Summary
The concept of hydrogen as an energy carrier can be realised only if efficacious storage media for hydrogen (H2) are found and developed unto technical maturity. The participants thus examine in this sub-project the H2 sorption behaviour of carbon nanofibres (CNF).
In order to facilitate measurement of CNF H2 sorption capacity depending on H2 pressure and on temperature, a gravimetric apparatus in the form of a modified beam balance was first tested. The measurements' quality and the possible evaluations were demonstrated using a standard sample (carbon). Subsequently, gravimetric determination of H2 sorption capacities of various CNF samples, some of them synthesised by the collaboration partners, and of the standard sample as a reference was determined under different temperatures and H2 pressures. As the CNF's storage capacity is heavily dependent on the thermal pretreatment, the carbon nanofibres were thermally pretreated in an inert-gas flow before the H2 sorption capacity was determined. To examine the correlation between the pretreatment and the adsorption properties, the CNF samples were subjected to thermal treatment in an argon flow and gravimetric measurements were then repeated.
Results:
- A thermogravimetric measurement setup with integrated super-micro scales was developed and optimised for determination of H2 content. It allows determination of sorption properties in gaseous or solid systems in a temperature range from -40° to 500°C.
- Irrespective of sample pretreatment, the various CNF samples show an H2 sorption of < 0.3 mass percent at an H2 pressure of 140 bar and a temperature of 25°C.
- H2 sorption is thus lower than for special activated carbons and for carbon nanotubes. Technical application is not recommended.
- The weak H2 bonding forces lead to a low influence of temperature on the sorption capacity.
