Bimetallic Copper/iron-Based Water Oxidation Catalysts: Catalysis And Mechanism

Water splitting is a promising approach to obtain the clean energy of hydrogen.In which,water oxidation has be the bottleneck for the constructing of artificial photosynthesis system because of its unfavourable thermodynamics and kinetics.Thus,to develop an efficient,cheap and stable water oxidation catalyst(WOC)becomes an essential issue to enhance the efficiency of the whole water splitting reaction.Currently,Non-precious metal catalysis is one of the fields of solar powered water splitting,such as the development of copper/iron-based water oxidation catalysts.In this thesis,a series of copper/iron-based complexes have been designed and studied as WOCs to probe the effect of the bimetallic cooperative interaction on O-O bond formation.The catalytic abilities and mechanisms have been investigated through electrochemical methods,spectroscopies and DFT calculations in detail.Firstly,a mononuclear copper-based complex has been investigated as WOC in neutral aqueous solution.Experimental and computational results show that this complex is a homogeneous electrocatalyst towards water oxidation.In this catalytic process,the initial oxidation from CuII-OH to CuIII=O is followed by further oxidation to the CuIV=O formation,then the CuIV=O was attacked by water to form the O-O bond and further oxidation to release O2 with a turnover frequency of 0.12 s-1.A preliminary mechanistic study revealed the O-O bond formed through the typical mechanism of WNA rather than the two moieties of CuIII=O coupling intermolecularly.Based on the previous study about the mononuclear copper-based complex,we have designed and synthesized a series of dicopper-based complexes,in which,both of the two Cu atoms are linked by bridged-OH.Experimental results show that all of these complexes can catalyze water to dioxygen effectively in neutral aqueous solution.Compared with the mononuclear catalyst,O-O bond can be formed through bimetallic cooperative interaction between two CuIII centers intramolecularly rather than the high-oxidation-state CuIV=O moiety attacked by molecular water;Meanwhile,the bridged-OH participates in the O-O bond formation.When there is no bridged-OH linked with the two Cu atoms,the dicopper complex exhibits different catalytic kinetics.All of these results indicate that bimetallic cooperative interaction promoted O-O bond formation can be an effective strategy for the design of WOCs.Using the strategy of bimetallic cooperative interaction,we have designed and synthesized a series of diiron complexes.Experimental results show that these diiron complexes can catalyze water oxidation into oxygen efficiently,in which,O-O bond may be formed by the intermolecularly coupling between the two moieties of Fe IV=O rather than by molecular water attacking the high-oxidation-state FeV=O moiety.All the results of electrode kinetics and Raman spectra show that the bimetallic cooperative interaction is essential to O-O bond formation.