The Performance of RuO2 and IrO2 Coating in Electrolysis Process

The Performance of RuO2 and IrO2 Coating in Electrolysis Process

Dissolution of the electrocatalytic coating can lead to electrode failure. An Increase in the anode current density due to partial removal/wear of coating from the substrate is dissolution. The pH of electrolytes and electrolyte impurities also influences coating dissolution.

In highly oxidizing environments, RuO2 is unstable and tends to oxidize to higher oxidation states. In acidic electrolytes, RuO2 tends to oxidize to soluble RuO3 or volatile RuO4. In alkaline electrolytes, RuO2 tends to oxidize to volatile RuO4 or to perruthenate species. These processes lead to the dissolution of the active material in the coating, thus leading to coating failure. The presence of TiO2 in the coating reduces dissolution; however, this may cause passivation leading to the selective dissolution of ruthenium ions at the surface. RuO2 is stable for ClERs but unstable under oxidizing conditions for OERs as ruthenium is believed to oxidize to a higher volatile oxidation state.

Slow dissolution rate has been reported for IrO2 under chlorine evolution conditions in straight polarity. Deactivation of iridium tantalum electrode is reported to be related to long term polarization at higher overpotentials of IrO2. This can be caused by IrO2 oxidizing to a higher valent state or decomposing to IrO3. IrO2, however, is much more stable than RuO2 under oxidizing conditions. Thus, commercial anodes used for oxygen evolution utilize IrO2 based coating instead of RuO2.