As part of a programme to develop a high power density, Al/air battery with a NaCl brine electrolyte, the high rate dissolution of an aluminium alloy containing tin and gallium was investigated in a small volume cell. The objective was to define the factors that limit aluminium dissolution in condition that mimic a high power density battery. In a cell with a large ratio of aluminium alloy to electrolyte, over a range of current densities the extent of dissolution was limited to ∼1000 C cm−2 of anode surface by a thick layer of loosely bound, crystalline deposit on the Al alloy anode formed by precipitation from solution. This leads to a large increase in impedance and acts as a barrier to transport of ions.

Imaging with a high-speed camera at a resolution of 10–20 μm has been used for the direct observation of the anodic dissolution of aluminium alloys containing Sn and Ga. The imaging allows confirmation that hydrogen bubble evolution occurs from the Sn inclusions within rounded pits during both open circuit corrosion and anodic dissolution. Using microelectrodes with only a few Sn inclusions in their surface, it is shown that the evolution of H2 is not continuous and may be correlated with a potential oscillations between −1.50 V (where H2 evolution occurs) and significantly less negative potentials (where no H2 is evolved). It is proposed that this potential shift is associated with pH changes resulting from H2 evolution itself.

The structure of thick lead dioxide deposits (approximately 1 mm) formed in conditions likely to be met at the positive electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. Compact and well adherent layers are possible with current densities >100 mA cm−2 in electrolytes containing 0.1–1.5 M lead(II) and methanesulfonic acid concentrations in the range 0–2.4 M; the solutions also contained 5 mM hexadecyltrimethylammonium cation, C16H33(CH3)3N+. From the viewpoint of the layer properties, the limitation is stress within the deposit leading to cracking and lifting away from the substrate; the stress appears highest at high acid concentration and high current density. There are, however, other factors limiting the maximum current density for lead dioxide deposition, namely oxygen evolution and the overpotential associated with the deposition of lead dioxide. A strategy for operating the soluble lead-acid flow battery is proposed.

The structure of lead deposits (approximately 1 mm thick) formed in conditions likely to be met at the negative electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. The quality of the lead deposit could be improved by appropriate additives and the preferred additive was shown to be the hexadecyltrimethylammonium cation, C16H33(CH3)3N+, at a concentration of 5 mM. In the presence of this additive, thick layers with acceptable uniformity could be formed over a range of current densities (20–80 mA cm−2) and solution compositions. While electrolyte compositions with lead(II) concentrations in the range 0.1–1.5 M and methanesulfonic acid concentrations in the range 0–2.4 M have been investigated, the best quality deposits are formed at lower concentrations of both species. Surprisingly, the acid concentration was more important than the lead(II) concentration; hence a possible initial electrolyte composition is 1.2 M Pb(II) + 5 mM C16H33(CH3)3N+ without added acid.

Aluminium alloys containing small additions of both tin (∼0.1 wt%) and gallium (∼0.05 wt%) are shown to dissolve anodically at high rates in sodium chloride media at room temperatures; current densities >0.2 A cm−2 can be obtained at potentials close to the open circuit potential, ∼−1500 mV versus SCE. The tin exists in the alloys as a second phase, typically as ∼1 μm inclusions (precipitates) distributed throughout the aluminium structure, and anodic dissolution occurs to form pits around the tin inclusions. Although the distribution of the gallium in the alloy could not be established, it is also shown to be critical in the formation of these pits as well as maintaining their activity. The stability of the alloys to open circuit corrosion and the overpotential for high rate dissolution, both critical to battery performance, are shown to depend on factors in addition to elemental composition; both heat treatment and mechanical working influence the performance of the alloy. The correlation between alloy performance and their microstructure has been investigated.

The electrochemistry of a 13% Cr stainless steel (API5CT L80-13Cr) in 3% NaCl containing acetate and either acetic acid or carbon dioxide at 333 K is explored using RDE voltammetry. The reduction of proton, carbonic acid and acetic acid occur simultaneously, immediately negative to the corrosion potential. Acetic acid gives a well formed reduction wave and the current densities increase with the equilibrium concentration of acetic acid in the medium; in the plateau region, the reduction is mass transport controlled. Despite this reduction process, the corrosion resistance and passivation current density are independent of the acetic acid concentration. It is confirmed that the 13% Cr stainless steel is much more resistant to corrosion that X65 carbon steel and, unlike the carbon steel, its rate of corrosion does not vary with acetic acid concentration. The properties of the passivating film appear to dominate the behaviour of the 13% Cr stainless steel.

The voltammetry of nanostructured palladium layers electrodeposited from a hexagonal liquid crystal phase onto platinum microdiscs show well defined peaks for the adsorption/desorption of hydrogen and surface oxidation/reduction in 2 M NaOH. These peaks are more clearly resolved than at smooth palladium and reveal the complications associated with hydrogen adsorption/desorption on palladium in aqueous alkaline solutions. The reduction of nitrite at the nanostructured palladium is also reported and it is shown that it occurs via a mechanism involving a chemical reaction between adsorbed hydrogen and adsorbed nitrite ion.

This series of papers will describe the chemistry, electrochemistry and performance of a flow battery with no separator and a single electrolyte, lead(II) in methanesulfonic acid. Voltammetry at rotating disc electrodes is used to define the conditions for the high rate deposition and dissolution of lead and lead dioxide in aqueous methanesulfonic acid. The determination of lead methanesulfonate solubility and solution conductivity as a function of lead methanesulfonate and methanesulfonic acid concentrations was carried out in order to aid the selection of the electrolyte for the battery.

The design and performance of a small redox flow battery is described; it is based on a single undivided, parallel plate cell with carbon electrodes and an acidic lead methanesulfonate electrolyte. It is shown that the cell operates as a secondary battery at charge/discharge current densities of 10–60 mA cm−2. Typically, the voltage during discharge is ∼1.55 V, Coulombic efficiency >85% and the energy efficiency ∼65%.

The corrosion of carbon steel, oilfield pipelines is accelerated when the anion of a weak acid (usually considered to be acetate) is present in the carbon dioxide saturated brines that usually accompany the production of the oil. This paper reports the voltammetry of such media at both platinum and carbon steel (X65) rotating disc electrodes in order to demonstrate that the solution composition as well as the surface films determine the rate of corrosion. It is shown that the cathode reactions at Pt and in the corrosion process at steel are the parallel reduction of free proton and the strongest proton donor in the solution. In these solutions, the strongest proton donor is acetic acid and at the usual pH of the brines, the concentration of acetic acid is substantially higher than that of the free proton. As a result, the concentration of the proton donor, the undissociated weak acid, rather than the pH, is a critical factor determining the rate of corrosion of the steel. A quantitative interpretation of the voltammetry and the corrosion behaviour requires a knowledge of the speciation within these complex aqueous solutions and in this paper, the speciation is calculated using equilibrium constants from the literature and a computer package (phreeqc 2.2).