Waste-polystyrene foams-derived magnetic carbon material for adsorption and redox supercapacitor applications

The current impact of plastic waste on the environment and nature pushes for coming up with methods for their efficient reuse and recycle. Expanded polystyrene waste, massively produced worldwide, is presented in this work as a novel precursor of magnetic activated carbons (MAC) for the first time. A simple methodology based on the impregnation of EPS samples with Fe3+ in solution, followed by pyrolysis under Ar pressure and chemical activation is proposed. The as-prepared carbonaceous magnetic materials present nanometric phases of Fe0, Fe3C, and Fe3O4, and showed high specific surface area (672 m2 g−1) and total pore volume (0.35 cm3 g−1), one of the highest found in the carbonaceous magnetic materials literature. Their excellent textural, chemical and electrical properties, combined with the possibility of magnetically collection and regeneration after operation guaranteed an excellent performance of MAC in two different applications: as adsorbents of organic contaminants and as electrodes of redox supercapacitors.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) for the financial support. P.F.R. Ortega acknowledges the FAPEMIG (DOF nº. 2720262/2018). The authors are also grateful to Rede Mineira de Química. R.L. Lavall is recipient of fellowship from CNPq (grant number 313304/2017-3). N. C. F. Machado, K. H. A. Mendes, and L. A. M. de Jesus would like to thank CEFET-MG and FAPEMIG for scholarships receivedPeer reviewe

A highly adhesive PIL/IL gel polymer electrolyte for use in flexible solid state supercapacitors

In this work we have demonstrated how to prepare a novel gel polymer electrolyte (GPE) with remarkable adhesive characteristics by combining a synthesized poly(ionic liquid) consisting of poly(1-vinyl-3-propylimidazolium bis(fluorosulfonyl)imide) (poly(VPIFSI)) and a commercial ionic liquid: 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMIFSI). For this purpose several PIL/IL-GPEs systems (considering the amount of IL) were subjected to electrochemical characterization. The influence of the PIL/IL-GPE (50 wt% of IL) on the properties of a flexible solid state supercapacitor was evaluated using electrochemical impedance spectroscopy, cyclic voltammetry and the galvanostatic charge/discharge technique that allows synchronous measurements of the cell voltage and the potential of the positive and negative electrodes. The influence of the ions on the formation of the electric double layer in the device during cycling employing different conditions and folding angles is discussed. The properties of the adhesive PIL/IL-GPE, such as high conductivity, good interaction between the PIL matrix and the IL liquid phase that prevents any leakage (thereby contributing to greater safety) together with the good adherability and wettability of the gel electrolyte on the electrode surface have produced a device with an improved rate capability and cyclability that undergoes hardly any changes in C,, E, and P of the cell when folded.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil, for the financial support received (Universal 2014, Process No. 458487/2014-7). The authors are also grateful to the Instituto Nacional de Ciência e Tecnologia em Nanomateriais de Carbono – INCT Nanocarbono and to profs. Dorila Piló Veloso and José Dias de Souza Filho (Department of Chemistry/UFMG/Brazil) for performing the NMR analysis. S.A.Alexandre also acknowledges the scholarship received from CNPq. R.L. Lavall is recipient of fellowship from CNPq (grant number 313304/2017-3). R. Santamaría would like to thank financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R)

Nanocompósitos de poliuretana termoplástica e nanotubos de carbono de paredes múltiplas para dissipação eletrostática Thermoplastic polyurethane and multi-walled carbon nanotubes nanocomposites for electrostatic dissipation

<abstract language="eng">Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 &#956;m length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT

High value activated carbons from waste polystyrene foams

Activated carbons (AC) with excellent textural properties have been obtained for the first time from waste polystyrene foam (PF), without any previous treatment, following a simple and conventional two-step procedure (formation of char followed by chemical activation). Even considering that the PF is not a graphitizable material, the best AC produced from this precursor has a very high BET surface area larger than 2700 m2 g−1 and a pore volume of 1.2 cm2 g−1, with a significant contribution of small mesopores. As a consequence, this AC reveals a surprising capacity to adsorption of relatively large molecules and a high specific capacitance when applied as a supercapacitor electrode. The maximum amount of adsorbed methylene blue obtained by batch equilibrium experiments are greater than 1 g g−1. In the context of the technical difficulties and low economic return of the reuse and recycling of waste PF, this work offers a strategic destination for this environmentally unfriendly residue.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) – Brazil for the financial support (PVE 2014, process number 400714/2014-0). Fabiano G. F. de Paula and Paulo F. R. Ortega also acknowledge CAPES and CNPq for the received scholarships, respectively. Financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R) and Principado de Asturias (Fondo Europeo de Desarrollo Regional (GRUPIN 14-118).Peer reviewe

LiFePO4/Mesoporous Carbon Hybrid Supercapacitor Based on LiTFSI/Imidazolium Ionic Liquid Electrolyte

This document is the Accepted Manuscript version of a Published Work that appeared in final form inJournal of Physical Chemistry C , copyright © American Chemical Society after peer review. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.7b09869A hybrid SC prepared with mesoporous carbon as the negative electrode, LiFePO4 as the positive electrode, and a LiTFSI/imidazolium ionic liquid solution as electrolyte is presented. The cell was conceived on the basis that it offers all of the safety features of ionic liquids (IL) and LiFePO4, in addition to the advantages of a high energy density device. Most of the high performance hybrids so far reported in the literature employ aqueous or organic electrolytes, whereas studies of hybrid cells based on IL are still rare. Here, a fundamental study was conducted to understand how the different interfaces and mechanisms operate in a hybrid system based on IL electrolyte and how this affects cell performance. This device was mainly characterized using cyclic chronopotentiometry that allows cell voltage and electrode potentials to be simultaneously recorded. By means of this technique, it was possible to evaluate the overall behavior of the hybrid cell and the faradaic and capacitive electrodes simultaneously and to compare it with the performance of selected standard cells. The results show that the cell is able to attain an energy density of 43.3 W h kg–1 at 0.010 A g–1 (C/5 in relation to LiFePO4), while maintaining a good cycling performance.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) – Brazil for the financial support (PVE 2014, process number 400714/2014-0). Financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R) and Principado de Asturias (Fondo Europeo de Desarrollo Regional (GRUPIN 14-118).Peer reviewe

Insights on the Behavior of Imidazolium Ionic Liquids as Electrolytes in Carbon-Based Supercapacitors: An Applied Electrochemical Approach

This study aims to increase the knowledge on the interactions that occur at the electrode/electrolyte interface in carbon-based electric double-layer capacitors (EDLCs) when solvent-free ionic liquids are used as electrolytes. Many previous studies found in the literature are conducted using theoretical approaches, and they are unable to model all the variables and the complexity of an actual device with a complex carbon surface and an ionic liquid (IL). Here, the compatibility between imidazolium ionic liquids and different carbon materials-an activated carbon (AC), a mesoporous carbon (MES), multiwalled carbon nanotubes (MWCNTs), and reduced graphene oxide (RGO)-is empirically investigated applying synchronous chronopotentiometric tests to various symmetrical EDLCs. The study of the simultaneous evolution of the cell and electrode potentials of the various carbon/ILs cells, monitoring the evolution of specific capacitances and electrical resistances for each independent electrode, allows inferring about the ion-electrode compatibility, the limiting factors for charge accumulation, and its impacts on the performance of the global cell. The results indicate that the sp2 structures of MWCNTs and RGO favor interactions with the EMI+ cation on the negative electrode. In the positive electrodes, MES and AC favor interactions with the BF4- and TFSI- anions, respectively, yielding a higher specific capacitance and lower resistance.The authors thank the Conselho Nacional de Desenvolvimento Cienti ico e Tecnoló gico (CNPq)−Brazil for the financial support (PVE 2014, process number 400714/2014- 0), the Spanish Government and European Union (AEI/ FEDER, EU; project MAT2016-77114-R), N.Q.’s predoctoral contract (BES2017-082038), and Principado de Asturias (FEDER: IDI/2018/000121). The work was partially supported by the Brazilian Institute of Science and Technology (INCT) in Carbon Nanomaterials. P.F.R.O. acknowledges the Fundaca̧ o de Amparo a ̃ ̀Pesquisa do Estado de Minas Gerais (FAPEMIG)−Brazil (DOF no. 2720262/2018). P.F.R.O. and G. A.d.S. also acknowledge the scholarships received from CNPq. R.L.L. is a recipient of a fellowship from CNPq (grant number 313304/2017-3). P.F.R.O, G.G.S., and R.L.L. are members of the Rede Mineira de Quimica (RQ-MG) ́ −Brazil

Mechanism and Stability of a Redox Supercapacitor Based on Methylene Blue: Effects of Degradation of the Redox Shuttle

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Energy Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsaem.8b00384The mechanism of operation of a supercapacitor based on methylene blue (MB) as redox shuttle in cells containing activated carbon as electrodes and aqueous electrolyte has been studied. Attention is focused on the instability of these molecules which can undergo secondary reactions that impact negatively on the cell, generating fluctuations in its performance and reducing its cycling life. It is demonstrated that MB interacts strongly with activated carbons and modifies their structure, decreasing the resistance of the electrodes and increasing the energy density of the cell by more than 40%. It is also shown that MB is not stable in acidic electrolyte at the high potentials attained by the electrodes of the supercapacitor. Demethylation byproducts and oxidized derivates of the MB were detected after cycling by means of electrospray ionization mass spectrometry. These products were observed to cause a constant change in the equilibrium potential of the cell, substantially modifying the storage mechanism and the ranges of operation potential of the electrodes.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) – Brazil for the financial support (PVE 2014, process number 400714/2014-0). Financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R) and Principado de Asturias (Fondo Europeo de Desarrollo Regional (GRUPIN 14-118).Peer reviewe