Insight into a hexanuclear cobalt complex: Strategy to construct efficient catalysts for visible light-driven water oxidation

Abstract

Water oxidation reaction is the bottleneck process of water splitting. The exploration of efficient water oxidation catalysts (WOCs) is of great importance for accelerating this reaction. Herein, a cobalt(II)-containing complex {K2[CoO3PCH2N(CH2CO2)2]}6 (K121) with symmetrical hexameric ring structure and polynuclearity as an efficient visible light-driven WOC is reported. Using [Ru(bpy)3](ClO4)2 as photosensitizer and Na2S2O8 as sacrificial electron acceptor, an optimal oxygen yield of 62.6%, turnover number (TON) of 4350 and turnover frequency (TOF) of 162.6 s−1 are obtained. To the best of our knowledge, this TON and TOF are the highest value among all the catalyst for light driven water oxidation. In addition, a high quantum yield of 60.6% is achieved. Investigation including UV–vis absorption, infrared (IR) spectroscopy, X-ray photoelectron spectroscopy and other techniques confirm that 1 is a stable and efficient catalyst for visible light-driven water oxidation. Collective experiments demonstrate that 1 catalyses visible light-driven water oxidation via water nucleophilic attack (WNA) process and its high activity may be originated from the multiple sites water oxidation catalysis.