硫酸酸性メタノール減極亜鉛電解用アノードの試作

抄録

Platinum-based catalytic films were formed on titanium rods by thermal decomposition technique to study their performance as anodes for methanol oxidation reaction in zinc electrowinning from sulfuric acid bath. The films were alloyed with other platinum group metals as iridium, ruthenium and rhodium to improve their catalytic activity for the methanol depolarization reaction, which was evaluated as roughness factor (RF) of the films by the cyclic voltammetry technique to determine the charge for the reduction of surface monolayer oxide. The values of RF were approximately doubled by the addition of collodion to the coating solution. The electrooxidation of methanol at constant current is accompanied by the degeneration of the catalyst observed as a rise in potential. The potential rise decreases linealy with the logarithm of the methanol concentration up to 1M at 20mA/cm² and 3M at 40mA/cm², and assumed already a steady value at higher concentrations. The extent of the degeneration was estimated as a function of rate constant and rate order of the reaction by formal application of the kinetic equation. liegeneration of the deactivated electrodes was also conducted by (a) applying current pulses to oxidate poisnous organic residues adsorbed, (b) breaking the electrolysis for 9 minutes at 0.78V vs. RHE and (c) exposing the electrodes to air for one hour every 47 hours. Technique (c) worked effectively to retain high activity for a long duration. Changes of the values of RF, determined after the operations for 2020 hours at 20mA/cm² and for 1600 hours at 40mA/cm², gave little losses of the platinum component of the catalysts showing the stability of the electrodes in long-term operations.