Development of hybrid materials based on sponge supported reduced graphene oxide and transition metal hydroxides for hybrid energy storage devices

Altres ajuts: Programa Beatriu de Pinós (BP-DGR-2013)Earnest efforts have been taken to design hybrid energy storage devices using hybrid electrodes based on capacitive (rGO) and pseudocapacitive (Ni(OH)₂ and Co(OH)₂) materials deposited on the skeleton of 3D macroporous (indicate sponge material) sponge support. Conducting framework was formed by coating rGO on macroporous sponge on which subsequent deposition of Ni(OH)₂ and Co(OH)₂ was carried out. The synergetic combination of rGO and Ni(OH)₂ or Co(OH)₂) provides dual charge-storing mechanisms whereas 3D framework of sponge allows excellent accessibility of electrolyte to hybrid electrodes. Moreover, to further increase the energy density, hybrid devices have been fabricated with SP@rGO@Ni or SP@rGO@Co and SP@rGO as positive and negative electrodes, respectively. These hybrid devices operate with extended operating voltage windows and achieve remarkable electrochemical supercapacitive properties which make them truly promising energy storage devices for commercial production

Characterization of NiO-Al2O3 composite and its conductivity in biogas for solid oxide fuel cell

NiO-Al O nanocomposite has been synthesized by mixing combustion synthesized powders. The nanocomposite is an effective anode/anode functional layer for intermediate temperature solid oxide fuel cells. The TEM of NiO and Al O revealed spherical particles of 30 nm and platelets of 70 nm, respectively. The XRD analysis of NiO-Al O composite sintered at 900 °C showed presence of cubic NiO and rhombohedral α-Al O which were chemically stable. However, above 1200 °C NiAl O started to appear. The conductivity of NiO-Al O was the highest in hydrogen (4.3 × 10 S/cm at 600 °C). In biogas, the conductivity was 3.2 × 10 S/cm with the activation energy of 0.67 eV. The stability of the composite in biogas was also examined

V2O5 encapsulated MWCNTs in 2D surface architecture : complete solid-state bendable highly stabilized energy efficient supercapacitor device

A simple and scalable approach has been reported for O encapsulation over interconnected multi-walled carbon nanotubes (MWCNTs) network using chemical bath deposition method. Chemically synthesized O/MWCNTs electrode exhibited excellent charge-discharge capability with extraordinary cycling retention of 93% over 4000 cycles in liquid-electrolyte. Electrochemical investigations have been performed to evaluate the origin of capacitive behavior from dual contribution of surface-controlled and diffusion-controlled charge components. Furthermore, a complete flexible solid-state, flexible symmetric supercapacitor (FSS-SSC) device was assembled with O/MWCNTs electrodes which yield remarkable values of specific power and energy densities along with enhanced cyclic stability over liquid configuration. As a practical demonstration, the constructed device was used to lit the 'VNIT' acronym assembled using 21 LED's

Polypyrrole Nanopipes as a Promising Cathode Material for Li-ion Batteries and Li-ion Capacitors : Two-in-One Approach

Lithium ion capacitor (LIC) is a promising energy storage system that can simultaneously provide high energy with high rate (high power). Generally, LIC is fabricated using capacitive cathode (activated carbon, AC) and insertion-type anode (graphite) with Li-ion based organic electrolyte. However, the limited specific capacities of both anode and cathode materials limit the performance of LIC, in particular energy density. In this context, we have developed "two in one" synthetic approach to engineer both cathode and anode from single precursor for high performance LIC. Firstly, we have engineered a low cost 1D polypyrrole nanopipes (PPy-NPipes), which was utilized as cathode material and delivered a maximum specific capacity of 126 mAh/g, far higher than that of conventional AC cathodes (35 mAh/g). Later, N doped carbon nanopipes (N-CNPipes) was derived from direct carbonization of PPy-NPipes and successfully applied as anode material in LIC. Thus, a full LIC was fabricated using both pseudo-capacitive cathode (PPy-NPipes) and anode (N-CNPipes) materials, respectively. The cell delivered a remarkable specific energy of 107 Wh/kg with maximum specific power of 10 kW/kg and good capacity retention of 93 % over 2000 cycles. Thus, this work provide a new approach of utilization of nanostructured conducting polymers as a promising pseudocapacitive cathode for high performance energy storage systems

Aqueous synthesis of LiFePO4 with Fractal Granularity

Altres ajuts: Beatriu de Pinos Program (BP-DGR-2013)Lithium iron phosphate (LiFePO) electrodes with fractal granularity are reported. They were made from a starting material prepared in water by a low cost, easy and environmentally friendly hydrothermal method, thus avoiding the use of organic solvents. Our method leads to pure olivine phase, free of the impurities commonly found after other water-based syntheses. The fractal structures consisted of nanoparticles grown into larger micro-sized formations which in turn agglomerate leading to high tap density electrodes, which is beneficial for energy density. These intricate structures could be easily and effectively coated with a thin and uniform carbon layer for increased conductivity, as it is well established for simpler microstructures. Materials and electrodes were studied by means of XRD, SEM, TEM, SAED, XPS, Raman and TGA. Last but not least, lithium transport through fractal LiFePO electrodes was investigated based upon fractal theory. These water-made fractal electrodes lead to high-performance lithium cells (even at high rates) tested by CV and galvanostatic charge-discharge, their performance is comparable to state of the art (but less environmentally friendly) electrodes

Direct electrodeposition of imidazole modified poly(pyrrole) copolymers : synthesis, characterization and supercapacitive properties

Altres ajuts: Beatriu de Pinós (BP-DGR-2013)In this manuscript we report the direct electrosynthesis of a new conducting copolymer based on the incorporation of imidazole molecules within the polypyrrole chain. Different proportions of the monomers were tested during the direct electropolymerization of the copolymer. The resulting materials were characterized by electrochemical and spectroscopic techniques (Raman and XPS) and a mechanism of polymerization is proposed. Our findings showed that imidazole acts as an inhibitor of the polymerization process, decreasing the overall number of actives sites for the polymerization on the electrode surface producing a polymeric morphology very different compared with pure polypyrrole, as observed by Scanning Electron Microscopy images and corroborated by Electrochemical Impedance Spectroscopy. This behavior significantly affects the supercapacitive performance of the resulting p(Py-IMZ) modified electrodes where the specific capacitance of the material increased from 122 to 201 Fg (64%) at 10 mV s. Furthermore, a unique pseudo-capacitive behavior described herein emphasizes the role of the imidazole as inductor of the morphology and co-monomer in the unique electrochemical signature of the material. The results suggest that the incorporation of IMZ increases the specific capacitance of PPy electrode by around 64%

Capacitive vs Faradaic Energy Storage in a Hybrid Cell with LiFePO4/RGO Positive Electrode and Nanocarbon Negative Electrode

We report an advanced device based on a Nitrogen-doped Carbon Nanopipes (N-CNP) negative electrode and a lithium iron phosphate (LiFePO) positive electrode. We carefully balanced the cell composition (charge balance) and suppressed the initial irreversible capacity of the anode in the round of few cycles.We demonstrated an optimal performance in terms of specific capacity 170 mAh/g of LiFePO with energy density of about 203 Wh kg and a stable operation for over 100 charge-discharge cycles. The components of this device (combining capacitive and faradaic electrodes) are low cost and easily scalable. This device has a performance comparable to those offered by the present technology of LIBs with the potential for faster charging; hence, we believe that the results disclosed in this work may open up new opportunities for energy storage devices

Synthetic approach from polypyrrole nanotubes to nitrogen doped pyrolyzed carbon nanotubes for asymmetric supercapacitors

Pseudocapacitive materials are highly capable to achieve high energy density integrated with high power electrostatic capacitive materials. However, finding a suitable electrostatic capacitive material to integrate with pseudocapacitive material in order to achieve high energy density with good rate capability is still a challenge. Herein, we are providing a novel synthetic approach starting from the synthesis of polypyrrole nanotubes (PPy-NTs) and ending up at the carbonization of PPy-NTs to obtain N-doped carbon nanotubes (N-CNTs). With highly porous nature of PPy-NTs and great graphitic texture with copious heteroatom functionalities, N-CNTs significantly promoted the faradic pseudo-capacitors, demonstrating high single-electrode capacitance over 332 F/g and 228 F/g in 1 M HSO aqueous solution. Further, a novel asymmetric supercapacitor with PPy-NTs as positive and N-CNTs as negative electrode has been fabricated. This PPy-NTs//N-CNTs cell effectively provides high operation voltage (1.4 V) and hence high energy density over 28.95 W h/kg (0.41 mW h/cm) with a high power density of 7.75 kW/kg (113 mW/cm) and cyclic stability of 89.98% after 2000 cycles

Design and Advanced Manufacturing of NU-1000 Metal–Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal–organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation

From thermal to electroactive graphene nanofluids

Here, we describe selected work on the development and study of nanofluids based on graphene and reduced graphene oxide both in aqueous and organic electrolytes. A thorough study of thermal properties of graphene in amide organic solvents (N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone) showed a substantial increase of thermal conductivity and specific heat upon graphene integration in those solvents. In addition to these thermal studies, our group has also pioneered a distinct line of work on electroactive nanofluids for energy storage. In this case, reduced graphene oxide (rGO) nanofluids in aqueous electrolytes were studied and characterized by cyclic voltammetry and charge-discharge cycles (i.e., in new flow cells). In addition, hybrid configurations (both hybrid nanofluid materials and hybrid cells combining faradaic and capacitive activities) were studied and are summarized here