Rupali Nagar

Synthesis of graphene-multiwalled carbon nanotubes hybrid nanostructure by strengthened electrostatic interaction and its lithium ion battery application

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.

Effect of nitrogen doping on hydrogen storage capacity of palladium decorated graphene.

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.

Synthesis and investigation of mechanism of platinum–graphene electrocatalysts by novel co-reduction techniques for proton exchange membrane fuel cell applications

In this paper, we demonstrate two novel green synthesis methods for preparing platinum–graphene catalysts for proton exchange membrane fuel cell (PEMFC) applications. Starting from graphite oxide, the platinum precursor is added and the composite is separately subjected to (a) focused solar radiation and (b) hydrogen gas, for carrying out simultaneous reduction of graphite oxide to graphene and platinum complexes to platinum nanoparticles. These co-reduction methods employ a single agent, namely either sunlight or hydrogen gas, to accomplish the reduction process. Both techniques are therefore cost and energy effective and capable of large scale production. Rotating disc electrode (RDE) and PEMFC measurements reveal the high performance of these electrocatalysts as compared to commercial Pt–C electrocatalysts due to high oxygen reduction reaction (ORR) activity. Stability studies show that both catalysts are highly stable under acidic medium. The proposed methods are quite general in their applicability and we believe that these can be extended for synthesizing a wide variety of electrocatalysts such as various metal, metal oxide or metal alloy nanoparticle decorated carbon nanostructures.

Solar light assisted green synthesis of palladium nanoparticle decorated nitrogen doped graphene for hydrogen storage application

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.

Recent advances in hydrogen storage using catalytically and chemically modified graphene nanocomposites

The need for efficient and renewable energy fuels is growing stronger with environmental consciousness, stringent emission norms, rising fossil fuel prices and their depleting stocks. Hydrogen could be a significant replacement for fossil fuels if targets of volumetric and gravimetric densities required for the automobile industry can be met. In this regard, hydrogen economy and hydrogen storage have become thrust areas of research in the past few decades. It is possible to store hydrogen in the solid state as chemically bound hydrogen using metal/alloy nanostructures with favorable adsorption sites. These nanoparticles when dispersed over suitable carbon nanomaterials exhibit better storage capabilities and improved adsorption–desorption kinetics. High surface area carbon supports such as graphene favor good dispersion of catalyst nanoparticles alleviating their agglomeration and modulating the interaction strength between hydrogen atoms and metal nanoparticles by providing pathways for chemi–physisorption of hydrogen in these nanocomposites. In this review, the contribution of chemically modified graphene-based materials and their composites with metal/alloy catalyst nanostructures in the field of hydrogen storage is reviewed and its future outlook discussed.

Investigation of oxygen reduction and methanol oxidation reaction activity of PtAu nano-alloy on surface modified porous hybrid nanocarbon supports

We investigate the electrocatalytic activity of PtAu alloy nanoparticles supported on various chemically modified carbon morphologies towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). The surface-modification of graphene nanosheets (f-G), multi-walled carbon nanotubes (f-MWNTs) and (graphene nanosheets-carbon nanotubes) hybrid support (f-G-MWNTs) were carried out by soft functionalization method using a cationic polyelectrolyte poly-(diallyldimethyl ammonium chloride). The Pt and PtAu alloy nanoparticles were dispersed over chemically modified carbon supports by sodium-borohydride assisted modified polyol reduction method. The electrochemical performance of all electrocatalysts were studied by half- and full-cell proton exchange membrane fuel cell (PEMFC) measurements and PtAu/f-G-MWNTs catalyst comparatively yielded the best catalytic performance. PEMFC full cell measurements of PtAu/f-G-MWNTs cathode electrocatalyst yield a maximum power density of 319 mW cm−2 at 60 °C without any back pressure,which is 2.1 times higher than that of cathode electrocatalyst Pt on graphene support. The high ORR and MOR activity of PtAu/f-G-MWNTs electrocatalyst is due to the alloying effect and inherent beneficial properties of porous hybrid nanocarbon support.

Photocatalysts for hydrogen generation and organic contaminants degradation

Abstract The availability of water, which is the basis for all life forms, makes life on our planet possible. Plants naturally convert water into hydrogen and oxygen by photosynthesis that is useful for sustaining life. However, with the world’s increasing population comes an increasing demand for water. In fact, many parts of the world face a water crisis either because of the geographical location, the misuse of water, and/or the mismanagement of the wastewater coming from residential areas and industrial complexes, problems that sooner or later will become a crisis if not managed in a timely and effective way. Therefore judicious use of the available water resources and development of a structured wastewater management system are needed. This chapter focuses on two solar energy-based uses of nanocomposites, namely decontamination of organic pollutants in water and hydrogen production. The hydrogen released via photocatalysis of water can be stored and used as an energy carrier. Semiconducting nanocrystals and polymer nanocomposites present viable options for solving the water contamination problems.

Metal-semiconductor core–shell nanomaterials for energy applications

Technological advances have led to higher energy demands across the world, which are largely met by fossil fuels. Many countries have resolved to bring down their carbon footprint by implementing newer, greener, and renewable sources of energy. Efforts to design materials with different physicochemical properties have led to engineering core–shell (CS) nanomaterials. The choice of shell and core is driven by the end-use for which nanoparticles are synthesized. CS nanomaterials have been successfully employed in energy conversion and storage applications like solar cells, fuel cells, rechargeable batteries, supercapacitors, and so on. This chapter discusses the role of CS nanomaterials for energy conversion and energy storage, especially by fuel cells, supercapacitors, and lithium-ion batteries and their structure-property relationship.

Metal-semiconductor core-shell nanomaterials for energy applications. A volume in micro and nano technologies

Technological advances have led to higher energy demands across the world, which are largely met by fossil fuels. Many countries have resolved to bring down their carbon footprint by implementing newer, greener, and renewable sources of energy. Efforts to design materials with different physicochemical properties have led to engineering core–shell (CS) nanomaterials. The choice of shell and core is driven by the end-use for which nanoparticles are synthesized. CS nanomaterials have been successfully employed in energy conversion and storage applications like solar cells, fuel cells, rechargeable batteries, supercapacitors, and so on. This chapter discusses the role of CS nanomaterials for energy conversion and energy storage, especially by fuel cells, supercapacitors, and lithium-ion batteries and their structure-property relationship.

Chapter 5 – Metal-semiconductor core–shell nanomaterials for energy applications

Technological advances have led to higher energy demands across the world, which are largely met by fossil fuels. Many countries have resolved to bring down their carbon footprint by implementing newer, greener, and renewable sources of energy. Efforts to design materials with different physicochemical properties have led to engineering core–shell (CS) nanomaterials. The choice of shell and core is driven by the end-use for which nanoparticles are synthesized. CS nanomaterials have been successfully employed in energy conversion and storage applications like solar cells, fuel cells, rechargeable batteries, supercapacitors, and so on. This chapter discusses the role of CS nanomaterials for energy conversion and energy storage, especially by fuel cells, supercapacitors, and lithium-ion batteries and their structure-property relationship.