Electro-polymerisation of 3,4-ethylenedioxythiophene on reticulated vitreous carbon in imidazolium-based chloroaluminate ionic liquid as energy storage material

This work shows the electro-polymerisation of thin film poly(3,4-ethylenedioxythiophene) on three-dimensional reticulated vitreous carbon substrates by cyclic voltammetry and pulsed polymerisation methods from a Lewis neutral chloroaluminate ionic liquid containing 3,4-ethylenedioxythiophene monomer. The polymer composite is attractive as an energy storage electrode for sustainable and high-performance technologies due to its unique properties of battery and capacitor in one system, i.e., the redox reaction occurring simultaneously with the anion doping/de-doping of the conductive polymer with AlCl4- ionic species contained in the ionic liquid. The structure of the polymer films, their doping/de-doping mechanism and the stability in the ionic liquid were characterised by scanning electron microscopy and cyclic voltammetry and compared with films electro-polymerised on planar vitreous carbon. The typical granular and nano/micro-porous polymer structure observed on planar vitreous carbon was successfully replicated on the macro-porous reticulated vitreous carbon surface. The polymer films show approximately 45% higher capacity than films on planar substrates and similar efficient redox behaviour, proofing that the material has hybrid battery-capacitor properties enhanced by the higher area per unit volume of reticulated vitreous carbon

Mass transport and active area of porous Pt/Ti electrodes for the Zn-Ce redox flow battery determined from limiting current measurements

The conversion of soluble cerium redox species in the zinc-cerium redox flow battery and other electrochemical processes can be carried out at planar and porous platinised titanium electrodes. The active area, current density, mass transfer coefficient and linear electrolyte flow velocity through these structures have a direct influence on the reaction yield and the relationship between cell potential and operational current density during charge and discharge of a flow battery. A quantitative and practical characterization of the reaction environment at these electrodes is required. The volumetric mass transfer coefficient, kmAekmAe has been calculated for diverse electrode structures from limiting current measurements for Ce(IV) ion reduction in a laboratory, rectangular channel flow cell. This factor can be used to predict fractional conversion and required electrode dimensions. Platinised titanium felt shows superior kmAekmAe values compared to other materials and is a practical, high performance electrode for the Ce(III)/Ce(IV) ion redox reaction

3D porous metal electrodes: fabrication, characterisation and use

Diverse 3D porous metal electrodes, including meshes, foams and felts, are used in electrochemical flow reactors for a wide range of industrial applications, such as energy storage, electrosynthesis and degradation of pollutants. Recent work centres on the hierarchical decoration and coating of 3D electrodes with catalysts, although the study of their performance in a controlled and reproducible flow and mass transfer environment ought to receive more attention. New advances have considered metal nanofelts and nanomesh porous electrodes with superior electrode surface area. Opportunities are found in additive manufacturing, advanced structural characterization by e.g., X-ray computed tomography, and in the modelling of hydrodynamic characteristics, current distribution and mass transfer coefficient of these electrode materials

Effect of RVC porosity on the performance of PbO2 composite coatings with titanate nanotubes for the electrochemical oxidation of azo dyes

Reticulated vitreous carbon (RVC) of different porosities (20, 45, 60, 80, and 100 ppi—pores per inch) has been used as a large surface area substrate for preparing 3D-like PbO2 coatings (RVC/PbO2) as well as composite coatings with hydrothermally synthesized titanate nanotubes (RVC/PbO2/TiNT) by galvanostatic electrodeposition from baths containing lead(II) methanesulfonate and methanesulfonic acid. The effect of the RVC porosity on the coating thickness, the electrocatalytic behaviour and the ability to remove the colour and total organic carbon (TOC) from solutions containing the azo dye Methyl Orange has been systematically assessed. As shown from scanning electron micrographs, the greatest thickness (up to 120 ?m) was obtained using > 60 ppi, but the ?-PbO2 nanocrystallytes mainly grew on the external surface, leaving mostly uncoated inner RVC stripes and ending in planar-like PbO2-based electrodes. In contrast, thinner but perfectly adherent and homogeneous coating of the inner and outer surface was achieved with 20-60 ppi, showing electrodes with an optimal three-dimensionallity. This was especially confirmed by cyclic voltammograms for the composite coatings, as deduced from their highest electroactivity that can be related to enhanced adsorption onto the TiNT clusters and the larger ability to produce active PbO2(radical dotOHOH). The comparative electro-oxidation of 0.25 × 10?3 mol dm?3 Methyl Orange acidic solutions in 0.05 mol dm?3 Na2SO4 at 0.6 A demonstrated that RVC (45 ppi)/PbO2/TiNT was the optimum material. It allowed the quickest decolourisation, reaching 60% in 2.5 min and > 98% at 45 min, and > 55% TOC abatement at 240 min. The anode presented a perfect surface coverage, with no evidence of RVC degradation. The effect of dye concentration and supporting electrolyte nature was studied, revealing a very positive effect of NaCl

The application of reticulated vitreous carbon rotating cylinder electrodes to the removal of cadmium and copper ions from solution

The removal of cadmium and cupric ions from 0.50 mol dm-3 Na2SO4 at pH 2 and 298 K was studied using a reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The cathode was a 100 pores per linear inch porosity grade with a radius of 0.5 cm, a height of 1.2 cm and a volume of 0.94 cm[3]. The cathode was rotated a constant speed of 1500 rev min-1. A rate enhancement of approximately three times is reported for the removal of cupric ions from a chloride solution (0.05 mol dm-3 cupric ions in 0.1 mol dm-3 NaCl at pH 7) when compared with the analogous reaction in acid sulfate solutions (0.50 mol dm-3 Na2SO4 at pH 2). SEM images of the metal deposit morphology allow the morphology of the metal deposits to be characterised. The deposits showed incomplete coverage of the RVC surface and appreciable roughness developed with time due to dendritic growths

Aluminium deposition in EMImCl-AlCl₃ ionic liquid and ionogel for improved aluminium batteries

Aluminium batteries with non-aqueous electrolyte have initially focused on Lewis acidic ionic liquid systems with heavy Al2Cl7-anions that limit the specific capacity, energy and power. In order to develop the secondary aluminium batteries further for future energy storage beyond lithium-ion, high performance electrolytes that enable efficient aluminium deposition/dissolution must be developed. This work studied the electrodeposition of aluminium from both 1-ethyl-3-methylimidazolium chloride aluminium chloride (EMImCl-AlCl3) ionic liquids with different Lewis acidities, and their gel form- the ionogel. Thereby, cyclic voltammetry, in-operando atomic force microscopy and scanning electron microscopy coupled with energy dispersive X-ray diffraction measurements were used to determine the characteristics of aluminium deposition in the ionic liquid depending on the ratio of AlCl3 to EMImCl. Based on these insights, Lewis acidic and neutral ionic liquids were gelified with polyethylene oxide. The focus was on the feasibility of aluminium deposition in Lewis neutral ionogels containing only lightweight AlCl4-anions. It was proven for the first time that aluminium can be deposited from a Lewis neutral ionogel without any dendrite growth within a very wide potential stability window of 5 V but at a low coulombic efficiency of ≤60%

New insights into the electrochemical formation of magnetite nanoparticles

The electrochemical mechanism of the formation of magnetite nanoparticles is studied. The proposed mechanism suggests the formation of iron hydroxide Fe(OH)2 in the presence of oxygen which produces lepidocrocite (γ-FeOOH) followed by its chemical dehydration. This is in contrast to other reported mechanisms that suggest the reduction of Fe(OH)3 at the cathode. Video frames captured during the electrosynthesis of magnetite, in a typical two-electrode cell, indicate that the nanoparticles form in the region close to the anode. The pH value near the anode and cathode changes with time, indicating the formation of nanoparticles. Additional experiments in a two-compartment cell fitted with a cationic membrane, to avoid direct intermixing of Fe2+ and OH− and possible oxide or oxyhydroxide reduction at the cathode, support this mechanism. The amount of dissolved oxygen in the electrolyte was found to be a key factor to produce magnetite by promoting the transformation of Fe(OH)2 into (γ-FeOOH). Hydrogen bubbling during electrosynthesis does not contribute to the reduction of the oxyhydroxides, according to X-ray diffraction results. The paper presents a proposed mechanism for the formation of magnetite, based on previous and new evidence

The continued development of reticulated vitreous carbon as a versatile electrode material: Structure, properties and applications

The limitations of two-dimensional electrodes can be overcome by using three-dimensional materials having sufficient porosity and active area while offering moderate mass transport rates and a relatively low pressure drop at controlled electrolyte flow rate. In concept, a wide variety of metal, ceramic and composite materials are possible but restrictions are imposed by the need to avoid materials degradation, while maintaining adequate electrical conductivity, sufficient robustness and the possibility of facile scale-up. Despite its fragility, one of the traditional electrode materials used as a porous, three-dimensional electrode is carbon foam, particularly in the 97% vol. porous form of reticulated vitreous carbon, RVC. A time-line indicates that the history of this material dates back over 50 years to the mid-1960s, when it was primarily used as an uncoated material in small-scale, laboratory electroanalysis. Surface modification and diverse coatings have considerably extended the use of RVC. Recent applications are found in sensors and monitors, electrosynthesis, environmental processing and energy conversion. This review highlights the fundamental structure and summarises the physicochemical properties of RVC. Fluid flow through various porosity grades of the material, their active electrochemical area and rates of mass transport are quantified. The diverse applications of RVC in energy conversion, environmental treatment and electrosynthesis are illustrated by selected examples from the authors’ laboratories and others over the last 30 years. Recent research on coated RVC, energy conversion environmental remediation and sensors is highlighted. Critical areas deserving further research and development are propose

Monitoring of zincate pre-treatment of aluminium prior to electroless nickel plating

Zincating is used as a pre-treatment for aluminium prior to electroless nickel deposition during preparation of magnetic computer memory discs. Four immersion zincating solutions were evaluated at 22 oC using single step or double zincating followed by electroless nickel deposition from a (high phosphorus) hypophosphite bath at 90 oC. The coating process was monitored by potential vs. time curves obtained under open-circuit conditions during zincating then electroless nickel plating. The surface morphology of the aluminium at various stages, was imaged by scanning electron microscopy and atomic force microscopy. Zero resistance ammetry was used to record galvanic currents between the aluminium and an inert platinum counter electrode during zincating

A high-performance, bifunctional oxygen electrode catalysed with palladium and nickel-iron hexacyanoferrate

The development of air-breathing cathodes, which utilise atmospheric oxygen, enables the construction of lightweight, high energy density metal-air batteries and fuel cells. Air electrodes can be very lightweight and thin because the active material, oxygen, does not need to be stored inside the cell. However, air electrodes are restricted by poor reaction kinetics and low activity of many catalysts towards the oxygen evolution and reduction reactions. In addition, it is a challenge to maintain chemical and mechanical stability of the catalyst and supporting materials at oxidising currents under the strong alkaline conditions commonly used,and gas evolution. This paper reports a novel bifunctional oxygen electrode with remarkable stability, able to perform at current densities up to 1,000 mA cm-2 and withstand 3,000 cycles continuously. The electrode is catalysed by a mixture of Pd/C and mixed nickel-iron hexocyanoferrate, which have high activities towards the ORR and OER reactions, respectively.<br/