Alumina composite electrodes

Shaw, B.R., and Creasy, K.E. 1988. Carbon composite electrodes containing alumina, layered double hydroxides, and zeolites. Journal of Electroanalytical Chemistry 243, 209-217. 

This move from the modification of electrodes to the modification of nonconducting surfaces in contact with electrodes is also seen in systems in which electrodes are modified using nonconduct ive particles. For example, Zak and Kuwana showed that the basic surface of alpha-alumina imbedded in glassy carbon electrodes caused catalysis of the electrooxidation of catechol and other organic species requiring loss of a proton for their oxidation JJ ), Similar results were obtained by Shaw and Creasy (78) using alumina or layered-double hydroxides in composite electrodes (vide infra). 

Particles may also be incorporated into composite-type electrodes. Zeolites have been incorporated into carbon paste (91,9 ) and TTF-TCNQ has been incorporated into polymer paste (115). Solid crosslinked-polystyrene-composite electrodes modified with alumina, layered double hydroxides, and zeolites were shown to have useful analytical and electrocatalytic properties (78). 

The investigations [40], using model fuel cells (Figure 2.5a), were started with iron oxides, magnesium ferrite (following Biefeld [41]) and composites of iron and alumina as electrodes and were continued mainly with thin porous layers of platinum, nickel and iron. Very soon it was seen that completely gastight solid electrolyte discs of highly pure substances had to be produced if the... 

The oxidation reactions were performed in a 200 cm glass reactor, equipped with gas distributer, condenser, thermometer, measuring and reference electrodes. The mixing frequency of the magnetic stirrer was 1500 min 75 mg Pt or 450 mg Pt-on-alumina catalyst was prereduced in nitrogen atmosphere at 60 °C with 3.67 g or 3.00 g 1-phenylethanol, respectively. The solvent composition was 35 cm water +... 

The resulting pastes, for all cases, were placed into a PVC cylindrical sleeve body. The conducting composite material glued to the copper contact was cured at 40°C during a week. Before each use, the surface of the electrode was wet with doubly distilled water and then thoroughly smoothed, first with abrasive paper and then with alumina paper (see more details on the preparation of GECE in Procedure 7). 

Incorporate the neodymium magnet into the body of the paste of graphite-epoxy composite, 2 mm under the surface of the electrode [1] and continue placing the paste until filling all the cavity. Cure the conducting composite at 40°C during 1 week. Once the resin is hardened, polish the surface first with abrasive paper and then with alumina paper. 

Instead of the system silica/silicate also other systems such as titania/titanate, zirconia/zirconate can be used as a reference system [xiv]. The response time of freshly fabricated thick-film sensors based on thin-film /3-alumina is very short (about 15 ms at 650 °C). After several weeks of operating this time increases 10 times (150 ms) [xv]. Solid electrolyte C02 sensors using Ni/carbonate composite as measuring electrode are suited for measuring of C02 in equilibrated water gases [xiv]. Using semiconducting oxides and carbonates like ITO (indium tin oxide) Nasicon-based C02 sensors are able to measure at room temperature [xvi]. 

The choice of the ingredients used for mechanical polishing (felt or cloth, alumina powder or diamond paste, etc.) is dictated by the hardness of the metal and its chemical properties. Soft metals (such as gold) are more difficult to polish than hard metals because the polishing material can possibly be buried into the metal and consequently modify the chemical composition of the electrode surface (see Section IV.6). 

The inlet gas composition is the MCFC anode inlet gas composition 64% hydrogens % carbon dioxide and 20% water vapour the carbonate used is an eutectic mixture of 62 % Li2C03 and 38 % K2C03. The cell temperature was kept constant at 923 K.The outlet gas was led through a water lock to prevent air inlet. The reference electrode consisted of an alumina tube filled with carbonate and with a small hole (app. 0.1 mm diameter) in the bottom. The function of the hole is to realise contact between the melt in the reference electrode compartment and in the working electrode compartment. The reference gas was a mixture of 14% oxygen and 30% carbon dioxide, balanced with nitrogen. 

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