No abstract

Experimental results for methane adsorption on two high-surface area carbons (TE7-20 and AX-21) and one metal-organic framework (MIL-101(Cr)) are presented, with isotherms obtained at temperatures ranging from 250 to 350 K and at pressures up to 15 MPa. The isotherms were analysed to determine if these materials could be viable alternatives for on-board solid-state storage of methane. The results show a very high adsorbate density in the pores of all materials, which for some can even exceed liquid methane density. At moderate pressures below 5 MPa, the calculated total energy densities are close to the energy density of methanol, and are almost 40 % of the energy density of gasoline (petrol). Compared with standard compression at the same conditions, the results show that adsorption can be a competitive storage alternative, as it can offer equal volumetric capacities at much lower pressures, hence reducing the energy penalty associated with compression. It is shown that the optimal conditions for adsorptive methane storage in these materials are at moderate pressure ranges, where the gains in amounts stored when using an adsorbent are more pronounced when compared to cylinders of compressed methane gas at the same operating conditions. Finally, a study on deliverable capacities for adsorbed methane was carried out, simulating two charging pressure scenarios of 3.5 and 6.5 MPa and discharge at 0.5 MPa. The results show that some of the tested materials have high working volumetric capacities, with some materials displaying more than 140 kg m-3 volumetric working capacity for charging at 6.5 MPa and delivery at 0.5 MPa.

Synthetic K + chabazite (KCHA), Cs + chabazite (CsCHA) and Zn 2+ chabazite (ZnCHA) have been synthesized and investigated in order to relate the differences in their crystalline structures to their thermal stability, moisture content and frequency dependent alternating current (AC) conductivity, permittivity and phase angle at a range of temperatures. The materials are shown to exhibit the universal dielectric response, which is typical of materials consisting of both conductive and insulating regions. Due to the presence of porosity the three chabazites were hydrated significantly at room temperature and so the dehydrated state was achieved by heating the chabazites to high temperatures to ensure that all different energetic types of water were removed. Cation migration activation energies for KCHA (0.66 ± 0.10) eV, CsCHA (0.88 ± 0.01) eV and ZnCHA (0.90 ± 0.01) eV were determined during the cooling cycle from the fully dehydrated state to provide an accurate measurement the activation energies. Good thermal stability of the materials was observed up to 710 °C and below 200 °C the electrical properties can be strongly influenced by hydration level. Overall, it was determined that when either hydrated or dehydrated, KCHA had the highest conductivity and lowest cation migration activation energy of the three studied chabazites and thus has the most promising electrical properties for potential use as a gas sensing material in next-generation electrical-based gas sensors.

No abstract

Synthetic K+ chabazite (KCHA), Cs+ chabazite (CsCHA) and Zn2+ chabazite (ZnCHA) have been synthesized and investigated in order to relate the differences in their crystalline structures to their thermal stability, moisture content and frequency dependent alternating current (AC) conductivity, permittivity and phase angle at a range of temperatures. The materials are shown to exhibit the universal dielectric response, which is typical of materials consisting of both conductive and insulating regions. Due to the presence of porosity the three chabazites were hydrated significantly at room temperature and so the dehydrated state was achieved by heating the chabazites to high temperatures to ensure that all different energetic types of water were removed. Cation migration activation energies for KCHA (0.66 ± 0.10) eV, CsCHA (0.88 ± 0.01) eV and ZnCHA (0.90 ± 0.01) eV were determined during the cooling cycle from the fully dehydrated state to provide an accurate measurement the activation energies. Good thermal stability of the materials was observed up to 710 °C and below 200 °C the electrical properties can be strongly influenced by hydration level. Overall, it was determined that when either hydrated or dehydrated, KCHA had the highest conductivity and lowest cation migration activation energy of the three studied chabazites and thus has the most promising electrical properties for potential use as a gas sensing material in next-generation electrical- based gas sensors.