Experimental and first principle studies on hydrogen desorption behavior of graphene nanofibre catalyzed MgH2

• Published in: International journal of hydrogen energy Vol. 42; no. 2; pp. 960 - 968
• Main Authors: Singh, Milind K., Bhatnagar, Ashish, Pandey, Sunita K., Mishra, P.C., Srivastava, O.N.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 12-01-2017
• Subjects: Carbon nanostructure; DFT; Gaussian 03; Hydrogen storage; MgH2; MgH2; Hydrogen storage; Carbon nanostructure; Gaussian 03; DFT
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2016.09.210

With the combination of experiment and first-principles theory, we have evaluated and explored the catalytic effects of graphitic nanofibres for hydrogen desorption behaviour in magnesium hydride. Helical form of graphene nanofibres (HGNF) have larger surface area, curved configuration and high density of graphene layers resulting in large quantity of exposed carbon sheet edges. Therefore they are found to considerably improve hydrogen desorption from MgH2 at lower temperatures compared to graphene (onset desorption temperature of MgH2 catalyzed by HGNF is 45 °C lower as compared to MgH2 catalyzed by graphene). Using density functional theory, we find that graphene sheet edges, both the zigzag and armchair type, can weaken MgH bonds in magnesium hydride. When the MgH2 is catalyzed with higher electronegative and reactive graphene edge of graphene, the electron transfer occurs from Mg to carbon, due to which MgH2 is dissociated into hydrogen and MgH component. The Mg gets bonded with the graphene edge carbon atoms in the form of CMgH and CH bonds. In the as formed CMgH, the graphene edges “grab” more electronic charge as compared to the normal charge donation of Mg to H. This leads to the weakening of the MgH bond, causing hydrogen to desorbs at lower temperatures.
With the combination of experiment and first-principles theory, we have evaluated and explored the catalytic effects of graphene nanofibres for hydrogen desorption behaviour in magnesium hydride. Helical form of graphene nanofibres (HGNF) have larger surface area, curved configuration and high density of graphene layers resulting in large quantity of exposed carbon sheet edges. [Display omitted]
•Experiment and first-principles study on graphene nanofibres for hydrogen desorption from MgH2.•As compared to graphene, HGNF can considerably improve the hydrogen desorption from MgH2.•Exposed graphene edges in HGNFs can explain the catalytic action of hydrogen desorption from MgH2.•Both the zigzag and armchair graphene edges, lead to a weakening of the MgH bonds in MgH2.•This MgH bond weakening is due to charge transfer to the carbon edges of graphene.