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The electrochemical stability window (EW) of polyether based salt-in-polymer electrolytes was investigated using density functional theory (DFT) calculations. The electrolyte systems investigated consisted of polyethylene oxide (PEO) in either lithium-bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium-hexafluorophosphate (LiPF6) salt and the EW was determined by performing calculations of reduction and oxidation potentials of isolated ethylene oxide (EO) oligomer and the respective salt species in a continuum solvent. The simulations suggest that the cathodic limit of the polymer-salt system is defined by the reduction potential of the salt anion and that both salt anions considered are unstable against Li anode. The anodic limit is defined by EO and it is stable against most commercial cathodes. Including explicit salt molecules in the calculations shows that the predicted EW is changed by ∼0.4 V. The calculations further reveal that the EW is dependent on the type of the salt molecule. Perfluoropolyether, a perfluorinated analog of PEO that has lower reduction potential and higher oxidation potential in isolation as compared to PEO, improved both oxidation and reduction stability of the polymer-salt system. Substitution of other functional groups to PEO improved the electrochemical stability to potentially accommodate higher voltage window requirements.

High performance membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs) are developed by changing the coating process, optimizing the structure of the catalyst layer, adding a pore forming agent to the cathode catalyst layer, and adjusting the hot-pressing conditions, such as pressure and temperature. The effects of these MEA fabrication methods on the DMFC performance are examined using a range of physicochemical and electrochemical analysis tools, such as FE-SEM, electrochemical impedance spectroscopy (EIS), polarization curves, and differential scanning calorimetry (DSC) of the membrane. EIS and polarization curve analysis show that an increase in the thickness and porosity of the cathode catalyst layer plays a key role in improving the cell performance with reduced cathode reaction resistance, whereas the MEA preparation methods have no significant effects on the anode impedance. In addition, the addition of magnesium sulfate as a pore former reduces the cathode reaction transfer resistance by approximately 30 wt%, resulting in improved cell performance.

This paper investigates changes in the performance of membrane electrode assemblies (MEAs) of Direct Methanol Fuel Cells (DMFC) that are caused by undergoing storage at −10 °C and 60 °C under different experimental conditions. Storage at 60 °C exhibited negative effects on an MEA’s performance only when storing the MEA at a 4 M CH 3 OH solution. Here, application of a reverse current for 10 s was found to reinstall the original performance. The effect of storage at −10 °C on an MEA’s performance strongly depends upon the MEA’s properties. MEAs are grouped into three different categories with regard to their suitability for low temperature storage: not affected, temporarily affected, irreversibly affected. The temporarily affected MEAs could be instantly and completely reactivated by a reverse current. Changes in the MEA properties that had been caused by being stored at −10 °C were investigated for two MEAs using electrochemical methods, scanning electron microscopy and porosity measurements. The following MEA materials and manufacturing methods had been found to be principally suitable to build MEAs tolerant to storage at −10 °C: the manufacturing methods CCM (catalyst coated on the membrane) and CCS (catalyst coated on the substrate), several hydrocarbon membranes, high Pt and Pt-Ru catalyst loadings. By carefully selecting the proper MEA material, MEAs with tolerance towards low and high storage temperatures can be designed.

The durability behavior of Pt–Ru anode catalysts under virtual direct methanol fuel cell (DMFC) operating conditions was investigated in the atomic scale using both high-resolution transmission electron microscopy (HR-TEM) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). We find here the crossover of ruthenium and platinum from the anode to the cathode due to the decomposition of active Pt–Ru anode catalysts. The Ru crossover measured at the cathode increases linearly with performance drop. The Ru contents determined by X-ray photoelectron spectroscopy (XPS) are less than 0.3 atom%. The platinum, newly deposited at the cathode with high performance drop, is formed with the intermixture of defective nanocrystalline (∼3 nm) and amorphous structure.

The catalyst layers, which were obtained from the aged membrane electrode assemblies (MEAs) showing performance loss, 17%, 37%, 45% as compared with that from the pristine MEA were investigated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) to understand the degradation mechanism of single-cell performance in direct methanol fuel cell. The metallic components in the PtRu anode catalyst layer was decreased significantly with the performance drop revealed from the change of the valance bands. It has been found that ruthenium and platinum were driven to the cathode by the gradient of electric field during the durability test. From the mass-resolved imaging technique of TOF-SIMS combined with a peel-off method, it was indicated that the traveled ruthenium from anode to cathode was not uniformly distributed within the cathode catalyst layer, but more accumulated at the surface of the catalyst layer, that is, the interface with the gas diffusion layer....

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