Hexagonally ordered microbowl arrays decorated with ultrathin CuInS_(2) nanosheets for enhanced photoelectrochemical performance

This paper demonstrates the design and fabrication of three-dimensional(3 D) hexagonally ordered microbowl arrays(MBAs) decorated with Cu In S2 nanosheets for enhanced photoelectrochemical(PEC) performance. The 3 D MBAs are fabricated by a micro-fabrication technique. The ultrathin CuInS2 nanosheets are grown on the 3 D electrodes by solvothermal transformation of Cu film. The photocurrent density of 3 D photocathode(CuInS2@MBAs) is about two times higher than that of the planar counterpart(CuInS2@Planar). The improved PEC performance can be ascribed to the elevated light trapping ability and the increased surface area for loading photocatalysts. In addition, CdS quantum dots as cocatalysts are modified onto the Cu In S2 nanosheets to further enhance the PEC activity because the formed p-n heterojunction can accelerate the separation of photogenerated carriers. As a result, the 3 D photocathode of CuInS2/CdS@MBAs shows an optimal incident photon to current efficiency of 10% at the wavelength of400 nm. It is believed that this work can be generalized to design other hierarchical 3 D photoelectrodes for improved solar water splitting.

Synthesis of defect-rich hierarchical sponge-like TiO2 nanoparticles and their improved photocatalytic and photoelectrochemical performance

Defect-rich hierarchical sponge-like TiO2 nanoparticles were successfully synthesized via the combined one-step hydrothermal method and chemical reduction approach.SEM and TEM images showed their porous structure densely packed with even smaller TiO2 particles,while photocatalytic results manifested their superior photocatalytic performance and high stability.The RhB solution(10 ppm)could be absolutely degraded in 60 min,and the degradation rate was twice that of the sample without the treatment by NaBH4.Besides,the TC solution(10 ppm)could be removed by 74.3%in 20 min.PEC measurements also displayed that the photoelectrode based on such defectrich TiO2 nanoparticles had small resistance and improved charge transfer rate.The improved performance can be assigned to rich defects and phase junctions,which was supported by characterization results.The presence of rich defects and phase junctions could not only promote the separation of photogenerated charge carriers,but also accelerate the electron transfer,beneficial for both the photocatalytic and the PEC performance.It is expected that the obtained hierarchical sponge-like TiO2 nanoparticles with rich defects have great potential for photocatalytic applications.

Photothermal‐boosted polaron transport in Fe_(2)O_(3)photoanodes for efficient photoelectrochemical water splitting

Introduction of the photothermal effect into transition-metal oxide photoanodes has been proven to be an effective method to improve the photoelectrochemical(PEC)water-splitting performance.However,the precise role of the photothermal effect on the PEC performance of photoanodes is still not well understood.Herein,spinel-structured ZnFe_(2)O_(4)nanoparticles are deposited on the surface of hematite(Fe_(2)O_(3)),and the ZnFe_(2)O_(4)/Fe_(2)O_(3)photoanode achieves a high photocurrent density of 3.17 mA cm^(-2)at 1.23 V versus a reversible hydrogen electrode(VRHE)due to the photothermal effect of ZnFe_(2)O_(4).Considering that the hopping of electron small polarons induced by oxygen vacancies is thermally activated,we clarify that the main reason for the enhanced PEC performance via the photothermal effect is the promoted mobility of electron small polarons that are bound to positively charged oxygen vacancies.Under the synergistic effect of oxygen vacancies and the photothermal effect,the electron conductivity and PEC performance are significantly improved,which provide fundamental insights into the impact of the photothermal effect on the PEC performance of small polaron-type semiconductor photoanodes.

Photoelectrochemical performance of La^(3+)-doped TiO_2

La-doped TiO_2 thin films on titanium substrates were prepared by the sol–gel method with titanium tetrachloride as a precursor and La_2O_3 as a source of lanthanum. The heat-treatment temperature dependence of the photoelectrochemical performance of the La-doped TiO_2 film in 0.2 mol/L Na_2SO_4 was investigated by the MottSchottky equation, electrochemical impedance spectroscopy, and the open-circuit potential test. The results from the Mott-Schottky curves show that the obtained films all were n-type semiconductors, and the film at 300 °C had the highest conduction band position and the widest space charge layer. The electrochemical impendence spectroscopy（EIS） tests of the 300 °C film decreased most during the change from illuminated to dark. The potential of the La–TiO_2 thin film electrode was the lowest after the 300 °C heat treatment. The open-circuit potential indicated that the photoelectrical performance of the La-TiO_2 films was enhanced with the addition of the La element and the largest decline（837.8 mV） in the electrode potential was achieved with the 300 °C heat treatment.

Photoelectrochemical activity of ZnO:Ag/rGO photo-anodes synthesized by two-steps sol-gel method

This work investigated the influence of silver plasmon and reduced graphene oxide(r GO)on the photoelectrochemical performance(PEC)of Zn O thin films synthesized by the sol-gel method.The physicochemical properties of the obtained photo-anodes were systematically studied by using several characterization techniques.The x-ray diffraction analysis showed that all samples presented hexagonal wurtzite structure with a polycrystalline nature.Raman and energy dispersive x-ray(EDX)studies confirmed the existence of both Ag and r GO in Zn O:Ag/r GO thin films.The estimated grain size obtained from scanning electron microscopy(SEM)analysis decreased with Ag doping,then increased to a maximum value after r GO addition.The UV-vis transmission spectra of the as-prepared Zn O:Ag and Zn O:Ag/r GO thin films have shown a reduction in the visible range with a redshift at the absorption edges.The bandgaps were estimated to be around 3.17 e V,2.7 e V,and 2.52 e V for Zn O,Zn O:Ag,and Zn O:Ag/r GO,respectively.Moreover,the electrical measurements revealed that the charge exchange processes were enhanced at the Zn O:Ag/r GO/electrolyte interface,accompanied by an increase in the(PEC)performance compared to Zn O and Zn O:Ag photo-anodes.Consequently,the photocurrent density of Zn O:Ag/r GO(0.2 m A·cm^(-2)) was around 4 and 2.22 times higher than photo-anodes based on undoped Zn O(0.05 m A·cm^(-2)) and Zn O:Ag(0.09 m A·cm^(-2)),respectively.Finally,from the flat band potential and donor density,deduced from the Mott-Schottky,it was clear that all the samples were n-type semiconductors with the highest carrier density for the Zn O:Ag/r GO photo-anode.

Enhancement of photocatalytic and photoelectrochemical properties of TiO_(2) nanotubes sensitized by SILAR-Deposited PbS nanoparticles

The aim of this work is to improve the photocatalytic and photoelectrochemical properties of TiO_(2) nanotubes(TiO_(2)-NTAs)by sensitizing them with PbS nanoparticles(NPs)prepared by the Successive Ionic Layer Adsorption and Reaction method(SILAR).The Microstructure,surface morphology,phase composition and optical properties of the prepared structure were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM and High-resolution mode HRTEM)and X-ray photoelectron spectroscopy(XPS).The TiO_(2) NTAs were loaded by PbS NPs,which contents increase by increasing the number of SILAR cycles.The PbS NPs,which have a size in the order of ~20 nm,were found to be uniformly distributed in the TiO_(2) NTAs without damaging the tubular ordered structure.The photocatalytic activity of the PbS/TiO_(2) NTAs system,toward Amido Black(AB),showed significant enhancement compared to the bare untreated TiO_(2) NTs.At 30 SILAR deposition cycles the PbS-NPs/TiO_(2) NTAs structure is able to remove 75% of BA under simulated solar light,considerably higher than the 40% removal obtained with unloaded TiO_(2) NTAs.A significant improvement of the Photoelectrochemical(PEC)efficiency has been also demonstrated for the PbS-NPs/TiO_(2) NTAs hybrid system.This improvement is mainly related to visible-light harvesting and reduced recombination of photo-generated electron-hole pairs due to the synergistic effect of the heterojunction and to the wellorganized morphology of the TiO_(2) NTAs.

Enhancement of mass transfer efficiency and photoelectrochemical activity for TiO_(2)nanorod arrays by decorating Ni^(3+)-states functional NiO water oxidation cocatalyst

Photoelectrochemical(PEC)water splitting is a promising technology to use solar energy.However,current metal oxides photoanode face the problem of sluggish water oxidation kinetic.In this study,we propose that the sluggish water oxidation process will cause slow mass transfer efficiency,which are rarely considered previously,especially at large bias and strong illumination.Mass transfer refers to the migration of reactants(like H_(2)O and OH^(-))to the photoanode surface,reaction with holes and diffusion of products(like radical and O^(2))to the bulk of the electrode.If the migration and diffusion are not fast enough,the mass transfer will inhibit the increase of PEC activity.This problem will be more apparent for nanorod arrays(NRAs),where the space among the NRAs is related narrow.Herein,we solve this problem by decorating the surface of the photoanode by NiO clusters with Ni3+state as water oxidation cocatalysts.This work studies the PEC process from the viewpoint of mass transfer and firstly demonstrates that mass transfer in NRAs structure can be promoted by using Ni-based water oxidation cocatalyst.