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Herein, we propose the topotactic and self-templated fabrication of Zn1-xCdxSe porous nanobelt-ZnO nanorod (termed as ZnCdSe/ZnO) photoelectrode via the cadmium (Cd2+) ion-exchange process on zinc (Zn) foil. Inorganic-organic hybrid ZnSe(en)0.5 nanobelt (NB) was synthesized on Zn foil by a facial solvothermal method at different temperatures of 140, 160, and 180 °C for 12 h. The interfacial properties and photoelectrochemical (PEC) performance of inorganic-organic ZnSe(en)0.5 NB fabricated through the Cd2+ ion-exchange method at different time durations of 6, 12, 18, and 24 h at 140 °C were investigated. The TEM analysis results indicate that the inorganic-organic ZnSe(en)0.5 NB transformed into ZnCdSe and a self-assembled ZnO formed on the Zn foil. In particular Cd2+ ion temperature (140 °C/18 h), the optimized ZnCdSe/ZnO-(F) photoelectrode shows an excellent photocurrent density of 14 mA·cm-2 at 0 V vs Ag/AgCl with 219 μmol·cm-2 hydrogen gas evolution for 3 h under 1 sun illumination. The higher photocurrent value resulted from the optimum growth of ZnO, the formation of porous ZnCdSe, and the effective electrolyte penetration for electron-hole pair separation. The photoluminescence spectroscopy shows that the photoexcited charged carriers promoted a longer lifetime. Furthermore, we provide a full account of the possible charge-transfer mechanism during PEC hydrogen production.

A strategy involving CoOx catalyst adsorption and acid treatment for modifying the surface properties of Zr-doped hematite nanocoral (NC) photoanodes has been proposed. Acid-treated Zr-Fe2O3 NCs exhibited a reduced electrode/electrolyte interface resistance and improved surface charge-injection efficiency. X-ray photoelectron spectroscopy data confirmed an increased number of hydroxy groups and the formation of Fe2+ sites on the surface of the acid-treated Zr-Fe2O3 NC, suggesting surface amendment. Furthermore, after surface amendment with a 1 mM Co(OAc)2 solution, the CoOx encapsulated acid-treated Zr-Fe2O3 NC photoanode exhibited a photocurrent density of 1.83 mA/cm2 at 1.23 V vs. RHE, following a 200-mV cathodic shift in the photocurrent onset compared with the bare Zr-Fe2O3 NC. The experimental results indicated the efficacy of acid treatment and CoOx adsorption for reducing the surface state and enhancing the photoelectrochemical water-oxidation performance. The acid-treatment step in the CoOx-encapsulated acid-treated Zr-Fe2O3 NC provided a CoOx catalyst adsorption bond and permitted the kinetics of the charge-transfer process. This synergistic strategy of acid treatment and CoOx adsorption for enhancing the PEC performance provides a reference for accelerating the charge separation for other photoelectrodes.

With regard to both the activity and stability of photoelectrode materials, in this study, a hematite cauliflower-like structure with irregularly loaded ZrO2 (ZrO2–Fe2O3 CF) was prepared from as-deposited samples. The effect of post-synthetic treatments such as systematic high-temperature heating at various temperatures (650, 700, 750, and 800 °C) for 10 min, followed by rapid cooling at room temperature (quenching) on interfacial properties and photoelectrochemical performance was investigated in detail. The photoelectrochemical performances of the quenched ZrO2–Fe2O3 CF samples were compared to those of conventionally synthesized hematite nanorod photoanodes quenched from 800 °C (PQ800). Interestingly, ZrO2–Fe2O3 CF photoanodes quenched from 650 °C exhibited 0.62 mA cm−2 photocurrent density at 1.23 V vs. RHE, which was 14 times higher than that of the conventionally synthesized hematite quenched from 650 °C (PQ650). Furthermore, ZrO2–Fe2O3 CF photoanodes quenched from 800 °C revealed a photocurrent density of 1.66 mA cm−2 at 1.23 V vs. RHE (twice that of PQ800) and improved charge separation efficiencies of ηbulk = 15.6% and ηsurface = 94.6%, respectively. The XPS and HRTEM results also confirmed the irregular ZrO2 loading on the surface of Fe2O3 CF. A possible formation and charge transfer mechanism of ZrO2–Fe2O3 CF was proposed based on a series of temperature-dependent experiments.

Herein, in situ zirconium-doped hematite nanocoral (Zr–Fe2O3 (I) NC) photoanode was prepared via a specially designed diluted hydrothermal approach and modified with Al3+ co-doping and electrodeposited cobalt–phosphate (“Co–Pi”) cocatalyst. Firstly, an unintentional in situ Zr–Fe2O3 (I)) NC photoanode was synthesized, which achieved an optimum photocurrent density of 0.27 mA/cm2 at 1.0 V vs. RHE but possessed a more positively shifted onset potential than conventionally prepared hematite nanorod photoelectrodes. An optimized amount of aluminum co-doping suppresses the bulk as well as surface defects, which causes a negative shift in the onset potential from 0.85 V to 0.8 V vs. RHE and enhances the photocurrent density of Zr-Fe2O3(I) NC from 0.27 mA/cm2 to 0.7 mA/cm2 at 1.0 V vs. RHE. The electrodeposited Co–Pi modification further reduce the onset potential of Al co-doped Zr–Fe2O3(I) NC to 0.58 V vs. RHE and yield a maximum photocurrent of 1.1 mA/cm2 at 1.0 V vs. RHE (1.8 mA/cm2 at 1.23 V vs RHE). The improved photocurrent at low onset potential can be attributed to synergistic effect of Al co-doping and Co–Pi surface modification. Further, during photoelectrochemical water-splitting, a 137 and 67 μmol of hydrogen (H2) and oxygen (O2) evolution was achieved over the optimum Co–Pi-modified Al-co-doped Zr–Fe2O3(I) NC photoanode within 6 h. The proposed charge transfer mechanism in optimum Co–Pi-modified Alco-doped Zr–Fe2O3(I) NC photoanodes during the photoelectrochemical water splitting was also studied.

The development of advanced assemblies of interfacial under- and overlayered photoanodes is an effective technique to overcome the problem of slow charge separation and enhance solar energy conversion. The present study reports in situ zirconium-doped zinc ferrite nanocorals (Zr-ZFO NCs) and introduces the concept of diffusion/doping and surface passivation using a TiO2 underlayer via quenching. The high-temperature quenching aids the Zr doping/Ti4+ diffusion in the bulk and, at the same time, the ZrO2/TiO2 composite layers passivate the surface of ZFO NC photoanodes. The optimum TiO2-underlayer-modified Zr-ZFO (TZF) photoanode shows a dramatically improved photocurrent (0.48 mA cm−2) at 1.23 V vs. RHE, which is twice that of the bare Zr-ZFO. Further, the addition of an Al2O3/CoOx cocatalyst further accelerates the surface reaction kinetics of the TZF, and significantly improved charge separation efficiency, photocurrent density (0.73 mA cm−2 at 1.23 V vs. RHE; and 0.97 mA cm−2 at 1.4 V vs. RHE), and stability were obtained. Compared to conventional ZFO nanorods (0.14 mA cm−2 at 1.23 V vs. RHE), the optimized sample shows a 421% increase in photocurrent density. Additionally, the TZF/Al2O3/CoOx_1 mM photoanode generates 65 and 130 μmol oxygen and hydrogen, respectively, under simulated 1 sun illumination. Thus, the “sandwich” strategy for Zr-ZFO with a TiO2 underlayer and spontaneous surface passivation via quenching could be expanded for the design and fabrication of many low-efficiency photocatalysts and the production of cost-effective PEC water splitting photoelectrodes.

ZnFe2O4 nanorods (NR's) were prepared by a chemical conversion method from β-FeOOH NRs grown on FTO substrates. To activate their photoactivity of ZnFe2O4 NRs for solar water splitting, the surface passivation was achieved with SiO2 layer via facile and effective spray pyrolysis method. The presence of SiO2 layer enhances the photocurrent density of the Pristine ZnFe2O4 from 143 µA/cm2 to 212 µA/cm2 at 1.23 VRHE for 0.25 mM Si–ZnFe2O4, representing two time increment in the photocurrent density. The influences of amount of Si precursor (Tetraethyl orthosilicate) solutions on the physical properties and the passivation effect of SiO2/ZnFe2O4 interfaces were investigated. This improved photoresponse of the Si-treated ZnFe2O4 NRs was attributed to the excellent charge transfer electrode/electrolyte interface. The effectively improved charge transfer properties of the Si-treated ZnFe2O4 NRs were demonstrated by the electrochemical impedance spectroscopy (EIS), Mott–Schottky (MS) and intensity-modulated photocurrent spectroscopy (IMPS) analyses.

The objective of this study was to report the preparation of a highly efficient hematite nanorod photoanode by H2 treatment of the β-FeOOH nanorod with subsequent quenching in air at lower temperature activation for photoelectrochemical (PEC) water oxidation. The hematite nanorod photoanode (H650) prepared by thermally treating the β-FeOOH nanorod at 360 °C for 1 h under H2 flow and quenching at 650 °C for 10 min in air exhibited a remarkable photocurrent of 1.17 mA cm−2 at 1.23 V vs. RHE, which was 20 times higher than that of hematite quenched at the same temperature without H2 treatment. Such enhanced PEC performance was attributed to high Sn4+ diffusion from the fluorine doped SnO2 (FTO) substrate via H2 treatment and Sn4+ doping by subsequent lower temperature quenching. Our density functional theory (DFT) calculation supports our experimental results and proposed mechanism in that the Sn replacement reaction of magnetite (Fe3O4, H2-reduced β-FeOOH) occurs at a lower temperature and requires a smaller energy than that of akaganeite (β-FeOOH).

To solve energy crisis, the engineering of highly efficient and cost-effective photoanodes is urgently required for clean fuel generation. Herein, CdSe(en)0.5 (en = ethylenediamine) hybrid photoanodes were synthesized by a solvothermal approach. It was revealed that a second in situ hydrothermal treatment successfully converts cadmium foil-based inorganic-organic CdSe(en)0.5 (en = ethylenediamine) hybrid nanosheets to an oriented cadmium hydroxide crowned CdSe nanowire-decorated porous nanosheet (Cd(OH)2/CdSe NW/NS) heterostructure by dissolution and regrowth mechanisms. The alteration in second hydrothermal reaction conditions could modify the morphology and optical properties of the Cd(OH)2/CdSe NW/NS heterostructure photoanodes. The possible growth mechanism of the Cd(OH)2/CdSe NW/NS porous structure is studied at various second hydrothermal times using the control experiments of the synthesis. The optimized 3D porous Cd(OH)2/CdSe NW/NS photoanodes exhibited an outstanding photocurrent density of 6.1 mA cm-2 at 0 V vs. Ag/AgCl, which is approximately 7.6 times higher than that of the inorganic-organic CdSe(en)0.5 hybrid under light irradiation (>420 nm cut off filter). A mechanism is proposed to explain the enhanced charge separation at the Cd(OH)2/CdSe NW/NS photoanode/electrolyte interface, which is supported by PL and photoelectrochemical analyses. These findings open an avenue of phase and morphology transmutation for efficient formation of other hierarchical structures of metal selenides and sulfides. Additionally, the Al2O3 co-catalyst can act as effective hole trapping sites and improves the stability of the photoelectrode through the timely consumption of photogenerated charges, particularly holes.

The 3D structure assembly of CdSe tetrakaidecahedron (TDH) modified with the oxygenated CdS nanorose (NR) structure plays a crucial role in the photoelectrochemical (PEC) performance because of its...

A highly three-dimensional CdIn2S4 deposited TiO2 (CdIS/TONR/FTO) heterostructured photoanode has been fabricated via a two-step hydrothermal process to enhance the photoelectrochemical (PEC) performance. In this work, bare TiO2 nanorods are grown successfully on the fluorine-doped tin oxide (FTO) substrate via a hydrothermal method (TONR/FTO), and a second-step hydrothermal synthesis is used to grow CdIn2S4 flower nanostructured layer over the top surface of the bare TONR/FTO. Structural, morphological, optical, and elemental analysis of CdIS/TONR/FTO heterostructure photoanode is investigated in detail. PEC performances are studied in 0.2 V versus Ag/AgCl in mixed sulfide-based electrolyte for various concentrations of CdIn2S4 deposited on photoanodes. The photocurrent density for optimized (×4)-CdIS/TONR/FTO heterostructure photoanode is observed to be three times higher than that of the bare TONR/FTO photoanode. This excellent PEC performance is ascribed to the way that the deposited CdIn2S4 layer and TiO2 nanorods synergistically allow the absorption of a wide portion of the solar spectrum under back illumination, and provide efficient separation of the electron-hole pairs in the photoanode architecture. The EIS and IMPS analysis also reveal the significance of CdIn2S4 layer that provides the lowest charge-transfer resistance at the interface and high electron-transfer rate in CdIS/TONR/FTO photoanode. Mainly, the deposited CdIn2S4 layer significantly broadens the optical absorption capacity, and provides efficient electrons-holes transfer that reduces the recombination losses of the charge carriers. The proposed charge transfer mechanism in CdIS/TONR/FTO heterojunction is well studied.

Herein, we report the surface treatment on Zr4+/Al3+ codoped α-Fe2O3 photoanode for high-performance photoelectrochemical water splitting. A high-temperature quenching exhibits the Zr4+/Al3+ codoping in α-Fe2O3 photoanode without damaging morphology. The presence of Zr4+/Al3+ codoping shows a cathodic shift in onset potential, but lack of increment in photocurrent reveals the major role of passivation and the minimum doping effect of aluminum. Additionally, CoOx cocatalyst exhibits increment in photocurrent with the greater cathodic shift in onset potential than the pristine α-Fe2O3 nanorods. The CoOx surface-reworked Zr4+/Al3+ codoped α-Fe2O3 photoanode displays the highest photocurrent of 1.5 mA/cm2 at 1.23 V vs. RHE (76% increment over the pristine α-Fe2O3) and 0.7 mA/cm2 at 1.0 V vs. RHE (102% increment over the pristine α-Fe2O3). The systematic characterization carried out using x-ray diffraction and scanning electron microscopy confirms that after Zr4+/Al3+ codoping, and surface treatment, the crystalline structure, and morphology of the photoanodes remains unchanged. X-ray photoelectron spectroscopy confirmed the existence of Zr4+/Al3+ codopants in the hematite nanostructure. The electrochemical properties of the photoanode suggest that Al3+ and Zr4+ codoping, as well as surface treatment with CoOx, cocatalyst lowers charge transfer resistance across the FTO/hematite interface, and hematite/electrolyte interface. This designs not only lowers onset potential but also offers the blueprint for the development of an efficient catalyst for solar water oxidation.

In this study, we have synthesized hierarchical TiO2@In2O3 heteroarchitecture photoanodes via a hydrothermal method and studied their interfacial charge carrier dynamics through water splitting and organic decomposition. Photoelectrochemical measurements show that the IN-0.4 exhibits an obvious enhancement in photocurrent density compared to the pristine TiO2. Electrochemical impendence spectroscopy (EIS) and Time-resolved photoluminescence (PL) have been employed to study the charge recombination in TiO2@In2O3 nanostructure. The surface passivation of TiO2 nanorods (NRs) with In2O3 nanostructures helps to the suppression of the surface defects. The surface-passivated photoanode (IN-0.4) has demonstrated the improved hydrogen generation activity (125 μmol∙h−1) of TiO2 nanorods (NRs) with In2O3 nanostructures during water splitting and organic decomposition. The probable causes of the enhancement in hydrogen evolution could be due to (i) enhanced photogenerated electron transport (ii) increased active surface area with In2O3 and/or (iii) catalytic activity of In2O3. Moreover, the photoelectrocatalytic activities of IN-0.4 were slight affect during degradation of Bisphenol A and methyl orange dye, which might be due to the lower hole mobility in TiO2@In2O3 heteroarchitecture photoelectrodes. These sightings and proposed schematic model can help to understand the charge transfer dynamics in hierarchical TiO2@In2O3 heteroarchitecture photoelectrodes as well as designing multifaceted photoelectrodes for solar energy conversion.

The surface modified tetravalent ions doped hematite nanorod photoanodes has been synthesized by successive hydrothermal and spin coating approaches. The effect of tetravalent ion (Sn, Ti, and Zr) doping and high temperature annealing on to the morphological, structural and photoelectrochemical properties has been investigated. Photoelectrochemical analyses indicate tetravalent doping (Sn, Ti, and Zr) and high-temperature annealing (800 °C) showed higher photocurrent and improved activity towards Orange-II dye degradation, compared to the pristine hematite film. Amongst tetravalent dopants, Zr4+ doped hematite can significantly enhance the photocurrent density (1.37 mA cm−2 at 1.23 V vs. RHE) as well as the Orange-II dye degradation activity (93% under one sun illumination in 270 min). Kinetic parameters are also investigated by first-order rate equation. Further, Zr–Fe2O3 photoanode modified with the appropriate composition of CoOx and specific structural features demonstrated improvement in photocurrent from 1.6 to 1.78 mA cm−2 (at 1.4 V vs. RHE). The efficient charge carrier separation and generated hydroxyl radicals led to enhancements of the Orange-II dye degradation efficiency up to 97% within 270 min. The significant decrease in chemical oxygen demand values suggests the removal of Orange-II dye. This work demonstrates that enhancement in photoelectrochemical activity is due to the combined effect of passivation of surface states and the formation of CoOx/Zr–Fe2O3 heterojunction.

We introduce a simple strategy to unintentional heterogeneous Ti4+/Sn4+ doping and surface passivation of hematite via TiO2 underlayers at high temperature quenching. The effects of the controlled ...

In this work, the hydrothermal approach has been used to prepare and control the morphology of Bi2S3 nanosheet (NS)/Zr doped Fe2O3 nanorod (NR) heterojunction grown on fluorine doped tin oxide (FTO) phoptoelectrodes. The effect of morphology of Bi2S3 NS was examined by comparing the photocatalytic activity of Zr:Fe2O3 nanorod with synthesized heterojunctions. This novel heterojunction photoanode exhibits the light harvesting, the photoinduced electron–hole separation and yielding a maximum photocurrent density of ∼1.27 mA cm−2 at −0.4 V vs. Ag/AgCl under one sun illumination. Bi2S3 NS on surface of the Zr:Fe2O3 NR will act as the active material which shows the dramatic improvement in photocurrent generation. Further, effect of silver interlayer on the interface properties of Bi2S3 NS/Zr:Fe2O3 NR heterojunction was also studied. The results indicated that the silver interlayer reduces charge recombination at interface of Bi2S3 and Zr:Fe2O3. Also, the surface plasmon resonance of Ag and controlled morphology enhances the performance (1.5 mA cm−2 at −0.4 V) as well as improves the stability of Bi2S3/Zr:Fe2O3 heterojunction photoelectrode. This unique design of the nanoarchitecture provides an attractive pathway for the photogenerated electrons and the silver interlayers has great impact on enhancing charge separation and improving stability of photoanode.

Various solar conversion materials with 1D nanostructure have been developed and are being widely investigated for various solar fuel generation applications. In this study, aligned and non-aligned CdS nanowires (NWs) were synthesized on Cd foil or in solution via solvothermal processes. In the case of aligned CdS NWs, the relative intensity of the (0 0 2) diffraction peak was higher than that of the non-aligned CdS NWs, which indicated that the NWs grew preferentially in the (0 0 1) direction. The systematic comparison between the photoelectrochemical properties of both electrodes revealed that the aligned CdS NW electrode displayed markedly enhanced photocurrent (by a factor of 7), photoelectrochemical hydrogen production (by a factor of 10), and photostability in comparison with those of the non-aligned NWs electrode fabricated on FTO glass. Resistance (Rµ) through the inner part of the aligned CdS NWs was very small due to a low grain-boundary resistance (by a factor of 130). This low resistance induced efficient charge transfer, reducing the charge recombination loss and assisting the charge transport along the axial direction of the aligned NWs. Time-resolved photoluminescence spectroscopy confirmed that the charge separation in the aligned CdS NWs is longer than that in the non-aligned CdS NWs (by a factor of 1.6).

In present work, we synthesized ZnFe2O4 nanorods on a fluorine-doped tin oxide substrate using spray coating method followed by two-step high-temperature quenching (HTQ). X-ray photoelectron spectroscopy (XPS) results indicate that Sn4+ is diffused from the FTO substrate after the second quenching, which could help in minimizing the recombination of photogenerated carriers. Photoelectrochemical measurements of the ZnFe2O4 nanorod photoelectrodes quenched at 780 °C, 800 °C, and 820 °C indicate that among the studied samples (ZFO1, ZFO2 and ZFO3), the highest photocurrent density was observed for nanotextured ZFO3 photoelectrodes (130 µA cm−2 at 1.23 V vs RHE). The photoelectrochemical performances of the ZnFe2O4 nanorods after the second quenching were compared with those of the firstly quenched ZnFe2O4 nanorod samples; water-oxidation photocurrent density of the former (ZFO3) was increased by 6.9 times compared with that of the first quenching (PZFO). Intensity modulated photocurrent spectroscopy (IMPS) and photoluminescence (PL) results confirm the faster charge extraction was achieved for the ZFO3 photoelectrode. Thus, the overall photocurrent density during the second quenching process results from the effectively improved crystallinity, the reduced strain and suppressed charge–carrier recombination's on both the surface as well as in the bulk of the ZnFe2O4 nanorods. In terms of solar water splitting, these research findings provide an effective route for the synthesis of other nanostructures.

Here, we establish a methodology and phenomena for systematically assessing the photoelectrochemical transformation of the BiVO4 to Bi2S3/BiVO4 hybrid heterostructure during in-situ solar hydrogen ...

This work focuses on dependence of incident light illumination direction on the photoelectrochemical performance of hydrothermally prepared two dimensional ZnIn2S4 nanosheets/one dimensional rutile TiO2 nanorod arrays (2D ZIS NS's/1D R-TNR's) heterostructure photoelectrodes. The 2D ZIS NS's are grown on the 1D R-TNR's/FTO substrates by varying the concentration of ZIS precursor in the hydrothermal method, forming 2D ZIS NS's/1D R-TNR's heterostructure. One dimensional rutile TiO2 nanorod arrays (1D R-TNR's) provide excellent electron transfer pathway and role of the 2D ZIS NS's is to offer effective visible light absorbing surface onto the 1D R-TNR's and extended the absorbance spectrum from ultraviolet to visible region; bathochromic shift occurs. This binary heterostructure provides the lower resistance, shortest electron transport time and less recombination under the back side illumination (BSI) and effectively contributed to charge separation and transport in 2D ZIS NS's/1D R-TNR's heterostructure. However, the results demonstrate that the front side illumination (FSI) results in poor PEC performance; because of blockage of light at the surface of 2D ZIS NS's. Further, these results show that BSI could also be applicable for other heterostructures, where the low band gap sulfide materials need to be engineered on large band gap metal oxide for energy harvesting in future prospect.

The vertically aligned TiO2 nanorod arrays (NRA) with manipulated aspect ratio were hydrothermally synthesized by changing the amount of the titanium (Ti) precursor in the initial growth solution. FE-SEM images show the optimum morphology, density and aspect ratio of the well-aligned TB-1.2 NRs on the surface of the FTO substrate. The UV-vis-absorption measurements revealed that a sample prepared at TB-1.2 can provide an increased light trapping effect. PEC analyses demonstrated that the TiO2 nanorods deposited at TB-1.2 of Titanium butoxide show a relatively high PEC conversion efficiency (3.5 times) compared with the TB-0.8 prepared TiO2 at a 1.0 V versus RHE. The higher PEC performance is believed to be the result of an enhancement of the optimum aspect ratio, light trapping, an efficient charge separation, and the high carrier transport in the vertically aligned TiO2 NRs. Further, the PEC based organic dye degradation experiments showed 77% and 94% removal of Orange II and methylene blue respectively. Additionally, 109 μmol h−1 cm−2 hydrogen generations were attributed using optimized vertically aligned TiO2 NRA’s. Thus, the appropriate morphology manipulated the TiO2 NRAs are useful for solar conversion applications.

In present article, WO3 thin films have been successfully synthesized by chemical spray pyrolysis approach. The effect of spraying quantity of solution onto the photoelectrochemical (PEC), structural, morphological, and optical properties has been studied. Film prepared at 40 ml solution quantity shows the excellent photoelectrochemical performance (Isc= 0.69 mA/cm2 and Voc = 0.64 V) in 0.05 M concentrated H2SO4 electrolyte. X-ray diffraction studies reveal that the synthesized WO3 thin films are polycrystalline with monoclinic crystal structure. The chief vibrational modes of the WO3 sample, located at 712.64 and 804.28 cm−1 corresponding to the stretching and the bending of O W O bond respectively and are consistent with a monoclinic structure. The estimated band gap energy of WO3 thin films varies from 2.37 to 2.45 eV with respect to quantities of spraying solution and it exhibits absorption in visible region. Film shows a maximum specific surface area of 31.63 m2/g. Photoelectrocatalytic degradation of brilliant blue dye in aqueous solutions is studied. The end result shows that the degradation percentage of brilliant blue using WO3 photoelectrode has reached 92% under visible light illumination after 240 min. The enhancement in photoelectrocatalytic activity of optimized 40 ml WO3 sample is mainly due to the suppressed the recombination rate of photogenerated electron–hole pairs. This study provides an effective WO3 photoelectrode for removing of organic pollutants present in the water.

The need to utilize TiO2 based metal oxide hetero nanostructures for the degradation of environmental pollutants like Rhodamine B and reactive red 152 from the wastewater using stratified WO3/TiO2 catalyst under sunlight illumination. WO3, TiO2 and stratified WO3/TiO2 catalysts were prepared by a spray pyrolysis method. It was found that the stratified WO3/TiO2 heterostructure has high crystallinity, no mixed phase formation occurs, strong optical absorption in the visible region of the solar spectrum, and large surface area. The photocatalytic activity was tested for degradation of Rhodamine B (Rh B) and reactive red 152 in an aqueous medium. TiO2 layer in stratified WO3/TiO2 catalyst helps to extend its absorption spectrum in the solar light region. Rh B and Reactive red 152is eliminated up to 98 and 94% within the 30 and 40 min respectively at optimum experimental condition by stratified WO3/TiO2. Moreover, stratified WO3/TiO2 photoelectrode has good stability and reusability than individual TiO2 and WO3 thin film in the degradation of Rh B and reactive red 152. The photoelectrocatalytic experimental results indicate that stratified WO3/TiO2 photoelectrode is a promising material for dye removal.

This data article presents the experimental evidences of the effect of TiO2-fluorine doped tin oxide interface annealing and Ni(OH)2 cocatalysts on the photoelectrochemical, structural, morphological and optical properties of Ni(OH)2/CdS/ZnIn2S4/TiO2 heterojunction. The Raman spectroscopy exhibits the sharp features of the rutile phase of TiO2 and in agreement with the X-ray diffraction data. The band gap energy of the 500 °C sample was found to be 3.12 eV, further it was increased to 3.20, 3.22 eV for samples annealed at 600 and 700 °C respectively. The decrease in the band gap energy at 500 °C related to the oxygen vacancies and was analysed by photoluminescence spectroscopy analysis. The synthesis, characterization methods and other experimental details of TiO2 based heterostructure are also provided. The presence of CdS and ZnIn2S4 coating on surface of TiO2 electrodes providing a high surface area, extended visible absorption and helps to improve the change separation. This data article contains data related to the research article entitled “Highly efficient and stable 3D Ni(OH)2/CdS/ZnIn2S4/TiO2 heterojunction under solar light: Effect of an improved TiO2/FTO interface and cocatalyst” (Mahadik et al., 2017) [1]. Keywords: Annealed TiO2 nanorods, CdS/ZnIn2S4/TiO2 heterostructure, Ni(OH)2 cocatalyst, TiO2-FTO interface

In this study, we present an advanced strategy of low-temperature hydrogen annealing combined with high- temperature quenching in air for activating α-Fe2O3 nanorod photoanodes to boost the photoelectrochemical performance. We report that various low-temperature annealing conditions (340, 360, 380, and 400 °C) under hydrogen gas flow convert β-FeOOH into magnetite (Fe3O4) as well as introduce Sn4+ diffusion from FTO substrates to its surface. Furthermore, high-temperature quenching (800 °C) resulted in the phase change of magnetite (Fe3O4) into hematite (α-Fe2O3) and self Sn4+ doping into the hematite lattice. Thus, the hydrogen-assisted thermally activated hematite photoanode achieved a photocurrent density of 1.35 mA cm-2 at 1.23 V vs. RHE and 1.91 mA cm-2 at 1.4 V vs. RHE, which is 70% and 80% higher than that of directly quenched hematite at 800 °C. These combined two step strategies provide new insight into high Sn-self doping for α-Fe2O3 photoanodes and allow for further development of more efficient solar water oxidation systems.

A novel inorganic-organic Se rich-ZnSe(en)0.5 red-brick (ZnSe(en)0.5 RB) was developed on Zinc (Zn) foil through a low-temperature solvothermal synthesis. The structure evolution and growth mechanism of ZnSe(en)0.5 RB were systematically proposed at 80 °C by varying the solvothermal times (2−12 h) . In the reaction system, adsorption of reduced Se2− in presence of ethylenediamine ((en)0.5) induced the red-brick (RB) color to ZnSe(en)0.5. Furthermore, Cd2+ ion-exchange strategy was adopted for converting ZnSe(en)0.5 RB into dual nanoarchitecture photoelectrode (ZnO-Zn1-xCdxSe). The optimum ZnO NR-Zn1-xCdxSe NP 160 photoelectrode converted from ZnSe(en)0.5 RB-12 exhibited a photocurrent density of 13.14 mA·cm-2 at -0.2 V vs. Ag/AgCl with 237.79 μmol·cm−2 hydrogen evolution over 3 h. The enhanced photocurrent performance was due to the effective light absorption, and the prolonged recombination lifetime. The charge separation and transport mechanisms during photoelectrochemical hydrogen production were also investigated in detail.

Highly crystalline Cu 2 ZnSnS 4 (CZTS) thin films have been deposited onto glass and FTO coated glass substrates by simple chemical spray-pyrolysis technique. It is an important material for solar energy conversion through the both photovoltaics and photocatalysis. The effect of substrate temperatures on the physico-chemical properties of the CZTS films is studied. The XRD study shows the formation of single phase CZTS with kesterite structure. FE-SEM analysis reveals nano flakes architecture with pin-hole and crake free surface with more adherent. The film deposited at optimized substrate temperature exhibits optical band gap energy of 1.90 eV, which lies in the visible region of the solar spectrum and useful for photocatalysis application. The photoelectrocatalytic activities of the large surface area (10 × 10 cm 2 ) deposited CZTS thin film photocatalysts were evaluated for the degradation of sugarcane factory wastewater under visible light irradiation. The results show that the CZTS thin film photocatalyst exhibited about 90% degradation of sugar cane factory wastewater. The mineralization of sugarcane factory wastewater is studied by measuring chemical oxygen demand (COD) values.

Anatase/rutile TiO 2 nanorods composites were prepared by a facile hydrothermal method followed by dip coating method using titanium isopropoxide in acetic acid and ethanol solvent. The effects of the titanium isopropoxide precursor concentration, on the formation of dip coated anatase/rutile TiO 2 nanorods composite were systematically explored. The growth of anatase on rutile TiO 2 nanorods can be controlled by varying the titanium isopropoxide concentration. The morphological study reveals that anatase TiO 2 nanograins formed on the surface of rutile TiO 2 nanorod arrays through dip coating method. Photoelectrochemical analyses showed that the enhancement of the photocatalytic activities of the samples is affected by the anatase nanograins present on the rutile TiO 2 nanorods, which can induce the separation of electrons and holes. To interpret the photoelectrochemical behaviors, the prepared photoelectrodes were applied in photoelectrochemical solar hydrogen generation and orange II dye degradation. The optimized photocurrent density of 1.8 mA cm −2 and the 625 μmol hydrogen generation was observed for 10 mM anatase/rutile TiO 2 NRs composites. Additionally, 96% removal of the orange II dye was achieved within 5 h during oxidative degradation under solar light irradiation. One of the benefits of high specific surface area and the efficient photogenerated charge transport in the anatase/rutile TiO 2 nanorod composite improves the photoelectrochemical hydrogen generation and orange dye degradation compared to the rutile TiO 2 . Thus, our strategy provides a promising, stable, and low cost alternative to existing photocatalysts and is expected to attract considerable attention for industrial applications.

In the present work, stratified WO 3 /ZnO thin films have been prepared by simple chemical spray pyrolysis technique. The structural, morphological, compositional and photoelectrocatalytic properties of the stratified WO 3 /ZnO thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (I sc ) and open circuit voltage (V oc ) are (I sc = 1.023 mA and V oc = 0.980 V) relatively high at 40 ml spraying quantity of ZnO solution on pre-deposited WO 3 thin films. XRD analysis reveals that stratified WO 3 /ZnO thin films are polycrystalline with monoclinic and hexagonal crystal structures for WO 3 and ZnO respectively. The specific surface area of the stratified WO 3 /ZnO thin film is found to be 48.12 m 2 g −1 . The enhanced photoelectrocatalytic activity of stratified WO 3 /ZnO is mainly due to the suppressing the recombination of photo generated electron-hole pairs. The end result shows that the degradation percentage of phthalic acid (PA) using stratified WO 3 /ZnO photo electrode has reached 63.63% after 320 min. under sunlight illumination. The amount of mineralization of phthalic acid is studied with the help of chemical oxygen demand (COD) measurement.

Layered WO3/TiO2 thin films have been deposited onto glass and FTO coated glass substrates using spray pyrolysis method. The structural, morphological, compositional and photocatalytic properties of layered WO3/TiO2 thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (Isc) and open circuit voltage (Voc) are (Isc = 0.575 mA and Voc = 0.485 V) relatively high at 15 ml spraying quantity of TiO2 solution on pre-deposited WO3. SEM images show that the substrate surface is well covered with a uniform and round shaped TiO2 nanoparticles. The AFM images show the rough nature of the film. The specific surface area of the layered WO3/TiO2 thin film is found to be 62.14 m2 g−1. Photoelectrocatalytic degradation of benzoic acid (BA) in aqueous solutions is studied. The end result shows that the degradation percentage of BA using layered WO3/TiO2 photoelectrode has reached 46.56% under sunlight illumination after 320 min. The amount of degradation is confirmed by COD analysis.

With the application of ethylenediamine (EDA) as a solvent, a template, and co-ordination agents, novel photoanode architecture of the cadmium sulfide (CdS) nanoflower (NF)/rutile(R)-TiO2 nanorod (NR) heterojunction is successfully synthesized using a facile two-step hydrothermal process. The optimized CdS (medium concentration; MC) NF/R-TiO2 NR heterojunction exhibited a greatly enhanced visible-light photoelectrochemical (PEC) performance, whereby the highest photocurrent density of 3.23 mA cm–2 at 0.1 V versus Ag/AgCl and a photoconversion efficiency (PCE) of 0.46% were achieved under solar light irradiation. The optimal photocurrent density of the CdS (MC) NF/R-TiO2 NR heterojunction, photoanode is 2.54 times (60.68%) higher than that of the pristine R-TiO2 NR because of an effective light absorption, an appropriate band-edge position, and the charge separation. Furthermore, the open circuit voltage (VOC) was shifted from −0.85 V to −1.34 V due to the grafting of the CdS NF onto the R-TiO2 NR facet; t...

In the present work, we accomplish the boosting of photocatalytic performance by the synergistic effect of acid treatment and transition metal oxide co-catalysts on molten salt rutile TiO2 nanorods. FT-IR and XPS (oxygen deconvolution) results confirmed that the amount of hydroxyl groups increased on the surface of rutile TiO2 nanorods (TO-NRs) after acid treatment. HR-TEM analysis revealed fine dispersion of metal oxide on the surface of acid treated TiO2 nanorods (ATO-NRs). The photocatalytic activities of as-prepared (TO-NRs), acid treated (ATO-NRs), metal oxide loaded (MTO-NRs), and both acid treated and metal oxide loaded (MATO-NRs) nanorods were compared based on the rate kinetics and dye degradation efficiencies. Cobalt oxide (1 wt %) loaded and 1.0 M acid treated TiO2 nanorods (Co/ATO-NR) exhibited the higher photocatalytic degradation efficiency for Orange-II dye degradation and inactivation of S. typhimurium pathogen compared to other photocatalysts under solar irradiation. Photoelectrochemical ...

Controlling the morphology of semiconductors at the nanoscale level is the key for efficient photoelectrochemical (PEC) water splitting systems. Herein, we report for the first time the fabrication of porous hematite nanoball array film on conducting FTO via a facile pulse reverse electrodeposition method using cetyltrimethylammonium bromide (CTAB) surfactant and a TiO2 underlayer (UL) on FTO. A prolonged low-temperature-annealing treatment is employed to convert iron into hematite (α-Fe2O3) and to remove the surfactant molecules gradually. Annihilation of surfactant molecules led to the creation of pores during crystallization of hematite nanoballs, thereby providing low-resistant diffusion pathways for the migration and incorporation of cations (Ti4+ from UL and Sn4+ from FTO) in hematite. The hematite photoanode with porous nanoball array exhibited significantly higher PEC performance than the flat hematite due to sixfold enrichment in the donor density, improved charge-transfer properties, and higher light absorption. The enhancement in photocurrent and water oxidation performance of porous hematite photoanode is also feasible when coupled with well-known Co and CoPi catalysts. Thus, our new approach allowed the simple fabrication of hematite films with nanoporous architecture for enabling high photon harvesting and maximized interfacial charge transfer to facilitate water oxidation reaction.

CdS-sensitized 1 D Zr:Fe2 O3 nanorod arrays were synthesized on fluorine-doped tin oxide substrates by a two-step hydrothermal method. The photoelectrochemical results demonstrate that the current density (4.2 mA cm-2 at 0 V vs. Ag/AgCl) recorded under illumination for the CdS/1 D Zr:Fe2 O3 photoanodes is 2.8 time higher than the bare 1 D Zr:Fe2 O3 . The extended absorbance spectrum, the reduced recombination, and the effective transport of photogenerated holes in CdS to the electrolyte facilitate enhancement in the photoelectrochemical performance. From X-ray photoelectron spectroscopy and TEM observations of the bare and aluminum oxide-treated CdS/1 D Zr:Fe2 O3 photoanodes, we could confirm that the 1 D Zr:Fe2 O3 nanorods were covered by the CdS layer and Al2 O3 layer present on surface of CdS. Furthermore, the photocurrent and stability of the CdS/1 D Zr:Fe2 O3 nanorods was significantly enhanced by Al2 O3 compared to bare CdS/1 D Zr:Fe2 O3 heterojunction owing to its ability to act as an effective holetransport- as well as photocorrosion-protecting layer. These remarkable enhancements in light-energy harvesting, improvement in charge transport, and stability directly suggest the usefulness of photoanodes for solar hydrogen generation.

The WO 3 and stratified WO 3 /TiO 2 thin films are successfully prepared by the spray pyrolysis method. The structural, morphological, compositional and photoelectrocatalytic properties of WO 3 and stratified WO 3 /TiO 2 thin films are studied. XRD analysis confirms that films are polycrystalline with monoclinic and tetragonal crystal structures for WO 3 and TiO 2 respectively. The SEM images clearly show 3D sheeted porous structure of the as-prepared TiO 2 forms on WO 3 in stratified WO 3 /TiO 2 samples. The synthesized photoelectrodes was used as catalyst for photoelectrocatalytic degradation of oxalic acid in aqueous medium. The rate constant (k) was evaluated as a function of the initial concentration of species. A significant decrease in concentrations of organic species was observed from COD analysis. The photoelectrocatalytic degradation effect is relatively higher in the case of the stratified WO 3 /TiO 2 than WO 3 thin film photoelectrode in the degradation of oxalic acid and 83% removal efficiency of oxalic acid is obtained after 180 min. Based on the obtained experimental data, the possible photoelectrocatalytic reaction mechanism was proposed. The photoelectrocatalytic experimental results indicate that stratified WO 3 /TiO 2 photoelectrode is the promising material for removing of water pollutants.

Well-defined CdS nanograin-sensitized one-dimensional (1D) Zr:α-Fe2O3 nanostructured arrays with enhanced photoelectrochemical performance are synthesized directly on F-doped SnO2 (FTO) using the hydrothermal method. Owing predominantly to the appropriate photogenerated electron-hole separation and charge collection in 1D Zr:α-Fe2O3 nanorods, hydrothermally deposited CdS/1D Zr:α-Fe2O3 samples exhibit improved photocurrent density over CdS/Fe2O3 nanosheets prepared by other methods. In our work, compared with 1D Zr:α-Fe2O3, the CdS-sensitized 1D Zr:α-Fe2O3 nanorod arrays show 1.9 times improved photoelectrochemical performance. Unfortunately, CdS nanograin-sensitized 1D Zr:α-Fe2O3 nanorod arrays suffer from instability problem. Nickel hydroxide loading, however, can boost the photoelectrochemical performance of the heterojunction and also act as a protective layer that improves the stability of the Ni(OH)2/CdS/1D Zr:α-Fe2O3 electrode compared to CdS/1D Zr:α-Fe2O3. This enhanced PEC activity may be ascribed to the strong heterojunctions between CdS nanograins and 1D Zr:α-Fe2O3 nanorod arrays as well as effective charge separation. This work will provide a new insight into the fabrication and protection of many new photosensitive electrode materials to engineer photoelectrochemical and photocatalytic devices in the near future.

A simple and effective strategy was used to fundamentally improve the performance of a heterostructured Ni(OH)2/CdS/ZnIn2S4/TiO2 photoanode. TiO2 nanorods grown hydrothermally on fluorine-doped tin oxide (FTO) and annealed at 500 °C yielded an optimal photocurrent density of ~988 μA cm–2 at 0.1 V vs. Ag/AgCl under simulated illumination conditions. The annealing process minimized the defects in TiO2 and assisted in the formation of close contacts between the FTO and TiO2 nanorods, which allowed for efficient electron transport. The stepwise introduction of ZnIn2S4 and CdS on annealed TiO2 enhanced absorption in the visible range and electron/hole separation in CdS/ZnIn2S4/TiO2. Additionally, the Ni(OH)2 cocatalyst functioned in hole trapping and improved the stability of the photoelectrode through timely consumption of the photogenerated charges, particularly the holes.

Synchronized surface modification and doping of hematite nanorod via sputtering is one of the impressive methods to develop photoanodes for practical application. In this paper, we report the role of Zr sputtering and 800 °C quenching on the structural and electrochemical properties of FeOOH NRs. The amount of ZrOx loading onto β-FeOOH NRs was controlled by varying the sputtering time. FESEM and TEM images revealed that high-temperature quenching of Zr-sputtered β-FeOOH NR’s confirms the Zr doping and non-uniform ZrO2 nanoparticles on vertically aligned Zr-doped hematite (Zr-Fe2O3 NRs). XPS analysis represented a tradeoff between extrinsic Zr doping and intrinsic Sn diffusion with increasing the thickness of deposited Zr layer in Zr-Fe2O3 NRs. A maximum achieved photocurrent density (1.23 mA/cm2 at 1.23 V vs RHE) for the 7 nm Zr-Fe2O3 sample is 48% higher than that of pristine photoanode (Fe2O3 NRs). The electrochemical impedance spectroscopy and Mott-Schottky analyses revealed that the charge transfer properties and donor densities were effectively improved for Zr-Fe2O3 NRs photoanode. The photoelectrochemical reactor consisted of an optimum 7 nm Zr-Fe2O3 based photoanode exhibits the 115 and 165 μmol, respectively O2 and H2 evolution over 10 h of 1 sun illumination. These results demonstrate the Zr sputtering approach followed by high-temperature quenching allows controlled Zr doping in vertically aligned Fe2O3 NRs for PEC water splitting applications.

Herein, dual nanostructured ZnO nanorod (NR)-Zn1-xCdxS porous nanosheet (PNS) photoanodes were produced on a zinc foil through cation exchange reaction of inorganic–organic hybrid ZnS(en)0.5 nanosheets. ZnS(en)0.5 NS’s photoanodes have been synthesized via a facile solvothermal method followed by a series of cadmium (Cd2+) ion-exchange using various ion-exchange reaction times and temperatures. During Cd2+ ion-exchange, the Zn1-xCdxS PNS and a new type of vertically aligned ZnO NR were subsequently grown on the zinc foil substrate. The different exposed surfaces of the vertically aligned hexagonal ZnO NR and Zn1-xCdxS PNS photoanodes contribute to appropriate morphology, effective light harvesting, and efficient charge separation in ZnO-NR-Zn1-xCdxS PNS160C. The optimum ZnO NR-Zn1-xCdxS PNS160C photoanode contributed the highest photocurrent density of 6.60 mA·cm−2 and hydrogen production of 250.65 μmol·cm−2 at 0 V vs. Ag/AgCl. Finally, the charge transfer mechanism in the optimum photoanode is discussed in detail.

A nanocomposite heterojunction photoanode involving CdS nanoflowers (NFs) and one-dimensional TiO 2 nanotube (NT) arrays was reported. The self-assembled TiO 2 NT arrays were fabricated by an anodization method and the surface of TiO 2 NT arrays was decorated with CdS NFs by employing hydrothermal method for the first time. The CdS NF morphology was optimized by controlling the hydrothermal reaction time from 0 to 72 h. Field-emission scanning electron microscopy (FESEM) study of the CdS-NF/TiO 2 -NT photoanode revealed good coverage of hydrothermally grown CdS NFs on the surface of TiO 2 NT arrays. The photoelectrochemical measurements were performed under 100 mW cm −2 illumination using polysulfide electrolyte. A 5.5-fold photocurrent enhancement was observed for the CdS-NF/TiO 2 -NT array photoanode synthesized with a 48 h CdS hydrothermal reaction compared to a pristine TiO 2 NT array film. Annealing of TiO 2 NTs as well as CdS NFs led to further improvement in the photocurrent on account of greater crystallinity, significantly higher visible light photon absorption and improved interface properties between CdS and TiO 2 . These findings were supported by optical absorption, electrochemical impedance spectroscopy and Mott–Schottky analyses.

We designed metal oxide coated ZnIn 2 S 4 /TiO 2 (ZT) heterostructure photoanodes for enhanced photoelectrochemical performance via hydrothermal and dip-coating methods. The effects of thin metal oxide coating layers, such as TiO 2 , Al 2 O 3 , and SiO 2 , on the structural, morphological, optical, and photoelectrocatalytic activity of ZT photoanodes were investigated in detail. The metal oxide coating layers significantly enhanced the photoelectrochemical performance of ZT in the following order: SiO 2 /ZT > Al 2 O 3 /ZT > TiO 2 /ZT > ZT, all at pH 11.5 under simulated one sun illumination. A two-fold boost in the photocurrent density of ZT was recorded after a surface coating of a thin SiO 2 layer among the studied metal oxide layers. The charge transfer resistance measured from the electrochemical impedance spectroscopy (EIS) analysis was less for the SiO 2 /ZT photoanode, indicating enhanced charge separation between the oxide surface layer and electrolyte. The enhanced photoelectrochemical performance due to the thin SiO 2 coating was attributed to the improved interface properties that led to the effective charge transfer processes in the vicinity of the electrolyte.

The Ni0.4Zn0.6Fe2O4 ferrite, BaTiO3 ferroelectric and Ni0.4Zn0.6Fe2O4–BaTiO3 bilayered magnetoelectric thin films have been synthesized onto the quartz substrates at optimized substrate temperatures (400, 250 °C) using the simple spray pyrolysis technique. These films were characterized for their structural, morphological, dielectric and magnetic properties. The XRD studies reveal that the films are polycrystalline in nature with spinel cubic structure. The morphological study shows the formation of agglomerated cubes like grains. The dielectric constant and dielectric loss is measured as a function of frequency in the frequency range 20 Hz–1 MHz. Impedance spectroscopy is used to study the electrical behavior of these thin films. The saturation magnetization of Ni0.4Zn0.6Fe2O4 ferrite and Ni0.4Zn0.6Fe2O4–BaTiO3 bilayered thin films are 141 and 111 emu cm−3, respectively. The value of magnetoelectric voltage obtained for Ni0.4Zn0.6Fe2O4–BaTiO3 bilayered thin films is about 221 mV.

WO3 thin films have been deposited onto glass and FTO coated glass substrates using a simple chemical spray pyrolysis technique. The structural, morphological, optical and photocatalytic properties of WO3 thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (Isc) and open circuit voltage (Voc) are (Isc=0.38 mA and Voc=0.59 V) relatively higher at 300 °C substrate temperature. The structure and morphology of WO3 thin films are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD study reveals that the films are polycrystalline in nature with monoclinic crystal structure. SEM images show that the substrate surface is covered with a uniform and grain like morphology. The AFM images show the rough nature of the film. The structure and local symmetry of the film are studied with the help Raman spectroscopy. The chief vibrational modes of the WO3 sample, located at 805, 715 and 269 cm−1 corresponding to the stretching and the bending of O–W–O bond respectively and are consistent with a monoclinic structure and the low-frequency peaks are observed at 269 and 325 cm−1 can be assigned due to the bending δ (O\W\O) vibrations in monoclinic structure. Photoelectrocatalytic degradation of methyl orange (MO) dye in aqueous solutions is studied. The end result shows that the degradation percentage of methyl orange (MO) using WO3 photoelectrode has reached 98% under visible light illumination after 320 min. The amount of degradation is confirmed by COD and TOC analysis.

Herein, we synthesized porous Zn1-xCdxS nanosheets (PNS)/ZnO nanorod (NR) heterojunction photoanode via self-templated conversion using successively hydrothermal and Cd2+ ion exchange methods. Moreover, after conversion of ZnO to inorganic–organic hybrid ZnS-1,6-hexanediamine (HDA)0.5nanosheets/ZnO NR material, Cd2+ ion exchange was conducted. It was confirmed from X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM) analyses that the inorganic–organic hybrid ZnS(HDA)0.5 NS was transformed into Zn1-xCdxS PNS/ZnO NR heterojunction photoanode via the replacement of Zn2+ by Cd2+ ion. Zn1-xCdxS PNS/ZnO NR-160C3H heterojunction photoanode synthesized at 160 °C for 3 h showed the highest photocurrent density of 4.10 mA cm−2 (vs. RHE) under 1.5 G illumination, which was 7.9 times higher than that of bare ZnO NR photoanode. The porous nanostructured morphology and larger surface area of Zn1-xCdxS PNS/ZnO NR heterojunction photoanode fabricated by Cd2+ ion exchange result in efficient light absorption and effective charge transfer pathway. The photoluminescence (PL) and time-resolved photoluminescence (TRPL) results show the shorter lifetime (37 ns) and reduced recombination in Zn1-xCdxS PNS/ZnO NR-160C3H heterojunction photoanode. During PEC analysis, the possible charge transfer mechanism in Zn1-xCdxS PNS/ZnO NR heterojunction photoanode was proposed. Surface passivated Zn1-xCdxS PNS/ZnO NR-160C3H photoanode shows improved photostability and exhibited 3.8 times higher H2 evolution (161 μmol) than the Zn1-xCdxS PNS/ZnO NR-160C3H (42 μmol) photoelectrode at 0.9 V vs. RHE.

To tackle the problem of bulk recombination and to solve the holes diffusion issue in hematite, the shape-guiding and in situ doping is an effective strategy. Herein, we developed a novel strategy for designing and fabricating zirconium-doped transparent hematite (Zr-Fe2O3(I)) photoanode through an in situ hydrothermal method and stoichiometric iron and zirconium dilution. The concentration of ZrO(NO3)2 and FeCl3·6H2O in the precursor solution effectively influenced the transparency and morphology of zirconium-doped Fe2O3. The XPS and TEM analyses confirms the co-existence of Zr doping and surface modification of Fe2O3 nanocoral diffused ZrO2 after high temperature quenching. Synergism between the Zr doping and ZrO2 layer facilizes the charge transfer in Zr-Fe2O3 nanocoral (NC) photoanodes. Among the photoanodes prepared by variously diluted concentrations of the iron and zirconium precursor, the in situ 1/32 Zr-Fe2O3 nanocoral (NC) photoanode achieved an excellent photocurrent density of 1.55 mA cm2 at 1.23 V vs. RHE, which is about doubles than that of the conventional pristine Fe2O3 (P-Fe2O3) NR. Additionally, as result of in situ Zr doping, favorable nanocoral morphology and ZrO2 surface modification exhibits the decreased changer transfer resistance and increased incident photon to current efficiency (IPCE) of 1/32 Zr-Fe2O3 NC upto 21.9%. This in situ Zr-doping and nanocoral morphology 1/32 Zr-Fe2O3 fulfills the requirements of both high charge separation efficiency and improved water oxidation kinetics. A novel 1/32 Zr-Fe2O3 (I) NC photoanode exhibits O2 and H2 evolution up to 69 and 138 μmol during 5 h of overall pure water splitting. This novel in situ hydrothermal dilution approach is feasible for fabricating a transparent hematite photoanode with NC morphology for practical PEC water splitting.

The Zr-doped ZnFe2O4 (Zr-ZFO) nanocorals photoanode have been synthesized from Zr-doped FeOOH (Zr–FeOOH) nanocorals on fluorine-doped tin oxide (FTO) substrate followed by Al2O3/Co–Pi surface modification for effective PEC water splitting. The hydrothermal method was adopted for the synthesis of in situ Zr doping in FeOOH, while Zr-ZFO nanocorals was fashioned by subsequent additional procedures, such as Zn(NO3)2 precursor dropping, first quenching, etching and second quenching. The Al2O3 layer decreases the over-potential of the Zr-ZFO photoanode‖electrolyte interface as well as lowers the charge transfer resistance which aids to increase in the photocurrent density from 0.24 mA/cm2 to 0.36 mA/cm2 at 1.23 V vs. RHE under 1 sun illumination condition. The subsequent loading of cobalt phosphate (Co–Pi) as a co-catalyst leads to an improved photocurrent density of 0.49 mA/cm2 at 1.23 V vs. RHE. These synergistic effects of Zr doping and surface modification led to remarkable improvement in photocurrent density from 0.19 mA/cm2 (at 1.4 V vs. RHE) for conventional ZFO nanorods to 0.65 mA/cm2 for the Zr-ZFO/Al2O3/CoPi photoanode. A systematic investigation into the effect of Zr doping and Al2O3/Co–Pi overlayer reveals the reduction of two distinct recombination processes (bulk and surface) in ZFO photoanode.

An inorganic–organic CdSe(en)0.5/CdIn2S4/TiO2 complex heterostructure was successfully synthesized using a facile solvothermal method. The morphology of a CdSe(en)0.5/CdIn2S4/TiO2 heterostructure was controlled by varying the concentrations of cadmium nitrate and selenium precursors in ethylenediamine. Intentionally controlling the morphology enhances the absorption within the visible region compared to a ZnIn2S4/TiO2 photoanode. The photoelectrochemical (PEC) study shows that the CdSe(en)0.5/CdIn2S4/TiO2 photoanode complex heterostructure exhibits a photocurrent density of 2.43 mA cm−2 at 0 V versus Ag/AgCl, which is 180% higher than that of a ZnIn2S4/TiO2 photoanode. The extra-delayed lifetime and photostability of CdSe(en)0.5/CdIn2S4/TiO2 complex heterojunction is cause of efficient hole scavenging. During the PEC measurement, the Se and ethylenediamine leaches out into the electrolyte while S2− from the Na2S + Na2SO3 electrolyte reacts with surface of the CdSe(en)0.5/CdIn2S4/TiO2 complex heterojunction. Such structure can effectively separate the charge carrier and yields 100 µmol of hydrogen within 3 h. The possible charge transfer mechanism during solar hydrogen generation in an inorganic–organic CdSe(en)0.5/CdIn2S4/TiO2 complex heterojunction structure has also been proposed.

In this paper, we focus on the controlled growth mechanism of α-Fe2O3 nanostructures via the hydrothermal method. The field emission scanning electron microscopy (FESEM) results reveal that at a lower hydrothermal time, the initial nucleation involves the formation of short and thin β-FeOOH nanorods. The subsequent increase in the hydrothermal time leads β-FeOOH to form thicker and longer nanorods. However, high-temperature quenching (HTQ) at 800 °C for 10 min causes the conversion of akaganeite to the hematite phase and activation of hematite by Sn4+ diffusion from a FTO substrate. Sn4+ diffusion from the FTO substrate to the hematite nanostructure was elaborated by X-ray photoelectron spectroscopy (XPS). An α-Fe2O3 nanorod photoanode prepared by a hydrothermal reaction for 3 h and HTQ exhibits the highest photocurrent density of 1.04 mA cm-2. The excellent photoelectrochemical performance could be ascribed to the synergistic effect of the optimum growth of α-Fe2O3 nanorod arrays and Sn4+ diffusion. Intensity modulated photovoltage spectroscopy (IMVS) studies revealed that the α-Fe2O3 photoanodes prepared at 3 h and HTQ exhibited a long electron lifetime (132.69 ms), and contribute to the enhanced PEC performance. The results confirmed that the controlled growth of the β-FeOOH nanorods, as well as Sn4+ diffusion, played a key role in charge transfer during the photoelectrochemical application. The charge transfer mechanisms in α-Fe2O3 nanostructure photoanodes prepared at different hydrothermal times and high-temperature quenching are also investigated.