Effectiveness factor of fast (Fe3+/Fe2+), moderate (Cl2/Cl−) and slow (O2/H2O) redox couples using IrO2-based electrodes of different loading

The effectiveness factor, E f , (fraction of the electrode surface that participates effectively in the investigated reaction) of fast (Fe 3+ /Fe 2+ ), moderate (Cl 2 /Cl − ) and slow (O 2 /H 2 O) redox couples has been estimated using IrO 2 -based electrodes with different loading. The method of choice was linear sweep voltammetry (measurement of the anodic peak current) for the Fe 3+ /Fe 2+ redox couple and steady-state polarization (determination of the exchange current) for the O 2 and Cl 2 evolution reactions. The results have shown that the effectiveness factor depends strongly on the kinetics of the investigated redox reaction. For the Fe 3+ /Fe 2+ redox couple, effectiveness factors close to zero (max 4%) have been obtained contrary to the O 2 evolution reaction where effectiveness factors close to 100% can be achieved, all being independent of IrO 2 loading. For the Cl 2 evolution reaction, intermediate values of the effectiveness factor have been found and they decrease strongly, from 100% down to about 60%, with increasing loading.