Improved Carrier Separation Research Articles

Optical and Photocatalytic Properties of Br-Doped BiOCl Nanosheets with Rich Oxygen Vacancies and Dominating {001} Facets.

Crystal facet engineering and nonmetal doping are regarded as effective strategies for improving the separation of charge carriers and photocatalytic activity of semiconductor photocatalysts. In this paper, we developed a facial method for fabricating oxygen-deficient Br-doped BiOCl nanosheets with dominating {001} facets through a traditional hydrothermal reaction and explored the impact of the Br doping and specific facets on carrier separation and photocatalytic performance. The morphologies, structures, and optical and photocatalytic properties of the obtained products were characterized systematically. The BiOCl samples prepared by the hydrothermal reaction exhibited square-like shapes with dominating {001} facets. Photodeposition results indicated that photoinduced electrons preferred to transfer to {001} facets because of the strong internal static electric fields in BiOCl nanosheets with dominating {001} facets. Br doping not only contributed to the formation of impurity energy levels that could promote light absorption but introduced a large number of surface oxygen vacancies (VO) in BiOCl photocatalysts, which was beneficial for photocatalytic performance. Moreover, the photocatalytic activities of these products under visible light were tested by degradation of rhodamine B (RhB). Because of the synergistic effect of the dominating {001} facets, Br doping, and rich VO, oxygen-deficient Br-doped BiOCl nanosheets exhibited improved carrier separation, visible light absorption, and photocatalytic efficiency.

Tuning electronic structure via CoS clusters for visual photocatalytic H2 production and mechanism insight

Clusters with this unique atomic arrangement and configuration are highly potential cocatalysts, but designing efficient clusters and clarifying the mechanism of action remains a challenge. Herein, CoS clusters are in-situ grown on CdS nanorods, which leads to the existence of Cd-S-Co bonds. It is found that the Cd-S-Co bonds could induce interfacial charge rearrangements. Theoretical calculations reveal that the charge redistribution of heterostructures at interfaces is conducive to modulating d-band center, reducing thermodynamic energy barriers, and improving carrier separation. The optimized CdS/CoS composite shows a great photocatalytic H2 production rate (65.7 mmol h−1 g−1), such a H2 evolution rate exceeded most reported CdS nanorods photocatalyst. This study provides an experimental and theoretical foundation for the preparation of cluster-semiconductors photocatalytic materials and explores the transfer pathway between clusters and catalysts at the atomic level, and deeply discusses the mechanism of their catalytic performance.

N-CQDs from reed straw enriching charge over BiO2−x/BiOCl p-n heterojunction for improved visible-light-driven photodegradation of organic pollutants

Green bismuth-based photocatalysts have attracted extensive attention in the field of PPCPs photodegradation. The improved carrier separation efficiency still remains a key factor to enhance photocatalytic performance. Herein, N-doped biomass carbon quantum dots (N-CQDs) decorated p-n heterojunction photocatalyst BiO2−x/BiOCl was prepared using a facile ion-etching strategy, and it displayed a markedly enhanced catalytic activity in the photodegradation of sulfonamide antibiotics. Calculated by the differential charge density, the doped N-CQDs could gather photogenerated electrons, which indicated that the introduction of N-CQDs into BiO2−x/BiOCl would effectively inhibit the recombination of photogenerated charge carriers. In addition, photocatalytic performance and density functional theory (DFT) calculation results revealed that the photogenerated electrons tended to transfer from p-BiOCl to n-BiO2−x through N-CQDs, which could generate ·O2- and photogenerated h+ to oxidize the target pollutants. Benefiting from the synergistic effect of accelerated separation of e--h+ in p-n heterojunction and the electron-rich performance of N-CQDs, the superb TOC removal efficiencies (89.40% within 120 min visible-light irradiation) and toxicity reduction performance of photodegradation intermediates were achieved. As a consequence, this work will provide a design of high-quality photocatalysts and a green-promising strategy for bismuth-based photocatalysts in the water treatment of PPCPs.

Oxygen vacancy-rich ultrafine CoP/Co3O4 nanoparticles as high-efficiency trifunctional electrocatalyst

Exploring highly stable and active electrocatalyst for hydrogen evolution, oxygen evolution and oxygen reduction reactions is an unremitting target for the supply and storage of sustainable energies. Here, we report a type of oxygen vacancy-rich nanostructure in which uniform CoP/Co3O4 nanoparticles (NPs) are coated and dispersed on an amorphous carbon network (pPVP). This hybrid nanostructure labeled as ‘CoP/Co3O4-fC-pPVP’ is synthesized by a pyrolysis-oxidation-phosphatization strategy, which can accelerate charge transfer and improve carrier separation owing to introducing copious oxygen vacancy. Benefiting from the modulated electronic structure and advantage of interfacial and synergistic effect among active CoP, Co3O4 and pPVP layer, the CoP/Co3O4-fC-pPVP hybrid structure exhibits excellent trifunctional electrocatalytic performance. The scattering wave vector (q) of the samples before and after catalytic reactions remains unchanged from small angle X-ray scattering (SAXS) tests, indicating the stable phase structure. As for CoP/Co3O4-fC-pPVP, only a very low potential of 1.585 V is needed to reach 10 mA cm−2 in the overall water splitting process. Furthermore, the peak power density of CoP/Co3O4-fC-pPVP-based Zn-air batteries reaches 154 mW cm−2 and the charge-discharge voltage gap almost maintains the initial overpotential after 727 h cycle test.

One-Step construction of Polyimide/NH2-UiO-66 heterojunction for enhanced photocatalytic degradation of sulfonamides

Photocatalysis treatment is a promising technology to eliminate water pollutants. Herein, we constructed polyimide/NH2-UiO-66 composites (PUs) through a facile one-step solvothermal method for the photocatalytic degradation of sulfonamides. The optimized photocatalyst PU1.5 was superior to the photocatalysts prepared through multi-step methods due to the more exposed (001) facets of polyimide and the better distribution of small NH2-UiO-66 particles. PU1.5 showed the highest photocatalytic activity, which was 9.5 and 92.0 times higher than that of polyimide and NH2-UiO-66. Such improvement was attributed to the improved carrier separation efficiency resulted from direct Z-scheme heterojunction. The probable degradation pathway of sulfathiazole was proposed by the LC-MS/MS and Density Functional Theory (DFT) calculation. Furthermore, the reduced toxicity and the little antibacterial activity of intermediates was investigated by the Quantitative Structure-Activity Relationship (QSAR) analysis and the residual antibiotic activity experiment. The study might provide a new strategy for designing composite photocatalyst to achieve efficient removal of pollutants.

Design and synthesis of Ti-peroxo/phosphorus heterostructures for enhanced photocatalytic hydrogen evolution

For the heterojunction composite photocatalyst, the contact interface is the key to charge carrier separation conditions. In order to present novel research through the interaction between these interfaces, the Ti based peroxo complex (TP)/red phosphorus (RP) composite system was introduced and designed to improve carrier separation and transport properties during photocatalytic hydrogen evolution. In this study, we have successfully synthesized TP/RP by facile solution process through stirring at room temperature and pressure. Regarding the specific surface area, which is one of the important factors in the photocatalytic activity, it was confirmed that the specific surface area of the TP (166.4 m2/g) and TP/RP (281.4 m2/g) samples was dramatically improved as the particle surface was oxidized based on TiH2 (0.613 m2/g), the precursor. And the photo-induced charge carrier life time of the TP/RP was extended by approximately 60% compared to the conventional TP. Finally, excellent research results were obtained in which the photocatalytic hydrogen evolution efficiency (17.05 μmol/h) under visible-light irradiation (200 W Xenon lamp) was improved by about 3 times than that of the conventional TP sample (5.26 μmol/h).

Improving carrier separation at the TiO2/CsPbIBr2 interface by gradient Sn-doping.

Subhani et al. found that Sm-doping in CsPbIBr2 decreased its bandgap from 2.05 eV to 1.8 eV; thus, the efficiency of CsPbIBr2 solar cells was improved by ∼30%. However, Sm is a vital strategic resource with high costs. Metal Sn is much more abundant and cheaper than Sm; meanwhile, it has been proven that Sn can adjust the bandgap of CsPbIBr2 in a broader range, 2.05 eV to 1.64 eV. Therefore, Sn-doping in CsPbIBr2 may improve the efficiency of CsPbIBr2 solar cells, even to a greater extent. In this work, we established the TiO2/CsPbIBr2 interface model by gradient Sn-doping in CsPbIBr2 and investigated the impacts of such gradient doping on the carrier separation behaviors at the TiO2/CsPbIBr2 interface from the aspects of the cross-interface electric field, bandgap, and band matching, based on first-principles calculations. It is found that gradient Sn-doping can transfer more electrons from TiO2 to perovskites, thus creating an enhanced cross-interface electric field conducive to the separation of carriers at the TiO2/CsPbIBr2 interface. Affected by the existence of the interface, the bandgap of each perovskite layer gradually increases as it moves away from the interface; in addition, due to the gradient Sn-doping, the steps between the bandgaps of adjacent perovskite layers become smaller and more uniform, which is favorable for the separation of electrons. In summary, gradient Sn-doping can improve the carrier separation at the TiO2/CsPbIBr2 interface.

Invoking Cathodic Photoelectrochemistry through a Spontaneously Coordinated Electron Transporter: A Proof of Concept Toward Signal Transduction for Bioanalysis.

Most of the cathodic photoelectrochemical (PEC) bioassays rely on electron accepting molecules for signal stimuli; unfortunately, the performances of which are still undesirable. New signal transduction strategies are still highly expected for the further development of cathodic photoelectrochemistry as a potentially competitive method. This work represents a new concept of invoked cathodic photoelectrochemistry by a spontaneously formed electron transporter for innovative operation of the sensing strategy. Specifically, the hexacyanoferrate(II) in solution easily self-coordinated with CuO nanomaterials and formed electron transporting copper hexacyanoferrate (CuHCF) on the surface, which endowed improved carrier separation for presenting augmented photocurrent readout. Exemplified by the T4 polynucleotide kinase (T4 PNK) and its inhibitors as targets, a homogenous cathodic PEC biosensing platform was achieved with the distinctive merits of label-free, immobilization-free, and split-mode readout. The mechanism revealed here provided a totally different perspective for signal transduction in cathodic photoelectrochemistry. Hopefully, it may stimulate more interests in the design and construction of semiconductor/transporter counterparts for exquisite operation of photocathodic bioanalysis.

Ag decorated CeO2-x nanojunctions with plasmon-enhanced catalytic performance for mono/multi-color switching

Oxide semiconductor nanoparticles (such as TiO2-x, SnO2-x, CeO2-x) with high concentrations of oxygen vacancies play a crucial photocatalytic role in photoreversible color switching systems (PCSSs), but some problems (such as limited photoabsorption and poor carrier separation efficiency) limit their practical applications. To address these issues, with CeO2-x as a model, we reported the construction of metal–semiconductor (Ag-CeO2-x) nanojunctions with plasmon-enhanced catalytic performance for mono/multi-color switching. Ag/CeO2-x nanojunctions were prepared by the solvothermal growth of CeO2-x nanospheres (∼50 nm) and then in-situ decoration with Ag0 nanoparticles (∼6 nm) via NaBH4 reduction. Ag/CeO2-x nanojunctions exhibit high concentration of oxygen vacancies, which results in narrowed bandgap of CeO2-x (Eg = 2.68 eV) and broadened photoabsorption (edge at ∼ 800 nm) compared with CeO2 (Eg = 2.74 eV, ∼650 nm). Simultaneously, Ag0 decoration confers a strong plasmon absorption peak at ∼ 460 nm and a weak/broad photoabsorption tail in visible-near-infrared region (600–1100 nm). Subsequently, by mixing Ag/CeO2-x nanojunctions and different redox dyes, several color switching inks were obtained, and these inks with polymer matrix could be further used to construct rewritable fabrics/papers. Under 435 nm light irradiation, the inks and fabrics/papers exhibit a rapid mono/multi-color switching, resulting from the reduction by photogenerated electrons aided by the plasmon-enhanced photoabsorption and the improved carrier separation. Conversely, 808 nm laser irradiation (in air) triggers the color recovery, due to the plasmonic high localized heating effect. Especially, remote printing/erasure of a broad range of mono/multi-colored images/letters can be performed on the rewritable fabrics/papers. Therefore, Ag/CeO2-x nanojunctions exhibit great potential for rewritable fabrics/papers, and the construction strategy of such metal–semiconductor junctions supplies some insights for the design of novel photocatalysts for color switching.

Molecular Self-Assembly of Oxygen Deep-Doped Ultrathin C3N4 with a Built-In Electric Field for Efficient Photocatalytic H2 Evolution.

Heteroatom-doped carbon nitride (C3N4) with a built-in electric field can reinforce the carrier separation; however, the stability will be greatly reduced due to the loss of surface-doped atoms. Here, molecule self-assembly, as a facile bottom-up approach, is explored for the synthesis and oxygen doping of C3N4. The obtained C3N4 presents a porous and ultrathin structure and oxygen deep-doping, which generate abundant nitrogen vacancies and a stable built-in electric field. Toward photocatalytic hydrogen evolution, the ultrathin and oxygen deep-doped C3N4 exhibits a 3.5-fold higher activity than bulk C3N4 under simulated sunlight, and 3.6 times higher stability than the oxygen surface-doped counterpart within five cycles. Femtosecond transient absorption spectroscopy indicates the improved carrier separation, and density functional theory (DFT) calculation reveals the promoted H2O adsorption and activation under the built-in electric field, which contribute to the excellent photocatalytic performance of oxygen deep-doped ultrathin C3N4.

Piezophototronic Effect Enhanced Perovskite Solar Cell Based on P(VDF‐TrFE)

As a candidate for next‐generation solar devices, perovskite solar cells are increasingly being studied for their rapid increased power conversion efficiency (PCE). One of the possible routes to further increase PCE is the introduction of polarization in the absorption layer which functions as a method for increasing the built‐in potential and reducing the interface barrier, leading to much improved carrier separation and extraction. This technique uses the principle of the piezophototronic effect utilized for obtaining enhanced optoelectronic performances. Herein, to introduce internal polarization while maintaining optical absorption performance of the perovskite, organic–inorganic hybrid perovskite composite film solar cells are fabricated by doping polarized polyvinylidenefluoride‐co‐trifluoroethylene (P(VDF‐TrFE)) into the perovskite. The composite film is polarized with an external potential, subsequently inducing the piezophototronic effect to enhance the performances of perovskite solar cells. Experimental results show that this simple polarization method has effectively improved several key characteristics of the solar cell. The PCE has reached up to 22.1%, the short‐circuit current (Jsc) increases to 24.2 mA cm−2, and the open‐circuit voltage (Voc) increases to 1.18 V.

Piezoelectric polarization assisted WO3/CdS photoanode improved carrier separation efficiency via CdS phase regulation

The key factor for efficient photoelectrochemical (PEC) water splitting is to design a semiconductor as photoanode with high carrier separation. Piezoelectric polarization is a considerable method to improve the carriers separation efficiency via providing a powerful built-in electric field. Herein, we synthesized WO3/CdS type II heterojunction and firstly explored the influence of CdS phase transition from sphalerite β-CdS to wurtzite α-CdS on piezoelectric polarization for WO3/CdS. Benefited from the asymmetric structure of α-CdS, fluctuation swings can be seen in the LSV curves of WO3/α-CdS due to piezoelectric polarization under ultrasound. The photocurrent density of WO3/α-CdS are enhanced with the increase of ultrasound frequency and the maximum of 2.13 mA/cm2 at 1.23 V vs. RHE, which is 1.61 times before ultrasound. The outstanding PEC performances of WO3/α-CdS under ultrasonic conditions are contributed to carrier separation driven by enhancing internal electric field between heterojunction, the built-in electric field inside the α-CdS and ballast carriers participating in water splitting reaction. This work provides a promising strategy for improving carrier separation efficiency in photoelectrodes via piezoelectric polarization.

Structural, optical and electrochemical transient photoresponse properties of ZnO/Ga2O3 nanocomposites prepared by two-step CVD method

The influence of ZnO layer thickness on the structural, optical and electrochemical transient photoresponse properties of Ga2O3/ZnO heterostructured nanocomposites is evaluated. The increasing thickness of ZnO layer from 0 to 7.868 μm on the nanocomposites show an increase in the concentration of photogenerated electron-hole pairs, improve carrier separation and transportation to the electrolyte. This results to an enhanced photocurrent density from 164 to 833 μA/cm2 at 1 V vs Ag/AgCl electrode. The unhybridized β-Ga2O3 film and the ZnO/Ga2O3 nanocomposites exhibit nanoblock-like and nanoplate-like morphologies, respectively. Structural studies reveal hexagonal ZnO and β-Ga2O3 crystalline phases for the nanocomposites. Optical bandgap of the reference β-Ga2O3 film is found to be 4.79 eV whereas, the nanocomposites exhibit two bandgaps: 3.30–3.25 eV belonging to the crystalline hexagonal ZnO phase, and 4.87–4.83 eV traced to the β-Ga2O3 phase. Photoluminescence spectroscopy exhibits blue-green emissions for the unhybridized film and ultraviolet-green emissions for the nanocomposites.

Suppression of Defects Through Cation Substitution: A Strategic Approach to Improve the Performance of Kesterite Cu2ZnSn(S,Se)4 Solar Cells Under Indoor Light Conditions

Recent efficiency advancements in kesterites have reinforced the use of Cu2ZnSn(S,Se)4 (CZTSSe) in indoor photovoltaic applications. However, the performance of kesterites under low light intensity conditions is mainly hindered by deep‐level defects. In this study, a strategic approach of silver (Ag) and germanium (Ge) cation substitution to cure these defects are employed. The Ag‐doped CZTSSe (CZTSSe:Ag) and Ge‐doped (CZTSSe:Ge) samples experimentally demonstrated a significant improvement in kesterite device performance under all intensities of LED and white fluorescent lamp conditions are prepared. Interestingly, the CZTSSe:Ag device exhibited the highest performance levels, i.e., 1.2–1.5 and 2.5–3 times better than those of Ge‐doped CZTSSe:Ge and undoped CZTSSe, respectively. This improved device performance is mainly attributed to the reduced energy level of deep‐level defects in CZTSSe:Ag. Moreover, these defects assisted in the generation of a larger potential difference between the grain boundary and grain interior in the CZTSSe:Ag sample, attracting minority carriers near the grain boundary. Consequently, the improved carrier separation process reduced the carrier recombination losses and enhanced the power output under low light intensity conditions. This Ag and Ge cation substitution in kesterite is found to be an effective approach to improve the device performance under low light intensity conditions.

Amorphous Co3O4 quantum dots hybridizing with 3D hexagonal CdS single crystals to construct a 0D/3D p-n heterojunction for a highly efficient photocatalytic H2 evolution.

Herein, a novel amorphous monodisperse Co3O4 quantum dots/3D hexagonal CdS single crystals (0D/3D Co3O4 QDs/CdS) p-n heterojunction was constructed by a simple hydrothermal and electrostatic self-assembly method. The amorphous monodispersed Co3O4 QDs (≈4.5 nm) are uniformly and tightly attached to the surface of the hexagonal CdS single crystals. The sample, 0.5% CQDs/CdS exhibits outstanding hydrogen evolution activity of 17.5 mmol h-1 g-1 with a turnover number (TON) of 4214, up to 10.3 times higher than that of pure CdS. The enhanced photocatalytic activity can be attributed to the synergistic effect of the p-n heterostructure and the quantum confinement effect of Co3O4 QDs, which significantly promoted the separation efficiency of photo-generated electrons and holes. Additionally, the sulfur vacancy also can act as electron trappers to improve carrier separation and electron transfer. The photoelectrochemical and time-resolved fluorescence (TRPL) results further certify the effective spatial charge separation. This work gives an insight into the design of the 0D/3D Co3O4 QDs/CdS p-n heterostructure for a highly efficient photocatalysis.

Molten-based defect engineering polymeric carbon nitride quantum dots with enhanced hole extraction: An efficient photoelectrochemical cell for water oxidation

Polymeric carbon nitride (g-C3N4) has emerged as a promising material for energy-related applications. However, the utilization of g-C3N4 in photoelectrochemical cells is still limited by poor exciton mobility, sluggish hole extraction, and short electron diffusion length. Here, we report a molten-based defect engineering strategy to prepare nitrogen-deficient g-C3N4 quantum dots (SxCNQD) for photoelectrochemical water splitting. This novel strategy requires no chemical etching or secondary treatments like recent state-of-the-art defect introduction methods, and for the first time achieves the in-situ integration of nitrogen-vacancy defects (NVs) during the polymerization of g-C3N4. Theoretical evaluation and experimental validation identified that the involved structural NVs redistribute the electrons on the delocalized π-conjugated networks of g-C3N4 and creates an additional sub-band on the optical bandgap, which can effectively improve carrier separation, facilitate charge transport dynamics, and boost hole extraction. Beneficial from its featured topological structures and electronic properties, the S600CNQD@ZnO photoanode exhibits a markedly high photocurrent density of 193.8 μA cm−2 at 1.23 V vs. RHE, long-term durability, as well as an impressive IPCE value in an alkaline solution in the absence of sacrificial agent under visible light illumination.

Improved Photoelectric Performance of UV Photodetector Based on ZnO Nanoparticle‐Decorated BiOCl Nanosheet Arrays onto PDMS Substrate: The Heterojunction and Ti3C2Tx MXene Conduction Layer

AbstractLarge‐area BiOCl nanosheet arrays grown on Cu substrate are transferred onto the polydimethylsiloxane (PDMS) substrate, while the as‐fabricated BiOCl/PDMS photodetector (PD) yields negligible photocurrents under UV light illumination. The introduction of a Ti3C2Tx MXene conduction layer at the interface increases both the photocurrent and dark current by 2–3 orders of magnitude. But this PD suffers from a large dark current (6.7 pA), a low on–off ratio (2.4), and a long decay time (6.87 s) under 350 nm light illumination at 5 V. After the deposition of ZnO nanoparticles (NPs), the optimized PD achieves a low dark current of 86 fA, a high on–off ratio of 7996.5, and a short decay time of 0.93 s. Additionally, the elimination of the Ti3C2Tx MXene layer causes decreased photocurrent and prolonged decay time. The greatly improved photoresponse and response speed of these PDs are ascribed to the increased light absorption brought by the ZnO NPs, the improved carrier separation promoted by the ZnO–BiOCl heterojunction, and the efficient carrier pathways provided by the Ti3C2Tx MXene conduction layers. The construction of heterojunctions and introduction of conduction additives improve the photodetecting performance of these BiOCl‐based PDs, promoting their practical applications in the photoelectric devices.

A mechanistic study of molecular CO2 interaction and adsorption on carbon implanted SnS2 thin film for photocatalytic CO2 reduction activity

Gas-phase photocatalytic reactions to convert carbon dioxide and water into oxygen and hydrocarbons are the foundation of life on earth. However, the efficiency of photosynthesis is relatively low (~1%), which leaves much room for artificial photosynthesis to reach the benchmark of the solar cells (>15%). In this work, carbon implanted SnS2 thin films (C–SnS2) were prepared to study photocatalytic activity and adsorbate-catalyst surface interactions during CO2 photoreduction. The electron density distribution in C–SnS2 and its contribution toward the photogenerated charge transfer process has been analyzed by the angle-dependent X-ray absorption near-edge structure (XANES) study. The C–SnS2 surface affinity toward the CO2 molecule was monitored by in-situ dark current and Raman spectroscopy measurements. By optimizing the dose during ion implantation, SnS2 thin film with 1 wt% carbon incorporation shows 108 times enhancement in the CO2 conversion efficiency and more than 89% product selectivity toward CH4 formation compared with the as-grown SnS2 without carbon incorporation. The improved photocatalytic activity can be ascribed to enhanced light harvesting, pronounced charge-transfer between SnS2 and carbon with improved carrier separation and the availability of highly active carbon sites that serve as favorable CO2 adsorption sites.

1D WO3 Nanorods/2D WO3-x Nanoflakes Homojunction Structure for Enhanced Charge Separation and Transfer towards Efficient Photoelectrochemical Performance.

Designing and fabricating photoelectrodes with low carrier recombination, high carrier transfer, and high light-capture capability is of great significance for achieving effective photoelectrochemical (PEC) water splitting. Herein, for the first time, 2D nonstoichiometric WO3-x nanoflakes (NFs) were vertically grown by hydrothermal synthesis on 1D WO3 nanorods (NRs) obtained by a hydrothermal method and high-temperature annealing (HTA). In this 1D HTA-WO3 /2D WO3-x photoanode, the 2D WO3-x NFs with active areas could maximize light harvesting, and the unique 1D/2D homojunction structure could improve the carrier-separation efficiency. At the same time, the 1D WO3 NRs with high aspect ratio were more beneficial to charge transfer after HTA. As expected, the 1D HTA-WO3 /2D WO3-x photoanode yielded an enhanced photocurrent density of 0.98 mA cm-2 at 1.23 V versus reversible hydrogen electrode, which is approximately 3.16 times that of pristine WO3 . The improvement could be attributed to the synergistic effect of HTA and the homojunction structure in the 1D HTA-WO3 /2D WO3-x photoanode, which could effectively improve carrier separation and transfer. Furthermore, this work may provide a promising strategy for the design and fabrication of semiconductor-based photoelectrodes.

Unique synergistic effects of ZIF-9(Co)-derived cobalt phosphide and CeVO4 heterojunction for efficient hydrogen evolution

The photocatalytic decomposition of water to produce hydrogen is an important process, through which solar energy can be converted to chemical energy. Non-precious metal phosphides have quietly attracted attention as an emerging inexpensive photocatalyst. In this study, we reported that a CoP/CeVO4 hybrid photocatalyst exhibited high hydrogen evolution efficiency owing to EY (eosin Y) sensitization under visible light irradiation for the first time, and the amount of generated hydrogen reached 444.6 μmol in 5 h. The CoP/CeVO4 nanohybrids were synthesized by a simple chemical precipitation method. The coupling of CoP and CeVO4 with ZIF-9 as a precursor could be completed in one step. The CeVO4 particles were firmly attached to the surface of the CoP particles to form a “small point” to “big point” heterojunction. The results of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, EDX, and transmission electron microscopy showed the formation of CoP and CeVO4 nanoparticles and the structure of the composite. Based on a detailed analysis of the Mott-Schottky plot, the UV-vis diffuse reflectance spectra, photocurrent-time (it) curve, Tafel curve, Nyquist curve (EIS), linear volt-ampere curve (LSV), and steady-state fluorescence spectra were studied. The time-resolved photoluminescence measurements indicated that the reason for the high-efficiency hydrogen evolution of CoP/CeVO4 was that the bands of CoP and CeVO4 were bent due to the existence of the Schottky barrier, and a heterojunction was formed between CoP and CeVO4, which generated an internal electric field and accelerated the charge transfer. In addition, the synergistic effect between CoP and CeVO4 provided a new hydrogen-evolution activity center for each of them. The improved carrier separation efficiency and the decrease in the photo-generated recombination rate led to the excellent photocatalytic hydrogen-evolution activity of the CoP/CeVO4 composite catalyst. This work provides a new strategy for modulating the electronic structure and carrier behavior of transition metal phosphide photocatalysts.