Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 140, Issue 4, Pages 1557-1565Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b00032
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Funding
- National Natural Science Foundation of China (NSFC) [21572113, 21661132006]
- Tsinghua University Initiative Scientific Research Program [20151080404]
- National Key Research and Development Program of China [2016YFB0401400]
- National Program for Thousand Young Talents of China
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Water oxidation is the key step in both natural and artificial photosynthesis to capture solar energy for fuel production. The design of highly efficient and stable molecular catalysts for water oxidation based on nonprecious metals is still a great challenge. In this article, the electrocatalytic oxidation of water by Na[(L4-)Co-III], where L is a substituted tetraamido macrocyclic ligand, was investigated in aqueous solution (pH 7.0). We found that Na[(L4-)Co-III] is a stable and efficient homogeneous catalyst for electrocatalytic water oxidation with 380 mV onset overpotential in 0.1 M phosphate buffer (pH 7.0). Both ligand- and metal-centered redox features are involved in the catalytic cycle. In this cycle, Na[(L4-)Co-III] was first oxidized to [(L2-)(CoOH)-O-III] via a ligand-centered proton-coupled electron transfer process in the presence of water. After further losing an electron and a proton, the resting state, [(L2-)(CoOH)-O-III], was converted to [(L2-)Co-IV=O]. Density functional theory (DFT) calculations at the B3LYP-D3(BJ)/6-311++G(2df,2p)//B3LYP/6-31+G(d,p) level of theory confirmed the proposed catalytic cycle. According to both experimental and DFT results, phosphate-assisted water nucleophilic attack to [(L2-)Co-IV=O] played a key role in O-O bond formation.
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