AbstractThe in situ spectrocyclic voltammetric investigations of the dimeric ruthenium complex used for water oxidation, (bpy)2(H2O)Ru–O–Ru(H2O)(bpy)24+(H2O–RuIII–RuIII–OH2), were carried out in a homogeneous aqueous solution and in a Nafion membrane under different pH conditions. The in situ absorption spectra recorded for the dimer show that the dimer H2O–RuIII–RuIII–OH2complex underwent reactions initially to give the detectable H2O–RuIII–RuIV–OH and H2O–RuIII–RuIV–OH2complexes, and at higher positive potentials, this oxidized dimer underwent further oxidation to produce a presumably higher oxidation state RuV–RuVcomplex. Since this RuV–RuVcomplex is reduced rapidly by water molecules to H2O–RuIII–RuIV–OH2, it could not be detected by absorption spectrum. Independent of the pH conditions and homogeneous solution/Nafion membrane systems, the dimer RuIII–RuIVwas detected at higher potentials, suggesting that the dimer complex acts as a three‐electron oxidation catalyst. However, in the Nafion membrane system it was suggested that the dimer complex may act as a four‐electron oxidation catalyst. While the dimer complex was stable under oxidation conditions, the reduction of the dimer RuIII–RuIIIto RuII–RuIIled to decomposition
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