Preparation And Photovoltaic Performance Of Polyoxometalates/BiVO₄ Composite Photoanodes

As energy crisis and environmental issue are getting worse nowadays,it shows significant importance to achieve the effective conversion and storage of solar energy utilizing semiconductor photoelectric functional materials.Monoclinic BiVO4,as a catalyst with good response to visible light,possesses various excellent qualities,such as non-toxicity,being economical,appropriate band gap and stable physicochemical properties.With these advantages,BiVO4 is widely used in water oxidation,degradation of pollutants and solar cell etc.However,BiVO4 has a bad photoelectric conversion in actual application,which is mainly due to the ultrafast recombination of photogenerated electron-hole pairs.As a class of good electron acceptors,polyoxometalates(POMs)can well capture and transport the photogenerated electrons in semiconductors to reduce the fast recombination of carriers and thus improve the photovoltaic performance of semiconductors.In this paper,BiVO4 and BiVO4/POMs composite film electrodes were prepared using different methods with BiVO4 as the main material and POMs as the modified component,and their photovoltaic performance were thoroughly investigated.Specific work is presented as follows:1.BiVO4 was synthesized by wet chemical method using Bi(NO3)3·5H2O and NH4VO3 as the raw materials.POMs were introduced through impregnation method;and BiVO4 and BiVO4/POMs composite film electrodes were fabricated by doctor blade technique.The photoelectrocatalytic test under visible light showed that the introduction of POMs remarkably improved the oxygen production ability of BiVO4.And the type and content of POMs had a relatively high impact on the photoelectric response.Among all the film electrodes,the B-Co-2 showed the best photoelectric response by an improving ratio of 2.6.It indicates that POMs can effectively inhibit the fast recombination of photogenerated electron-hole pairs in BiVO4,which is further confirmed by the experimental data of surface photovoltage spectroscopy and fluorescence analysis.2.The BiVO4,BiVO4/NiTsPc,BiVO4/PW12,and BiVO4/PW12/NiTsPc nanofilm electrodes were prepared by a modified metal-organic decomposition method.The linear sweep voltammetry tests showed that the incorporation of PW12 significantly enhanced the photoelectrocatalytic water oxidation performance of BiVO4 by an improving ratio of 4.0;and the introduction of NiTsPc further strengthened the photoelectric response of BiVO4/PW12 composite by an improving ratio of 5.4.In addition,the introduction of NiTsPc alone could also improve the photovoltaic performance of BiVO4 to a certain extent.The results of transient photocurrent curve and electrochemical impedance spectroscopy also confirmed the above conclusions.In composite system,the PW12 effectively captured and transmitted photogenerated electrons,while the NiTsPc functioned well as hole-transporting agent.3.BiVO4 nanoparticles were prepared by ball milling using Bi2O3 and V2O5 as raw materials.After the incorporation of PW12,BiVO4 and its composite were prepared into film electrodes by screen printing.Dye-free solar cells were fabricated with the above electrodes as photoanodes,and I-V curves were tested.Compared with the BiVO4 photoanode,the short-circuit current and open-circuit voltage of the composite photoanode were substantially increased by 2.9 and 2.1 times respectively.The data of electrochemical impedance spectroscopy and surface photovoltage spectroscopy showed that the addition of PW12 effectively restrained the fast recombination of carriers in BiVO4 and speeded up their transfer,thus increasing the energy conversion efficiency of BiVO4.