell. In addition, polyarylene block copolymer membranes have been investigated as an option for fluorine-free membranes. The electrocatalysis of Pt in acidic solution and in contact with a solid electrolyte, the development of new methanol oxidation and oxygen reduction catalysts, and co-sputtering of Pt and carbon as an alternative method for catalyst preparation are areas of fundamental research. More applied research is performed in the characterization of commercial electrodes in single cells, using standard as well as advanced diagnostic tools developed in-house. This article gives an overview over the research and development projects in Switzerland related to materials and components for the PEFC

Carbon-Doped TiO₂ and Carbon, Tungsten-Codoped TiO₂ through Sol–Gel Processes in the Presence of Melamine Borate: Reflections through Photocatalysis

A series of C-doped, W-doped, and C,W-codoped TiO₂ samples have been prepared using modified sol–gel techniques. Reproducible inexpensive C-doping arises from the presence of melamine borate in a sol–gel mixture, whereas W-doping is from the addition of tungstic acid to the sol. The materials have been characterized using elemental analysis, N₂ physisorption (BET), thermogravimetric analysis, X-ray diffraction, Raman, X-ray photoelectron, UV–vis spectroscopies, and photocatalytic activity measurements. Doping C and W independently results in an increased absorbance in the visible region of the spectrum with a synergistic effect in increased absorbance when both elements are codoped. The increased visible-light absorbance of the W-doped or codoped materials is not reflected in photocatalytic activity. Visible-light-induced photocatalytic activity of C-doped material was superior to that of an undoped catalyst, paving the way for its application under only visible-light irradiation conditions. A significant fraction of the spectral red shift commonly observed with doped catalysts might be due to the formation of color centers as a result of defects associated with oxygen vacancies, and bandgap-related narrowing or intragap localization of dopant levels are not the only factors responsible for enhanced visible-light absorption in doped photocatalysts. Furthermore, bandgap narrowing through increases in the energy of the valence band may actually decrease photo-oxidation activity through a curtailment of one route of oxidation

Historical development of hybrid materials

Hybrid material sourced from nature has existed for billions of years. Nature developed hybridorganic – inorganic materials with exceptional fracture resistance and structural capabilities with complex design (Wegst et al., 2015). Examples of hybrid organic– inorganic materials in nature include bone and narge. Hybrid material sare defined as the combination of organic and inorganic materials, where the range of the hybrid composite is from a few nanometers to tens of nanometers (Mammeri et al., 2005). The organic and inorganic materials result in different properties. The combination of the organic and in organic components in the formation of hybrid materials is limitless (Kickelbick, 2007). Thus, a new combination can lead to a new type of hybrid material