Electron tubular electrodes

In order to determine whether the new nanotubule electrode shows improved performance, a control electrode composed of the same material but prepared via a more conventional method is required. This control LiMn204 electrode was prepared by applying the precursor solutions described above directly onto a 1 cm Pt plate and thermally processing as before. Scanning electron micrographs showed that these films consisted of LiMn204 particles with diameters of —500 nm [124]. Spectrophotomet-ric assay showed that this control electrode also contained 0.75 mg of LiMn204 per cml A polypyrrole coat identical to that applied to the tubular electrode (0.065 mg) was also applied to this control electrode. 

The microtubular electrode concept described here also offers another possible advantage. In these concentric tubular electrodes, each particle of the Li intercalation material (the outer tube) has its own current collector (the inner metal microtubule). This could be an important advantage for Li+ intercalation materials with low electrical conductivity. This advantage was not demonstrated here because TiS2 has relatively high electronic conductivity. We have recently shown that electrochemical synthesis can be used to coat the gold microtubular current collector with outer mbes of a... 

Definition of terms a = diameter of inlet, A = electrode area, b = channel height, C = concentration (mM), F = Faraday constant, D = diffusion coefficient, v = kinematic viscosity, r = radius of tubular electrode, U = average volume flow rate, u = velocity (cm/s), n = number of electrons. Source Adapted from Ref. 84. 

Whilst the kinetic parameters of an electron-transfer reaction can be obtained in an identical fashion under laminar conditions [where u is now given by eqn. (58)] as illustrated by Blaedel [66], it is evident that the dependence of u on the cube root of the solution velocity in the laminar case [eqn. (58)] compared with the -dependence under turbulent conditions [eqn. (166)], implies that faster electron-transfer reactions can be investigated via the latter route. This is best illustrated with a practical example. Using flow rates characterised by Reynolds numbers up to 2 x 105 at a tubular electrode 7 pm in length within a tubular cell of radius 5 mm, Vielstich and co-workers [99] were able to measure a and ke for the ferro-ferricyanide redox couple (at 33.5°C). Their experimental data, in terms of a plot of In ut vs. (E - Ee), is represented in Fig. 50. The slope of both of the linear... 

An optimized design employing a tubular electrode in a cylindrical cavity has been described [638]. The mechanism and kinetics of the electrooxidation of several para-haloanilines and the follow-up reactions in acetonitrile have been investigated with this cell [639]. A similar design that is suitable for low temperature measurements (233 K) has been reported [640]. It has been employed in a study of the temperature dependence of the reduction of bromonitrobenzene in acetonitrile solution. The electroreduction of perinaphthenone in a single electron process has been investigated with this cell [641]. The lifetime of the neutral radical formed by deprotonation of the radical anion has been estimated to be around 1 min. A similar electrochemical behavior of benzanthrone was observed. 

The decreased contribution due to slow electron transfer kinetics for the microtubular electrode is also attributable to the higher underlying surface area of the tubular current collector. Because the surface area is higher, the effective current density for the microtubular TiS2 is less than for the thin film TiS2, which has a conventional planar current collector. The decreased contributions of film resistance and slow electron transfer kinetics also account for the higher peak current density of the microtubular electrodes (Fig. 27). 

Kobayashi et conducted steam electrolysis experiments using SrZrg gYbo.iOj. 5 tubular electrolytes (2-mm walls) with platinum electrodes (cermet with the electrolyte powder) at low temperatures (460 to 600°C) and was successful in generating hydrogen and oxygen. They used the low temperatures in an attempt to avoid excessive electronic (hole) conductivity in the electrolyte. 

Two-electrode cells have also been used in measurements of the solid-state electronic conductivity of nanoparticles and other materials. A typical cell is a concentric tubular structure with an inner dimension on the order of a few mm where a pair of disk-shaped electrodes can be plugged in and sandwich the electrol)de confined within a tubular interior (Figure 2.2). To maintain good contact between the electrode and the electrolyte, the two electrodes have to be pressed in where the interelectrode distance can be accurately... 

---