• Energy Research

Numerical simulations of the non-uniform current, potential and concentration distributions along the cathode of a rotating cylinder Hull (RCH) cell (RotaHull® cell) are performed using finite element methods. Copper electrodeposition from an acid sulfate electrolyte is used as a test system. Primary, secondary and tertiary current distributions are examined. The importance of controllable and uniformly accessible hydrodynamics along the length of the RCH cathode is demonstrated. Charge transfer kinetics are described by a Tafel approximation while mass transport is considered using a Nernstian diffusion layer expression. The effects of applied current density and electrode rotation speeds on the distribution of potential and current along the RCH cathode are investigated. An expression of the primary current distribution and a dimensionless mass transport correlation facilitate comparisons with the simulations.

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.

A review of micro to macro-scale activities, challenges and perspectives for redox flow battery modelling is presented.

Abstract The technical performance for the operation of a stand alone redox flow battery system for solar energy storage is presented. An undivided reactor configuration has been employed along with porous graphite felt electrodes and ruthenium acetylacetonate as electrolyte in acetonitrile solvent. Limiting current densities are determined for concentrations of 0.02 M and 0.1 M ruthenium acetylacetonate. Based on these, operating conditions for 0.02 M ruthenium acetylacetonate are determined as charging current density of 7 mA/cm2, charge electrolyte superficial velocity of 0.0072 cm/s (through the porous electrodes), discharge current density of 2 mA/cm2 and discharge electrolyte superficial velocity of 0.0045 cm/s. An optimum power output of 35 mW is also obtained upon discharge at 2.1 mA/cm2. With an increase in the concentration of ruthenium species from 0.02 M to 0.1 M, the current densities and power output are higher by a factor of five approximately (at same superficial velocities) due to higher mass transport phenomenon. Moreover at 0.02 M concentration the voltage efficiency is better for battery full of electrolytes prior to charging (52.1%) in comparison to an empty battery (40.5%) due to better mass transport phenomenon. Voltage efficiencies are higher as expected at concentrations of 0.1 M ruthenium acetylacetonate (55% when battery is full of electrolytes and 48% when empty) showing that the all-ruthenium redox flow battery has some promise for future applications in solar energy storage. Some improvements for the system are also discussed briefly.

Abstract In this article, the novel concept of using magnetic nanofluidic electrolyte for redox flow batteries is demonstrated for the first time. In this regard, the stable magnetic nanofluidic electrolytes are prepared by dispersing magnetic modified multiwalled carbon nanotubes (MMWCNTs) in the positive electrolyte of a polysulfide-iodide redox flow battery at mass concentrations of less than 0.3 g L−1. The electrochemical behavior of magnetic nanofluidic electrolyte was examined using cyclic voltammetry at different mass concentrations of MMWCNTs with a carbon felt electrode. Higher and stable peak current densities were observed at larger mass concentrations of MMWCNTs. A polysulfide-iodide redox flow battery was employed to evaluate the influence of magnetic nanofluidic electrolyte on the battery performance for various mass concentrations, velocities of flowing electrolyte, and current densities using electrochemical impedance spectroscopy, polarization, and galvanostatic charge-discharge experiments. A decrease in ohmic resistance as well as reductions in the charge-transfer and mass-transfer resistances were observed for the magnetic nanofluidic electrolyte compared to those obtained in the absence of MMWCNTs. Adding MMWCNTs to the positive electrolyte at the mass concentration of 0.3 g L−1 results in enhanced performance of the polysulfide-iodide redox flow battery, whereby the peak power density increases by 45% and an energy efficiency of 79.91% was obtained at a current density of 20 mA cm−2. Moreover, high coulombic efficiency close to 100% and stable cycling performance over 200 cycles were achieved using magnetic nanofluidic electrolyte. After 50 cycles, at a current density of 30 mA cm−2, the energy efficiency of the battery operated with magnetic nanofluidic electrolyte remains 10% greater than that obtained in the absence of MMWCNTs. Besides improving the battery performance, MMWCNTs can be separated and recovered using magnetic decantation during electrolyte replacement for redox flow batteries involving high capacity fade and precipitation, which preserves system cost-benefits. The magnetic nanofluidic electrolyte could be applied for different redox solutions using appropriate magnetic nanoscale conductors. This innovative concept opens up a new opportunity to develop the next generation of high-performance and low-cost flow batteries.

Abstract We have observed the formation of substoichiometric TiC 1− x on the surface of cathodes during the solid state electroreduction of TiO 2 to Ti in CaCl 2 melt electrolytes at ∼950 °C for 11–22 h. This synthetic method for generating TiC 1− x relies on reducing carbonate ions, transported from a graphite annulus anode to a partially reduced cathode, to CaO and C followed by the interstitial diffusion of C into α-Ti at the cathode surface.

A numerical model of flow-through porous electrodes is presented. This model simulates the distribution of potential and current density within a porous electrode. The model includes consideration of the electron transfer control regime of the electrode reaction, mass transport limitations and the finite conductivity of the electrode material. The results show an optimum in the total current per unit of projected area.