The Synthesis And Photoelectrochemical Performances Of Double-armed Polyoxometalates

Solar energy is inexhaustible and clean(green)energy.In recent years,as the world's emphasis on environmental issues,the solar cells with converting solar energy into electrical energy are becoming a hot spot of national scientific researches and focus of industry development and promotion.Dye-sensitized solar cells(DSSCs)have extremely broad application prospect due to the advantages,such as low cost,simple manufacturing process and high stability.The photoanode,as the most important component part of DSSCs,plays the role of transporting electrons,so it is the main factor affecting the photoelectric conversion efficiency and the key research content.At present,increasing the conversion efficiency,reducing cost and improving stability of DSSCs are major development targets.Therefore,it is necessary to further explore low cost and excellent photoelectric materials for speeding up the industrialization of DSSCs.Polyoxometalates(POMs),as a class of metal-oxygen nanoclusters with abundant elements,have the advantages of excellent photoelectric chemical properties and high stability,thus it has important practical significance to research their performances and applicarions in DSSCs.In this paper,on the basis of our previous work,we used trivacant Dawson-and Keggin-type POMs(i.e.{P2W15}and {PW9})as building blocks,and a estertin compound Cl3SnCH2CH2COOCH3 as an organic precursor,respectively,two new double-armed sandwich-type tungstophosphates were designed and synthesized in aqueous solutions by self-assembly,meanwhile the transition metal Co2+ions were also introduced.Especially,a new kind of POM-based photoanode materials were prepared for the first time through grafting these double-armed POMs on TiO2 film.(1)Two double-armed POMs,i.e.carboxyethyltin and Co2+functionalized {PW9}2 and{P2W15}2:Na3K7[{Sn(CH2)2COO}2Co2(B-?-PW9O34)2]·17H2O(PW9-Co-SnR)and {C(N H2)3}12H4[{Sn(CH2)2COO}2Co2(P2W15O56)2]·14H2O(P2W15-Co-SnR)were successfully synthesized.They were determined with X-ray crystallography,element analysis,IR,NMR and etc.The above analytical results confirmed that the organotin groups were successfully introduced into the POM skeletons resulting in two novel inorganic-organic hybrid materials.(2)By ultraviolet-visible spectroscopy,ultraviolet photoelectron spectroscopy,solid diffuse reflection spectrum and surface photovoltage spectrum,the photoelectric properties of PW9-Co-SnR and P2W15-Co-SnR have been characterized.(3)PW9-Co-SnR and P2W15-Co-SnR were attempted to load on the surface of TiO2,which can enhance the photovoltaic performance and photocurrent response of TiO2.Selecting the photoelectrochemical oxidation of methanol as a model reaction,the photoelectrocatalytic activities of the two were evaluated.The photocatalytic performances of TiO2/PW9-Co-SnR and TiO2/P2W15-Co-SnR composite materials were preliminary evaluated.The results exhibited that the TiO2/POMs composite photoelectrodes have higher photoelectrooxidation catalytic activities for methanol in comparison with single TiO2 film.(4)After exploring the photoelectric activities of a series of carboxyethyltin-POM derivatives,it was concluded that the structure of POMs and the species of transition metals affect the photocurrent response of TiO2/POMs photoelectrodes.