Highly Stable Mixed Metal Oxide Anodes for Industrial Electrochemical Processes

Abstract

The development of an efficient and stable anode for electro-oxidation of water or electrochemical oxygen evolution has great potential in several commercially significant industrial electrochemical processes. In many of these electrochemical processes the oxygen evolution overpotential and physicochemical properties of the anode needs to be tailored to achieve required current efficiency without compromising the durability characteristics of the electrode. However, the existence of porous morphology in the surface layer of many commercially available mixed metal oxide electrodes significantly impacts the durability characteristics when employed in electroplating, electrowinning and metal recovery processes. The generation of the gas within the pores of the surface layer disintegrates the electrode material and leads to mechanical instability during extended periods of operation. In addition, the mixed metal oxide electrodes with porous structure deteriorate rapidly in certain organic solvents, such as methanol under acidic conditions.1 The rapid dissolution of the titanium substrate occurs when this electrolyte enters through pores and cracks into the active oxide coating layer, eventually resulting in the passivation of the titanium substrate surface under electrochemical control or disintegration of the surface layer. Further, electrochemical advanced oxidation process for wastewater treatment applications require anodes having high oxygen evolution overpotential.2 Antimony-doped tin oxide3 and boron-doped diamond4electrodes are considered as possible electrode materials for these applications. However, the stability of the tin oxide based electrodes is limited and the cost effective large scale production of boron-doped diamond coated titanium is yet to be developed. For this instance, the right combination of physical and chemical properties is crucial to the successful fabrication of a highly stable and efficient anode. In this study, a fine distribution of the platinum group metal oxide and valve metal oxides were achieved in different layers of the catalyst coating in order to achieve the required combination of physical and electrochemical properties to suit a specific electrochemical application.5 This fine distribution of the metal oxides in different layers of the coating avoids the formation of porous structure and forms a compact and smooth layer and alters the conductivity, oxygen evolution overpotential of the electrodes. Further, a specific metal oxide layer was coated on top of the titanium substrate in order to reduce the oxidation of organic additives such as levelers and brighteners used in electroplating processes and to suppress the corrosion of the titanium substrate. These tailored modifications in turn greatly enhance the electrochemical activity of the anode and improve the stability of the electrode. Therefore, the developed anodes have required oxygen evolution overpotential and structural stability to sustain in different environments for extended periods. The developed anodes have great potential in various electrochemical processes e.g., electroplating, electrowinning, metal recovery, advanced oxidation process during wastewater treatment, cathodic protection and water electrolysis.