Hydrogen storage in Nickel dispersed boron doped reduced graphene oxide

Abstract

Graphene oxide (GO) based derivatives have been explored for hydrogen storage application, owing to their high surface area, low density and tunable pore size. However, under ambient conditions as desired for transport application, their storage capacity is poor. The use of nanohybrids of graphene oxide decorated with catalyst nanoparticles is emerging as a promising strategy to store atomic forms of hydrogen by invoking the spillover mechanism (in addition to storing molecular forms of hydrogen). Also, doping the substrate (GO) with light heteroatoms such as boron (B) have been envisaged for improving the enthalpy of adsorption of molecular hydrogen on the substrate. In the current work, GO based hybrids namely boron doped reduced graphene oxide (B-rGO) and Ni nanoparticle dispersed B-rGO (Ni-B-rGO) has been synthesized via freeze drying and hydrothermal route. The presence of various phases in the samples was identified using X-ray diffraction. Field-emission scanning electron microscopy was used to study the morphology; especially the 'wrinkling' in the GO based structures. The size and distribution of Ni nanoparticles was studied using transmission electron microscopy (size ∼1–2 nm and inter-particle distance of ∼20 nm). Raman spectroscopy was used to quantify the degree of disorder in the samples and additionally to demonstrate the existence of adsorbed molecular hydrogen. Fourier transform infrared spectroscopy studies showed the presence of various functional groups on carbon and further revealed the presence of atomic hydrogen generated by the spillover mechanism. X-ray photoelectron spectroscopy studies augmented the investigations to show the surface composition of Ni-B-rGO sample. The samples were further characterized for their hydrogen storage capacity using Sieverts apparatus (pressure-composition-isotherms) at three temperatures (77 K, 273 K and 298 K) and 20 bar H2 pressure. The B-rGO sample, showed promising storage capacity of ∼0.24 wt.% at 298 K, which increased to ∼0.58 wt.% at 273 K; which further increased to 8.2 wt.% at 77 K. The storage capacity of the Ni-B-rGO hybrid at the three temperatures (77 K, 273 K and 298 K) are: ∼6.9 wt.%, ∼0.41 wt.% and 0.16 wt.%, respectively.