•A novel Co9S8/NPCP@rGO hybrid is prepared by pyrolysis and sulphuration of ZIF/GO.•The Co9S8/NPCP@rGO hybrid shows a great catalytic efficiency and stability.•The performance of Co9S8/NPCP@rGO hybrid outperforms that of Pt/C electrocatalyst.•Our work may open up a new avenue to design novel and efficient catalyst for ORR.Development of efficient electrocatalysts for the oxygen reduction reaction (ORR) is vitally important for the commercialization of metal–air batteries. In this work, we demonstrate a novel graphene coated/Co9S8 nanoparticles-embedded nitrogen doped porous carbon dodecahedron hybrid (Co9S8/NPCP@rGO) prepared by the pyrolysis and sulphuration of precursors composing of graphene oxide and zeolitic imidazolate-frameworks (ZIF). The Co9S8/NPCP@rGO hybrid is used as a highly efficient nonprecious metal electrocatalyst for oxygen reduction and exhibits more positive onset potential and half-wave potential, higher limiting current density, lower Tafel slope, and better durability and methanol tolerance in alkaline media in comparison to the commercial 20 wt.% Pt/C catalyst. The greatly improved electrocatalytic performance of Co9S8/NPCP@rGO can be attributed to the unique structure with Co9S8 nanoparticles dispersed uniformly inside nitrogen doped porous carbon matrix, and the synergistic effect between Co9S8/NPCP polyhedral hybrid and rGO.Download high-res image (226KB)Download full-size image

Samarium doped tungsten oxide film was synthesized by a hydrothermal method with sodium tungstate as W precursor and samarium oxide as dopant. After annealing at 450 °C for 0.5 h, the morphology and structural characterization of as-prepared films were determined with scanning electron microscopy, X-ray diffraction and high-resolution transmission electron microscope. For the pure and Sm-doped WO3 films serving as the photoanodes, photoelectrocatalytic properties were demonstrated by degrading methyl orange and methylene blue solution, showing that Sm-doped WO3 film has faster degrading rate than pure WO3 film. Photoelectrochemical properties were investigated using linear sweep voltammetry, electrochemical impedance spectroscopy, Mott–Schottky and incident photon to current conversion efficiency. Sm-doped WO3 achieves a high photocurrent of 1.50 mA cm−2 at 1.4 V versus. Ag/AgCl, which is 1.8 times as high as that of pure WO3 film (0.83 mA cm−2). Moreover, photogenerated hole injection efficiency was improved by retarding the recombination at the interface of electrode/electrolyte. The results indicate the Sm2O3 formed by excess doping led to a better photoelectrocatalytic and photoelectrochemical activities of Sm-doped WO3 film, suggesting that the doping of Sm is a favorable strategy to improve the performance of WO3 film photoanode.

•CdS/CdWO4/WO3 heterojunction photoanode was fabricated through a facile method.•The heterojunction films exhibit increased visible light absorption.•The heterojunction films exhibit high photoelectrochemical activity.•The in situ formation of heterojunction optimizes the charge transfer.CdS/CdWO4/WO3 heterojunction films on fluorine-doped tin oxide (FTO) substrates are for the first time prepared as an efficient photoanode for photoelectrochemical (PEC) hydrogen generation by an in situ conversion process. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet visible spectrometry (UV–vis) and X-ray photoelectron spectroscopy (XPS). The CdS hollow spheres (∼80 nm) sensitized WO3 plate film with a CdWO4 buffer-layer exhibits increased visible light absorption and a significantly improved photoelectrochemical performance. The photocurrent density at 0 V (vs. Ag/AgCl) of the CdS/CdWO4/WO3 anode is ∼3 times higher than that of the CdWO4/WO3 anode, and ∼9 times higher than that of pure WO3 under illumination. The highest incident-photon-to-current-efficiency (IPCE) value increased from 16% to 63% when the ternary heterojunction was formed. This study demonstrates that the synthesis of ternary composite photocatalysts by the in situ conversion process may be a promising approach to achieve high photoelectric conversion efficiency.

•A plate-like WO3 film with surface oxygen vacancies is fabricated by low temperature processing.•The concentration of oxygen vacancies could be controlled by tuning the treatment time in H2O2 solution.•Appropriate surface oxygen vacancies could improve light-to-electricity conversion efficiency.The plate-like WO3 photo-electrode with surface oxygen vacancies was fabricated via a H2O2 treatment method for the first time. The concentration of oxygen vacancies could be controlled by tuning the treatment time in H2O2 solution. Under visible light, the WO3 plate anodes with different concentration of surface oxygen vacancies were evaluated for photoelectrochemical water splitting and the optimum photocurrent was about 1.5 times as high as that of pure WO3. This study presents a new insight into improving the light-to-electricity conversion efficiency of WO3 by introducing surface oxygen vacancies.

•CoOx surface modified 2D-WO3 photoanode was fabricated through a facile method.•CoOx/WO3 plate array films exhibited high photoelectrochemical activity.•CoOx may be a good oxygen evolution electrocatalyst to cover on WO3 photoanodes.We report the synthesis and photoelectrochemical characterization of CoOx oxygen evolution catalyst modified two-dimensional (2D) WO3 plate arrays photoelectrode. The 2D-WO3 plate arrays were prepared perpendicularly on the FTO substrate by hydrothermal method. The CoOx nanoparticles were deposited on the surface of WO3 plate arrays on FTO by chemical deposition process. The CoOx nanoparticles are distributed on the surface of WO3 plates with a diameter of about 20 nm. The CoOx/WO3 film shows enhanced photoelectrochemical performance than the bare WO3 film. The highest incident-photon-to-current-efficiency (IPCE) value increases from 24.9% to 49.1% when introducing CoOx. The deposited CoOx electrocatalyst on WO3 surface can transfer holes effectively through the cobalt ion valency cycle, suppress the hole's accumulation and recombination at the electrode surface, achieve the superior kinetics and consequently enhance the overall solar water oxidation efficiency.

•There is no linear connection between the nitrogen content and catalytic activity.•The Al–air battery with mass ratio of 1:200 N-graphene displays better discharge performance.•The DFT method was used to calculate the adsorption energy of nitrogen species.•The graphitic N is proved to play a positive role in catalyzing ORR.The relationship of nitrogen species and catalytic activity of nitrogen doped graphene for oxygen reduction reaction (ORR) is extensively studied but is still inconclusive. In this paper, the specific nitrogen types in N-graphene are controlled by regulating the mass ratio of graphene oxide (GO) and urea. The detection of groups on the surface of N-graphene is carried out by X-ray photoelectron spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. The catalytic activity of N-graphene catalysts with different nitrogen configurations is evaluated by cyclic voltammograms (CV), rotating disk electrode (RDE), and electrochemical impedance spectroscopy (EIS) measurements in O2-saturated 0.1 M KOH electrolyte. It is found that the N-graphene with the mass ratio of 1:200 (containing graphitic N configuration) shows better oxygen reduction catalytic activity than that of other mass ratio (without graphitic N configuration) catalysts. Furthermore, the Al−air battery with the mass ratio of 1:200 N-graphene cathode displays higher open circuit voltage and energy density. Density functional theory (DFT) quantum chemical calculations are used to investigate the influence of different nitrogen species on adsorption energy of oxygen atoms. The calculated results indicate graphitic N is more conducive for the adsorption of oxygen atoms.

•A novel Bi2S3 nanobelt/WO3 nanoplate arrays film was fabricated by a facile two-step hydrothermal method.•Bi2S3 nanobelts epitaxially grow on the surface of WO3 nanoplates.•A high photocurrent density could be obtained from the film photoelectrode.In this work, a novel Bi2S3 nanobelt/WO3 nanoplate array film was prepared firstly by a facile two-step hydrothermal method with a successive annealing treatment. The as-prepared sample was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and ultraviolet visible spectrometry (UV–vis). The results show that Bi2S3 nanobelts epitaxially grow on the surface of WO3 nanoplates and the films have an excellent visible light absorption performance. Moreover, when investigated as photoanode for photoelectrochemical (PEC) cells, such novel Bi2S3 nanobelt @ WO3 nanoplate photoanodes exhibited a high PEC activity and generated a photocurrent density of 8.91 mA cm−2 at −0.1 V vs. Ag/AgCl in the electrolyte solution containing 0.1 M Na2SO3 and 0.1 M Na2S. The remarkable PEC activity of the photoanode may be ascribed to the efficient charge transfer and increased surface areas in the photoelectrode.A novel Bi2S3 nanobelt/WO3 nanoplate arrays film was prepared by a facile two-step hydrothermal method with a successive annealing treatment, exhibited an excellent photoelectrochemical activity.

In this work, DyVO4/WO3 heterojunction plate arrays were first fabricated on FTO using a hydrothermal method for WO3 vertical plate arrays and a dipping–annealing process for the deposition of DyVO4 nanoparticles. The samples were characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Photoelectrochemical activities were investigated by linear sweep voltammetry (LSV) and incident photon to current conversion efficiency (IPCE). The DyVO4/WO3 heterojunction electrode exhibited a maximum photocurrent density of 0.78 mA cm−2 at +1.2 V (vs. Ag/AgCl), while the photocurrent density of pure WO3 was just 0.49 mA cm−2 under illumination. And the highest IPCE value increased from 27.4% to 54.1% after the DyVO4 nanoparticle deposition. The enhanced PEC performance was attributed to the longer electron lifetime, increased carrier density and high charge separation efficiency at the interface of heterojunction, which were confirmed by electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. The study demonstrates that metal orthovanadates may be good heterojunction candidates to couple with WO3 to provide promising photoanodes for water splitting.

In this work, we demonstrate a facile strategy to synthesize a novel three-dimensional (3D) graphene aerogel-supported and graphene quantum dots-modified γ-MnOOH nanotubes as a highly efficient electrocatalyst. The structure, morphology, and chemical composition of γ-MnOOH@GA/GQDs are investigated by X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of catalysts is discussed by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and rotating disk electrode (RDE) measurements in O2-saturated 0.1 M KOH electrolyte. The γ-MnOOH@GA/GQDs hybrid exhibits more positive onset potential and half-wave potential, faster charge transfer, lower Tafel slope than that of γ-MnOOH@GA, GA and γ-MnOOH, and mainly undergoes a direct 4e− reaction pathway. Furthermore, its electrocatalytic performance is comparable with the commercial 20 wt% Pt/C, which is attributed to the unique 3D crumpled porous nanostructure of GA with large specific area and fast electron transport, and the synergic covalent coupling between the γ-MnOOH nanotubes and GA. More importantly, the GQDs structural defects can facilitate the adsorption of oxygen and charge transfer. As a highly efficient surface “sensitizer”, GQDs are modified on the γ-MnOOH surfaces to further boost the electrocatalytic property.

ZnxBi2S3+x sensitized platelike WO3 photoelectrodes on FTO substrates were for the first time prepared via a sequential ionic layer adsorption reaction (SILAR) process. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet visible spectrometry (UV–vis), and Raman spectra. The results show that the ZnxBi2S3+x quantum dots (QDs) are uniformly coated on the entire surface of WO3 plates, forming a WO3/ZnxBi2S3+x core/shell structure. The ZnxBi2S3+x/WO3 films show a superior ability to capture visible light. High-efficiency photoelectrochemical (PEC) hydrogen generation is demonstrated using the prepared electrodes as photoanodes in a typical three-electrode electrochemical cell. Compared to the Bi2S3/WO3 photoelectrodes, the ZnxBi2S3+x/WO3 photoelectrodes exhibit good photostability and excellent PEC activity, and the photocurrent density is up to 7.0 mA cm–2 at −0.1 V versus Ag/AgCl under visible light illumination. Investigation of the electron transport properties of the photoelectrodes shows that the introduction of ZnS enhances the photoelectrons’ transport rate in the photoelectrode. The high PEC activity demonstrates the potential of the ZnxBi2S3+x/WO3 film as an efficient photoelectrode for hydrogen generation.Keywords: Bi2S3; hydrogen generation; photoelectrochemical; WO3; ZnS;

•NGA was used as catalyst support to improve ORR catalytic activity.•The CMO/NGA hybrid proceeds via a 4e− transfer process.•NGA with a porous conducting network can facilitate the charge transfer during ORR.•CMO/NGA hybrid can be used as a promising cathode catalyst for metal–air batteries.Spinel CoMn2O4 (CMO) nanoparticles grown on three-dimensional (3D) nitrogen-doped graphene areogel (NGA) is prepared by a facile two-step hydrothermal method. The NGA not only possesses the intrinsic property of graphene, but also has abundant pore conformations for supporting spinel metal oxide nanoparticles, thus would be suitable as a good electrocatalysts' support for oxygen reduction reaction (ORR). The structure, morphology, porous properties, and chemical composition of CMO/NGA are investigated by X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption–desorption measurements, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of catalysts is discussed by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and rotating disk electrode (RDE) measurements in O2-saturated 0.1 M KOH electrolyte. The CMO/NGA hybrid exhibits more positive onset potential and half-wave potential, faster charge transfer than that of CMO and NGA, and its electrocatalytic performance is comparable with the commercial 20 wt.% Pt/C. Furthermore, it mainly favors a direct 4e− reaction pathway, and has excellent ethanol tolerance and high durability, which is attributed to the unique 3D crumpled porous nanostructure of NGA with large specific area and fast electron transport, and the synergic covalent coupling between the CoMn2O4 nanoparticles and NGA.

A ZnO/TiO2 composite layer was fabricated on top of a nanoporous TiO2 layer to form a heterostructure bilayer photoanode (P-PZ). The in-situ scattering sites of ZnO were formed inside the assembled photoanode (P-PZ) through the dissolution of ZnO particles caused by soaking in titanium tetrachloride solution. In comparison, the conventional TiO2 photoanodes (2P) and photoanodes with incorporation of the commercial large TiO2 particles (P-PT) were also prepared, and the three photoanodes (2P, P-PT, P-PZ) were all with the thickness of about 14.2 μm. A light-to-electricity conversion efficiency (η) of 7.50% was received for the P-PZ-based DSSCs, much higher than that of the DSSCs with 2P (5.34%) and P-PT (5.96%) photoanodes. The superior performance of the DSSC with P-PZ photoanode is mainly attributed to the following factors. (i) The in-situ scattering sites exhibit great light scattering ability, resulting in the great improvement in the short-circuit current density (Jsc). (ii) The ZnO-coated TiO2 structure shifts the conduction band of TiO2, leading to the great increase in the open circuit voltage (Voc).

•HfO2 was loaded on the surface of WO3 nanoparticles as a passivation layer.•It was prepared by a simple solovethermal method instead of atomic layer deposition.•The passivation layer inhibits the electron-hole recombination on the surface of WO3.•Photoelectrochemical performance of WO3 has been improved after loading HfO2.In this article, Hafnium oxide (HfO2) overlayer was reported to be loaded on the surface of WO3 nanoparticles by a simple solvothermal method for the first time. HfO2 powders were dissolved in the concentrated sulfuric acid as raw material. The physicochemical properties of WO3 nanoparticles with and without HfO2 passivation layer were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). For the film electrode prepared with doctor-blade method, scanning electron microscopy (SEM) and UV–vis absorbance spectroscopy (UV–vis) were used to determine the morphological and optical properties. Meantime, the photoelectrochemical properties of two samples were evaluated by means of liner sweep voltammogram, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectrum (IMPS) and incident photon to current conversion efficiency (IPCE). The WO3 film with HfO2 passivation layer showed better photoelectrochemical performance which could be ascribed to the inhibition of the recombination of electron-holes.

•CuWO4/WO3 heterojunction photoanode was fabricated through a facile method.•The in situ formation of heterojunction optimizes the charge transfer.•CuWO4/WO3 heterojunction plates array films exhibited high photocurrent density.•The low-dimensional heterojunction structures provide a promising photoanode.CuWO4/WO3 heterojunction photoanode based on WO3 plates arrays and CuWO4 nanoparticles was fabricated to enhance the photoelectrochemical performance. WO3 plates array films were prepared through a simple hydrothermal method, then a facile dipping-annealing process was employed to fabricate CuWO4/WO3 films. The crystal structure, morphology, composition and optical properties of the samples were analyzed by X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and UV–vis spectrometry. As-prepared CuWO4/WO3 heterojunction films achieved a photocurrent density of 1.21 mA/cm2 at 1.5 V vs. Ag/AgCl, which was almost 2-fold higher than that of the pure WO3 film (0.64 mA/cm2) under illumination. The enhanced photocurrent was attributed to the extension of visible light response, increased carriers density, effective separation at the interface of heterojunction and better electron transport properties, which were confirmed by Mott–Schottky and electrochemical impedance spectroscopy. This study reveals that the low-dimensional morphological structure and heterojunction structure are expected to provide a promising photoanode for water splitting.

Mn-doped CdS quantum dots sensitized WO3 photoelectrodes were successfully synthesized by a combination of hydrothermal and chemical bath deposition (CBD) methods. To improve the stability of the photoelectrodes in an alkaline environment, the electrodes were treated with TiCl4 to form a nano-TiO2 buffer layer on the WO3 plate surface before depositing CdS quantum dots (QDs). The resulting electrodes were applied as photoanodes in the photoelectrochemical cell for water splitting. The photoelectrochemical (PEC) properties were investigated by the photocurrent density curves and incident photon-to-current conversion efficiency (IPCE). The as-prepared Mn-CdS QDs sensitized WO3 plate-like photoelectrodes exhibit a significant improvement in their photoelectrochemical performance compared with undoped photoelectrodes. To better understand the enhanced PEC properties, the electron transport properties and efficient electron lifetime were studied in detail using electrochemical impedance spectroscopy (EIS), transient photocurrent spectroscopy and intensity modulated photocurrent spectroscopy (IMPS). The results show that the Mn-CdS QDs/TiO2/WO3 photoelectrodes exhibit a higher electron transit rate and a longer electron lifetime. This is most likely due to the existence of electronic states in the mid-gap region of the Mn-CdS QD.

g-C3N4/WO3 heterojunction plate array films with enhanced photoelectrochemical (PEC) performance were successfully synthesized through a combination of hydrothermal and dipping-annealing methods. Urea aqueous solutions were prepared as the precursors to in situ synthesize g-C3N4 nanoparticles on the surface of WO3 platelets. The PEC performances of the photoanodes were investigated by the photocurrent density and incident photon-to-current conversion efficiency (IPCE). As-prepared g-C3N4/WO3 heterojunction films achieved a maximum photocurrent density of 2.10 mA cm−2 at +2.0 V (vs. RHE), which was almost 3-fold higher than that of the pure WO3 film (0.78 mA cm−2) under illumination. And the highest IPCE value increased from 25.1% to 53.1% after the g-C3N4 nanoparticles deposition. The enhanced PEC performance was attributed to the increased carriers density, better electron transport properties, longer electron lifetime and effective charge separation at the interface of heterojunction, which were confirmed by Mott–Schottky and electrochemical impedance spectroscopy (EIS). This study demonstrates that the low-dimensional morphological structure and in situ formation of heterojunction structure are expected to provide a promising photoanode for photoelectric catalysis.

In this paper, a novel Bi2S3/BiVO4 heterojunction film was prepared by a facile drop-casting and hydrothermal method for the first time. The as-prepared films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet visible spectrometry (UV-Vis). Interestingly, the heterojunction film was formed by epitaxial growth of Bi2S3 nanowires on BiVO4 nanostructures and exhibited a good visible light absorption performance. Photoelectrochemical (PEC) hydrogen generation was demonstrated using the prepared films as photoanodes. The heterojunction photoelectrode showed an excellent PEC activity and generated a photocurrent density of 7.81 mA cm−2 at 0.9761 V vs. RHE (0.1 V vs. Ag/AgCl) in the electrolyte solution containing 0.35 M Na2SO3 and 0.25 M Na2S. The present study provides new insight into the design of highly efficient heterojunction photoelectrodes for hydrogen generation.

•The Al-air batteries with LMO/N-rGO cathode displayed better discharge performance.•The improved catalytic activity of LMO/N-rGO can be attributed to nitrogen species.•LMO/N-rGO hybrid has the synergic covalent coupling between N-rGO and LiMn2O4.•LMO/N-rGO is a promising material with good activity and stability in Al-air battery.Nitrogen-doped reduced graphene oxide nanosheets modified with LiMn2O4 (LMO) nanoparticles as low cost, nontoxic and efficient catalyst for oxygen reduction reaction (ORR) were synthesized by a simple two step hydrothermal method. The physical properties and the activity of the composites toward ORR were investigated using X-ray diffraction (XRD) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) spectra, and electrochemical measurements, including cyclic voltammograms (CV), steady state polarization curves and electrochemical impedance spectroscopy (EIS) in O2-saturated 0.1 M KOH electrolyte. The LiMn2O4 supported on nitrogen-doped reduced graphene oxide (LMO/N-rGO) showed more positive onset potential, half wave potential, faster charge transfer, and a higher cathodic peak current in alkaline media than that of LiMn2O4/rGO and N-rGO. Furthermore, air electrodes with hybrid catalysts were fabricated to test the discharged performance in Al-air batteries under ambient air condition. The batteries with LMO/N-rGO cathode displayed the higher energy density of 585 mAh g−1 and sluggish potential drop. The improved catalytic activity and battery performance of LMO/N-rGO can be attributed to the effect of active sites induced by nitrogen, and synergic covalent coupling between the nitrogen-doped graphene sheets and spinel lithium manganese oxide. These results confirm that LMO/N-rGO is a promising material for air cathodes with good activity and stability in aluminium-air battery.

In this work, ZnO NPs-functionalized WO3 vertical plate-like arrays were first fabricated on FTO with a hydrothermal process for WO3 vertical plate-like arrays and an electrodeposition process for the functionalization of ZnO. The ZnO nanoparticles are preferentially loaded on the active points of WO3 in the shape of a sphere about 10 nm. The samples were characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Photoelectrochemical properties were investigated by photoelectrochemical measures, such as linear sweep voltammograms, electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS) and incident photon to current conversion efficiency (IPCE). The results show that the photocurrent of WO3 increases from 0.88 to 1.23 mA cm−2 at 1.2 V (vs. Ag/AgCl) after functionalized with ZnO. Furthermore, the lifetime of the electron–hole has been prolonged from 6.44 to 8.56 ms, but there is no decrease in the electron transport time. In this case, the enhancement of the photoelectrochemical performance is attributed to effective transfer of photo-generated holes so as to retard the recombination of electrons and holes.

In this work, a p–n heterojunction film consisting of n-type WO3 and p-type CuFe2O4 was synthesized via two steps. The n-type WO3 film was deposited on the FTO substrate by a doctor-blade method and then modified with p-type CuFe2O4 nanoparticles by a deposition-annealing method. The composite film was characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy, showing that the CuFe2O4 nanoparticles were deposited on the surface of WO3 film. Meanwhile, photoelectrochemical measurements were used to investigate the photoelectrochemical properties. A photocurrent of 0.75 mA cm−2 at 0.6 V (vs. Ag/AgCl) was achieved with CuFe2O4/WO3, resulting in a 2.68 fold increase compared to pristine WO3. The presence of a p–n heterojunction facilitates the separation of photoinduced electrons and holes, leading to more efficient charge transfer, resulting in a significant improvement in PEC performance.

In this study, WO3 nanoplates modified by doping with gadolinium (Gd) were synthesized by a hydrothermal method. The effect of the rare-earth element on the photoelectrochemical (PEC) performance of WO3 one- or two-dimensional (2D) materials was examined. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were employed to examine the crystal phase and morphology of the Gd-doped nanoplates thus prepared. Results of UV–vis spectroscopy, valence-band (VB) X-ray photoelectron spectroscopy, and Mott–Schottky analyses indicated that the conduction band and VB potentials of WO3 shifted to negative values. Linear sweep voltammetry results indicated that the photocurrent density increased by 153% after modification by doping with Gd. In addition, the PEC properties of the WO3 nanoplates obtained by the intensity-modulated photocurrent spectrum and incident photon-to-current conversion efficiency measurements indicated that modification by doping with Gd has a scintillating application in improving the PEC conversion properties of WO3-based 2D materials.

•A simple deposition-annealing method was used to fabricate high-performance NiWO4/WO3 heterojunction photoanode.•NiWO4 serves as a functional component of the heterojunction for the photoelectrochemical (PEC) water splitting reaction.•Effective separation of the electron–hole pairs is achieved by the heterojunction structure.•Mechanism of the photo-generated carriers transport process was put forward and proved.NiWO4/WO3 heterojunction photoanode was fabricated for the first time to enhance the photoelectrochemical (PEC) performance under visible light irradiation. Such a photoanode was prepared using a simple deposition-annealing method of NiWO4 nanoparticles onto the surface of porous WO3 films. It was found that the NiWO4/WO3 film synthesized with 25 mM Ni(NO3)2 in ethanol exhibited the best PEC performance, which achieved a 70% increase compared with the pure WO3 film under similar conditions. The promising composite photoanode is desired to be employed for water splitting in the PEC cells. The heterojunction structure offers enhanced photoconversion efficiency and increased the density of carriers. This study reveals that introducing NiWO4 into WO3 films could facilitate the separation and restrain the recombination of photo-generated electron–hole pairs and accelerate the electrons transfer. Synthesis details are discussed, with film morphologies and structures characterized by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy.

Tungsten oxide (WO3) photoelectrodes with the surface tuned by Fe(Ⅲ) for photoelectrochemical water splitting were successfully synthesized. Nanostructured WO3 films were prepared using doctor blade method, then a facile and economical deposition-annealing process was employed to fabricate Fe(Ⅲ) modified WO3 films. The resulting composite's structural and optical properties were analyzed by SEM, EDX, XRD, UV–Vis spectrometry and XPS. The photoelectrochemical properties were evaluated by photocurrent density under 500 W Xe lamp with an intensity of 100 mW/cm2. The Fe(Ⅲ) modified WO3 electrode exhibited a larger photocurrent than the pure WO3 electrode. Significantly, the optimized Fe(Ⅲ) modified WO3 film achieved the maximum photocurrent density of 1.18 mA/cm2 at 0.8 V vs. Ag/AgCl in the 0.2 M Na2SO4. The enhanced photocurrent was attributed to the extension of the light response and the electron hole separation at the interface Fe(Ⅲ)/WO3 which was confirmed by Mott–Schottky and electrochemical impedance spectroscopy.Highlights► WO3 electrodes by surface tuning with Fe(Ⅲ) were fabricated. ► Original morphologies of WO3 electrodes are not changed. ► 80% increase in photoelectrochemical water splitting reaction. ► Fe(Ⅲ) helps hole electron separation.

•Co2P@CoNPGcompositewassynthesizedbysupramoleculargel-assistedstrategy.•Multielement doped graphene was used as support to improve the conductivity of Co2P.•Co2P@CoNPG exhibited superior bifunctional activities toward both ORR and OER.•Co2P@CoNPG is a promising bifunctional catalyst for renewable energy systems.Developing highly cost-effective bifunctional oxygen electrode catalysts for renewable energy technologies (e.g. metal-air batteries and fuel cells) is highly desirable but remains challenging. In this work, we demonstrate a novel composite of Co2P particles anchored in cobalt, nitrogen and phosphorus co-doped graphene nanosheets (Co2P@CoNPG) prepared via supramolecular gel-assisted strategy. In virtue of the positive synergistic effect originating from the Co2P, Co-Nx active sites and N/P co-functionalized graphene in the composite, the optimized Co2P@CoNPG-900 exhibits superior bifunctional activities and strong durability for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline solution. The value of ΔE (bifunctional performance parameter) for Co2P@CoNPG-900 is only 0.92 V. Compared to the noble metal-based catalysts, Co2P@CoNPG-900 has the obvious advantages in durability and bifunctional activities. The integration of Co2P and multielement co-doped graphene into a hybrid material is a new and promising strategy to design bifunctional oxygen electrode catalysts for renewable energy technologies.