Oxide Coated Titanium Electrode for Oxygen Evolution

This paper gives the review of oxide coated titanium electrodes prepared by thermal decomposition for oxygen evolution in industrial electrolysis such as electrowinning and electroplating. The electrode is prepared by calcination of a precursor solution containing platinum group metals (Ir, Ru) and valve metals (Ta, Ti) on a titanium substrate. The crystallographic structure and surface morphology of the oxide coating depend on the pretreatment of the substrate, the composition and preparation procedure of the precursor solution, thermal decomposition temperature, the coating thickness, and others. The catalytic activity for oxygen evolution is strongly influenced by the structure, particle size, and distribution of platinum group metal oxides such IrO2 and RuO2; a low temperature thermal decomposition produces a mixture of amorphous platinum group metal oxides and valve metal oxides in which platinum group metal oxides are uniformly dispersed in nano size in amorphous valve metal oxide matrix. This unique coating structure results in a high catalytic activity for oxygen evolution in acidic solutions, because of the increase in active surface area. The overpotential for oxygen evolution is reduced compared to traditional Pb alloy electrodes or crystalline oxide coated titanium electrodes, so that the cell voltage of zinc or copper electrowinning is significantly decreased and some unwanted side reactions, i.e., anodic deposition of PbO2 or MnO2 induced by oxidation of Pb (II) or Mn (II) contained in electrowinning solutions, is suppressed. The commercial production and application to electrowinning plants of amorphous oxide coated titanium electrodes for oxygen evolution are in progress, and this new technology is expected to realize a more environmentally friendly electrowinning process.