This thesis describes an investigation into the hydrogen storage properties of zeolites and high surface area carbons. In particular, zeolite X, zeolite Y, zeolite A, zeolite Rho, carbon nanotubes and activated carbons materials were studied. The zeolites encompass a range of different pore geometries and compositions. The aim was to investigate the potential of zeolites as an alternative to carbons in low-cost, safe hydrogen stores, particularly for large-scale stationary applications. Zeolites were synthesised by hydrothermal methods, and different cation-exchanged forms were prepared. through ion exchange from aqueous metal nitrate solutions. All hydrogen storage capacities were measured at room temperature or 77 K and a pressure range of 0 to 15 bar, using a constant pressure thermogravimetric analyser. The results show that, zeolites exhibit diverse behaviour with respect to hydrogen uptake, dependent on both the framework structure and the nature of the cations present. A major factor influencing uptake is the available void space: in zeolites A and Rho, pore blocking by large extraframework cations is a prominent phenomenon restricting hydrogen uptake, but in zeolites X and Y, blocking of supercages by exchangeable cations does not occur. In general, gravimetric uptake is affected by the weight of the zeolite since hydrogen uptakes in heavier zeolites were relatively lower. Volumetric hydrogen storage capacities show that zeolites are roughly twice as efficient in binding hydrogen than activated carbons. This study also suggests that, extraframework cations act as binding sites for hydrogen molecules. In both zeolites and carbons, hydrogen adsorption occurs by physisorption, and the adsorption - desorption process is fast and completely reversible. Preliminary adsorption theory analysis shows that, the hydrogen adsorption isotherms conform reasonably well to the Langmuir equation. For carbons, zeolite X and zeolite Y, hydrogen uptake relates closely with the BET surface area. Suitably ion-exchanged zeolites offer great promise as low-cost, safe hydrogen storage media for stationary applications. Further work, involving detailed characterisation, needs to be carried out to fully explore the hydrogen storage and engineering properties of these materials.

With annual global energy consumption predicted to double by 2050 and CO2 emissions having already reached crisis point, the growing demand for renewable and environmentally clean power sources has been propelled to the forefront of academic and industrial research. One strategy currently under investigation is the employment of enzymes in enzymatic fuel cells (EFCs), which convert chemical energy to electrical energy. This research focused on comparing the use of different protein-stabilising agents in low-cost bilirubin oxidase (DOD) from Mycothecium verrucaria cathodes with sandwich architcctures, for biocatalysis of the electrochernical oxygen reduction reaction (ORR). As a novel route towards EFC cost reduction, Super P (carbon black powder, CBP) was initially selected as an electronically conductive enzyme support material. To increase direct electron transfer, COOH functionalisation of the CDP was investigated and characterised with ATR-FTIR, CHN and thermogravimetric analysis and the Boehm titration technique. Chemical oxidation yielded surface COOH concentrations ranging between 0.16 - 1.70 mmol g-I, which was determined with cyclic voltammetry (CV) to be outside of the sui table range for application within BOD cathodes. This resulted in the use of multi -walled carbon nanotubes (MWCNTs) as the enzyme supp0l1 material. The effect of several room temperature ionic liquids (RTlLs) on BOD activity was also investigated, resulting in the novel identification of three RTlLs that are BOD-compatible in the absence of water: l-ethyl-3-methylimidazolium ethylsulfate (EMIM-EtS04), l-elhyl-3- methylimidazolium diethylphosphate (EMIM-Et2P04) and 1,3-methylimidazoliulll dimethylphosphate (MMIM-Me2-P04). Two BOD cathodes, utilising the non-ionic surfactants (N ISs) Triton X-l00 and Tween 20, were developed, optimised and characterised. 1'riton X-lOO was detennined to be the favourable NIS for three-layer BOO cathode fabrication, compared to Tween 20, especially with respect 10 electrode current densities (-81 vs. -60μA cm-2 at 0.3 V vs. Ag/AgCI at pH 5.0) attributed to the BOD-catalysed ORR. Chronoamperornetric studies over a period of 8 days showed no difference between the stability of the two BOD cathodes.

Biological Fuel Cells (BFCs) use biological catalysts to convert chemical energy into electrical energy; enzymatic BFCs utilise enzymes as biocatalysts, which often results in the production of electricity from simple molecules such as glucose (in the presence of 02). Glucose oxidase (GOd) was utilised as a glucose-oxidising bioanodic enzyme. Initially, direct electron transfer (DET) of GOd was investigated using lightlyoxidised multi-walled carbon nanotubes (MWCNTs). Although GOd appeared to undergo DET, further investigation revealed that GOd did not undergo DET. Mediated electron transfer (MET) of GOd and flavin adenine dinucleotidedependent glucose dehydrogenase (F AD-GDH) was then investigated, using ferrocene (Fc) as an electron mediator. The resulting GOd and FAD-GDH bioanodes were then coupled with laccase and bilirubin oxidase (BOd) biocathodes, resulting in the enzymatic BFCs operating on glucose (in the presence of O2). Maximum power densities of 113.1 ± 1.5 /-LW cm-2 and 122.2 ± 5.8 /-LW cm-2 were obtained for GOd/laccase and F AD-GDHllaccase enzymatic BFCs, respectively (hydrostatically operating on 200 mM glucose in aerated citrate/phosphate buffer (PH 5.5)). Similarly, maximum power densities of 46.5 ± 2.8 /-LW cm-2 and 35.9 ± 1.3 /-LW cm-2 were obtained for GOd/BOd and FAD-GDHlBOd enzymatic BFCs, respectively (hydrostatic ally operating on 200 mM glucose in aerated citrate/phosphate buffer (pH 6.5)). It was also discovered that GOd produces significant quantities of H202 to deleteriously affect both laccase and BOd and their resulting bioelectrodes/biocathodes; this also results in decreased performances and operational stabilities of GOd-containing BFCs. H20 2 production (by GOd) was shown to rapidly inhibit laccase bioelectrode performances by up to 94%; 50% inhibition of laccase was observed at 1.94 mM H202. Although laccase and BOd are both significantly affected by H20 2, it is demonstrated that bioelectrocatalytic currents of laccase-containing cathodes that are lost in the presence of H20 2 can be recovered by the decomposition of H202 (by catalase). Lost bioelectrocatalytic currents of BOd-containing bioelectrodes cannot be recovered by that same treatment and the production of H20 2 should therefore be avoided. 111

Enabling inexpensive and ubiquitous steels for use as solid oxide fuel cell interconnects has two major hurdles to overcome. Firstly, corrosion must be limited such that the interconnect can have longevity. Secondly, the evaporation of chromium from the corrosion layer must also be limited such that the fuel cell can have longevity. The evaporation of chromium from chromia, titanium doped chromia, and chromium cobalt spinels was studied and characterized. Spinels lost the least amount of mass during evaporation experiments, and changed the least after experimental conditions were imposed on them that. Chromium titanate samples retained a significant amount of chrome that would have evaporated had the sample been chromium oxide alone. This was due to local changes at the surface with titanium becoming enriched and blocking loss of further chromium. Various methods of depositing titanium doped chromia on the surface of SS430 were investigated. Sol-gel was attempted, but proved problematic. Evaporation of elemental titanium onto SS430 followed by conversion to rutile by heating followed by the evaporation of chromium into the rutile layer was investigated at length. These layers are nanoscale when evaporated and about 10 times thicker after oxidation. Characterization of the resulting Ti layers showed that at low temperatures a thick dense layer of rutile could be observed. At higher oxidation temperatures, the titanium was difficult to find. Evaporation of cobalt onto SS430 created thin films when oxidized. The films were shown to control the evaporation of chromium by production of spinels. These layers were characterized with X-Ray Diffraction and scanning electron microscopy and impedance spectroscopy. They were shown to be quite conductive compared to the titanium coatings.

This study involved two avenues of investigation: a new concept of Direct Carbon Fuel Cell (DCFC) and the production of carbon from biomass. The new concept of DCFC merges a solid oxide electrolyte and a molten carbonate electrolyte called the “hybrid direct carbon fuel cell” using tubular geometry. The tubular cell was chosen for several reasons, such as sealing process, reduction of stress during the sintering process and reduction of the final size of the stack. In addition, it makes the fuelling process easier than in planar geometry. The previous tests carried out on tubular hybrid direct carbon fuel cell at the University of St Andrews showed promising results. In fact, a power of 85 mW was achieved at 800ºC. However this temperature was too high and so the focus of the new project was on decreasing the operating temperature to 650ºC, replacing the YSZ electrolyte used in the previous configuration with an electrolyte such as GDC, which showed better performance at low temperature. YSZ was substituted for GDC in the anodes and cathode in order to prevent an increase in the interface resistance due to the possible reaction between electrolyte and electrodes at the interface. Anodes with different proportions of NiO and GDC were investigated in order to understand the electrochemical phenomena in the presence of GDC compared to YSZ. Three different electrical configurations were investigated by AC impedance studies because the electrochemistry of the cell changes as function of the position and the surface of the current collector, which is dipped into the anode chamber. Performance improved when the surface area of the current collector increased, which combined a silver wire with strip of nickel mesh. Two types of seals (552 ceramabond and ToKu adhesive) and the sealing process were also studied in order to prevent leakage, which affects the performance of the entire cell. The leakages were reduced using a composite seal composed of alumina paste and a combination of flexi disks of mica and alumina fibre disk. In the preliminary test using 70-30%wt NiO GDC and LSM-GDC with composite nickel mesh and silver wire current collector and the composite seal, a promising value of power of 191mW was achieved at 700ºC using GDC electrolyte. The value of power was improved by reducing the thickness of the electrolyte and the cathode manufacture. However, the best performance was achieved when LSM-GDC cathode was replaced with LSCF- GDC. LSCF was chosen for the promising results shown at low temperature, and a power of 240mW was achieved at 650ºC when it was used as the cathode in our cell. The carbon fuel used for these fuels was a medium density fibreboard pyrolysed at 500°C. The choice of this carbon fuel was based on the production and characterization of carbon fuels in this project. The investigations were focused on the production and characterization of carbon fuel from biomass such as MDF and pellet wood produced by pyrolysis. Secondary products resulting from the pyrolysis process were also investigated in order to use them as alternative fuels. All of the types of carbons produced and 3 commercial carbons were characterized by SEM, XRD, infrared spectroscopy, surface area and elemental analysis, while their electrochemical performances were investigated by hybrid direct carbon fuel cell with planar geometry. The investigations highlight that the structure of the carbon used does not affect the performance of the cell, which is in fact affected by the ability of the carbon to gasify in the presence of carbonate.

No description available.

No description available.

No description available.

No description available.

No description available.