Nanochromics: old materials, new structures and architectures for high performance devices

Due to the development of nanoscience, the interest in electrochromism has increased and new assemblies of electrochromic materials at nanoscale leading to higher efficiencies and chromatic contrasts, low switching times and the possibility of color tuning have been developed. These advantages are reached due to the extensive surface area found in nanomaterials and the large amount of organic electrochromic molecules that can be easily attached onto inorganic nanoparticles, as TiO2 or SiO2. Moreover, the direct contact between electrolyte and nanomaterials produces high ionic transfer rates, leading to fast charge compensation, which is essential for high performance electrochromic electrodes. Recently, the layer-by-layer technique was presented as an interesting way to produce different architectures by the combination of both electrochromic nanoparticles and polymers. The present paper shows some of the newest insights into nanochromic science.Com o desenvolvimento da nanociência, o estudo do fenômeno do eletrocromismo desperta forte e continuado interesse devido à possibilidade de obter maiores eficiências eletrocrômicas, contrastes cromáticos, sintonização de cores e baixos tempos de resposta por meio da montagem de nanomateriais. Estas vantagens são possíveis devido à alta área superficial que os nanomateriais possuem e a enorme quantidade de moléculas orgânicas eletrocrômicas que podem ser facilmente ligadas a nanopartículas inorgânicas como TiO2 ou SiO2. Somado a isto, o contato direto entre o eletrólito e os nanomateriais produz altas velocidades de transferência iônica, com a concomitante compensação de carga rápida, o que é essencial para preparar eletrodos eletrocrômicos de alto desempenho. Recentemente a técnica de deposição eletrostática camada por camada foi apresentada como uma maneira interessante de preparar diferentes arquiteturas combinando nanopartículas e polímeros. O presente trabalho mostra alguns dos últimos avanços em nanocromismo.FAPESPCNPqInstituto do Milênio de Materiais Complexo

Hydrogel-Based Flexible Energy Storage Using Electrodes Based on Polypyrrole and Carbon Threads

Developing new flexible and electroactive materials is a significant challenge to producing safe, reliable, and environmentally friendly energy storage devices. This study introduces a promising electrolyte system that fulfills these requirements. First, polypyrrole (PPy) nanotubes are electropolymerized in graphite-thread electrodes using methyl orange (MO) templates in an acidic medium. The modification increases the conductivity and does not compromise the flexibility of the electrodes. Next, flexible supercapacitors are built using hydrogel prepared from poly(vinyl alcohol) (PVA)/sodium alginate (SA) obtained by freeze–thawing and swollen with ionic solutions as an electrolyte. The material exhibits a homogenous and porous hydrogel matrix allowing a high conductivity of 3.6 mS cm−1 as-prepared while displaying great versatility, changing its electrochemical and mechanical properties depending on the swollen electrolyte. Therefore, it allows its combination with modified graphite-thread electrodes into a quasi-solid electrochemical energy storage device, achieving a specific capacitance (Cs) value of 66 F g−1 at 0.5 A g−1. Finally, the flexible device exhibits specific energy and power values of 19.9 W kg−1 and 3.0 Wh kg−1, relying on the liquid phase in the hydrogel matrix produced from biodegradable polymers. This study shows an environment friendly, flexible, and tunable quasi-solid electrolyte, depending on a simple swell experiment to shape its properties according to its application

Enhancement of organophosphate degradation by electroactive pyrrole and imidazole copolymers

Many chemical warfare agents and agrochemicals are composed by organophosphates, that present high toxicity and difficult spontaneous degradation. Amongst the different catalysts to degrade these compounds, heterogeneous systems stand out since they provide easy recovery of the catalyst. However, the limited diffusion of the substrate decreases the rate of the reactions when compared to homogeneous catalysis. To reach a good efficiency in the dephosphorylation, we created heterogeneous catalysts based on pyrrole and imidazole that can enhance the degradation by different effects; both catalytic activity of imidazole and electroactivity of polypyrrole were evaluated. Spectroelectrochemical studies evidenced that the rate constant changes with the applied potential, indicating different reaction mechanisms with the material in the oxidized and neutral states. In summary, a new perspective allying conducting polymers with chemical catalysts was explored. This cooperative effect should be considered in future works concerning the search for new materials to monitor and eliminate organophosphates

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%

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

Synthesis and characterization of modified electrodes by nanoparticles, looking for a high performant electrochromic material

O presente trabalho descreve a síntese e caracterização de nanopartículas de hidróxido de níquel, puras e aditivadas por cobalto e cádmio, empregando a radiação sonoquímica. Foram obtidas partículas de aproximadamente 5 nm de diâmetro, sendo caracterizadas por HRTEM, espectroscopia Raman e no Infravermelho, Termogravimetria, ICP-OES e Difração de Raios-X. A imobilização das nanopartículas sobre o eletrodo transparente condutor foi efetuada pela técnica de deposição de camadas eletrostáticas e pela deposição eletroforética. Foram obtidos eletrodos eletrocrômicos de alto desempenho, apresentando altos valores de eficiência eletrocrômica e baixos tempos de resposta, evidenciando a arquitetura nanométrica do hidróxido de níquel. A incorporação de aditivos às nanopartículas conferiu uma grande melhora nas propriedades do hidróxido de níquel. A adição de cobalto levou ao deslocamento dos picos redox para valores de potenciais menos positivos, se afastando da reação de desprendimento de oxigênio. A incorporação de cádmio levou a uma diminuição da repulsão eletrostática entre as lamelas do hidróxido, impedindo o chamado efeito , conferindo ao eletrodo uma alta durabilidade.The present work describes the synthesis and characterization of pure Nickel Hydroxide nanoparticles, and with cobalt and cadmium as additives, by applying ultrasound radiation. Were obtained nanoparticles of about 5 nm, being characterized by HRTEM, Raman and Infrared spectroscopies, thermogravimetric, ICP-OES and X-ray diffraction. Nanoparticles immobilization onto conducting glass substrates was performed by adsorption of electrostatic layers and by electrophoretic deposition. High performant electrochromic electrodes were obtained, showing high electrochromic efficiencies and low response times, evidencing the nickel hydroxide nanometric architecture. Additives incorporation on nickel hydroxide nanoparticles provided high improvements on electrochromic properties. Cobalt addition shifted the redox peaks to lower potentials, avoiding by this way the oxygen reaction. Cadmium addition diminished the electrostatic repulsion between layers, avoiding the so-called effect, providing a high durability to the electrochromic electrode

Electrostatic layer-by-layer and electrophoretic depositions as methods for electrochromic nanoparticle immobilization

The present paper describes the immobilization of nanoparticles onto conducting substrates by using both electrostatic layer-by-layer and electrophoretic deposition (EPD) methods. These two techniques were compared in high-performance electrochromic electrodes based on mixed nickel hydroxide nanoparticles. In addition to easy handling, EPD seems to be the most suitable method for the immobilization of nanoparticles, leading to higher electrochromic efficiencies, lower response times and higher stability upon coloration and bleaching cycling. (C) 2008 Elsevier Ltd. All rights reserved.FAPESP[03/10015-3]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP[03/00629-4]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq[152312/2007-2

Eletrodos modificados por hidróxido de níquel: um estudo de revisão sobre suas propriedades estruturais e eletroquímicas visando suas aplicações em eletrocatálise, eletrocromismo e baterias secundárias Nickel hydroxide modified electrodes: a review study concerning its structural and electrochemical properties aiming the application in electrocatalysis, electrochromism and secondary batteries

<abstract language="eng">The present review paper describes the main features of nickel hydroxide modified electrodes covering its structural and electrochemical behavior and the newest advances promoted by nanostructured architectures. Important aspects such as synthetic procedures and characterization techniques such as X-Ray diffraction, Raman and Infrared spectroscopy, Electronic Microscopy and many others are detailed herein. The most important aspect concerning nickel hydroxide is related to its great versatility covering different fields in electrochemical-based devices such as batteries, electrocatalytic systems and electrochromic electrodes, the fundamental issues of these devices are also commented. Finally, some of the newest advances achieved in each field by the incorporation of nanomaterials will be shown

Hybrid core-shell nanostructured electrodes made of polypyrrole nanotubes coated with Ni(OH)2 nanoflakes for high energy-density supercapacitors

This work describes the design of Ni(OH)@PPy-NTs core-shell nanostructures with potential application as an electrode material for supercapacitors. Initially, one dimensional (1D) polypyrrole nanotubes (PPy-NTs) were synthesized through a chemical oxidation mediated soft template-directed route using as the anion the azo dye methyl orange (MO). Subsequently, three dimensional (3D) Ni(OH) nanoflakes were grown onto PPy-NTs by a simple hydrothermal route. This exclusive Ni(OH)@PPy-NTs nano-architecture helps to improve the overall electrochemical performance of the electrode, due to the high surface area provided by 3D nanoflakes and excellent electronic/ionic conductivity of 1D nanotubes. The maximum specific capacitance obtained for Ni(OH)@PPy-NTs was 536 F g with good capacity retention after 1000 charge/discharge cycles. Last but not least, EIS technique showed a low electrochemical series resistance for Ni(OH)@PPy-NTs confirming their promise as a high-performance energy storage material.The authors acknowledge the financial support of the CAPES Foundation, Ministry of Education of Brazil: Process BEX 3196/14-3. Authors appreciate the award to DPD with the support of the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia and the Co-fund programme of the Marie Curie Actions of the 7th R&D Framework Programme of the European Union. Partial funding from Spanish Grant MAT2012-39199-C02-01 is acknowledged. ICN2 acknowledges support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295.Peer Reviewe