Efficient charge separation and transfer of a TaON/BiVO4 heterojunction for photoelectrochemical water splitting

The separation and transfer of photogenerated electron–hole pairs in semiconductors is the key point for photoelectrochemical (PEC) water splitting. Here, an ideal TaON/BiVO₄ heterojunction electrode was fabricated via a simple hydrothermal method. As BiVO₄ and TaON were in well contact with each other, high performance TaON/BiVO₄ heterojunction photoanodes were constructed. The photocurrent of the 2-TaON/BiVO₄ electrode reached 2.6 mA cm⁻² at 1.23 V vs. RHE, which is 1.75 times as that of the bare BiVO₄. TaON improves the PEC performance by simultaneously promoting the photo-generated charge separation and surface reaction transfer. When a Co-Pi co-catalyst was integrated onto the surface of the 2-TaON/BiVO₄ electrode, the surface water oxidation kinetics further improved, and a highly efficient photocurrent density of 3.6 mA cm⁻² was achieved at 1.23 V vs. RHE. The largest half-cell solar energy conversion efficiency for Co-Pi/TaON/BiVO₄ was 1.19% at 0.69 V vs. RHE, corresponding to 6 times that of bare BiVO₄ (0.19% at 0.95 V vs. RHE). This study provides an available strategy to develop photoelectrochemical water splitting of BiVO₄-based photoanodes.

TaON/BiVO₄ heterojunction electrodes exhibited significant enhancement in the photoelectrochemical water oxidation.     

Efficient photoelectrochemical water oxidation using a TiO2 nanosphere-decorated BiVO4 heterojunction photoanode

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting. In this work, we fabricated a highly efficient TiO₂/BiVO₄ heterojunction photoanode for PEC water oxidation via a simple hydrothermal method. The resulting heterojunction photoanodes show enhanced PEC performance compared to the bare BiVO₄ due to the simultaneous improvements in charge separation and charge transfer. Under simulated sunlight illumination (AM 1.5G, 100 mW cm⁻²), a high photocurrent of 3.3 mA cm⁻² was obtained at 1.23 V (vs. the reversible hydrogen electrode (RHE)) in a neutral solution, which exceeds those attained by the previously reported TiO₂/BiVO₄ heterojunctions. When a molecular Co–cubane catalyst was immobilized onto the electrode, the performance of the TiO₂/BiVO₄ heterojunction photoanode can be further improved, achieving a higher photocurrent density of 4.6 mA cm⁻² at 1.23 V, an almost three-fold enhancement over that of the bare BiVO₄. These results engender a promising route to designing an efficient photoelectrode for PEC water splitting.

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting.     

Highly efficient hamburger-like nanostructure of a triadic Ag/Co3O4/BiVO4 photoanode for enhanced photoelectrochemical water oxidation

The combination of a semiconductor heterojunction and oxygen evolution cocatalyst (OEC) is an important strategy to improve photoelectrochemical (PEC) water oxidation. Herein, a novel hamburger-like nanostructure of a triadic photoanode composed of BiVO₄ nanobulks, Co₃O₄ nanosheets and Ag nanoparticles (NPs), that is, Ag/Co₃O₄/BiVO₄, was designed. In our study, an interlaced 2D ultrathin p-type Co₃O₄ OEC layer was introduced onto n-type BiVO₄ to form a p–n Co₃O₄/BiVO₄ heterojunction with an internal electric field (IEF) in order to facilitate charge transport. Then the modification with Ag NPs can significantly facilitate the separation and transport of photogenerated carriers through the surface plasma resonance (SPR) effect, inhibiting the electron–hole recombination. The resulting Ag/Co₃O₄/BiVO₄ photoanodes exhibit largely enhanced PEC water oxidation performance: the photocurrent density of the ternary photoanode reaches up to 1.84 mA cm⁻² at 1.23 V vs. RHE, which is 4.60 times higher than that of the pristine BiVO₄ photoanode. The IPCE value is 2.83 times higher than that of the pristine BiVO₄ at 400 nm and the onset potential has a significant cathodic shift of 550 mV for the ternary well-constructed photoanode.

A novel hamburger-like nanostructure of a triadic photoanode Ag/Co₃O₄/BiVO₄ was designed to enhance photoelectrochemical water splitting, providing a fascinating pathway to efficiently improve the PEC conversion efficiency.     

Interrogating solar photoelectrocatalysis on an exfoliated graphite–BiVO4/ZnO composite electrode towards water treatment

A novel photoanode consisting of an exfoliated graphite–BiVO₄/ZnO heterostructured nanocomposite was fabricated. The material was characterised with scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Photoelectrochemical studies were carried out with cyclic/linear sweep voltammetry and chronoamperometry. The solar photoelectrochemical properties of the heterojunction photoanode were investigated through the degradation of rhodamine B in water. The results revealed that the nanoparticles of BiVO₄ and ZnO were well entrapped within the interlayers of the exfoliated graphite (EG) sheets. Improved charge separation was achieved in the EG–BiVO₄/ZnO composite electrode which resulted in superior photoelectrochemical performance than individual BiVO₄ and ZnO electrodes. A higher degradation efficiency of 91% of rhodamine B was recorded using the composite electrode with the application of 10 mA cm⁻² current density and a solution pH of 7. The highest total organic carbon removal of 74% was also recorded with the EG–BiVO₄/ZnO. Data from scavenger studies were used to support the proposed mechanism of degradation. The electrode has high stability and reusability and hence lends itself to applications in photoelectrocatalysis, especially in water treatment.

Band alignment between ZnO and BiVO₄ on exfoliated graphite (EG) support.     

Green fabrication of nanoporous BiVO4 films on ITO substrates for photoelectrochemical water-oxidation

A new green method was developed to prepare nanoporous BiVO₄ films on ITO substrates for photoelectrochemical (PEC) water-oxidation under visible light irradiation. The films can be prepared by simple drop-casting of a stable aqueous solution of Bi³⁺ and V⁵⁺ complexes with tartaric acid and ethylenediaminetetraacetic acid, followed by drying and calcination in air. Thanks to these ligands, the aqueous precursor solution is remarkably stable over a wide range of pH (pH 4–9). The BiVO₄ films on ITO substrates possess a 3D-network structure comprised of nanoparticles with a scheelite–monoclinic phase and a diameter of ca. <100 nm, after calcination at 450–500 °C for 1 h. The PEC performance clearly depended on the film thickness that can be controlled by coating times, and calcination conditions (temperature and time). The CoPi-loaded BiVO₄ electrodes exhibited relatively high performance for PEC water oxidation (ABPE of 0.35% at 0.8 V vs. RHE) under simulated sunlight irradiation.

Nanoporous BiVO₄ photoanodes for efficient water oxidation were directly fabricated on an ITO substrate using an aqueous solution of mild pH.     

The design and growth of peanut-like CuS/BiVO4 composites for photoelectrochemical sensing

In this study, the CuS/BiVO₄-X (where X represents the mass percentage of CuS associated with CuS/BiVO₄; X = 2%, 5% and 7%) p–n heterostructures were fabricated using a two-step hydrothermal method. The structural and morphological features were ascertained in great detail using several physical characterization processes. According to the results of the photoelectrochemical (PEC) experimental processes, the PEC properties of CuS/BiVO₄-5% were much more obvious as compared to those of pure BiVO₄, CuS and CuS/BiVO₄-X. Moreover, the photoluminescence (PL) and UV-vis diffuse reflection spectra (DRS) affirmed that the CuS/BiVO₄-5% demonstrates an excellent capacity for absorbing visible light and low electron recombination rate as compared with the other composites. Accordingly, PEC sensors with CuS/BiVO₄-5% were fabricated for the detection of dopamine (DA) and bisphenol A (BPA) with outstanding selectivity and stability. For DA, it implied a broad linear range from 0.01–10 μM and 10–120 μM, and for BPA, the broad linear range was 0.01–90 μM. Thus, the PEC sensor has significant potential application when it comes to DA and BPA detection.

In this study, the CuS/BiVO₄-X (where X represents the mass percentage of CuS associated with CuS/BiVO₄; X = 2%, 5% and 7%) p–n heterostructures were fabricated using a two-step hydrothermal method.     

Photoelectrochemical performance of a spin coated TiO2 protected BiVO4-Cu2O thin film tandem cell for unassisted solar water splitting

A tandem cell consisting of a Mo-BiVO₄/TiO₂/FeOOH photoanode–Cu₂O/TiO₂/MoS₂ photocathode was prepared for unassisted solar water splitting. The protective TiO₂ layer was prepared by a cost-effective spin coating technique. The individual Mo-BiVO₄/TiO₂/FeOOH photoanode and the Cu₂O/TiO₂/MoS₂ photocathode yielded a current density of ∼0.81 mA cm⁻² at 1.23 V vs. RHE and ∼−1.88 mA cm⁻² at 0 V vs. RHE, respectively under 100 mW cm⁻² xenon lamp illumination. From the individual photoelectrochemical analysis, we identify the operating points of the tandem cell as 0.66 V vs. RHE and 0.124 mA cm⁻². The positive current density from the operating points proves the possibility of non-zero operation of the tandem cell. Finally, a two-electrode Mo-BiVO₄/TiO₂/FeOOH-Cu₂O/TiO₂/MoS₂ tandem cell was constructed and analysed for unassisted operation. The obtained unassisted current density of the tandem cell was ∼65.3 μA cm⁻² with better stability compared to the bare BiVO₄-Cu₂O tandem cell. The results prove that the spin coated TiO₂ protective layer can be a viable approach to protect the photoelectrodes from photocorrosion with better stability and enhanced photoelectrochemical (PEC) performance.

Mo-BiVO₄/TiO₂/FeOOH photoanode–Cu₂O/TiO₂/MoS₂ photocathode tandem cells with photoelectrochemical stability testing.     

Insight into the PEC and interfacial charge transfer kinetics at the Mo doped BiVO4 photoanodes

BiVO₄ is a promising photoanode material for the photoelectrochemical (PEC) oxidation of water; however, its poor charge transfer, transport, and slow surface catalytic activity limit the expected theoretical efficiency. Herein, we have investigated the effect of Mo doping on SnO₂ buffer layer coated BiVO₄ for PEC water splitting. SnO₂ and Mo doped BiVO₄ layers are coated with layer by layer deposition through a precursor solution based spin coating technique followed by annealing. At 5% doping of Mo, the sample (SBM5) shows a maximum current density of 1.65 mA cm⁻² at 1.64 V vs. RHEl in 0.1 M phosphate buffer solution under AM 1.5 G solar simulator, which is about 154% improvement over the sample without Mo (SBM0). The significant improvement in the photocurrent upon Mo doping is due to the improvement of various bulk and interfacial properties in the materials as measured by UV-vis spectroscopy, electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis, and open-circuit photovoltage (OCPV). The charge transfer kinetics at the BiVO₄/electrolyte interface are investigated to simulate the oxygen evolution process in photoelectrochemical water oxidation in the feedback mode of scanning electrochemical microscopy (SECM) using 2 mM [Fe(CN)₆]³⁻ as the redox couple. SECM investigation reveals a significant improvement in effective hole transfer rate constant from 2.18 cm s⁻¹ to 7.56 cm s⁻¹ for the hole transfer reaction from the valence band of BiVO₄ to [Fe(CN)₆]⁴⁻ to oxidize into [Fe(CN)₆]³⁻ with the Mo doping in BiVO₄. Results suggest that Mo⁶⁺ doping facilitates the hole transfer and suppresses the back reaction. The synergistic effect of fast forward and backward conversion of Mo⁶⁺ to Mo⁵⁺ expected to facilitate the V⁵⁺ to V⁴⁺ which has an important step to improve the photocurrent.

BiVO₄ is a promising photoanode material for the photoelectrochemical (PEC) oxidation of water; however, its poor charge transfer, transport, and slow surface catalytic activity limit the expected theoretical efficiency.     

Black Si-doped TiO2 nanotube photoanode for high-efficiency photoelectrochemical water splitting

Black Si-doped TiO₂ (Ti–Si–O) nanotubes were fabricated through Zn metal reduction of the Ti–Si–O nanotubes on Ti–Si alloy in an argon atmosphere. The nanotubes were used as a photoanode for photoelectrochemical (PEC) water splitting. Both Si element and Ti³⁺/oxygen vacancies were introduced into the black Ti–Si–O nanotubes, which improved optical absorption and facilitated the separation of the photogenerated electron–hole pairs. The photoconversion efficiency could reach 1.22%, which was 7.18 times the efficiency of undoped TiO₂. It demonstrated that a Si element and Ti³⁺/oxygen vacancy co-doping strategy could offer an effective method for fabricating a high-performance TiO₂-based nanostructure photoanode for improving PEC water splitting.

Black Si-doped TiO₂ (Ti–Si–O) nanotubes were fabricated through Zn metal reduction of the Ti–Si–O nanotubes on Ti–Si alloy in an argon atmosphere.     

Superior visible light photocatalytic performance of reticular BiVO4 synthesized via a modified sol–gel method

Reticular BiVO₄ catalysts were successfully synthesized via a modified sol–gel method. Here, citric acid (CA) was used as the chelating agent and ethylenediaminetetraacetic acid (EDTA) was used as the chelating agent and template. Furthermore, the effects of pH values and EDTA on the structure and morphology of the samples were studied. We determined that EDTA and pH played important roles in the determination of the morphology of the as-prepared BiVO₄ samples. Photocatalytic evaluation revealed that the reticular BiVO₄ exhibited superior photocatalytic performance characteristics for the degradation of methylene blue (MB) under visible-light (λ > 400 nm) exposure, about 98% of the MB was found to degrade within 50 min. Moreover, the degradation kinetics of MB was in good agreement with pseudo-first-order kinetics. The obtained apparent reaction rate constant k_app of reticular BiVO₄ was much higher than that of BiVO₄ synthesized by the citric acid sol–gel method.

Reticular BiVO₄ catalysts with superior visible light photocatalytic performance were successfully synthesized via a modified sol–gel method.     

Ag2O-decorated electrospun BiVO4 nanofibers with enhanced photocatalytic performance

Semiconductor photocatalysts are emerging as tools for pollutant degradation in industrial wastewater, air purification, antibacterial applications, etc. due to their use of visible light, which is abundant in sunlight. Here, we report a new type of p–n junction Ag₂O/BiVO₄ heterogeneous nanostructured photocatalyst with enhanced photocatalytic performance. P-type Ag₂O nanoparticles were in situ reduced and assembled on the surface of electrospun BiVO₄ nanofibers using ultraviolet (UV) irradiation; this process hindered the recombination of localized photogenerated electron–hole pairs, and hence resulted in the enhanced photocatalytic activity of the BiVO₄/Ag₂O nanocomposites. The photocatalytic activities of the obtained BiVO₄ and BiVO₄/Ag₂O nanocomposites were assessed by measuring the degradation of rhodamine B (RhB) under visible light. The 10 wt% Ag₂O/BiVO₄ sample yielded the optimum degradation of RhB (98.47%), much higher than that yielded by pure BiVO₄ nanofibers (64.67%). No obvious change in the XRD pattern of an Ag₂O/BiVO₄ sample occurred as a result of its use in the photocatalytic reaction, indicating its excellent stability. The high photocatalytic performance observed was attributed to the large surface-to-volume ratio of the essentially one-dimensional electrospun BiVO₄ nanofibers and to the in situ growth of p-type Ag₂O on the surface of the n-type BiVO₄ nanofibers.

Ag₂O doped electrospun BiVO₄ nanofibers with p–n junction heterogeneous structures show enhanced photocatalytic activity under visible light (photocatalytic efficiency: 98.47% within 100 min) and good cycling stability.     

Facile and rapid synthesis of a novel spindle-like heterojunction BiVO4 showing enhanced visible-light-driven photoactivity

A spindle-like monoclinic–tetragonal heterojunction BiVO₄ was successfully synthesized by a pressure-controllable microwave method. The as-prepared BiVO₄ samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, transient photocurrent responses and electrochemical impedance spectroscopy (EIS). The visible-light-driven photocatalytic activity of the BiVO₄ samples was evaluated for the degradation of Rhodamine B (RhB) and tetracycline (TC). The synthesis process needs microwave irradiation for only 10 min without the addition of any auxiliary reagent, pH adjustment, and calcination. The as-prepared spindle-like monoclinic–tetragonal heterojunction BiVO₄ exhibits excellent photocatalytic activity for the degradation of both RhB and TC. The photocatalytic degradation rates of RhB and TC over spindle-like BiVO₄ are 1.77 and 1.64 times higher, respectively, than that measured over monoclinic BiVO₄. The enhanced photocatalytic activity is mainly attributed to the fact that the existence of a heterojunction effectively promotes the separation of photo-generated carriers and extends the visible-light absorption of BiVO₄.

A novel spindle-like monoclinic–tetragonal BiVO₄ heterojunction is rapidly synthesized via a pressure-controllable microwave method.     

New aspects of improving the performance of WO3 thin films for photoelectrochemical water splitting by tuning the ultrathin depletion region

In this work, we explored a facile, scalable and effective method for substantially enhancing photocurrent and incident-photon-to-current efficiency of WO₃ thin-film photoanodes by a mild reduction treatment under low oxygen pressure. Experimental data from photoelectrochemical and electrochemical impedance spectroscopies have shown that such treatment can increase the charge carrier density on WO₃ photoanode surfaces resulting in improvements in hole collection efficiency and reduction in charge recombination. Despite a much thinner layer of WO₃ (about 500 nm) compared to those in other published studies, the electrodes exhibited an ultra-high photocurrent density of 1.81 mA cm⁻² at 1.23 V vs. RHE. This current density is one of the highest ones among WO₃-based photoanodes described in literature. The proposed surface modulation approach offers an effective and scalable method to prepare high-performance thin film photoanodes for photoelectrochemical water splitting.

Surface modulation approach offers an effective and scalable method for high-performance WO₃ photoanodes.     

Z-scheme BiVO4/Ag/Ag2S composites with enhanced photocatalytic efficiency under visible light

The Z-scheme BiVO₄/Ag/Ag₂S photocatalyst was fabricated via a two-step route. The as-prepared samples were characterized by XRD, FE-SEM, HRTEM, XPS and UV-vis diffuse reflectance spectroscopy. The results of PL and photocurrent response tests demonstrate that the ternary BiVO₄/Ag/Ag₂S composites had a high separation and migration efficiency of photoexcited carriers. As a result, the ternary photocatalyst exhibits enhanced photocatalytic activity for decomposing Rhodamine B (RhB) under LED light (420 nm) irradiation. The results of trapping experiments demonstrate both h⁺ and ˙OH play crucial roles in decomposing RhB molecules. Additionally, the energy band structures and density of states (DOS) of BiVO₄ and Ag₂S were investigated via the density functional theory (DFT) method. Finally, a Z-scheme electron migration mechanism of BiVO₄ → Ag → Ag₂S was proposed based on the experimental and calculated results.

The Z-scheme BiVO₄/Ag/Ag₂S photocatalyst was fabricated via a two-step route.     

Highly efficient and self-supported 3D carbon nanotube composite electrode for enhanced oxygen reduction reaction

A binder-free and self-supported 3D carbon nanotube composite electrode with NiFe nanoalloys, N doping and Fe/Ni–N_x–C structures was fabricated by a facile method. The strong synergistic effects of multi-components and the unique structural merits of the optimized sample endowed it outstanding oxygen reduction reaction activity with an onset potential of 1.048 V vs. RHE in 0.1 M KOH solution.

A binder-free and self-supported 3D-CNT composite electrode was prepared, containing multi-components of NiFe nanoalloys, N doping and Fe/Ni–N_x–C structures, synergistically promoting the electrocatalytic activity of oxygen reduction reaction.     

Three-dimensional NiCoP hollow spheres: an efficient electrode material for hydrogen evolution reaction and supercapacitor applications

A binary metal phosphide (NiCoP) has been synthesized in a single-step hydrothermal method, and its energy conversion (hydrogen evolution reaction; HER) and energy storage (supercapacitor) performances have been explored. The physicochemical characterization of the NiCoP nanostructures show that they have a highly crystalline phase and are formed uniformly with a sphere-like surface morphology. In acidic electrolytic conditions, the NiCoP shows excellent HER performance, requiring only 160 and 300 mV overpotential to deliver 10 and 300 mA cm⁻² current density, respectively. Interestingly, it follows the Volmer–Heyrovsky reaction pathway to execute the HER with robust durability (∼15 mV increase in overpotential even after 18 h of electrolysis). In an alkaline medium (5 M KOH), NiCoP shows specific capacitance of 960 F g⁻¹ with higher energy density (33.3 W h kg⁻¹) and power density (11.8 kW kg⁻¹). Moreover, it shows better reversibility (∼97% coulombic efficiency) and long cycle life (∼95% capacitance retention after 10 000 repeated cycles). The unique surface morphology and phase purity of the binary metal phosphide avails more electroactive surface/redox centers, thereby showing better electrocatalytic as well as energy storage performances. Therefore, we presume that the NiCoP would be a suitable material for future energy conversion and storage systems.

This work reports a single-step hydrothermal method for the scalable synthesis of binary metal phosphide (NiCoP). Further, the electrocatalytic performance for HER and electrochemical charge-storage performance towards a supercapacitor were explored.     

Surface plasmon-driven photoelectrochemical water splitting of a Ag/TiO2 nanoplate photoanode

A silver/titanium dioxide nanoplate (Ag/TiO₂ NP) photoelectrode was designed and fabricated from vertically aligned TiO₂ nanoplates (NP) decorated with silver nanoparticles (NPs) through a simple hydrothermal synthesis and electrodeposition route. The electrodeposition times of Ag NPs on the TiO₂ NP were crucial for surface plasmon-driven photoelectrochemical (PEC) water splitting performance. The Ag/TiO₂ NP at the optimal deposition time of 5 min with a Ag element content of 0.53 wt% demonstrated a remarkably high photocurrent density of 0.35 mA cm⁻² at 1.23 V vs. RHE under AM 1.5G illumination, which was 5 fold higher than that of the pristine TiO₂ NP. It was clear that the enhanced light absorption properties and PEC performance for Ag/TiO₂ NP could be effectively adjusted by simply controlling the loading amounts of metallic Ag NPs (average size of 10–30 nm) at different electrodeposition times. The superior PEC performance of the Ag/TiO₂ NP photoanode was attributed to the synergistic effects of the plasmonic Ag NPs and the TiO₂ nanoplate. Interestingly, the plasmonic effect of Ag NPs not only increased the visible-light response (λ_max = 570 nm) of TiO₂ but also provided hot electrons to promote photocurrent generation and suppress charge recombination. Importantly, this study offers a potentially efficient strategy for the design and fabrication of a new type of TiO₂ hybrid nanostructure with a plasmonic enhancement for PEC water splitting.

A hybrid nanostructure Ag/TiO₂ photoelectrode for PEC water splitting with a remarkable high photocurrent density, 0.35 mA cm⁻² (5 fold higher than that of the pristine TiO₂ photoeletrode) was fabricated by a facile one-pot hydrothermal and electrodeposition method.     

Synthesis and characterization of BiVO4 nanoparticles for environmental applications

In the present study, a chemical precipitation method is adopted to synthesize bismuth vanadate nanoparticles. The calcination temperature dependent photocatalytic and antibacterial activities of BiVO₄ nanoparticles are examined. The structural analysis evidences the monoclinic phase of BiVO₄ nanoparticles, where the grain size increases with calcination temperature. Interestingly, BiVO₄ nanoparticles calcined at 400 °C exhibit superior photocatalytic behaviour against methylene blue dye (K = 0.02169 min⁻¹) under natural solar irradiation, which exhibits good stability for up to three cycles. The evolution of antibacterial activity studies using a well diffusion assay suggest that the BiVO₄ nanoparticles calcined at 400 °C can act as an effective growth inhibitor of pathogenic Gram-negative (P. aeruginosa & A. baumannii) and Gram-positive bacteria (S. aureus).

In the present study, a chemical precipitation method is adopted to synthesize bismuth vanadate nanoparticles.     

Co2+ substituted for Bi3+ in BiVO4 and its enhanced photocatalytic activity under visible LED light irradiation

We investigated the fabrication of Co-doped BiVO₄ (Bi_1−xCo_xVO_4+δ, 0.05 < x < 0.5) by the substitution of Co ions for Bi sites in BiVO₄. The X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) results indicated that the substitution of Co²⁺ ions for Bi³⁺ sites in BiVO₄ was successful, although a change in the crystal phase of BiVO₄ did not occur. UV-vis DRS and PL results suggested that the Co-incorporation could slightly improve the visible light absorption of BiVO₄ and induce the separation of photoinduced electron–hole pairs; therefore, a significant enhancement of photocatalytic performance was achieved. The Bi_0.8Co_0.2VO_4+δ sample showed superior photocatalytic activity in comparison with other samples, achieving 96.78% methylene blue (MB) removal within 180 min. In addition, the proposed mechanism of improved photocatalytic activities and the stability of the catalyst were also investigated.

We investigated the fabrication of Co-doped BiVO₄ (Bi_1−xCo_xVO_4+δ, 0.05 < x < 0.5) by the substitution of Co ions for Bi sites in BiVO₄.     

In situ synthesis of MoS2/graphene nanosheets as free-standing and flexible electrode paper for high-efficiency hydrogen evolution reaction

In this article, an exquisite flexible hybrid MoS₂/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process. The assembled MoS₂/graphene catalysts exhibit significantly enhanced electrocatalytic activity and cycling stability towards the splitting of water in acidic solution. Furthermore, a strategic balance of abundant active sites at the edge of the S–Mo–S layers with efficient electron transfer in the MoS₂/graphene hybrid catalyst plays a key role in controlling the electrochemical performance of the MoS₂ nanosheets. Most importantly, the hybrid MoS₂/graphene nanosheet paper shows excellent flexibility and high electrocatalytic performance under the various bending states. This work demonstrates an opportunity for the development of flexible electrocatalysts, which have potential applications in renewable energy conversion and energy storage systems.

An improved flexible hybrid MoS₂/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process for hydrogen evolution reaction applications.