Construction The System Of Photocatalytic Water Splitting Base On In-situ Oxygen Reduction Effect

Photocatalytic hydrogen evolution,as one of the most potential energy conversion technologies,is a promising approach to solve the energy crisis and environmental problems.Since the phenomenon of photocatalysis has been discovered,researchers have been paying great attention to it.Nowadays,most of the research focuses on the design and development of photocatalysts,such as element doping,construction of heterojunction structure and loading noble metal,to facilitate the separation of photogenerated electron-hole pairs.However,the physicochemical modification of photocatalysts mostly involves complex synthesis processes,which may lead to uncontrolled structure of photocatalysts or unsustainable photocatalytic performance.Moreover,the high cost of using noble metals as co-catalysts will hinder the large-scale application of photocatalysis in the future.In this paper,a new technology of visible-light photocatalytic hydrogen evolution is developed by adjusting the reaction mechanisms to overcome the technical bottlenecks in the field of photocatalytic hydrogen evolution.A scheme of improving the efficiency of photocatalytic water splitting by modifying the mechanism of photocatalytic reaction is proposed in this project.Both g-C₃N₄ based and Cd S based photocatalysts,under the guidance of in-situ oxygen reduction,exhibit highly efficient visible-light photocatalytic partial water splitting properties.Related work is as follows:1.This paper demonstrates a disparate mechanism from traditional beliefs of photocatalytic partial water splitting.When O₂ exists in the system,H₂ can evoluted by photocatalytic partial water splitting with g-C₃N₄ as photocatalyst,and the hydrogen evolution rate is extremely dependent on the oxygen partial pressure in the whole system.This promotion is called in-situ O₂ reduction.The whole reaction can be divided into two parts:methanol oxidation and formaldehyde dehydrogenation,in which O₂ is involved as oxidant and catalyst,respectively.By combining the experimental results with DFT theoretical calculation,a reasonable reaction path is obtained,which have almost no energy barrier.And it is suggested that the in-situ O₂reduction effect can change the mechanism of the reaction and accelerate the kinetic of hydrogen evolution by photocatalytic partial water splitting.2.P and S co-doped g-C₃N₄ synthesized by thermal condensation.And based on the in-situ O₂ reduction effect,the hydrogen evolution rate of g-C₃N₄ photocatalytic partial water splitting is further improved.The corresponding characterization shows that the doping of P and S co-regulates the electronic structure of the g-C₃N₄framework and provides more channels for the efficient transport of photogenerated charge carriers.Moreover,the band structure of P and S co-doped g-C₃N₄ does not migrate,so that the in-situ oxygen reduction effect can still work,maximum catalytic activity to HCHO solution up to 1127.3μmol·h^-1·g^–1_catalyst,which proved it can be generally used on the g-C₃N₄ based photocatalyst to change the reaction mechanism to promote H₂ evolution.3.This paper also discovered that in-situ O₂ reduction not only has effect on g-C₃N₄,but also has similar functions on traditional photocatalyst Cd S.And the photocatalytic activity of Cd S particles was further improved by doping P on the surface of the particles via a thermal phosphorization reaction.P atoms replace the S,and then bond with the Cd to change the conduction and valence band position on the surface of the Cd S particles,forming a built-in electric field with the internal undoped part,which prevents the recombination of photogenerated carriers.The overall photocatalytic reaction,only on the guidance of the in-situ O₂ reduction effect,can satisfy the more efficient photocatalytic partial water splitting without the addition of any noble metal cocatalyst,which The maximum catalytic rates for CH₃OH and HCHO solutions can reach 922.4μmol·h^-1·g^-1_catalyst and 3409.6μmol·h^-1·g^-1_catalyst,respectively.In summary,the in-situ O₂ reduction effect with wide universality has been found in this paper,and O₂ molecule plays the vital role in the whole photocatalytic process.This modification from the photocatalytic reaction mechanism is different from the traditional focus on regulating the properties of the photocatalyst itself,which provides a new idea and direction for improving the photocatalytic hydrogen evolution and energy storage technology.