John D. Watkins

Ion-transfer- and photo-electrochemistry at liquid|liquid|solid electrode triple phase boundary junctions: perspectives

Ion transfer at liquid|liquid junctions is one of the most fundamental processes in nature. It occurs coupled to simultaneous electron transfer at the line junction (or triple phase boundary) formed by the two liquids in contact to an electrode surface. The triple phase boundary can be assembled from a redox active microdroplet deposit of a water-immiscible liquid on a suitable electrode surface immersed into aqueous electrolyte. Ion transfer voltammetry measurements at this type of electrode allow both thermodynamic and kinetic parameters for coupled ion and electron transfer processes to be obtained. This overview summarises some recent advances in understanding and application of triple phase boundary redox processes at organic liquid|aqueous electrolyte|working electrode junctions. The design of novel types of electrodes is considered based on (i) extended triple phase boundaries, (ii) porous membrane processes, (iii) hydrodynamic effects, and (iv) generator-collector triple phase boundary systems. Novel facilitated ion transfer processes and photo-electrochemical processes at triple phase boundary electrodes are proposed. Potential future applications of triple phase boundary redox systems in electrosynthesis, sensing, and light energy harvesting are indicated.

Carbon nanoparticle surface functionalisation: converting negatively charged sulfonate to positively charged sulfonamide.

The surface functionalities of commercial sulfonate-modified carbon nanoparticles (ca. 9-18 nm diameter, Emperor 2000) have been converted from negatively charged to positively charged via sulfonylchloride formation followed by reaction with amines to give suphonamides. With ethylenediamine, the resulting positively charged carbon nanoparticles exhibit water solubility (in the absence of added electrolyte), a positive zeta-potential, and the ability to assemble into insoluble porous carbon films via layer-by-layer deposition employing alternating positive and negative carbon nanoparticles. Sulfonamide-functionalised carbon nanoparticles are characterised by Raman, AFM, XPS, and voltammetric methods. Stable thin film deposits are formed on 3 mm diameter glassy carbon electrodes and cyclic voltammetry is used to characterise capacitive background currents and the adsorption of the negatively charged redox probe indigo carmine. The Langmuirian binding constant K = 4000 mol(-1)dm(3) is estimated and the number of positively charged binding sites per particle determined as a function of pH.

Eutectic ionic liquid mixtures and their effect on CO2 solubility and conductivity

A simple binary system of compounds resembling short-chain versions of popular ionic liquids has been shown to have surprisingly complex properties. Combining methylated versions of pyridinium and pyrrolidinium bis[(trifluoromethyl)sulfonyl]imide gave desirable properties such as low viscosity and high conductivity solubility per unit volume. The binary combinations studied in this study showed that these materials were stable liquids at 50 °C and had a threefold improvement in conductivity over [C6C1im][Tf2N]. Despite the high densities of these materials, 2D-IR studies indicate increased ion mobility, likely due to the lack of hindering alkyl chains.

DEMS-monitoring liquid | gas interfacial ammonia oxidation at carbon nanofibre membranes

Electrochemical ammonia oxidation is of interest in waste treatment as well as in electrochemical sensing applications and demonstrated here at a carbon nanofibre (“bucky-paper”) electrode. The electrode is placed at the aqueous electrolyte | gas interface, and current (cyclic voltammetry) as well as ambient differential electrochemical mass spectrometry (DEMS, cyclic voltbarometry) data are recorded as a function of solution composition and pH. The oxidation of oxalate to CO2 is employed as a test and calibration system. Anodic polarization of the carbon nanofibre membrane in inert aqueous electrolyte is shown to result in direct sustained anodic CO2 evolution. In alkaline aqueous media (starting at pH 9) significant levels of nitrogen from ammonia are produced in competition to CO2 formation from carbon nanofibres without the need for additional catalysts. However, for applications with low level ammonia, catalysts will be required to minimize current losses, carbon nanofibre corrosion, and side product formation.