Design,Fabrication Of Photoanodes And Their Explorations In New Photoelectrochemical Catalytic Reactions

With the increasing demand of energy,it is an important and challenging task for the development of renewable and clean power sources.Due to the characteristics of unlimited and sustainable influx from the sun,solar energy has been recognized as one of the most promising energy sources for human consumptions.Compared to pure photocatalyst,photoelectrochemical(PEC)water splitting is a more attractive technology to provide cost-effective hydrogen fuel with a relatively high solar to chemical energy conversion.In the PEC water splitting system,photoelectrodes plays a key role for the high efficient energy conversion.The generation,migration,and reaction of photogenerated charge carriers are three key steps which are involved in the PEC solar energy conversion processes.Although various types of semiconductors(e.g.,TiO2,a-Fe2O3,BiVO4 and WO3)have been extensively studied,they normally suffer from poor charge carriers transfer efficiency and sluggish surface chemical reaction.To solve these problems,suppression of recombination centers and acceleration of charge transport have been considered as necessary approaches.In addition,the enhancement of surface reaction kinetics is a strategy to improve the photocatalytic activity of semiconductors.In this dissertation,the effect of oxygen vacancy on the migration of charge carriers in metal oxide semiconductor was firstly discussed.Charge carriers migaration ability is essential for the final PEC performance.Semiconductor/cocatalyst,semiconductor/semiconductor heterojunction were constructed by photo-assisted electro-synthesis,in situ growth or precursor transformation method.Due to the rational interface design and fabrication,enhanced charge carriers separation and injection efficiency were achieved in these photoanodes.In addition,several new types of photoelectrochemical catalysis coupling with chemical reactions were explored.The detailed research contents are as follows:(1)Modulation of oxygen vacancy on TiO2 and its influence on charge migrationA series of TiO2 nanoarrays with different density of oxygen vacancy were prepared by controlling the calcination temperature.Although the morphology and crystallinity of those TiO2 are similar,a totally different PEC water splitting performance is achieved.The activity of obtained TiO2 photoanodes is related to the density and migration rate of generated charge carriers.When the calcination temperature is low,the migration rate of TiO2 samples is too small.But at high calcination temperature,a low density of charge carriers is obtained,which results in a low PEC water splitting performance.In case of the TiO2-400 sample,it shows a relatively high charge density(1.06× 1012 cm-3)and the fastest carriers migration rate(2.31× 104 cm2 V-1 s-1),giving rise to the highest photocurrent density(1.43 mA cm-2).Stable and orderly oxygen vacancy with a suitable density facilitates the migration of charge carriers in metal oxide semiconductors.(2)Influence of semiconductor/electrolyte interface on the charge carriers mlgrationOxygen vacancy-rich layer modified WO3-OV was fabricated by a facile precursor transformation method.The WO3/WOx heterojunction promotes the formation of self-build electric filed in the semiconductor/eleclyte region,which results in a high charge separation efficiency(from 25.1%to 65.9%).Well-aligned TiO2/LDH photoanode was prepared by direct synthesis of ZnFe-LDH on Ti02 nanoarrays via a photo-assisted electro-synthesis method.Photocurrent density of the obtained Ti02/ZnFe-LDH-PE reaches to 1.51 mA cm-2 at 1.23 V vs.RHE,1.91 and 1.20 times higher than that of the pristine Ti02 and Ti02/ZnFe-LDH-E NAs samples,respectively.It is found that a defect-less grain boundary with matched bandgap,surface with rich catalytic active sites are important to the characters of semiconductor/electrolyte interface,which finally facilitate the utilization of photo generated charge carriers.(3)Explorations of new types of photoelectrochemical catalytic reactionsPhotoelectrochemical catalysis toward selective oxidation of alcohols with high reaction rate and selectivity were achieved on TiO2/C photoanode.Compared with photocatalysis process,the PEC catalysis yields an order of magnitude enhancement in reaction rate(76 mmol g-1 h-1).It is found that the holes at the valence band of TiO2 oxidize the aryl alcohols to carbocations(ROH*+).Then the superoxide radicals(O2·-)further react with ROH*+ to produce the final aldehyde compounds.In addition,an ATP and hydrogen cogeneration artificial synthesis process was achieved with the assembled Fe2O3/LDH/ATPase photoanode in a hybrid photo-bioelectrochemical cell.The Fe2O3/LDH/ATPase photoanode was constructed by spin-coating FoF1-ATPase/proteoliposomes on the obtained Fe2O3/LDH.NiFe-LDH acts as a cocatalyst enhances the charge injection efficiency.High specific surface area of LDH nanosheets is favorable for the assembly of FoF1-ATPase,which improves the utilization of generated proton gradient.After 0.5 h measurement,0.7 nmol cm-2 ATP and 14.92 ?mol cm-2 H2 were produced.These explorations offer new avenues for highly-efficient transformation of solar energy into fine chemicals.