Water oxidation catalyzed by two cobalt complexes: new challenges and questions

Abstract

Herein, the water oxidation activities of two cobalt complexes (cobalt(II) phthalocyanine and N,N′-bis(salicylidene)ethylenediamino cobalt(II)) were studied. The experiments showed that at pH 11, N,N′-bis(salicylidene)ethylenediamino cobalt(II) and cobalt(II) perchlorate were active for water oxidation. On the other hand, for cobalt(II) phthalocyanine as a stable complex, no water oxidation was observed. The role of nanosized particles containing Co, P, and O in the electrochemical oxidation of water by cobalt complexes was investigated by some methods. After the water oxidation reaction, both complexes and the cobalt salt were studied and a relationship between the decomposition of the cobalt complex and water oxidation was proposed. A critical point is that on the surface of the electrode, there are some areas without any detectable nanoparticles, and thus, the detection of such cobalt compounds on the surface of the electrode is not easy even by high-resolution visible spectroelectrochemistry and scanning electron microscopy. Such experiments showed that to propose a molecular mechanism for water oxidation in the presence of metal complexes, careful analysis is necessary to rule out the role of nanoparticles.