Production and characterisation of molecular hydrogen storage materials

Mileeva, Z

Abstract

The subject of the present work is the characterization of potential materials for
molecular hydrogen storage with a stress on the use of Small Angle Neutron Scattering
(SANS).
This research is dedicated mainly to a study of the porous structure of activated
carbon. Employment of the contrast matching technique together with SANS led to an
understanding of the process of pore filling resulting from an increase of partial pressure of
contrast matching liquid (deuterated toluene). The Author has designed a special Al alloy
sample cell for the variable vapour pressure SANS experiments. The accessible empty pores
fraction at each p/po is calculated using the Porod Invariant. The data obtained matches the
results from gravimetric measurements of D-toluene adsorption. The fractal nature of
activated carbon is determined via application of the neutron scattering technique. The density
of activated carbon - an important characteristic affecting the total hydrogen uptake - is
found to be Q-dependent with an average saturation limit of 1.85 g/cc. The effect of the
carbon activation process, i.e. the formation of micropores, is illuminated by SANS. Finally, a
novel model, implying exponential decay of the pore size distribution with a lower cut-off, is
proposed and the minimum pore radius is calculated for each experimental partial pressure of
wetting liquid. These results are compared with those derived from the standard Guinier
approximation. The proposed model yields the exact value of D-toluene surface tension when
the derived pore radii are associated to the corresponding pressures via the Kelvin equation
(within the range of its applicability), whereas the Guinier approximation gives an average
value of the D-toluene surface tension approximately twice the tabulated value. Thus, it is
concluded that the novel model presented in this thesis is an improved approximation to the
porous structure of activated carbon.
Additionally, a complimentary double-Gaussian pore size distribution model is
suggested. It highlights the presence of ultramicro- and microporosity and shows a good
agreement with the SANS data for dry activated carbon.

Citation

Mileeva, Z. Production and characterisation of molecular hydrogen storage materials. (Thesis). Salford : University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2011