A Study Of Z-scheme Photocatalytic System And Solar Energy Water Splitting Device

The energy and environmental problems brought by the use of fossil fuels have become increasingly severe.Using solar energy to produce hydrogen is a possible way to solve the energy crisis fundamentally.Since the discovery of the"Fujishima-Honda"effect,photocatalytic water decomposition technology has attracted much attention,and it is the key that to realize the fully decomposed water technology under visible light.The construction of a"Z-scheme reaction"system that simulates natural photosynthesis can effectively expand the photocatalytic material system to fully decompose water and provide a broader prospect for the effective use of visible light.In this paper,a Z-scheme water splitting system was constructed with SrTiO₃ and BiVO₄ materials,and the influence of factors such as sacrificial system,co-catalyst and pH value on the performance of the system were studied.It is found that in the IO₃^-ion sacrificial solution,the support of the co-catalyst can effectively improve the oxygen production performance of BiVO₄,especially the load of Co₃O₄,which can increase the oxygen production activity of BiVO₄ by 1 times.However,in the Fe³⁺ion sacrificial agent,the performance of BiVO₄ almost does not change with the support of the catalyst.The performance of SrTiO₃ is related to the type of redox couple and the pH value of the reaction liquid.Based on the above exploration,the Z-scheme system was constructed by using Co₃O₄ loaded BiVO₄ and SrTiO₃ loaded Pt as photocatalyst and I^-/IO₃^-ion pair as redox pair.The new photocatalytic material g-C₃N₄ was applied to Z-scheme system,and it was found that the redox ability between hydrogen production and oxygen production was not matched if we took the method of regulating pH only.After doping Zn element into g-C₃N₄,the Z-scheme photocatalytic system is obtained,in which BiVO₄ was applied as oxygen producing catalyst and Fe²⁺/Fe³⁺as electron transport medium.The system maintained a complete decomposition of water in 12 hours,that means,the ratio of hydrogen production to oxygen production is 2.The effect of Zn elements was studied by different loading and characterization methods.It was found that the Zn element entered into the framework of g-C₃N₄ with the form of Zn-N bond.With the difference between doping mode and the doping concentration,the effect on the structure of three azine ring on the surface of g-C₃N₄ was different,thus the photocatalytic activity of g-C₃N₄ material was changed.Direct using the solar cell voltage to achieve electrolyzed water is another way to gain solar energy production.A preliminary experimental device has been designed and made in this paper.By optimizing the electrode materials,setting the electrolyzer series and increasing the electrode area,the working point of the experimental device can be adjusted to the best position.Preliminary test results show that the conversion efficiency is about 3%,up to 6%.To sum up,this thesis has realized the construction of various Z systems and made an experimental device that directly uses solar energy to produce hydrogen.Some experiences and conclusions gained in the study of related topics will serve as a reference for further research.