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Developing efficient semiconductor photoanodes demonstrating strong light absorption, efficient separation of photogenerated charge carriers, and reduced charge carrier recombination rate can benefit PEC water splitting. Integrating a wide band gap semiconductor with narrow bandgap material with suitable band alignment can enhance PEC performance. Herein, we have fabricated novel MoO3/γ-In2Se3 heterostructure photoanodes using RF magnetron sputtering. The films structural, optical, morphological, and elemental composition were investigated in detail using low-angle XRD, Raman spectroscopy, XPS analysis, EDAX, and FESEM. The XRD, Raman, XPS, and EDAX results strongly confirmed the presence of desired phases of MoO3 and γ-In2Se3 layers in heterostructure without forming any impurity or alloy. FESEM micrographs revealed a uniform, dense grain structure. Optical analysis of MoO3/γ-In2Se3 done by UV–Visible spectroscopy shows increased absorption compared to pristine-MoO3. Conduction and valence band-edge potential values indicate that MoO3/γ-In2Se3 films are suitable for PEC hydrogen production. The PEC performance of these heterostructure photoanodes was evaluated by performing LSV, Chronoamperometry, EIS, and Mott–Schottky analysis. LSV results of MoO3/γ-In2Se3 showed a 10-fold increase in photocurrent density and attained higher photoconversion efficiency (0.5%) compared to pristine-MoO3 photoanode. EIS analysis revealed that MoO3/γ-In2Se3 photoanodes had small charge transfer resistance. Investigation of Mott Schottky results shows carrier density increases from 2.8 × 1019 cm−3 to 2.1 × 1020 cm−3 after incorporating γ-In2Se3 over MoO3. An increase in time-dependent photocurrent density reveals that MoO3/γ-In2Se3 films have effective electron-hole separation. Our finding suggests that MoO3/γ-In2Se3-based heterostructure photoanode can enhance light harvesting capacity and suppresses carrier recombination rate, eventually boosting PEC performance. Moreover, these results encourage the development of highly efficient photoelectrodes based on heterostructures for solar water-splitting applications. [ABSTRACT FROM AUTHOR]

Indium selenide (γ-In2Se3) films were prepared using RF magnetron sputtering. Influence of deposition time on structural, optical, morphological, and photoelectrochemical (PEC) performance was studied. Formation of γ-In2Se3 is confirmed by low angle XRD, Raman spectroscopy, and XPS analysis. Surface morphology investigated using FE-SEM shows that γ-In2Se3 films are uniform and have a dense grain structure, without cracks and holes. Optical properties show that γ-In2Se3films absorb mainly in the UV region, and the bandgap energy decreases from 2.81 to 2.27 eV as deposition duration increases. Conduction and valance band-edge potential values show that γ-In2Se3 films are suitable for photoelectrochemical hydrogen evolution. PEC activity of γ-In2Se3 photoanodes was evaluated using linear sweep voltammetry (LSV), and there was an increase in photocurrent density with deposition time. Electron impedance spectroscopy (EIS) analysis revealed that γ-In2Se3 photoanodes had high charge transfer resistance, and it decreases with deposition time, which leads to improved PEC performance. Investigation of Mott Schottky's (MS) results shows a shifting of flat band potential towards negative potential, suggesting movement of fermi level towards conduction band edge. Carrier density increases from 3.7 × 1019 cm−3 to 8.9 × 1020 cm−3 and depletion layer width of γ-In2Se3 photoanodes are found in the range of ~ 2.67–9.10 nm. The gradual increase in electron lifetime indicates a decrease in the recombination rate of photo-generated charge carriers. An increase in time-dependent photocurrent density reveals that γ-In2Se3 films have effective electron–hole separation. Our work demonstrates that γ-In2Se3 can be a probable candidate for PEC water splitting and opto-electronic applications. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of ZnO nanorod films onto FTO (fluorine-doped tin oxide) substrates using the solution-processed electrodeposition method. As-synthesized ZnO nanorod films obtained from electrodeposition were modified to form zinc ferrite (ZnFe2O4) thin films by Fe incorporation through varying molar concentrations. The formation of ZnFe2O4 films was confirmed by XRD and Raman spectroscopy. FE-SEM analysis shows a significant change in the growth morphology with an increase in Fe molar concentration. UV-Visible spectroscopy analysis showed that with an increase in Fe molar concentration, the absorption edge in ZnFe2O4 films shifts towards a higher wavelength with a reduction in the direct band gap. Finally, the PEC properties of ZnFe2O4 photoanodes were investigated for water splitting. The highest photocurrent density of ~ 353 μA/cm2 has been observed for ZnFe2O4 photoanode prepared at 2.0 M. Shift of flat band potential shift from −0.25 to −0.61 V with an increase in Fe molar concentration indicates a shift in the Fermi level towards the conduction band, which leads to an efficient charge transfer process across the electrolyte. Furthermore, increased carrier density and decreased depletion width with increased Fe molar concentration suggest easier diffusion of photo-generated charge carriers. The obtained results demonstrate that ZnFe2O4 can be a promising candidate for efficient PEC water splitting over the traditional ZnO photoanode. [ABSTRACT FROM AUTHOR]

Zinc oxide nano-sheets (ZNS) loaded with Zeolitic Imidazole Framework 8 (ZIF8) nanocrystals, i.e. (ZNS@ZIF8) thin films, were successfully synthesized using electrodeposition and facile chemical bath deposition (CBD) for photoelectrochemical (PEC) splitting of water. The formation of ZNS nano-sheets and ZIF8 nano-crystals has been confirmed by field emission scanning electron microscopy (FE-SEM), low angle X-ray diffraction (XRD), micro-Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy analysis. PEC activity of ZNS@ZIF8 photoanodes was evaluated using the linear sweep voltammetry (LSV) technique, and the photocurrent density is significantly enhanced when ZNS are decorated with ZIF8 nanocrystals. Electrochemical impedance spectroscopy (EIS) revealed that ZNS@ZIF8 had low charge transfer resistance compared to pristine ZNS counterparts. This led to considerably improved PEC performance of ZNS@ZIF8. Mott–Schottky (M–S) analysis of ZNS and ZNS@ZIF8 revealed a shift of flat band potential for the ZNS and ZNS@ZIF8 photoanodes, respectively. The shift of flat band potential indicates a clear shift in the Fermi level towards the conduction band, leading to an efficient charge transfer process across the electrolyte. The carrier density of ZNS and ZNS@ZIF8 photoanodes increases from 3.67 × 1019 cm−3 to 4.11 × 1020 cm−3. The enhanced applied bias photon conversion efficiency (ABPE) of ZNS@ZIF8 photoanodes suggests that ZNS@ZIF8 can be a prospective candidate for PEC and optoelectronic applications. [ABSTRACT FROM AUTHOR]

One step electrodeposition method has been used to realize highly porous ZnO pin hole (ZP) and ZnO rosette sheets (ZS) nanostructure based photo-anodes for efficient photoelectrochemical (PEC) splitting of water. Electrodeposited ZP and ZS based photo-anodes exhibit enhanced photocurrent density of 0.62 mA/cm2 and 0.76 mA/cm2 respectively (at a bias of 0.75 V). Further on hydrothermal amination (A), these electrodeposited ZP and ZS (A-ZP and A-ZS) nanostructure based photo-anodes had shown enhanced photocurrent density of 1.02 mA/cm2 and 1.27 mA/cm2, respectively. Surface morphology, evolution and elemental study were done using FESEM and EDX. Raman spectra of aminated photo-anodes have peaks at ∼270 cm−1 and ∼511 cm−1 related to stretching vibration mode between Zn N and Zn O. The peaks at wave number ∼558 cm−1 and ∼571 cm−1 is due to formation of Zn C bonds and because of complex defects respectively. ZnO exhibits low PEC activity, but on nano-structuring in the form of ZP and ZS improves its light absorption capacity. Hydrothermal amination red shifts (∼25 nm) the absorption band at ∼ 425 nm. The N and C act as electron reservoirs in A-ZP and A-ZS photo-anodes and efficiently separate the photo-generated electron/hole pairs and restrain charge recombination to generate photo-reactive sites. Electrochemical impedance spectroscopy (EIS) revealed that A-ZP and A-ZS had low charge transfer resistance compared to their bare counterparts. This lead to considerably improved PEC performance. An unprecedented increase in IPCE values in A-ZP and A-ZS can be assigned to the decrease in band gap and thereby significant enhancement in photocurrent density. These result in to proper charge segregation and improved charge transportation. The maximum value of IPCE is 9.6% for A-ZS sample and it is also clear that ZP and ZS nanostructured film have higher IPCE values at ∼400 nm than traditional ZnO thin film. A-ZP and A-ZS based photo-anodes have exhibited enhanced PEC performance as evident from IPCE measurements and thus can be a prospective candidate for PEC and optoelectronic applications. • Influence of amination on zinc oxide nanostructures is discussed in detail. • N and C act as electron reservoirs in A-ZP and A-ZS based photoanodes. • A-ZP and A-ZS exhibited photocurrent density of 1.02 mAcm−2 and 1.27 mAcm2. • Aminated zinc oxide nanosheets exhibited an IPCE ∼9.6%. [ABSTRACT FROM AUTHOR]

Hydrogen production via photoelectrochemical water splitting is a promising route to convert solar energy into chemical fuel, reducing energy crises and boosting environmental health. Here, we report the fabrication of ternary ZnO/CuO/Au heterostructures by electrodeposition and chemical bath deposition methods. The heterojunction formed can enhance the optical absorption, and photogenerated electrons and holes can efficiently separate due to the built-in electric field, which reduces recombination losses. Au plasmons incorporated in ZnO/CuO heterojunction enhance the optical absorption and promote fast free charge carrier transport at the interface through the surface plasmon resonance (SPR) effect. The ZnO/CuO/Au photoanode exhibits a photocurrent density of 1.08 mA/cm2 at 1.6 V Vs RHE, two times higher than pristine ZnO. The ZnO/CuO/Au photoanode exhibits the lowest charge transfer resistance of 600 Ω from electrochemical impedance spectra(EIS). The Bode plot revealed that the most extended lifetime of 8.69 μs is observed for ZnO/CuO/Au photoanode, which is larger than pristine ZnO. The synthesized thin films showed good stability and reusability for the photooxidation of water. • Fabrication of ternary ZnO/CuO/Au heterostructures by electrodeposition and chemical bath deposition methods. • Enhancement of optical absorption and reduction in recombination losses due to heterojunction. • Au plasmons incorporated in ZnO/CuO heterojunction enhances the optical absorption. • Au plasmons promote fast charge carrier transport at interface via surface plasmon resonance (SPR) effect. • ZnO/CuO/Au photoanode exhibits photocurrent density ∼ 1.08 mA/cm2, higher than pristine ZnO. [ABSTRACT FROM AUTHOR]