Efficient Photocatalytic H2 Evolution Research Articles

S‐Scheme g‐C3N4/CdS Heterostructures Grafting Single Pd Atoms for Ultrafast Charge Transport and Efficient Visible‐Light‐Driven H2 Evolution

AbstractEmerging step‐scheme (S‐scheme) heterostructures hold unique superiority in steering directional charge transport and reinforcing redox capacity, yet rational modification of S‐scheme heterostructures by single atoms (SAs) for efficient photocatalytic H2 evolution is rarely reported. In this work, Pd SAs‐modulated organic–inorganic g‐C3N4/CdS S‐scheme heterostructures are designed and prepared by a one‐pot mechanochemical approach allowing for g‐C3N4 nanosheets/CdS nanoparticles to confine atomically dispersed Pd co‐catalysts. The g‐C3N4/CdS S‐scheme charge‐transfer pathway is corroborated by a combination of in situ irradiated X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and Kelvin probe force microscopy. Density functional theory (DFT) calculations, high‐angle annular dark‐field scanning transmission electron microscopy, and X‐ray absorption fine structure identify Pd‐S3 and Pd‐N2 atomic moieties underpinned by the electronic interaction between Pd SAs and g‐C3N4/CdS heterostructures, in which the d‐band center of Pd SAs is optimized for proton adsorption thermodynamically. Further, the g‐C3N4/CdS S‐scheme heterostructures alongside Pd SAs in concert boost the rapid migration of photogenerated electrons (1.05 ps) via Pd─S and Pd─N bond‐derived channels. A maximal H2 evolution rate of 85.66 mmol h−1 g−1 is achieved by 1 wt% Pd‐20 wt% g‐C3N4/CdS hierarchical composites. This work may guide the design of high‐efficiency S‐scheme‐based photocatalysts for solar‐to‐H2 conversion and beyond.

Surface cyano groups optimize the charge transfer of poly heptazine imide for enhanced photocatalytic H2 evolution

Surface functionalization has been considered as an effective strategy to manipulate charge separation of carbon nitride and therefore to largely improve the photocatalytic H2 evolution efficiency. Poly heptazine imide (PHI) is a new class of crystalline carbon nitride frameworks that exhibits remarkable photocatalytic performance for hydrogen evolution. To further improve the H2 evolution performance of PHI and explore the reaction mechanism, ammonium thiocyanate was used as a precursor for the synthesis of poly heptazine imide at elevated temperatures under molten salt conditions. The optimized PHI with an abundance of surface cyano groups shows a significantly enhanced photocatalytic performance for H2 evolution, which is 4.3 times that on pristine PCN. Most importantly, the surface cyano group adjusts the electron intensity of the polymeric framework, enhances the light absorbance, reduces the bandgap, and improves the charge separation efficiency. The synthetic technique also could be applied to other sulfur-containing precursors for the synthesis of PHI frameworks with excellent hydrogen evolution production performance.

Embedding ZnCo2O4 quantum dots onto graphdiyne (g-CnH2n-2) nanosheets as a 0D/2D S-scheme heterojunction for highly efficient photocatalytic H2 evolution

The design of environmentally friendly and cost-effective S-scheme heterojunctions with robust interfacial interactions is pivotal for enhancing photocatalytic performance and facilitating practical application. In this work, ZnCo2O4 quantum dots (QDs)/graphdiyne (ZCOG) S-scheme heterojunction was synthesized by a simple hydrothermal method. ZnCo2O4 QDs with quantum size effect were prepared by calcination, while graphdiyne (GDY) nanosheets were synthesized by reduction-elimination reaction using CuBr as catalyst. The maximum hydrogen production rate of ZCOG reaches 2472.80 μmol g-1h−1, which is 30.75 and 10.84 times higher than that of ZnCo2O4 QDs and GDY, respectively. This significantly enhanced photocatalytic activity is attributed to the strongly coupled S-scheme heterojunction between GDY and ZnCo2O4 QDs, which accelerates the photogenerated electron transfer while effectively suppressing the recombination of photogenerated carriers. In addition, the quantum size effect of the ZnCo2O4 QDs leads to an increase in the width of the electronic forbidden band, which enhances the energy of electrons (holes) in the conduction band (valence band). The S-scheme mechanism of ZCOG was revealed by in situ XPS, UPS and TRPL spectroscopy, and the reliability of the conclusions was further verified by DFT calculations. This work provides an efficient strategy for the construction of GDY-based photocatalysts with quantum size effect.

Efficient photocatalytic reforming of cellulose for H2 production enabled by oxygen-vacancy rich SrMoO4/palygorskite nanocomposite

Photocatalytic reforming of biomass into hydrogen along with the simultaneous production of high-value chemicals, plays a significant role in advancing a sustainable economy. A major challenge in this process is the effective utilization of photogenerated holes while simultaneously preventing the rapid recombination of photoinduced carriers, which is crucial for optimizing solar-to-hydrogen conversion efficiency. In this study, an exquisite oxygen-rich vacancy (OV) plasmonic SrMoO4/phosphor acidized palygorskite (H-Pal) nanocomposite was prepared for efficient photocatalytic H2 evolution while producing high value-added lactic acid (LA) simultaneously. Results showed that the integration of local surface plasmon resonance (LSPR) effect and OV enhanced the photothermal catalytic conversion of cellulose reaching as high as 87%. Notably, the selectivity of LA reached as high as 31% while the H2-evolution efficiency reached 906 μmol•g-1•h-1. The local thermal effect improved the conversion efficiency of cellulose, and the OV in SrMoO4 introduced instantaneous Lewis acid sites during light irradiation, which improved the selectivity for LA. Moreover, the formation of an S-scheme SrMoO4-OV/H-Pal heterostructure effectively inhibited the recombination of photogenerated electron-hole pairs and maintained a high redox potential. This work demonstrates a promising strategy for efficient photocatalytic H2-evolution, coupled with production of high-valuable chemicals from biomass resources by taking advantage of clay materials.

Multishelled hollow CaTiO3 cubes decorated with Co0.2Cd0.8S nanoparticles for efficient photocatalytic H2 evolution via S-scheme charge transfer

Rationally designing S-scheme heterostructures with boosted charge separation efficiency and superior redox ability is regarded as an appealing strategy to conquer the shortcomings of mono-component and conventional heterojunction photocatalysts. Herein, a novel hierarchical S-scheme heterostructured photocatalyst was constructed by integrating Co0.2Cd0.8S nanoparticles on multishelled hollow CaTiO3 cubes to substantially improve the photocatalytic hydrogen production activity. An internal electric field (IEF) is formed at the heterojunction interfaces owing to the significant disparity in Fermi level (EF) between Co0.2Cd0.8S and CaTiO3, accompanied by the energy band bending, which enables the S-scheme charge transport route in the Co0.2Cd0.8S/CaTiO3 heterostructure, as verified by electron paramagnetic resonance and theoretical calculations. Benefiting from the boosted separation efficiency and superior redox capability of photocarriers within the constructed S-scheme heterostructure, the optimized Co0.2Cd0.8S/CaTiO3 sample exhibited a significantly improved photocatalytic hydrogen evolution rate of 8.13 mmol h−1 g−1, far exceeding that of mono-component counterparts and previously reported Co0.2Cd0.8S- or CaTiO3-based photocatalysts. This study is anticipated to inspire the strategic development of other economical and efficient S-scheme photocatalytic systems with enhanced H2 evolution activity.

Double S-scheme Cu2−xSe/twinned-Cd0.5Zn0.5S homo-heterojunctions with surface plasmon effects for efficient photocatalytic H2 evolution

The enhancement of charge separation and utilization efficiency in both the bulk phase and interface of semiconductor photocatalysts, as well as the expansion of light absorption range, are crucial research topics in the field of photocatalysis. To address this issue, twinned Cd0.5Zn0.5S (T-CZS) homojunctions consisting of wurtzite Cd0.5Zn0.5S (WZ-CZS) and zinc blende Cd0.5Zn0.5S (ZB-CZS) were synthesized via a hydrothermal method to facilitate the bulk-phase charge separation. Meanwhile, Cu2−xSe with localized surface plasmon resonance effect (LSPR) generated by Cu vacancies was also obtained through a hydrothermal process. Due to their opposite electronegativity, a solvent evaporation strategy was employed to combine Cu2−xSe and T-CZS by intermolecular electrostatic. After optimization, the photocatalytic hydrogen (H2) evolution rate of 5 wt% Cu2−xSe/T-CZS reached an impressive value of 60 mmol∙h−1∙g−1, which was 4.6 and 66.6 times higher than that of pure Cu2−xSe and T-CZS, respectively. Furthermore, this composites demonstrated a remarkable rate of 0.46 mmol∙h−1∙g−1 under near-infrared (NIR) wavelength (>800 nm). The enhanced performance observed in Cu2−xSe/T-CZS can be attributed to its unique and efficient double S-scheme charge transfer mechanism which effectively suppresses rapid recombination of electron-hole pairs both within the bulk phase and at the surface interfaces; this conclusion is supported by Density Functional Theory (DFT) calculations as well as electron paramagnetic resonance spectroscopy analysis. Moreover, incorporation of Cu2−xSe enables effective utilization ultraviolet visible-near infrared (UV–Vis-NIR) light by the composites while facilitating injection “hot electrons” into T-CZS for promoting photocatalytic reactions. This study provides a potential strategy for achieving efficient solar energy conversion through synergistic integration of non-stoichiometric plasmonic materials with photocatalysts with twinned-twinned structures.

MoB2 modified g-C3N4: A Schottky junction with enhanced interfacial redox activity and charge separation for efficient photocatalytic H2 evolution

The g-C3N4 material, which exhibits a sensitivity to visible light and has a band position that is appropriate for the photoreduction of H2, has garnered significant interest. However, the ability of g-C3N4 to use light for photocatalysis is restricted due to its insufficient capacity to absorb light and its poor reaction kinetics on the surface. The researchers opted for the metallic MoB2 to create a Schottky junction coupled with g-C3N4. The incorporation of MoB2 nanoparticles onto g-C3N4 enhances its light absorption capacity and promotes the efficient separation and transfer of photogenerated charge. In addition, MoB2 nanoparticles served as active sites to accelerate H2 evolution. Compared to g-C3N4, the MoB2@g-C3N4 composite exhibited a nearly 51-fold increase in H2 production rate, indicating a significant improvement in photocatalytic activity. The present investigation demonstrated the potential of metallic MoB2 as a modified material during a photocatalytic H2 evolution reaction.

In situ anchoring of Ni12P5 on ZnIn2S4 for efficient and stable photocatalytic H2 evolution

It is a great challenge to develop efficient, stable and inexpensive hydrogen evolution reaction (HER) catalysts for photocatalytic water-splitting. In this paper, Ni12P5 (NP) was in situ anchored on the surface of ZnIn2S4 (ZIS) via a solvothermal route with nickel chloride and red phosphorus as ingredients. Using triethanolamine as sacrificial agent, the photocatalytic hydrogen evolution activity of NP/ZIS was studied under visible light irradiation. At the same time, the composition, structure, morphology and photoelectrochemical properties of the as-obtained samples were analyzed through a sequence of characterization techniques. ZIS loaded with 6 wt% NP (6NP/ZIS) exhibits the best hydrogen evolution activity and excellent stability. The H2 evolution rate of 6NP/ZIS is 5.4 times higher than that of pristine ZIS and well beyond that of the physical mixture (6NP + ZIS) or even that of the optimal Pt/ZIS under the same conditions. The maximal apparent quantum yield (AQY) of 22.7 % at 400 nm is achieved, superior to the most reported performance of ZnIn2S4-based photocatalysts for HER. The anchor of NP can not only enhance the visible light absorption intensity, but also reduce the HER overpotential. More importantly, the intimate interface between ZIS and NP can promote the separation and migration of photo-excited carriers, thereby enhancing the activity of photocatalytic hydrogen evolution. The possible photocatalytic reaction mechanism was discussed.

Cr dopants and S vacancies in ZnS to trigger efficient photocatalytic H2 evolution and CO2 reduction

Driven by endless solar energy, photocatalytic H2 evolution from water splitting and CO2 conversion to hydrocarbon fuels over semiconductor photocatalysts are of great potential to simultaneously settle the greenhouse effect and energy shortage. Herein, Cr-doped zinc sulfide (ZnS) with accompanying sulphur vacancies (Vs) photocatalytic materials is developed by a facile hydrothermal method. The Cr dopants centralize photoinduced holes and Vs trap electrons, forming a synergistic effect for accelerating charge separation and transfer. The reaction energy barrier for both H2 evolution and CO2 reduction has been optimized. Therefore, in the absence of a cocatalyst, the optimal catalyst (Zn0.94Cr0.06S) achieves an outstanding H2 evolution activity of 20.3 mmol g−1 h−1, which is approximately 2.9 times higher than 6.9 mmol g−1 h−1 for pristine ZnS. In addition, in the gas-solid reaction system without co-catalysts or sacrificial agents, the Zn0.94Cr0.06S exhibits a considerable CO evolution rate of 19.56 μmol g−1 h−1, about 10.1 times higher than ZnS (1.94 μmol g−1 h−1). Both the performances for H2 evolution and CO2 reduction of Zn0.94Cr0.06S outperform most of the previously reported photocatalysts. Particularly, the Zn0.94Cr0.06S possesses superior stability, the photoactivity of which exhibits no noticeable deactivation after six cycles’ reactions. This work may shed light on the rational design and fabrication of highly efficient materials via combining individual element doping and defect engineering.

Efficient photocatalytic H2 evolution over NiMoO4/Twinned-Cd0.5Zn0.5S double S-scheme homo-heterojunctions

The effectiveness of charge transfer and separation between bulk phase and the interface is crucial for evaluating the performance of photocatalysts. In this study, NiMoO4 was employed to enhance the photocatalytic activity for hydrogen (H2) evolution in twinned Cd0.5Zn0.5S (T-CZS) homojunctions comprising of wurtzite Cd0.5Zn0.5S (WZ-CZS) and zinc blende Cd0.5Zn0.5S (ZB-CZS) with alternating arrangements. The investigation reveals that the introduction of NiMoO4 can lead to an increase of active sites for H2 evolution, a prolongation of charge carrier lifetime, and a decrease of H2 evolution overpotential. The H2 production rate of 8 wt% NiMoO4/T-CZS reaches up to 71.2 mmol h−1 g−1, while its apparent quantum efficiency (AQY) is 8.23% at 400 nm. The enhanced activity can be attributed to the synergistic effects of homojunctions and heterojunctions in NiMoO4/T-CZS. According to the density functional theory (DFT), photoelectric response, and radical trapping experimental analysis, the charge transfer between WZ-CZS and ZB-CZS in T-CZS, as well as NiMoO4 and T-CZS, both follow the S-scheme pathway under the influence of band bending, Coulombic force, and built-in electric field. This leads to an effective internal and interfacial charge separation in NiMoO4/T-CZS homo-heterojunctions, while maintaining their high reactivity. Additionally, the H2 evolution activity of T-CZS can also be increased in different degrees by various metal molybdates (MMoO4) including CoMoO4, Ag2MoO4, Bi2(MoO4)3, BaMoO4, ZnMoO4, and CdMoO4. The bulk and interfacial synergistic double S-scheme homo-heterojunctions in this study provide new insights for targeted solar driven H2 evolution engineering.

Highly efficient photocatalytic H2 evolution and degradation properties over NiO/Mn0.5Cd0.5S S-scheme photocatalyst

Well-designed and high-performance S-scheme photocatalysts for the fabrication of green hydrogen are of significant practical significance in solving the environmental and energy crises. In this study, NiO/Mn0.5Cd0.5S S-scheme heterojunctions were triumphantly prepared by electrostatic adsorption, and the formation of energy band bending and internal electric field at the interfacial contact site between NiO and Mn0.5Cd0.5S resulted in a good photogenerated carrier separation ability and enhanced hydrogen reduction performance and Rhodamine B (RhB) degradation performance. The hydrogen production rate of NiO/Mn0.5Cd0.5S S-scheme heterojunction was enhanced to three folds of the unitary Mn0.5Cd0.5S, with an apparent quantum yield (AQY) of 15.28% at 400 nm and a degradation rate of 91.5%. In addition, the NiO/Mn0.5Cd0.5S S-scheme heterojunction has enhanced and sustainable hydrogen precipitation and RhB degradation performance.

Design of p–n heterojunction between CoWO4 and Zn-defective Zn0.3Cd0.7S for efficient photocatalytic H2 evolution

To enhance the efficiency of photocatalytic H2 evolution, numerous methods are employed by increasing the utilization of photogenerated charge carriers (PCCs), including catalyst design, defect regulation, and selection of suitable H+ resources. Using self-assembly method, CoWO4/ZnxCd1−xS with p–n heterojunction was synthesized. Although CoWO4 (CW) cannot produce H2 under visible light irradiation, it can provide photogenerated electrons (e−) to Zn0.3Cd0.7S (ZCS), and largely increase the photocatalytic activity of ZCS. The optimal CW/ZCS composite can reach 15.58 mmol·g−1·h−1, which is 45.8 and 24.3 times higher than the values of the pure CdS and ZCS, respectively. The largely enhanced photocatalytic H2 production is attributed to the Zn vacancies (VZn), p–n heterojunction, and p-chlorobenzyl alcohol (Cl–PhCH2OH) as the H+ source of H2 production. VZn on the ZCS surface as the capture center of photogenerated holes (h+), can regulate the carrier distribution, which results in more photogenerated e− and less generated h+. The combination of p–n heterojunction and VZn can enhance the separation and transfer efficiency of PCCs, and effectively inhibit the recombination of charge carriers. To further improve the utilization rate of PCCs, the photocatalytic H2 evolution is proceeded by Cl–PhCH2OH oxidation in N,N-dimethylformamide solution, with 4-chlorobenzaldehyde (Cl–PhCHO) generated. The separated photogenerated e− and h+ both participated in the redox reaction of H+ reduction and Cl–PhCH2OH oxidation, considering that the amount of H2 and Cl–PhCHO products are close to 1:1. This work not only facilitates the separation and transfer of PCCs, but also provides directions for the design of efficient photocatalysts and H2 evolution in the organic phase.

Polar Aromatic Two‐dimensional Dion‐Jacobson Halide Perovskites for Efficient Photocatalytic H2 Evolution

AbstractPolar materials with spontaneous polarization (Ps) have emerged as highly promising photocatalysts for efficient photocatalytic H2 evolution owing to the Ps‐enhanced photogenerated carrier separation. However, traditional inorganic polar materials often suffer from limitations such as wide band gaps and poor carrier transport, which hinders their photocatalytic H2 evolution efficiency. Here, we rationally synthesized a series of isostructural two‐dimensional (2D) aromatic Dion–Jacobson (DJ) perovskites, namely (2‐(2‐Aminoethyl)pyridinium)PbI4 (2‐APDPI), (3‐(2‐Aminoethyl)pyridinium)PbI4 (3‐APDPI), and (4‐(2‐Aminoethyl)pyridinium)PbI4 (4‐APDPI), where 2‐APDPI and 4‐APDPI crystalize in polar space groups with piezoelectric constants (d33) of approximately 40 pm V−1 and 3‐APDPI adopts a centrosymmetric structure. Strikingly, owing to the Ps‐facilitated separation of photogenerated carriers, polar 2‐APDPI and 4‐APDPI exhibit a 3.9‐ and 2.8‐fold increase, respectively, in photocatalytic H2 evolution compared to the centrosymmetric 3‐APDPI. As a pioneering study, this work provides an efficient approach for exploring new polar photocatalysts and highlights their potential in promoting photocatalytic H2 evolution.

Polar Aromatic Two-dimensional Dion-Jacobson Halide Perovskites for Efficient Photocatalytic H2 Evolution.

Polar materials with spontaneous polarization (Ps) have emerged as highly promising photocatalysts for efficient photocatalytic H2 evolution owing to the Ps-enhanced photogenerated carrier separation. However, traditional inorganic polar materials often suffer from limitations such as wide band gaps and poor carrier transport, which hinders their photocatalytic H2 evolution efficiency. Here, we rationally synthesized a series of isostructural two-dimensional (2D) aromatic Dion-Jacobson (DJ) perovskites, namely (2-(2-Aminoethyl)pyridinium)PbI4 (2-APDPI), (3-(2-Aminoethyl)pyridinium)PbI4 (3-APDPI), and (4-(2-Aminoethyl)pyridinium)PbI4 (4-APDPI), where 2-APDPI and 4-APDPI crystalize in polar space groups with piezoelectric constants (d33) of approximately 40 pm V-1 and 3-APDPI adopts a centrosymmetric structure. Strikingly, owing to the Ps-facilitated separation of photogenerated carriers, polar 2-APDPI and 4-APDPI exhibit a 3.9- and 2.8-fold increase, respectively, in photocatalytic H2 evolution compared to the centrosymmetric 3-APDPI. As a pioneering study, this work provides an efficient approach for exploring new polar photocatalysts and highlights their potential in promoting photocatalytic H2 evolution.

Enhanced Spin-Polarized Electric Field Modulating p-Band Center on Ni-Doped CdS for Boosting Photocatalytic Hydrogen Evolution.

It is a challenge to regulate charge separation dynamics and redox reaction kinetics at the atomic level to synergistically boost photocatalytic hydrogen (H2 ) evolution. Herein, a robust Ni-doped CdS (Ni-CdS) photocatalyst is synthesized by incorporating highly dispersed Ni atoms into the CdS lattice in substitution for Cd atoms. Combined characterizations with theoretical analysis indicate that local lattice distortion and S-vacancy of Ni-CdS induced by Ni incorporation lead to an increased dipole moment and enhanced spin-polarized electric field, which promotes the separation and transfer of photoinduced carriers. In this contribution, charge redistribution caused by enhanced internal electric field results in the downshift of the S p-band center, which is conducive to the desorption of intermediate H* for boosting the H2 evolution reaction. Accordingly, the Ni-CdS photocatalyst shows a remarkably improved photocatalytic performance with an H2 evolution rate of 20.28mmolg-1 h-1 under visible-light irradiation, which is 5.58 times higher than that of pristine CdS. This work supplied an insightful understanding that the enhanced polarization electric field governs the p-band center for efficient photocatalytic H2 evolution activity.

In-situ generation of Au–carbon–TiO2 Ohmic junction from Ti3C2 MXene for efficient photocatalytic H2 evolution

Photogenerated charge separation is a challenging step in semiconductor-based photosynthesis. Though numerous efforts have been devoted to developing multi-component photocatalyst heterostructures for improving charge separation efficiency, the short distance between electrons and holes-aggregated regions still leads to undesirable charge recombination. Herein, a facile and commercial in-situ synthesis method was designed to directly prepare a three-component Au–carbon–TiO2 photocatalyst from Ti3C2 MXene, air, CO2, and HAuCl4, in which the carbon layer bridged Au and TiO2 nanoparticles for stable and efficient photocatalytic hydrogen production. Kelvin probe measurements and density functional theory (DFT) calculations demonstrated that a multi-interfacial charge transmission network was successfully constructed to achieve a directional and long-distance spatial charge separation/transfer channel between TiO2 and Au through carbon layer, desirably inhibiting the recombination of photogenerated charge carriers. The hydrogen production rate of the formed three-component Au/C–TiO2 (CTA) photocatalyst was demonstrated to be 27 times higher than that of Au–TiO2, which also surpassed many reported Ti3C2 MXene-derived carbon–TiO2 photocatalysts. This work sheds light on the ingenious use of 2D MXene to form a well-behaved TiO2-based photocatalytic system and helps to propose future design principles in accelerating charge transfer.

Green synthesis of 3D core-shell SnS2/SnS-Cd0.5Zn0.5S multi-heterojunction for efficient photocatalytic H2 evolution.

Low charge carrier separation efficiency is one of the key factors restricting photocatalytic hydrogen evolution performance. It is an effective strategy to build heterojunctions to steer charge migration. Herein, a series of x-SnS2/SnS-Cd0.5Zn0.5S (x-SS-CZS) nanosphere composites with varying mass ratios of SnS2/SnS (SS) were prepared through in situ hydrothermal synthesis. Moreover, XRD, TEM, and XPS were used to characterize the 3D core-shell SS-CZS multi-heterojunction composite. The 5-SS-CZS heterojunction composite with 5 wt% content of SS exhibits a remarkable hydrogen evolution rate of 168.85 mmol g-1 h-1, which is 5.4 times higher than that of pristine twin CZS (31.08 mmol g-1 h-1) and 1.9 times higher than that of 5-SnS2-CZS (88.21 mmol g-1 h-1). Furthermore, the composite catalyst showed excellent photostability after four cycles of reactions under visible light illumination. The apparent quantum yield at λ = 420 nm could reach up to 24.78%. The excellent hydrogen evolution performance of 5-SS-CZS nanospheres is ascribed to the following factors: (1) a core-shell catalyst with broad spectral absorption improves light utilization efficiency, (2) hybrid material with large surface area provides more active sites and shows the highest H2 activity, (3) a multi-heterojunction composite extends the lifetime of photoinduced carriers and accelerates charge separation and migration, and (4) SS as a hole trapping agent enhances the photocatalytic stability performance. This work proposes a possible photocatalytic mechanism, while also providing a novel approach for the synthesis of highly active and stable photocatalysts.

Cd(Eu)Se/CdS/CdZnS/ZnS quantum dots with hydrophilic alloy shell supported by flower-like ZnIn2S4: A S-scheme for efficient photocatalytic H2 evolution

Photocatalytic hydrogen evolution via water splitting based on semiconductor technologies is a vital way to tackle environmental problems and the energy crisis in a sustainable manner. Carrier separation efficiency, light absorption capacity and microstructure of photocatalysts are key factors affecting the efficiency of photocatalytic hydrogen evolution. However, there exist problems like low separation of photogenerated electrons and holes and limited light absorption for traditional semiconductors. Here we prepared Eu3+ doped CdSe quantum dots with hydrophilic alloy shell CdS/CdZnS/ZnS and anchored it on flower-like ZnIn2S4 to construct S-scheme heterojunction. Characterizations of photocatalytic performance indicate that the hydrogen production performance is improved. What can be found is that the optimized composite photocatalyst has photocatalytic hydrogen evolution efficiency of 3888.79 μmol‧g−1‧h−1 and it is 6 times higher than unmodified ZnIn2S4. Furthermore, the creation of S-scheme heterojunction improves the disadvantages of ZnIn2S4 in visible light absorption and accelerates charge separation markedly. This work provides a distinctive perspective on the photocatalysts of photocatalytic hydrogen evolution.

In situ XPS demonstrated efficient charge transfer of ohmic junctions based on graphdiyne (g-CnH2n-2) nanosheets coupled with porous nanoflowers Ni5P4 for efficient photocatalytic H2 evolution

The photocatalytic hydrogen evolution ability of catalyst can be effectively improved by constructing suitable heterojunction. The present study involves a new type of carbon-material semiconductor graphdiyne (GDY) was prepared by ball milling assisted reduction elimination reaction, and introduced into metal-rich Ni5P4 nanoflowers by hydrothermal method. GDY/Ni5P4 ohm junction was successfully constructed to regulate the electron direction. The C ≡C bond in GDY exhibits high reducibility, which is conducive to inhibiting the oxidation of Ni5P4. The unique porous nanoflower-like structure of Ni5P4 enables it to achieve complete contact with solvents, thereby enhancing proton absorption capabilities. The construction of an ohmic junction is confirmed to induce electron transfer from GDY to Ni5P4 through situ XPS characterization, thereby suppressing the recombination of electron-hole pairs in GDY. Among them, 15%GDY/Ni5P4 has the best photocatalytic hydrogen evolution activity of 11713.6 μmol h−1 g−1, which is about 15 times higher than that of GDY (755.4 μmol h−1 g−1) and 5 times that of Ni5P4 (2369.6 μmol h−1 g−1). This work provides a new way to construct ohm junction based on GDY for photocatalytic hydrogen evolution.

Construction of in-situ core-shell Cu2-xS@Mn0.3Cd0.7S S-scheme heterojunction with efficient photocatalytic H2 evolution

Improving the stability and electron-hole separation efficiency of semiconductor photocatalysts has always been a hot topic in the field of catalysis. In the present study, a novel Cu2-xS@Mn0.3Cd0.7S (Cu2-xS@MCS) core-shell heterojunction has been constructed by the in-situ traditional hydrothermal reaction on the basis of hollow Cu2-xS nanocubes. The optimized Cu2-xS@MCS-2 photocatalyst with expanded light absorption exhibits excellent stability and a higher hydrogen evolution rate of 42.43 mmol g−1 h−1, which is 2.3 times and more than 1400 times contrasting to the pure Mn0.3Cd0.7S and Cu2-xS, respectively. Multiple characterizations and structure analysis revealed that the Cu2-xS@MCS heterojunction possesses outstanding charge separation efficiency and a wider specific surface area which can provide abundant active sites. Furthermore, the mechanism of photocatalytic H2 evolution for Cu2-xS@Mn0.3Cd0.7S S-scheme heterojunction is also proposed. This work thus provides a favorable strategy to inhibit the photogenerated charge carrier recombination and drive highly efficient photocatalytic hydrogen generation by synthesizing photocatalyst with in situ core-shell structures.