Optical And Electrical Performance In Hydrogen-Modulated Chromogenic Materials

Electrochromic materials have broad application prospects in the fields of photoelectric switches,smart windows,etc.due to their characteristics of reversibly changing their optical state under different physical and chemical external field stimulations such as light,electricity,heat,and gas.Among them,the electrochromic material represented by tungsten trioxide(WO₃)can regulate the transmittance of visible light and solar energy through an electric field,thereby realizing the reversible conversion of color and energy.The color-changing material can intelligently adjust its near-infrared light transmittance according to the ambient temperature,and control the heat exchange between indoor and outdoor.In addition,a new type of photochromic material based on oxygen-containing yttrium hydride(YO_xH_y)can quickly respond to ambient light stimuli and achieve wide-spectrum adjustment from visible light to near-infrared.It is considered to be a rising star in the field of photochromism.Researchers have greatly promoted the progress of the above-mentioned material theory and performance through unremitting efforts,but there are still some key problems that need to be solved urgently before the actual commercialization and application.For the VO₂ thermochromic material,its optical modulation ability has been greatly improved in the past two decades,but it is easily chemically reacted with environmental substances during use,resulting in performance degradation,making its service performance tested.For WO₃ electrochromic materials,the discoloration process is limited by the ion transmission speed,and it is often impossible to achieve rapid switching between colored and faded states.As for the new YO_xH_y photochromic material,its research is still in the initial stage,resulting in the unclear mechanism of its color change.Modulation methods based on substance doping are widely used to control or improve the properties of the above substances and to study their mechanism of action.Among the many modulation methods,the use of hydrogen source modulation has attracted much attention.Due to its strong electron donating ability and small atomic radius,hydrogen atoms are hopeful to achieve rapid and effective regulation of material properties without destroying the material's lattice structure.Therefore,this article focuses on the hydrogen source modulation method,introduces it into different electrochromic material systems in order to improve the optical and service performance of the material,understands its mechanism of action,and finds common laws.The specific description is as follows:(1)Hydrogen doping of VO₂ nano-particles with ascorbic acid improves the acid resistance of the material.The results showed that electrons were transferred from the ascorbic acid molecule to VO₂.In an acidic environment,this charge transfer will directly use the electrostatic force to drive the protons in the environment to transfer to the VO₂ lattice,thus completing the hydrogen doping.This increase in the formation energy of oxygen vacancies in VO₂ brought about by hydrogen doping can achieve its stability in an acidic environment.At the same time,the use of the environmental acid resistance of this hydrogen-doped VO₂ can realize the coating of metal oxides that require an acidic experimental environment,and further improve its environmental weather resistance.This work proposes a simple method to achieve the environmental acid resistance and weather resistance of VO₂,and provides the possibility for the subsequent further metal oxide coating.(2)The electric field is used to inject hydrogen ions in the solution into the VO₂film,and an infrared adjustment film with a controllable electric field is successfully prepared.In addition,this paper combines this thin film with WO₃ thin film to prepare a novel electrochromic device with adjustable broad spectrum.At 0 V("bright"mode),the visible light and near-infrared light show high transmittance;at 1.5 V("cool"mode),the film can block most of the near-infrared light transmission while maintaining good visible light transmittance:When the applied voltage is adjusted to 3.5 V,the film switches to"dark"mode,in which the film can block 94.2%of visible light and 96.6%of near-infrared light.This work provides a more controllable adjustment method for the VO₂-based smart window,and further improves its adjustment ability in the visible light region,greatly expanding its application range.(3)PEDOT:PSS is used as a solid hydrogen source to realize the rapid transfer of hydrogen ions in WO₃.In addition,this paper uses sodium ion as the relay ion of hydrogen ion to realize the continuous and rapid transfer of hydrogen ion in WO3.The electrochromic device designed based on this structure has high optical modulation(the adjustment range is greater than 92%at 650 nm),and ultra-fast response speed(0.7 s coloring to 90%,0.9 s color fading to 65%,7.1 s color fading up to 90%)and excellent cycle stability(less than 10%performance degradation after 3000 cycles).This work creatively proposed a new type of high-efficiency hydrogen ion-based electrochromic structure,which is of great significance to the practical application of electrochromic devices.(4)The photochromic mechanism of YO_xH_y was studied by molecular dynamics based on first principles.The results show that the metastable state of a dimer structure is likely to be an intermediate in triggering its discoloration.In addition,simulations using density functional theory show that oxygen concentration has a significant influence on the photochromic effect of this material.Using the rapid transformation characteristics of the photochromic behavior of this material and the VO₂thermochromic material to form a new structure(YO_xH_y/VO₂),in order to achieve full-spectrum modulation of sunlight from visible light to near-infrared region.On the basis of the above research,a new photochromic mechanism was proposed,which successfully explained the existing photochromic phenomenon,and provided a good theoretical basis for the follow-up research of YO_xH_y.