Why IrO2 Ta2O5 Coating on Titanium Substrate is the Best Anode for Oxygen Evolution Reaction (OER)?

Why IrO2 Ta2O5 Coating on Titanium Substrate is the Best Anode for Oxygen Evolution Reaction (OER)?

Efficient electrowinning (EW) in aqueous sulfate electrolytes depends on fast reaction kinetics, low ohmic resistance, and suppression of parasitic and detrimental reactions. The overall cell voltage is determined by the thermodynamic potentials for metal deposition (cathode) and oxygen evolution (anode), in addition to overpotentials and ohmic voltage drops. The sluggish reaction kinetics of the oxygen evolution reaction (OER) in low-pH sulfate electrolytes leads to rather a high anode overpotential at industrial relevant current densities, thus being a significant contributor to an increased cell voltage.

The low pH, moderate temperature, and high anode potential in aqueous metal electrowinning limit the anode material selection significantly, a few materials are stable at these operating conditions. Therefore, identifying an efficient anode catalyst to facilitate the OER by lowering the overpotential is important in copper electrowinning.

The stability and service lifetime of the anodes are just as important as the electrocatalytic activity. Ru oxide catalysts are known to be the most active for OER, but not stable enough for long term operation in the acidic environment. IrO2 is also very active toward OER and significantly more stable than RuO2, but also suffers from some degradation during prolonged operation.  

It is reported that the 70 mol% IrO2 – 30 mol% Ta2O5 catalyst coating on titanium substrate gave by far the best electrocatalytic activity toward the OER. Thus, the industrial OER catalyst benchmark today is comprised of an oxide mixture of IrO2 and Ta2O5, where both catalytic activity and stability are considered. These oxide catalysts are deposited onto pretreated titanium substrate and commonly referred to as dimensionally stable anodes (DSA).