E.P.L. Roberts

Chromium redox couples for application to redox flow batteries

Abstract Both anodic and cathodic chromium–EDTA (ethylenediaminetetra-acetate) complex redox processes have been studied using cyclic voltammetry. Their potential use in a redox battery has been evaluated by comparing the charge and discharge performance of a simple redox battery employing several redox couples including the conventional Fe–Cr redox couples. The cyclic voltammetry experiments suggested that oxidation of Cr(III)–EDTA formed Cr(V)–EDTA rather than a hexavalent chromium species. It was found that the kinetics of the Cr(III)–EDTA/Cr(II)–EDTA redox reaction are fast at a graphite rod electrode, whereas the Cr(V)–EDTA/Cr(III)–EDTA redox reaction is relatively slow. In spite of the slow kinetics, the battery employing solely these chromium–EDTA based redox couples provided higher energy output and longer life than the conventional Fe–Cr redox system.

A review of metal separator plate materials suitable for automotive PEM fuel cells

In this paper we review the range of materials which have been studied for use as separator plates in automotive PEM fuel cells, with particular emphasis on metals. For commercial application separator plates must be resistant to corrosion, durable and offer low contact resistance in a fuel cell stack. Graphite and carbon composite materials have been widely used, as they offer durability and give reliable performance. For portable and transport applications, new materials offering reduced cost, weight and volume are needed. Metal plates may offer a compact, low cost alternative to graphite and carbon based composites. However in the aggressive fuel cell environment, corrosion of metal plates can significantly effect fuel cell performance while passivation can also lead to increased ohmic losses. The only metal plate material studied in the literature which meets the performance targets for contact resistance and corrosion is gold coated stainless steel. New corrosion resistant coatings are being developed in order to address these significant issues and this review paper evaluates them in the context of the DOE targets established for 2010.

Structural and electrochemical characterisation of Pt and Pd nanoparticles electrodeposited at the liquid/liquid interface

We present the first reported characterisation by x-ray diffraction and high resolution transmission electron microscopy of metals electrodeposited at the bare and templated liquid/liquid interfaces. Additional structural information is also obtained using ion transfer voltammetry as an in situ characterisation tool. In particular, the metallic deposits are shown to consist of aggregates of discrete nanoparticles, predominantly between 3 and 5 nm in diameter. Deposition of platinum at the liquid/liquid interface is reported for the first time, which enables a preliminary comparison to be made between the growth mechanism of this metal and the growth of palladium, previously reported at this interface.

Electrodeposition of palladium nanoparticles at the liquid-liquid interface using porous alumina templates

Abstract Alumina membranes, with mean pore diameters of 100 nm, have been used as templates to control the electrodeposition of palladium. Deposition occurs at the polarised water–organic interface, leading to the formation of nanoparticles. The particles are formed at the mouth of the alumina pores, the locus of their formation being dictated by the position of the organic–water interface. It is shown that the relative position of the liquid phases with respect to the alumina is controlled by the surface wetting properties of the liquids, rather than gravity. This in turn controls the interfacial position and hence the size of the particles deposited. The presence of the alumina membrane prevents agglomeration. Electrochemical and electron microscopy data are presented in support of this proposed deposition mechanism.

Continuous water treatment by adsorption and electrochemical regeneration

This study describes a process for water treatment by continuous adsorption and electrochemical regeneration using an air-lift reactor. The process is based on the adsorption of dissolved organic pollutants onto an adsorbent material (a graphite intercalation compound, Nyex(®)1000) and subsequent electrochemical regeneration of the adsorbent leading to oxidation of the adsorbed pollutant. Batch experiments were carried out to determine the adsorption kinetics and equilibrium isotherm for adsorption of a sample contaminant, the organic dye Acid Violet 17. The adsorbent circulation rate, the residence time distribution (RTD) of the reactor, and treatment by continuous adsorption and electrochemical regeneration were studied to investigate the process performance. The RTD behaviour could be approximated as a continuously stirred tank. It was found that greater than 98% removal could be achieved for continuous treatment by adsorption and electrochemical regeneration for feed concentrations of up to 300 mg L(-1). A steady state model has been developed for the process performance, assuming full regeneration of the adsorbent in the electrochemical cell. Experimental data and modelled predictions (using parameters for the adsorbent circulation rate, adsorption kinetics and isotherm obtained experimentally) of the dye removal achieved were found to be in good agreement.

Segregated Hybrid Poly(methyl methacrylate)/Graphene/Magnetite Nanocomposites for Electromagnetic Interference Shielding

Nanocomposites of poly(methyl methacrylate)/reduced graphene oxide (PMMA/rGO) without and with decorated magnetite nanoparticles with a segregated structure were prepared using emulsifier-free emulsion polymerization. Various characterization techniques were employed to validate the presence of the nanofillers and the formation of the segregated structure within the nanocomposites. The percolation threshold of the nanocomposites was found to be 0.3 vol %, while a maximum electrical conductivity of 91.2 S·m-1 and electromagnetic interference shielding effectiveness (EMI SE) of 63.2 dB (2.9 mm thickness) were achieved for the PMMA/rGO nanocomposites at a loading of 2.6 vol % rGO. It was also observed that decorating rGO with magnetite nanoparticles (hybrid nanocomposites) led to a tremendous increase in EMI SE. For instance, 1.1 vol % PMMA/rGO nanocomposites indicated an EMI SE of 20.7 dB, while adding 0.5 vol % magnetite nanoparticles enhanced EMI SE to 29.3 dB. The excellent electrical properties obtained for these nanocomposites were ascribed to both superiorities of the segregated conductive structure and magnetic properties of the magnetite nanoparticles.

Reaction and diffusion in a lamellar structure: the effect of the lamellar arrangement upon yield

The yield of a competitive–consecutive chemical reaction in a lamellar structure is shown to be strongly influenced by the order in which the lamellae are arranged. Average measures of lamellar width, which take no account of the particular arrangement of the lamellae, perform poorly in predicting the yield. As the number of lamellae is increased, the range of possible yields grows with the number of permutations of the lamellae. The results are a warning that in order to match results from a lamellar model with experiment one needs a good deal of detailed information about the lamellae, beyond their mean width.

All-Chromium Redox Flow Battery for Renewable Energy Storage

The charge/discharge characteristics of an undivided redox flow battery, using porous electrodes and chromium-EDTA electrolyte are discussed. The results indicate that a high current efficiency can be achieved using this system with single pass, flow through electrodes. With 0.2 M electrolytes and a charging current density of 30 mA cm−2, 100% current efficiency was achieved with 48% conversion of Cr(III) to Cr(II). However, the overall energy efficiency of charge/discharge of this redox flow battery was less than 7%. The results suggest that this poor efficiency was associated with the slow kinetics and consequently large overpotential of the Cr(V)-EDTA/Cr(III)-EDTA redox couple.

Charge–Discharge Performance of a Novel Undivided Redox Flow Battery for Renewable Energy Storage

The redox flow battery is ideal for utility-scale renewable energy storage applications. In this work, a novel undivided battery employing porous flow through electrodes is investigated. Because of low charge–discharge efficiencies reported in previous work employing high superficial electrolyte velocities and current densities, three electrolyte systems are investigated here at two concentrations (0.02 and 0.1 M) employing low-current densities and superficial velocities: [Ru(acac)3] in acetonitrile, [Fe(bpy)3(ClO4)2] in acetonitrile, and VOSO4 in aqueous sulphuric acid (all-vanadium system). The highest energy efficiencies are obtained with the all-vanadium system: 13.4% for 0.02 M electrolyte and 12.0% for 0.1 M electrolyte.

Electrochemical quantification of high-affinity halide binding by a steroid-based receptor

The strength of binding between a cholapod receptor and halide anions is quantified using voltammetry at the liquid/liquid interface, revealing very high affinities and size-selectivity peaking at chloride.