Tri-nuclear Metal-oxo Sub-nanometer Clusters In Photocatalytic Hydrogen Evolution From Water Splitting And Mechanism Study

A crucial issue that with the increasing demand for the booming of human social progress and development,the fierce energy shortage is getting more severe.It is kind of the time when familiar patterns fade,familiar solutions fail,and familiar options disappear.Today,the world is feeling the effects of global warming,including extreme weather raging and rising sea levels,which have posed a serious threat to the survival of humans and other species.For the sustainable development strategy,we still need to develop and increase the use of novel energy in order to gradually reduce the consumption rate of fossil energy.How to use solar energy,a common clean energy,reasonably and effectively has always been one of the research hotspots.The use of materials with semiconductor properties for the utilization of solar energy to convert water into storable and energy-efficient hydrogen energy shows an easy way to explore new energy sources.The conventional photocatalytic water splitting method adopts heterogeneous catalysis,which means that the solid photocatalyst is mainly used in the photocatalytic reaction process.If a larger reaction interface area and a more direct electron transport process can be achieved in the form of a homogeneous reaction which also can show a considerable photocatalytic efficiency,the homogeneous reaction process can overcome the difficult separation of the photocatalysts and shows a special way for hydrogen evolution by photocatalytic water splitting.Based on this,this paper aims to design a cheap,easily available,stable and efficient photocatalyst and investigate its photocatalytic hydrogen production performance by building a homogeneous photocatalytic reaction system.The specific research content includes the following four aspects:1.For common metal salt or metal oxide photocatalyst,the exposed area of the metal sites in the molecular structure is limited.This article tries to stably gather three metal iron atoms in a single molecule at the same time in a coordinated form to obtain[Fe₃O（HCOO）₆（H₂O）₃]⁺water-soluble complex,and uses it in the experiment of photocatalytic water splitting to produce hydrogen.The results of photocatalytic water splitting to produce hydrogen show that[Fe₃O（HCOO）₆（H₂O）₃]Cl（FOF）has a certain photocatalytic activity,and about 85.2μmol of hydrogen can be obtained during a 6-hour photocatalytic process.The selection of this structure not only overcomes the limited contact area between the catalyst and the substrate water in the heterogeneous reaction,but also concentrates more metal sites and exerts a satisfied hydrogen production performance.2.Rather than the utilization of conventional noble metal based co-catalyst materials,this paper selects low-cost non-noble metal element iron,and for the first time tries to use water-soluble ionic complex FOF as the co-catalyst to further improve the photocatalytic reaction activity of a polyoxometalate strycture PWT(K₁₂P₂W₁₂（Ta O₂）₆O₅₆).The photocatalytic water splitting test results show that the PWT+FOF system has achieved more efficient hydrogen production results than both pure PWT and FOF systems.The PWT+FOF system gathers about 129.6μmol of hydrogen in the photocatalytic process for up to 6hours.In addition,the hydrogen production efficiency of the PWT+FOF system is 19 times that of the corresponding iron salt solution,which also indicates that the increase of active metal sites density can improve the hydrogen production efficiency.3.Since the hydrogen production performance of the PWT+FOF system is mainly determined by the amount of trinuclear metal-oxo clusters,this paper selects trinuclear iron-oxo clusters to combine with trinuclear chromium-oxo clusters and trinuclear cobalt-oxo clusters to design the binary trinuclear metal-oxo clusters based water-soluble photocatalytic systems.The trinuclear metal-oxo cluster structures selected in this chapter include:[Fe₃O（HCOO）₆（H₂O）₃]（OOCH）is the trinuclear iron-oxo cluster（Fe OF）;[Cr₃O（HCOO）₆（H₂O）₃]（OOCH）is the trinuclear chromium-oxo cluster（Cr OF）;[Co₃O（HCOO）₆（H₂O）₃]is the trinuclear cobalt-oxo cluster（Co OF）.From the perspective of the binary photocatalytic hydrogen production effect,both Fe OF+Cr OF and Fe OF+Co OF systems have doubled the hydrogen production amount compared to the simple trinuclear iron-oxo cluster system.In addition,in the 48-hour photocatalytic reaction experiments,the constructed binary trinuclear metal-oxo cluster systems can both continuously produce hydrogen,which also indicates that the compound Fe OF is no longer consumed during the reaction process and has turn out to be a stable photocatalyst.In the simulated seawater photocatalysis experiment with/without sodium chloride,a comparative analysis of the aqueous solution which contains the gas product of the photocatalytic system was carried out by ion chromatography,and the presence of chlorine in the gas product was verified.This kind of photocatalyst is stable and can obtain chlorine along with the photocatalytic hydrogen production process,which also shows a new exploration method for photocatalytic seawater decomposition.4.On the basis of a preliminary understanding of photocatalytic reaction,this article briefly explores the photo-electro catalytic system.In this paper,a furfural fuel cell device based on semiconductor photocathode material is designed,and the basic performance of the fuel cell is investigated by using the traditional semiconductor material bismuth oxychloride instead of the precious metal platinum as the electrode material.Transient photocurrent response test clearly shows the increase in current value under light conditions,and the current intensity of 12.5μA can be obtained.In the system without furfural,the current value is only about 1μA under light conditions,which also indicates that the chemical energy in the fuel furfural is successfully converted into electricity.In this paper,bismuth oxychloride is selected as the photocathode material,which can guarantee its stability under light conditions.The peaks in the X-ray powder diffraction pattern of the photocathode before and after the fuel cell reaction do not change or disappear,which also verified the stability of this material as the suitable photocathode of the photo-electro catalytic fuel cell.