Electrochemical Polymerization Provides a Function-Integrated System for Water Oxidation.

Water oxidation (2H 2 O → O 2 + 4H + + 4e - ) is a key reaction for obtaining the protons and electrons required to produce chemical energy from abundant source. In nature, the reaction is efficiently catalyzed by a metal-complex-based catalyst, so-called the oxygen evolving complex (OEC). In the OEC, several amino acid residues surrounding the catalytic center act as hole transporter, and greatly contribute for promoting the efficiency of the reaction. In other words, the catalytic center surrounded by hole transporters is essential to achieve efficient water oxidation. However, in the artificial systems, there is no example of the water oxidation system which has a catalytic center surrounded by hole transporters. Here, we present a facile strategy to integrate catalytic centers and hole transporters into one system. Electrochemical polymerization of a tetranuclear cobalt cubane complex with carbazole moieties afforded the polymer-based material ( Poly-1 ) with hole-transporting biscabazole moieties. Poly-1 was confirmed to exhibit excellent hole-transporting ability and catalyze water oxidation with high faradaic efficiency and a low overpotential. Control experiments revealed that the catalytic activity was almost suppressed in the absence of biscarbazole moiety, which indicates the importance of the integration of catalytic center and hole transporters. The present study provides a novel strategy for constructing efficient molecule-based systems for water oxidation.