Daniel Cossement

The Influence of the Range of Electroactivity and Capacitance of Conducting Polymers on the Performance of Carbon Conducting Polymer Hybrid Supercapacitor

Hybrid electrochemical supercapacitors based on carbon and conducting polymers as negative and positive electrodes, respectively, have been investigated. Poly-(3-fluorinatedphenyl)thiophene and poly(ethylenedioxythiophene) derivatives showing various ranges of electrochemical activity and capacitance values were evaluated as positive electrodes. It was shown that the mass and capacitance of the polymers have a significant effect on the charge/discharge characteristics and performance of such hybrid electrochemical supercapacitors. The experimental conditions that should be used to obtain specific charge/discharge curves are presented. A linear charge/discharge curve can be obtained between 0 and 3 V when the weight of conducting polymer is larger than that of the negative carbon electrode. In contrast, a battery-like charge/discharge curve is recorded when a smaller conducting polymer weight, relative to that of the carbon electrode, is used.

Volumetric hydrogen sorption capacity of monoliths prepared by mechanical densification of MOF-177

Bulk powdered MOF-177 is mechanically compressed to prepare monoliths with bulk densities more than three times its crystallographic density, and their excess and total gravimetric and volumetric hydrogen storage capacities are measured over a pressure range of 0–13 MPa at 77 K and room temperature. The maximum excess volumetric hydrogen storage capacity of these monoliths at ∼6 MPa and 77 K is 25.8 ± 1.2 g L−1, which is a 78% increase of that of powdered bulk MOF-177 and 80% of the theoretical maximum excess volumetric hydrogen storage capacity predicted on the basis of the materials crystallographic density. The monoliths show diminishing excess gravimetric capacity with increasing density which is attributed to their decreasing micropore volume, which in turn stems from the progressive collapse of MOF-177 crystals to an amorphous phase when they are subjected to densification. A modified Dubinin–Astakhov (DA) model is adapted to describe the excess gravimetric adsorption of samples with varying bulk densities. The total volumetric capacity of monoliths prepared from MOF-177 is 48.0 ± 2.1 g L−1 at 13 MPa and 77 K; if a complete storage system that does not reduce this capacity by more than 20% is designed, it can then meet the DOE 2015 volumetric system target at 77 K. Under the same conditions, it is easier to meet the DOE 2015 gravimetric system target of 5.5 wt% as the materials total gravimetric storage capacity is ∼10.3 ± 0.3 wt%.

Altered reaction pathways of eutectic LiBH4–Mg(BH4)2 by nanoconfinement

The effects of nanoconfinement on the dehydrogenation rate and reaction pathways of the eutectic LiBH4–Mg(BH4)2 have been comprehensively investigated. By means of thermal analysis, mass spectroscopy and solid state 11B MAS NMR, it has been revealed that the multistep thermal decomposition pattern of the binary LiBH4–Mg(BH4)2 has been altered in a two-step reaction and the desorption kinetics has also been significantly improved after infiltration. The formation of diborane and stable MnB12H12 intermediates of the bulk LiBH4–Mg(BH4)2 has been found to be inhibited by nanoconfinement.

Synthesis and Characterization of Carbon Nanostructures as Catalyst Support for PEMFCs

A detailed procedure for synthesis, characterization, and possibility of carbon nanostructures (CNS) as support for catalysts in polymer electrolyte membrane fuel cells (PEMFCs) is presented. The fabrication process is two-staged ballmilling of carbon graphite in the presence of hydrogen and transition metals (Fe, Co) followed by heating of the milled carbon initially in an argon atmosphere. The milling induces amorphous forms of carbon and metal, as well as C-H bonds. During the second stage, the production of methane by catalytic reaction of the bonded carbon and hydrogen is first observed, followed by the formation of metallic nanocrystals, and, finally, the formation of carbon structures on the metallic nanocrystals at a temperature of 700°C. Subsequently, metals and carbon nanoparticles are removed from the as-prepared sample. The purified samples are platinized after surface treatment by either air or chemical oxidation. Material characterization results obtained by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectrocopy, and atomic adsorption spectroscopy are presented. In addition, we also report their measured electrical conductivity, specific surface, and porosity. The real electrochemical active surface area was evaluated by cyclic voltammetry on a thin porous coated electrode.

Systematic evaluation of the adsorption of organic vapors onto a miniaturized cartridge device using breakthrough tests in parallel experiment with a full size respirator cartridge

Breakthrough experiments are essential for the characterization of the adsorption capacity and micropore volume of activated carbon respiratory cartridges and for the validation and determination of cartridge service life models. In an effort to gain better control over environmental conditions in breakthrough tests and to obtain reliable data, a novel experimental approach using a miniaturized (Mini) cartridge was designed to replicate a small section of a respiratory cartridge. The Mini device and the organic vapor respiratory cartridge were tested in single and parallel experiments where in the former, one filter was tested one at a time and in the latter both devices were exposed simultaneously to the same conditions. The Mini device gave comparable results to the 10% breakthrough times and adsorption capacities of the organic vapor cartridges. The reproducibility of the packed carbon bed of the Mini provided strong support for using the Mini in breakthrough experiments for the characterization of the activated carbon adsorption capacity and estimation of cartridge service life.