Study On Hot Electron Properties Of Metallic Nanoparticle In Application Of Solar-hydrogen Conversion

Hydrogen production by photo-electrochemical water splitting is one of the most effective ways to transform endless solar energy to hydrogen which has a high energy density.As an alternative material of photoanode,TiO₂ has some shortcomings including a limited available range of solar energy,and a high recombination rate of carriers,for which it needs more modification on TiO₂-based material for promoting energy transform efficiency.Based on modification by depositing noble metal nanoparticle,our research is focused on analyzing and evaluating the ability of providing energetic plasmon electrons of adopted nanoparticle.Specifically,using free-electron model,we calculate hot electron property's quantitative dependence on nanoparticle's material,geometric factors and surrounding dielectric,and also how incident light direction and energy affect the hot electron property.The influences of nanoparticle's material and outside dielectric on hot electron's property are firstly investigated.The results show amounts of hot electrons are entirely different in each kind of metal because of different light response property,and the regularity how hot electron's amount gets affected by different materials is not totally same in different shape of nanoparticles.For nanorod,Au,Ag and Cu all show high generation rate of hot electrons in visible region,and Au and Ag have stronger photoelectric response under visible and ultraviolet light while Cu shows better photoelectric performance in infrared region.For nanocuboid,hot electron's amount in Ag has a monotonous increase with energy of incident photon,which is higher than Cu and Au in ultraviolet region.But in visible region,hot electrons in Au and Cu are more than Ag.When outside dielectric(or environment)changes,for nanorod,the outside dielectric(or environment)which has a permittivity closed to 2,such as SiO₂,can make the highest hot electron's generation.For nanocuboid,the hot electrons in it also grow more with outside permittivity's increase,which leads that surrounding dielectric with large permittivity can generate most hot electrons.In research of nanoparticle's geometric factors'effect on hot electrons'generation and injection rate,the geometric factors mainly include the particle's volume,aspect ratio and dimension along polarized field's direction.Meanwhile,we explain how particle's geometric factors influence hot electrons.The results show,nanorod can usually generate larger amount of hot electrons for its more transition energy states,and its generation peak that appears in changing aspect ratio is mainly brought by the strongest field enhancement in special aspect ratio.What's more,volume's increase of nanorod can apparently make higher generation rate of hot electrons,that's because the larger size along polarized field can bring more transition quantum states.When nanoparticle forms a core-shell structure with outside dielectric,the electron's injection efficiency to neighboring semiconductor can be heavily affected by energy component that's perpendicular to interface,and the ratio that the component accounts for is decided by relative size among each direction.Because hot electron in nanocuboid has larger proportion of the perpendicular component,it usually has a larger efficiency of injection.The third and the last section is the incident light's influence on hot electron's property,involving the direction and wavelength of light.The result shows when direction of incident light changes from radial light to longitudinal along axis,hot electron's energy distribution in nanorod has an obvious difference,but in nanocuboid there is comparatively little change.It owes to the restrictive boundary's change,specifically,it turns from plane boundary(top and bottom surface)to curved boundary(side surface)in nanorod,while in nanocuboid the restrictive boundary is always plane,and this doesn't change the transition electron's wave function and energy level too much.When the energy of incident photon changes,the generation amount of hot electrons is totally different,because the nanoparticle has different light response depended on its material and shape.But the change regularities between hot electron's amount and particle's geometric factor are not changed under different incident light.