Carlos Ponce de León

Progress in redox flow batteries, remaining challenges and their applications in energy storage

Redox flow batteries, which have been developed over the last 40 years, are used to store energy on the medium to large scale, particularly in applications such as load levelling, power quality control and facilitating renewable energy deployment. Various electrode materials and cell chemistries have been proposed; some of the successful systems have been demonstrated on a large-scale in the range of 10 kW–10 MW. Enhanced performance is attributable to the improvements in electrodes, separator materials and an increasing awareness of cell design. This comprehensive review provides a summary of the overall development of redox flow battery technology, including proposed chemistries, cell components and recent applications. Remaining challenges and directions for further research are highlighted.

The Rotating Cylinder Electrode (RCE) and its Application to the Electrodeposition of Metals

The application of rotating cylinder electrodes (RCEs) to electrodeposition has progressed significantly over the last decade. New tools for theoretical and experimental investigations have been developed in academia and in industry, with some RCE devices being commercially developed. This paper reviews the continued application of RCEs to quantitative electrodeposition studies of single metals, alloys, and composite, multilayered, and nanostructured electrodeposits with a constant or controlled range of current densities along the RCE under turbulent flow conditions. Rotating cylinder electrode electrochemical reactors, enhanced mass transport, rotating cylinder Hull cell, and uniform and non-uniform current and potential distributions are considered. The applications of ultrasound, porous reticulated vitreous carbon cathodes, expanded metal/baffles, and jet flow around the RCE are also included. The effects of electrolyte flow and cathode current density on electrodeposition have been rationalized. Directions for future RCE studies are proposed.

The 3D Printing of a Polymeric Electrochemical Cell Body and its Characterisation

An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell is highlighted.

Research and development techniques 1: Potentiodynamic studies of copper metal deposition

Summary The electrochemistry of copper (II)/(I) ions in aqueous chloride solution, at pH2, is used to demonstrate the application of voltammetry techniques in characterising electrode processes. The electrolyte used is 1.5 M sodium chloride containing 20 to 50 × 10−3 M cupric chloride at 20°C, in which both Cu(II) and Cu(I) ions are stable. A platinum rotating disc electrode (RDE, radius 0.365 cm) is used to provide controlled mass transport under laminar flow conditions. Cyclic voltammetry, at a stationary disc electrode, is used to characterise the general electrochemistry. Four current peaks due to reduction of Cu(II) ions to Cu(I) ions, deposition of Cu from Cu(I) ions, anodic stripping of Cu to form Cu(I) ions and oxidation of Cu(I) ions to Cu(II) ions are seen. Analysis of the Cu(II)/Cu(I) couple indicates a reversible process. A potential sweep rate experiment allows the diffusion coefficient of Cu(II) ions to be calculated. The anodic stripping peak in the cyclic voltammogram is used to estimate the amount of copper deposited. Reduction of Cu(II) to Cu(I) then to Cu is examined at a range of rotation speeds (150–1870 rpm) using linear sweep voltammetry at the RDE. Mass transport data are obtained in the form of limiting current density as a function of the RDE speed, allowing the diffusion coefficients of Cu(II) and Cu(I) ions to be calculated.

Recent Developments in Borohydride Fuel Cells

Developments in direct borohydride fuel cells (DBFC) are considered together with electrolyte stability and the choice of membrane and electrode materials. The cyclic voltammetry of borohydride oxidation was studied at three electrodes: a) gold on carbon, Au/C, b) gold on titanate nanotubes, Au/TiN and (c) gold foil. Similar currents were observed from the three electrodes. A DBFC in a single, 2- and 4-bipolar cell configuration with Au/C anode and Pt/C cathode produced 2.2, 3.2 and 9.6 W showed cell voltages of 1.06, 0.81 and 3 V, respectively. In another single cell, the reduction of peroxide on a Pd/Ir coated microfibrous carbon cathode was catalytically more active than a platinised-carbon one. The maximum power density achieved was 78 mW cm-2 at a cell voltage of 1.09 V. The need for further research is highlighted, particularly into new electrocatalyst materials

Reactor Design for Advanced Oxidation Processes

Electrochemical reactor design for oxidation processes follows similar engineering principles used for typical electrosynthesis reactors and include considerations of the components materials, electrode and cell geometries, mass transport conditions, rate of reactions, space–time yield calculations, selectivity, modeling, and energy efficiencies. It is common practice to optimize these characteristics at laboratory scale level followed by more practical considerations to build a larger reactor able to accomplish a required performance that can be easily assembled and requires low maintenance and monitoring. The scaling-up process should involve testing a variety of electrode configurations and cell designs to maximize the degradation of a particular pollutant. In this chapter, we describe the general principles of reactor design and list the most typical reactor configurations and performance followed by some recent advances in modeling and further developments.

The influence of iodate ion additions to the bath on the deposition of electroless nickel on mild steel

ABSTRACT An alkaline hypophosphite bath (0.1 M nickel sulphate, 0.2 M sodium hypophosphite, 0.2 M sodium acetate and 0.1 M malic acid, adjusted to pH 5) was used to produce Ni–P coatings on uncoated and electroless nickel pre-plated mild steel. The deposition was monitored by open-circuit potential-time monitoring vs. a saturated calomel reference electrode and potentiostatic current–time monitoring together with anodic and cathodic polarisation. Classical mixed potential theory was applied to the polarisation data to calculate the effect of controlled iodate ion additions (0–1000 ppm) as an accelerator to the electrolyte on the plating rate. The mixed potential and deposition current density increased gradually with potassium iodate concentration. The use of electrochemical data allowed the optimum iodate additive concentration to be established using simple instrumentation.

Understanding the charge storage mechanism of conductive polymers as hybrid battery-capacitor materials in ionic liquids by in situ atomic force microscopy and electrochemical quartz crystal microbalance studies

Safe and sustainable energy storage systems with the ability to perform efficiently during large numbers of charge/discharge cycles with minimum degradation define the main objective of near future energy storage technologies. Closing the gap between high power and energy per unit weight requires new materials that can act as a battery and capacitor at the same time. Conductive polymers have attracted attention as hybrid battery-capacitor materials. However, their potential impact has not been fully investigated because their behaviour, especially in non-aqueous electrolytes such as ionic liquids, is not completely understood. Here, we aim to clarify the fundamental functionality of these hybrid characteristics while studying the interaction between a conductive polymer and an ionic liquid by in situ atomic force microscopy and electrochemical quartz crystal microbalance. The main achievement is the visualisation of the morphological modifications of the conductive polymer depending on the state of charge. These modifications significantly influence the viscoelastic material properties of the polymer. Our combined findings provide a model which explains why conductive polymers behave like (pseudo)-capacitors at a high state of charge and as batteries at a low state of charge. This understanding enables application-orientated synthesis of conductive polymers and their use as high-performance energy storage materials.