(585n) Transition Metal Halides for Solid State Ammonia Storage: The CoX2-NH3 System (X=Cl-I)

Transition Metal
Halides for Solid State Ammonia Storage; the CoX₂-NH₃
System (X=Cl-I)"

J.Alnawmasi, D.H.Gregory,*

*  School of Chemistry, University
of Glasgow, G12 8QQ,  Glasgow. Tel: 0141 330 8128, duncan.gregory@glasgow.ac.uk

 Keywords:
ammonia, storage, cobalt, halides,
reversible, solid state.

Abstract:
Ammonia has attracted interest as a promising alternative fuel for internal
combustion engines due to the fact that ammonia does not release carbon dioxide
during combustion but equally NH₃ could be used directly with fuel
cells.[1] Storing ammonia in the form of metal ammines is the most notable way
to overcome the challenges that are related to the use of NH₃ in
liquid form namely the toxicity and corrosive nature of ammonia.[2] Ammine
complexes of light transition metal halides such as (Co, Ni) are very promising
candidates because they exhibit high ammonia contents and they are relatively stable
at room temperature.We have found that the CoX₂ (X = Cl, Br, I)
systems are interesting candidates and especially cobalt chloride as it
possesses a NH₃ capacity of 44 wt. % and desorption is completed by
330 °C. We are currently investigating the chemical and structural properties
of the Co halides during both ammonia uptake (at ambient conditions) and
ammonia release (upon heating). The ammoniated metal halides were studied by
powder X-ray diffraction, FTIR and Raman spectroscopy. The crystal structure of
the hexammine has been determined and the products of the first and second
decomposition steps were confirmed as the respective diammine and monoammine.
The thermal properties of the hexammine cobalt halides were studied by
TPD(TG-DTA-MS) measurements. These measurements were intended to investigate
their deammoniation properties and the products of decomposition. In addition,
the cycling behaviour and the stability of the ammoniated cobalt chloride in
air were also investigated (figure1).

Figure1.
The
cycling  behaviour of CoCl₂.6NH₃.

 References:

[1]
Steele, R. B. Chemtech 1999, (August), 28.

[2]
C. H. Christensen, R. Z. Sørensen, T. Johannessen, U. J. Quaade, K. Honkala, T.
D. Elmøe, R. Køhler, J. K. Nørskov, J. Mater. Chem., 2005, 15, 4106–4108.