Bicarbonate/carbonate are efficient co-catalysts in a variety of water oxidation processes. Their role in these processes is due to one or more of the following: the redox potential of the couple CO3 ⋅−/CO3 2– is considerably lower than that of OH[rad]/H2O or that of OH[rad]/OH−. The CO3 ⋅− thus formed is transformed into HCO4 −/H2O2. The latter are easily oxidized to form O2. Furthermore CO3 2– as a ligand stabilizes transition metal complexes at high-oxidation states that are essential intermediates in the catalytic processes. Finally, the carbonate facilitates proton transfer near the anode that is often an essential step.