Study on Morphological Properties and Mass Transport Parameters of ORR in Recast Ion- exchange Polymer Electrolyte Membranes

ABSTRACT We have investigated the effect of the recast temperature, i.e., heat treatment of a polymer electrolyte, on the diffusion coefficient and solubility of oxygen in the electrolyte and also on the morphological properties of recast ion-exchange membranes for improving the cathode activity in PEFCs. The recast membranes were prepared at different recast temperatures from Nafion ® and Aciplex ® solutions. Based on the chronoamperometric measurements, it was found that the diffusion coefficient and solubility of oxygen were deeply affected by the recast temperature. The diffusion coefficient increased with the decreasing recast temperature while the solubility had the opposite tendency. The water uptakes and ionic cluster size also varied with the recast temperature. Based on the X-ray measurements, it is considered that the differences in the mass transport parameters, the cluster sizes and water uptakes are due to the growth of clusters and crystallinity in the electrolyte

Ternary Non-Noble Metal Chalcogenide as Electrocatalyst for Oxygen reduction reaction

NRC publication: Ye

The effect of synthetic reducing agents on morphology and ORR activity of carbon-support Pd-Co alloy electrocatalysts

NRC publication: Ye

Transition metal chalcogenides for oxygen reduction electrocatalysts in PEM fuel cells

This chapter covers the process of oxygen-reduction reaction (ORR) for fuel-cell systems of nonprecious electrocatalyst centers explored since the 1960s, showing the progress achieved with regard to their catalytic activity and stability. The catalytic centers investigated so far are transition metal chalcogenides and metal-macrocycles; in particular, the chalcogenides and the macrocycles containing cobalt or iron metals. The chapter also displays the progress made via theoretical studies on non-noble metal chalcogenides made in understanding of the ORR mechanism and factors that affect the ORR activity and stability.Peer reviewed: YesNRC publication: Ye

Preparation and characterization of polysulfones containing both hexafluoroisopropylidene and trimethylsilyl groups as gas separation membrane materials

Trimethylsilylated derivatives of hexafluoropolysulfone (6FPSf) and tetramethylhexafluoropolysulfone (TM6FPSf) were prepared by reaction of lithiated polymer intermediates with halotrimethylsilane electrophiles for a membrane gas separation study to compare improvements in gas permeabilities with those of unmodified polymers. Ortho sulfone substituted 6FPSf and TM6FPSf having pendant trimethylsilyl (TMS) groups were obtained by a two-step process involving first direct lithiation of 6FPSf and TM6FPSf solutions with n-butyllithium to afford ortho sulfone dilithiated intermediates, followed by reaction with a TMS electrophile. The corresponding ortho ether 6FPSf derivative was obtained by lithiation of dibrominated 6FPSf at the bromine sites, followed by reaction with a TMS electrophile. The degree of substitution (DS) of the TMS groups was 2.0 and was dependent on the molar ratio of n-butyllithium and electrophile quantity, electrophile reactivity, and reaction conditions. Detailed structural characterization and DS of the modified polymers were obtained by nuclear magnetic resonance spectroscopy. The glass transition temperatures and thermal stabilities were determined by differential scanning calorimetry and thermogravimetric analysis, respectively. Polymer chain d-spacing was investigated using wide-angle X-ray diffraction. Polymer free volume was calculated from the polymer density and specific van der Waals volume. The polymer gas permeability coefficients (P) were measured for He, CO2, O2, and N2. Both CO2 and O2 permeabilities of modified 6FPSf increased by 8-9-fold (P(CO2) = 110 barrers, P(O2) = 28 barrers) compared with those of the starting polymer 6FPSf (P(CO2) = 12 barrers, P(O2) = 3.4 barrers), which gives P and properties very close to the upper bound line.1 Almost no reduction in permselectivity () was observed for the CO2/N2 gas pair, while the O2/N2 gas pair showed moderate reduction.NRC publication: Ye

Pt nanoparticles deposited on TiO2 based nanofibers: Electrochemical stability and oxygen reduction activity

The electrochemical stability of Pt deposited on TiO2 based nanofibers was compared with commercially available carbon supported Pt. Prior to the Pt deposition the TiO2 material, which was either undoped or Nbdoped, was air calcined. In one case the undoped TiO2 was also reduced in a hydrogen atmosphere.XRD analysis revealed that the unreduced TiO2 was present in the anatase phase, irrespective of whether the Nb dopant was present, whereas the rutile phase was formed due to reduction with H2. The diameter of the TiO2 fibers varied from 50 to 100 nm, and the average Pt particle diameter was approximately 5 nm. Pt supported on TiO2 was more stable than Pt supported on C when subjected to 1000 voltammetric cycles in the range of 0.05\u20131.3V vs. RHE. Nb doped TiO2 showed the highest stability, retaining 60% of the electrochemically active surface area after 1000 cycles compared to the state after 100 cycles, whereas the carbon supported catalyst retained 20% of the active surface area. The commercial catalyst had the highest oxygen reduction activity due to its larger specific area (17.1m2 g 121 vs. 5.0m2 g 121 for Pt/TiO2\u2013Nb, measured after 100 cycles) and the higher support conductivity. The Pt supported on Nb doped or on H2 reduced TiO2 was more active than Pt supported on air calcined and otherwise unmodified TiO2.Peer reviewed: YesNRC publication: Ye

Correlation between Structure and Gas Transport Properties of Silyl-Modified Polysulfones and Poly(phenyl sulfone)s

An improvement in gas permeation properties has been obtained by introducing bulky silyl side groups at sites ortho to either the ether or sulfone linkage of polysulfone and poly(phenyl sulfone) chains. The sizes of the substituents were systematically increased from trimethylsilyl, to dimethylphenylsilyl, and to diphenylmethylsilyl, and the degree of substitution was also controlled. The sterically smallest trimethylsilyl group substituted at the ortho ether site markedly increased the oxygen permeability from 1.1 to 7.1 barrers compared with that of unmodified polysulfone at a small tradeoff in oxygen/nitrogen selectivity. Unexpectedly, the oxygen permeability remained almost unchanged from polysulfone with the introduction of more bulky dimethylphenylsilyl and diphenylmethylsilyl substituents. It was also found that substitution at the sites ortho to ether linkage was more effective than the sulfone linkage in improving transport properties. The improved gas separation properties appear to be associated with increased free volume, evidenced from the increased d-spacing and specific volume. Further, the mobility of pendant substituents, characterized by dynamic mechanical analysis, correlated strongly with the d-spacing and specific volume. This leads us to the conclusion that it is substituent mobility rather than the size of the pendant side group that is the critical factor in determining free volume and transport properties.NRC publication: Ye