Nanomaterials Embedded Nitrogen-Doped Graphene for Advanced Energy Storage and Conversion

A facile synthesis of nitrogen-doped graphene with high atomic percentage of Nitrogen (9.2 at%) including high ratio of pyridinic N and graphitic N has been reported via thermal annealing of graphene oxide with uric acid. The resultant material shows efficient electrochemical properties for capacitances and bifunctional electrocatalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In spite of its remarkable electrochemical properties, the major limitation of the two-dimensional graphene like materials for device fabrication or commercial applications is the restacking nature of the layers. Designing a three-dimensional nanostructure via inserting metal nanoparticles or one-dimensional carbonaceous nanomaterials inside the graphene layers can prevent the restacking of the layers and hence enhance the electrochemical properties of the composites by providing higher electroactive surface area for electrolyte permeation, charge storage as well as active sites for electrocatalysis. To enhance the electrocatalytical activity of the synthesized nitrogen-doped graphene, a hybrid of nickel embedded nitrogen-doped graphene is developed. The composite shows superior noble-metal-free quadrafunctional electrocatalysis of oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and hydrogen peroxide oxidation reaction (HPOR) compared to commercial electrocatalysts of Pt/C and Ru/C. Alternatively, the insertion of carbon nanotubes inside the graphene layers and fabricating a lamellar three-dimensional nanostructure exhibit excellent supercapacitor behavior as fabricated as solid-state supercapacitor and high-rate capable anode for Li-ion battery as well as metal-free bifunctional electrocatalysis of ORR and OER. In addition, the decoration of copper nanoparticles in the three-dimensional nanostructured nitrogen-doped graphene/carbon nanotube composite further improves the conductivity and electrochemical properties via interconnecting network of copper nanoparticles and carbon nanotubes with the graphene layers and have been evaluated for high performance metal-ion battery applications. The resultant composites show promising electrochemical performances for developing as electrode materials for next generation energy storage and conversion devices like solid-state supercapacitor, metal-ion battery, metal-air battery and rechargeable fuel cells

Synthesis of nitrogen-doped graphene via thermal treatment of graphene oxide within methylimidazole and its capacitance performance as electric double layer capacitor

Nitrogen-doped graphene was successfully synthesised from graphene oxide (GO) and 2-methylimidazole composite via thermal treatment under argon flow at 700oC within 1h. This synthesised N-doped graphene exhibits homogeneous nitrogen doping with concentration of ~5% in three different nitrogen configuration namelypyridinic N, pyrrolic N and graphitic N. The electric double layer capacitor (EDLC) made up with this N-doped graphene showed excellent specific capacitance 274 F/g at current density of 1A/g, which was ~7 times higher than GO. This EDLC capacitor showed excellent cyclic stability up to 5000 cycles with capacity retention of ~91%

An Actuarial Analysis of Calibration of Crop Insurance Premiums to Heterogeneous Risks

This paper examines whether the loadings on the crop insurance premium rates for risks such as moral hazard and adverse selection are adequate. From the discrete choice (tobit) analysis conducted, we discover that the premium loadings for 75% coverage level are not adequate, resulting in losses for the Risk Management Agency

Liquid-Crystal-Mediated 3D Macrostructured Composite of Co/Co3O4 Embedded in Graphene: Free-Standing Electrode for Efficient Water Splitting

A free-standing, 3D, macro/microstructured atomic-cobalt/cobalt-oxide-reduced-graphene-oxide (Co/Co3O4-Gr) composite has been developed for complete water splitting. The self-assembled porous morphology associated with the metal/metal oxide active sites makes the whole surface of the electrode conducive toward catalyzing hydrogen and oxygen evolution in alkaline media at a low onset potential. The liquid-crystal-mediated free-standing electrocatalyst shows oxygen evolution at the onset potential of 1.38 V and at the potential of 1.66 V for a current density of 10 mA cm−2. These potentials are comparable to the corresponding values for Ru/C (1.46 and 1.62 V, respectively). In addition, the promising hydrogen evolution performance of our composite compared to Pt/C in alkaline media makes it an efficient bifunctional electrocatalyst for comprehensive water splitting, as well as provides guidance for future electrochemical energy material technologies

Self-assembled N/S codoped flexible graphene paper for high performance energy storage and oxygen reduction reaction

A novel flexible three-dimensional (3D) architecture of nitrogen and sulfur codoped graphene has been successfully synthesized via thermal treatment of a liquid crystalline graphene oxide−doping agent composition, followed by a soft self-assembly approach. The high temperature process turns the layer-by-layer assembly into a high surface area macro- and nanoporous free-standing material with different atomic configurations of graphene. The interconnected 3D network exhibits excellent charge capacitive performance of 305 F g−1 (at 100 mV s−1), an unprecedented volumetric capacitance of 188 F cm−3 (at 1 A g−1), and outstanding energy density of 28.44 Wh kg−1 as well as cycle life of 10 000 cycles as a free-standing electrode for an aqueous electrolyte, symmetric supercapacitor device. Moreover, the resulting nitrogen/sulfur doped graphene architecture shows good electrocatalytic performance, long durability, and high selectivity when they are used as metal-free catalyst for the oxygen reduction reaction. This study demonstrates an efficient approach for the development of multifunctional as well as flexible 3D architectures for a series of heteroatom-doped graphene frameworks for modern energy storage as well as energy source applications

Three dimensional cellular architecture of sulfur doped graphene: self-standing electrode for flexible supercapacitors, lithium ion and sodium ion batteries

Tailoring the planar morphology of graphene and the generation of electron-dense active sites on its surface by heteroatom doping is one potential approach to enhance the charge storage performance of graphene based electrode materials. Herein, we have reported the preparation of a three-dimensional self-standing cellular architecture as sulfur-doped graphene foam (SGF) by using the simple self-assembly of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymer chains on graphene oxide followed by thermal treatment. Successful homogeneous sulfur doping in a three-dimensional (3D) framework of graphene allowed the material to have a large surface area with bulk electroactive regions on the surface for better interfacial contact with electrolyte ions and hence resulted in unprecedented energy storage capability in a flexible aqueous symmetric supercapacitor (367 F g-1 at 1 A g-1), a lithium ion battery (1697 mA h g-1 at 100 mA g-1), and a sodium ion battery (472 mA h g-1 at 50 mA g-1) as a binder-free electrode material. The outstanding electrochemical performance of the material demonstrates the potential of this synthesis approach for various heteroatom-doped self-standing nano-carbon monoliths on a small as well as a large scale for high-performance energy device fabrication for the advancement of modern electronic devices

Edge-Functionalized Graphene/Polydimethylsiloxane Composite Films for Flexible Neural Cuff Electrodes

The design of neural electrodes has changed in the past decade, driven mainly by the development of new materials that open the possibility of manufacturing electrodes with adaptable mechanical properties and promising electrical properties. In this paper, we report on the mechanical and electrochemical properties of a polydimethylsiloxane (PDMS) composite with edge-functionalized graphene (EFG) and demonstrate its potential for use in neural implants with the fabrication of a novel neural cuff electrode. We have shown that a 200 μm thick 1:1 EFG/PDMS composite film has a stretchability of up to 20%, a Young’s modulus of 2.52 MPa, and a lifetime of more than 10000 mechanical cycles, making it highly suitable for interfacing with soft tissue. Electrochemical characterization of the EFG/PDMS composite film showed that the capacitance of the composite increased up to 35 times after electrochemical reduction, widening the electrochemical water window and remaining stable after soaking for 5 weeks in phosphate buffered saline. The electrochemically activated EFG/PDMS electrode had a 3 times increase in the charge injection capacity, which is more than double that of a commercial platinum-based neural cuff. Electrochemical and spectrochemical investigations supported the conclusion that this effect originated from the stable chemisorption of hydrogen on the graphene surface. The biocompatibility of the composite was confirmed with an in vitro cell culture study using mouse spinal cord cells. Finally, the potential of the EFG/PDMS composite was demonstrated with the fabrication of a novel neural cuff electrode, whose double-layered and open structured design increased the cuff stretchability up to 140%, well beyond that required for an operational neural cuff. In addition, the cuff design offers better integration with neural tissue and simpler nerve fiber installation and locking

Self-Assembled N/S Codoped Flexible Graphene Paper for High Performance Energy Storage and Oxygen Reduction Reaction

A novel flexible three-dimensional (3D) architecture of nitrogen and sulfur codoped graphene has been successfully synthesized via thermal treatment of a liquid crystalline graphene oxide–doping agent composition, followed by a soft self-assembly approach. The high temperature process turns the layer-by-layer assembly into a high surface area macro- and nanoporous free-standing material with different atomic configurations of graphene. The interconnected 3D network exhibits excellent charge capacitive performance of 305 F g^–1 (at 100 mV s^–1), an unprecedented volumetric capacitance of 188 F cm^–3 (at 1 A g^–1), and outstanding energy density of 28.44 Wh kg^–1 as well as cycle life of 10 000 cycles as a free-standing electrode for an aqueous electrolyte, symmetric supercapacitor device. Moreover, the resulting nitrogen/sulfur doped graphene architecture shows good electrocatalytic performance, long durability, and high selectivity when they are used as metal-free catalyst for the oxygen reduction reaction. This study demonstrates an efficient approach for the development of multifunctional as well as flexible 3D architectures for a series of heteroatom-doped graphene frameworks for modern energy storage as well as energy source applications