Study On The Preparation And Photoelectric Properties Of Bismuth Vanadate/porphyrin Composites

With the increasing population of the world and its demand for energy,there is an urgent need to transition from the current fossil-based energy system to a sustainable clean energy system.Solar energy is the most promising of all sustainable energy sources.Converting solar energy into clean energy through photoelectrochemical（PEC）water splitting is one of the effective strategies to solve current energy and environmental problems.However,PEC performance is severely limited by fast charge recombination and slow water oxidation kinetics.Although the coupled electrocatalyst（OEC）significantly accelerate the water oxidation kinetics,the recombination of photogenerated electrons and holes at the semiconductor/electrocatalyst interface results in a large loss of energy.Therefore,it remains challenging to increase the water oxidation efficiency of PEC to the required level.In this paper,we used BiVO₄as the research model,to repair surface states,we first convert porphyrin to metal oxide（i.e.,NiOx）via calcination aiming at the little energy loss at the semiconductor/electrocatalyst interface.In addition,we further studied the changes of PEC performance by the intensity modulated photocurrent（IMPS）test and scanning photoelectrochemical microscopy（SPECM）from the perspective of kinetics.Our work mainly consists of the following three parts:1.Study on the preparation and photoelectric properties of BiVO₄/NiO_X/CoFe（OH）_XcompositesBiVO₄is widely used in PEC due to the narrow band gap（2.6 eV）,suitable water oxidation band structure,and excellent optical and electrical properties.However,the existence of surface states makes electrons and holes recombine seriously.In this chapter,in order to suppress the recombination of electrons and holes,we propose a strategy to repair the surface state.First,Ni TCPP is coupled to the BiVO₄surface by spin coating,followed by annealing treatment to convert Ni TCPP into NiO_X,and finally by electrodeposition CoFe（OH）_Xaccelerates water oxidation kinetics.The results show that the photocurrent and photoelectric conversion efficiency of the integrated photoanode system were improved significantly.IMPS and SPECM also prove that this strategy can accelerate the transfer of holes,and the system maintains a good stability within two hours.2.Study on the preparation and photoelectric properties of TiO₂/NiO_X/CoFe（OH）_X compositesIn the first chapter,we proved that the BiVO₄/NiO_X/CoFe（OH）_Xcomposite photoanode has excellent PEC performance and good stability.In this chapter,we mainly studied the general applicability of this strategy,constructed a TiO₂/NiO_X/CoFe（OH）_Xphotoanode system,and tested the PEC performance of the system under visible light irradiation.The results show that the photocurrent and photoelectric conversion efficiency of the integrated photoanode system were significantly improved.In addition,we also tested the kinetics of the system through IMPS and SPECM.The trends of all experimental results are consistent with the BiVO₄/NiO_X/CoFe（OH）_Xsystem,which suggests that the repair surface state strategy is universal.3.The preparation of BiVO₄/ZnTCPP composites and its photoelectric sensoring for dopamineAs a neurotransmitter,dopamine plays an important physiological role in nervous system function.In this chapter,we use BiVO₄as a substrate,coupled ZnTCPP to construct an electrochemical sensor for dopamine.When dopamine is present,on the one hand,dopamine,as a substance that is easily oxidized,quickly consumes the holes on the porphyrin LUMO orbital,thereby separating electrons and holes to increase the photocurrent signal.On the other hand,dopamine will coordinate with the Zn in ZnTCPP to form a five-membered ring,which speeds up the charge transfer and improves the photocurrent signal.Therefore,under this dual effect,BiVO₄/ZnTCPP has a better photocurrent response to dopamine.