A novel synthesis procedure is devised to obtain nitrogen‐doping in hydrogen‐exfoliated graphene (HEG) sheets. An anionic polyelectrolyte–conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen‐containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen‐doped graphene (N‐HEG) sheets are used as catalyst support for dispersing platinum and platinum–cobalt alloy nanoparticles synthesized by the modified‐polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt–Co/N‐HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt–Co alloy nanoparticles on the N‐HEG support, the alloying effect of Pt–Co, and the high electrocatalytic activity of the N‐HEG support. A stability study shows that Pt/N‐HEG and Pt–Co/N‐HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts.

We report a novel way of synthesizing graphene-carbon nanotube hybrid nanostructure as an anode for lithium (Li) ion batteries. For this, graphene was prepared by the solar exfoliation of graphite oxide, while multiwalled carbon nanotubes (MWNTs) were prepared by the chemical vapor deposition method. The graphene-MWNT hybrid nanostructure was synthesized by first modifying graphene surface using a cationic polyelectrolyte and MWNT surface with acid functionalization. The hybrid structure was obtained by homogeneous mixing of chemically modified graphene and MWNT constituents. This hybrid nanostructure exhibits higher specific capacity and cyclic stability. The strengthened electrostatic interaction between the positively charged surface of graphene sheets and the negatively charged surface of MWNTs prevents the restacking of graphene sheets that provides a highly accessible area and short diffusion path length for Li-ions. The higher electrical conductivity of MWNTs promotes an easier movement of the electrons within the electrode. The present synthesis scheme recommends a new pathway for large-scale production of novel hybrid carbon nanomaterials for energy storage applications and underlines the importance of preparation routes followed for synthesizing nanomaterials.

A high hydrogen storage capacity for palladium decorated nitrogen-doped hydrogen exfoliated graphene nanocomposite is demonstrated under moderate temperature and pressure conditions. The nitrogen doping of hydrogen exfoliated graphene is done by nitrogen plasma treatment, and palladium nanoparticles are decorated over nitrogen-doped graphene by a modified polyol reduction technique. An increase of 66% is achieved by nitrogen doping in the hydrogen uptake capacity of hydrogen exfoliated graphene at room temperature and 2 MPa pressure. A further enhancement by 124% is attained in the hydrogen uptake capacity by palladium nanoparticle (Pd NP) decoration over nitrogen-doped graphene. The high dispersion of Pd NP over nitrogen-doped graphene sheets and strengthened interaction between the nitrogen-doped graphene sheets and Pd NP catalyze the dissociation of hydrogen molecules and subsequent migration of hydrogen atoms on the doped graphene sheets. The results of a systematic study on graphene, nitrogen-doped graphene, and palladium decorated nitrogen-doped graphene nanocomposites are discussed. A nexus between the catalyst support and catalyst particles is believed to yield the high hydrogen uptake capacities obtained.

Porous activated carbon or nanostructured carbon materials have a promising future as hydrogen storage media. The hydrogen storage capacity of nanostructured carbon materials can be further enhanced by spillover of atomic hydrogen from a supported catalyst. In the present work, both of these factors have been put to test to study the hydrogen storage capacity of palladium (Pd) nanoparticles dispersed over the surface of functionalized hydrogen-exfoliated-graphene (Pd/f-HEG). The high-pressure hydrogen storage measurements of HEG and Pd/f-HEG show a hydrogen storage capacity of 0.5 and 1.76 wt % respectively at 25 °C and 2 MPa pressure. Functionalization of graphene facilitates uniform dispersion of Pd nanoparticles, which result in an increased hydrogen storage capacity of graphene by 69%. Heats of adsorption have been calculated for HEG and Pd/f-HEG that are consistent with the theoretical calculations from literature and provide an experimental evidence for the spillover effect.

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Recent research developments reveal that nanomaterials, especially carbon nanomaterials, can play a significant role in the performance enhancement of energy conversion and storage devices. The synthesis procedure of nanomaterials, however, remains one of the governing factors for their wide scale implementation. In this paper, an in situ synthesis method to prepare palladium nanoparticle decorated nitrogen doped graphene sheets (Pd/N-SG) using focused solar radiation is developed. The present synthesis technique combines three processes simultaneously, namely (a) graphene sheet formation, (b) nitrogen doping of graphene sheets and (c) metal precursor reduction to metal nanoparticles, in one step through a green approach. The hydrogen storage properties of the Pd/N-SG sample are investigated using high pressure Sievert's apparatus and the sample exhibits an excellent hydrogen storage capacity of 4.3 wt% at room temperature (25 C and 4 MPa hydrogen pressure). The method developed for the synthesis is environmentally benign, easy to adopt and economical. Also, the proposed one-step synthesis method can be easily scaled up to large quantities and this opens a new pathway for the synthesis of nanomaterials for use in the renewable energy field.

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