Graphene trap to store hydrogen
doi:10.1038/nindia.2011.23 Published online 18 February 2011
Here's a new way to go around the tough challenge that scientists and industries face while trying to store hydrogen in a solid matrix. Scientists at Bangalore-based Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR ) have worked out a unique storage medium — extremely thin graphite flakes called few-layer graphene — which can capture the gas and release it upon heating or ultra-violet irradiation.
Hydrogen storage solutions in a solid matrix have been proposed earlier in the shape of carbon nanotubes. However, they were capable of storing around three per cent of their weight worth of hydrogen. The JNCASR team has bettered this to five per cent, buried in the layers of graphene.
The team believes that the storage capacity can be increased by another half or one weight percent (wt %). "If so, the storage ability of the graphene would approach the value required by India's Department of Energy," team leader C. N. R. Rao told Nature India.
They employed the common organic reaction called Birch reduction on few-layer graphene samples. The method is widely used to hydrogenate carbon-based materials. They used it successfully to produce hydrogenated samples that contained up to 5 wt % of hydrogen. The hydrogenated graphene broke down readily on heating to 500 °C or on irradiation with UV or laser decomposing the carbon-hydrogen bonds to give back the hydrogen. This demonstrates the possible use of few-layer graphene for chemical storage of hydrogen, the scientists report.
It may be possible to to carry out hydrogenation more effectively by other methods to incorporate an optimum of 7.7 wt % hydrogen, Rao said.
Describing the results as 'important', Rao said they got interested in graphene as a possible storage medium after studies showed that hydrogenation of graphene may be more feasible with multilayer graphene than that with single-layer graphene.
"Such chemical storage of a substantial amount of hydrogen in graphene is indeed noteworthy. We have carried out first-principles calculations to understand the nature of hydrogen in reduced graphene," Rao said.
Since the hydrogen comes out easily on heating or by ultraviolet irradiation, it can be used for various purposes including 'probably for running engines', he added.
The scientists report that the hydrogenated graphene is stable and can be stored over long periods. Gas chromatography studies showed that the hydrogen release began at around 200 °C and the entire amount got released at 500 °C.
- Subrahmanyam, K. S. et al. Chemical storage of hydrogen in few-layer grapheme. P. Nat. Acad. Sci. USA 108, 2674-2677 (2011) | Article |