Efficient Photocatalytic Hydrogen Evolution Research Articles

Engineering hollow Ni–Fe-based mesoporous spherical structure derived from MOF for efficient photocatalytic hydrogen evolution

Endowing photocatalyst with functional nanostructure can effectively improve its performance towards solar energy conversion. Here, a unique Ni–Fe-based mesoporous hollow spherical nanostructure (NiFeOx/NC-t) was facilely constructed via the direct thermal decomposition of Ni-BTC@PBA composites. The hybrids consist of in-situ formed nitrogen-enriched carbon layers constituting the mesoporous walls of hollow spherical, and amorphous NiFeOx nanoparticles and a small fraction of FeNi3 are embedded on the spherical walls during carbonization. After loading EY molecules on NiFeOx/NC-t as solar light absorbers, an optimal photocatalytic hydrogen evolution rate of 5352.7 μmol g−1 h−1 was achieved with excellent stability under visible light (λ > 420 nm) in the absence of co-catalyst. The excellent photocatalytic activity was revealed to be ascribed to: ⅰ) mesoporous hollow spherical structure having a large surface area, thus exposing more active sites; ⅱ) efficient injection of photo-generated electrons from excited EY− into NiFeOx and FeNi3 by the bridge of high-conductive nitrogen-enriched carbon layer. In brief, the structural and compositional features synergistically strengthen the photocatalytic activity of NiFeOx/NC-t. It is worth noting that MOF-derived route can significantly simplify the preparation process of mesoporous hollow spherical nanostructure. This work provides an approach for facile preparation of versatile photocatalysts with high efficiency for solar energy conversion.

Interface engineering of ZnO/In2O3 Z-scheme heterojunction with yolk-shell structure for efficient photocatalytic hydrogen evolution

Photocatalytic activities based on charge transfer and separation at interfaces can be effectively promoted by matching chemical Z-scheme heterojunctions and electronic structures. However, the fabrication of morphology-controlled heterojunctions has been a challenge to many researchers. Herein, hollow spheres ZnO/In2O3 was constructed via hydrothermal strategy by fine-tuning the concentration of metal nitrate precursors, and special yolk-shell morphology was generated by the symmetrical Ostwald ripening process. The fabricated Z-Scheme heterojunction exhibited characteristic multi-channel charge transfer properties, which favors the spatial separation of carriers. The ZnO/In2O3 hollow spheres increased the utilization of light source, and the yolk-shell structure increased the interface area and the active sites. Benefiting from the synergistic effect, the ZnO/In2O3 exhibited excellent photocatalytic activities for H2 production, which was comparatively 26.7 times that obtained using ZnO nanoparticles. From calculations based on DFT, the Z-scheme photogenerated charge transfer mechanism was proposed. The proposed mechanism was verified by analyzing the chemical properties (surface) and the •O2− and •OH free radical concentrations before and after the photoreaction. The mechanism presented the ZnO/In2O3 with strong capabilities for H2 production and elucidated the improved photocatalytic performances. This work creates an innovative route for constructing Z-scheme photocatalytic systems with great photocatalytic activities for H2 production.

Fabrication of Ni2P Cocatalyzed CdS Nanorods with a Well-Defined Heterointerface for Enhanced Photocatalytic H2 Evolution

Developing non-noble metal photocatalysts for efficient photocatalytic hydrogen evolution is crucial for exploiting renewable energy. In this study, a photocatalyst of Ni2P/CdS nanorods consisting of cadmium sulfide (CdS) nanorods (NRs) decorated with Ni2P nanoparticles (NPs) was fabricated using an in-situ solvothermal method with red phosphor (P) as the P source. Ni2P NPs were tightly anchored on the surface of CdS NRs to form a core-shell structure with a well-defined heterointerface, aiming to achieve a highly efficient photocatalytic H2 generation. The as-synthesized 2%Ni2P/CdS NRs photocatalyst exhibited the significantly improved photocatalytic H2 evolution rate of 260.2 μmol∙h−1, more than 20 folds higher than that of bare CdS NRs. Moreover, the as-synthesized 2%Ni2P/CdS NRs photocatalyst demonstrated an excellent stability, even better than that of Pt/CdS NRs. The photocatalytic performance enhancement was ascribed to the core-shell structure with the interfacial Schottky junction between Ni2P NPs and CdS NRs and the accompanying fast and effective photogenerated charge carriers’ separation and transfer. This work provides a new strategy for designing non-noble metal photocatalysts to replace the noble catalysts for photocatalytic water splitting.

Sandwich-like P-doped h-BN/ZnIn2S4 nanocomposite with direct Z-scheme heterojunction for efficient photocatalytic H2 and H2O2 evolution

The sustainable conversion from solar energy to chemical energy is realized by using photocatalytic technology to produce hydrogen and hydrogen peroxide. In this work, the construction of a direct Z-scheme heterojunction is of great significance for improving the efficiency and stability of photocatalytic hydrogen evolution (PHE) and photocatalytic hydrogen peroxide production (PHP). In this study, P-doped h-BN (PBN) nanosheets are used to support the in-situ growth of ZnIn2S4 nanoflowers via wet chemical method, and sandwich-like PBN/ZnIn2S4 hierarchical heterostructures are successfully synthesized. The PHE performance of PBN/ZnIn2S4 (∼59.46 μmol/h) is ∼ 2.35 times than that of the original ZnIn2S4 (∼25.27 μmol/h), and the PHP performance (∼122.82 μmol/L/h) is 39.37 times than that of PBN (∼3.12 μmol/L/h). The excellent photocatalytic performance of PBN/ZnIn2S4 can be attributed to the following points: (1) the acceleration of the separation of photogenerated electron-hole pairs induced by the formation of Z-scheme heterostructure; (2) reasonable design and construction of sandwich-like PBN/ZnIn2S4 hierarchical heterostructure; (3) the promotion the migration and separation of photogenerated carriers by the built-in electric field. This work provides new ideas for the development of high-efficiency PHE and PHP Z-scheme heterojunction photocatalyst design.

Generation of long-lived charges in organic semiconductor heterojunction nanoparticles for efficient photocatalytic hydrogen evolution

Organic semiconductor photocatalysts for the production of solar fuels are attractive as they can be synthetically tuned to absorb visible light while simultaneously retaining suitable energy levels to drive a range of processes. However, a greater understanding of the photophysics that determines the function of organic semiconductor heterojunction nanoparticles is needed to optimize performance. Here, we show that such materials can intrinsically generate remarkably long-lived reactive charges, enabling them to efficiently drive sacrificial hydrogen evolution. Our optimized hetereojunction photocatalysts comprise the conjugated polymer PM6 matched with Y6 or PCBM electron acceptors, and achieve external quantum efficiencies of 1.0% to 5.0% at 400 to 900 nm and 8.7% to 2.6% at 400 to 700 nm, respectively. Employing transient and operando spectroscopies, we find that the heterojunction structure in these nanoparticles greatly enhances the generation of long-lived charges (millisecond to second timescale) even in the absence of electron/hole scavengers or Pt. Such long-lived reactive charges open potential applications in water-splitting Z-schemes and in driving kinetically slow and technologically desirable oxidations.

Ion-Induced Synthesis of Crystalline Carbon Nitride Ultrathin Nanosheets from Mesoporous Melon for Efficient Photocatalytic Hydrogen Evolution with Synchronous Highly Selective Oxidation of Benzyl Alcohol.

Crystalline carbon nitride (CCN) with a poly(heptazine imide) structure is efficient in photocatalytic hydrogen evolution (PHE), but synthesis of CCN ultrathin nanosheets (CCNuns) and their use in PHE with selective organic oxidation are still rare. Herein, CCNuns with Na+ doping are prepared using NaCl as the ion-induction and templating agent and mesoporous melon as the feedstock, exhibiting efficient synchronous PHE and benzyl alcohol oxidation to benzaldehyde, with an apparent quantum yield of 10.5% at 420 nm and a visible light PHE rate that is 94.3 times that of bulk polymeric carbon nitride (PCN). The selectivity of benzaldehyde formation (90.5%) is also much higher than that of PCN (40.7%). Interestingly, this selectivity increases gradually with increasing light wavelengths. The high photoactivity of CCNuns originates from their ultrathinness and Na+ doping, which considerably enhance the photogenerated charge separation. This work opens up an avenue for the synthesis of CCNuns and extends their application.

Direct Z-Scheme Heterojunction Catalysts Constructed by Graphitic-C3N4 and Photosensitive Metal-Organic Cages for Efficient Photocatalytic Hydrogen Evolution.

The demand for improving the activity, durability, and recyclability of metal-organic cages (MOCs) that work as photocatalytic molecular devices in a homogeneous system has promoted research to combine them with other solid materials. An M2L4 type photosensitive metal-organic cage MOC-Q2 with light-harvesting ligands and catalytic Pd2+ centers has been synthesized and further heterogenized with graphitic carbon nitride to prepare a robust direct Z-scheme heterojunction photocatalyst for visible-light-driven hydrogen generation. The optimized g-C3N4/MOC-Q2 (0.7 wt%) sample exhibits a high H2 evolution activity of 6423 μmol g−1 h−1 in 5 h, and a total turnover number of 39,695 after 10 h, significantly superior to the bare MOC-Q2 used in the homogeneous solution and the comparison sample Pd/g-C3N4/L-4. The enhanced performances of g-C3N4/MOC-Q2 can be ascribed to its direct Z-scheme heterostructure, which effectively improves the charge separation and transfer efficiency. This work presents a rational approach of designing a binary photocatalytic system through combing micromolecular MOCs with heterogeneous semiconductors for water splitting.

Organic dyes with multi-branched structures for highly efficient photocatalytic hydrogen evolution under visible-light irradiation

Direct photocatalytic water splitting is an attractive strategy for clean energy, in which, organic photocatalytic systems with broad light-harvesting region and efficient charge separation are highly desired and still challenging. In this paper, three multi-branched organic dyes were designed and synthesized with dipolar, V-shaped, and octupolar geometries, respectively. The multiple intramolecular charge transfer processes by electronic pull-push effect along the branches can provide more channels for light-harvesting and carrier transporting. Also, the interactions with polymeric carbon nitride (PCN) can be optimized by multiple anchoring units and defect filling effect, resulting in the gradually enhanced photocatalytic hydrogen evolution performance with the increased number of branches. Accordingly, the highest one of 996.9 μmol h−1 was achieved, which is over 40-folders that of PCN/Pt (24.8 μmol h−1) under the same conditions. It provides an efficient strategy for molecular design of organic dyes as photocatalyst, promoting development of PHE system from the molecular level.

NiSx modified Mn0.5Cd0.5S twinned homojunctions for efficient photocatalytic hydrogen evolution

Twinned Mn0.5Cd0.5S homojunction (T-MCS) was synthesized via a simple hydrothermal process, and then NiSx was precipitated on the surface of T-MCS by in situ precipitation process. The type-II staggered band alignment between zinc-blende (ZB) and wurtzite (WZ) Mn0.5Cd0.5S can form a homojunction in bulk T-MCS, and the introduction of NiSx nanoparticles can construct a heterojunction between NiSx and T-MCS. The synergistic of homojunction and heterojunction can effectively promote the separation of charge carriers in the bulk phase and surface of T-MCS, meanwhile, NiSx can reduce the H2 evolution overpotential and induce more active sites, leading to an increased H2 production efficiency. The 0.5 wt% NiSx/T-MCS shows a great H2 evolution rate of 111.5 mmol∙g−1∙h−1 in Na2S/Na2SO3 solution under visible light (λ ≥ 420 nm) irradiation, which is 2.3-fold higher than that of the pure T-MCS. Its apparent quantum efficiency (AQE) is 10.4% under 400 (±5) nm light irradiation. This research sheds light on the exploration of homo-heterojunction photocatalysts for efficient H2 evolution.

2D/2D heterostructured MoS2/PtSe2 promoting charge separation in FTO thin film for efficient and stable photocatalytic hydrogen evolution

2D/2D heterostructured MoS2/PtSe2 promoting charge separation in FTO thin film for efficient and stable photocatalytic hydrogen evolution

High-yield exfoliation of MoS2 (WS2) monolayers towards efficient photocatalytic hydrogen evolution

Monolayer MoS2 (WS2) nanosheets have triggered tremendous interest due to their fascinating unique properties, but high-yield production of single-layer MoS2 (WS2) still remains an enormous challenge and of great interest. Herein, we report a facile efficient partial etching strategy to tailor thickness and lateral size of MoS2 (WS2) so as to increase the fraction of edges, which remarkably enhanced the yield of monolayer MoS2 (20%) and WS2 (12%) nanosheets by liquid phase exfoliation. As a proof of concept, the exfoliated monolayer MoS2 (WS2) nanosheets were applied as the cocatalysts for photocatalytic hydrogen evolution. Notably, the optimized hybrids exhibit excellent hydrogen evolution performance, which are over 31-fold (MoS2/CdS) and 47-fold (WS2/CdS) higher that of bare CdS counterpart, respectively. Hence, this work not only may pave the new way for the high-yield production of transition-metal dichalcogenides monolayers by liquid phase exfoliation, but also provide the possibility for the further efficiently exfoliating other two-dimension layered materials.

Ag–AgBr/g-C3N4/ZIF-8 prepared with ionic liquid as template for highly efficient photocatalytic hydrogen evolution under visible light

In this study, a ternary photocatalyst named Ag–AgBr/g-C3N4/ZIF-8 (A/g/Z) was prepared by ionic liquid assisted in-situ growth method. The structure and composition of samples are studied by means of XRD, SEM, XPS, TEM, EIS, etc. The AgBr prepared by ionic liquid assisted method has good dispersion, and the protonated carbon nitride has better specific surface area and morphology structure. The structure of the composites is optimized by modifying g-C3N4 with MOFs and noble metals, and the existence of Ag+ can play a bridging role, so as to form multi-path electronic transmission route. The high efficiency of electron transfer greatly improved the efficiency of hydrogen evolution. It is worth noting that the surface plasmon resonance (SPR) effect produced by silver ions on the surface of g-C3N4 can improve the absorption of visible light. The A (1.1)/g/Z (6.5) exhibit high hydrogen evolution efficiency (2058 μmol g−1 h−1, which is 49 times than g-C3N4) at the absence of Pt co-catalyst. Furthermore, the transient photocurrent density of the composites is much higher than that of g-C3N4 and AgBr, the semicircle radius of EIS is also less than both. Through the five cycle experiment, the photocatalytic efficiency of the composite material remained above 91%.

Pt modified TiO2/NiO p-n junction with enhanced surface reaction and charge separation for efficient photocatalytic hydrogen evolution

Efficient charge separation is crucial for solar energy conversion in semiconductor-based systems. Creating p-n junction is an effective strategy to enhance charge separation because the built-in electric field could inhibit charge recombination. However, in many situations, the high reaction barrier will limit the surface reaction rate, resulting in poor carrier utilization of the p-n junction. Here, with carefully designed cocatalyst loading, we successfully overcome the limitation and obtain the full effectiveness of the p-n junction. When used for photocatalytic water splitting, the well-designed catalyst exhibits excellent photocatalytic activity, with a hydrogen evolution rate as high as 13.2 mmol h −1 g −1 , which is 18 times higher than that of the pristine p-n junction. Further investigation reveals that the enhancement should be attributed to the synergistic effect between cocatalyst and p-n junction, with the cocatalyst improves reaction rate on the surface and the p-n junction accelerates charge separation in the bulk simultaneously. This work provides an effective strategy to modify the surface properties of p-n junction through cocatalysts-loading for efficient photocatalytic hydrogen evolution. • Cocatalyst is effective to improve the sluggish surface reaction of p-n junction. • TiO 2 /NiO–Pt showed high stability and excellent photocatalytic hydrogen evolution activity of 13.2 mmol g −1 h −1 . • Efficient charge separation and carrier utilization can be realized in the system of cocatalyst loaded p-n junction. • Cocatalyst and p-n junction contribute a synergistic effect towards photocatalytic water splitting.

Fe2O3 hexagonal nanosheets assembled with NiS formed p–n heterojunction for efficient photocatalytic hydrogen evolution

Fe2O3 hexagonal nanosheets assembled with NiS formed p–n heterojunction for efficient photocatalytic hydrogen evolution

Anchoring nickel complex to g-C3N4 enables an efficient photocatalytic hydrogen evolution reaction through ligand-to-metal charge transfer mechanism

The development of stable and efficient non-noble metal-based photocatalysts for water splitting is currently a key but challenging process for effective conversion and storage of sustainable energy. Here, we designed a new non-noble metal composite photocatalyst by covalently connecting nickel molecular ligand (NiL) to the graphitized carbon nitride (CN) framework for photocatalytic hydrogen evolution under visible light irradiation. Compared to CN, NiL-modified CN (NiL/CN) shows excellent photogenerated carrier migration rate. Without Pt as a co-catalyst, NiL/CN exhibits high photocatalytic activity (23.4 μmol h−1) with high stability. Experiments and theoretical calculations disclose that ligand–metal charge transfer (LMCT) mechanism plays a key role on the enhancement of photocatalytic activity. This work provides a promising method for future designing low-cost, high-performance photocatalysts for hydrogen production under solar light.

Graphdiyne based GDY/CuI/NiO parallel double S-scheme heterojunction for efficient photocatalytic hydrogen evolution

As a new kind of two-dimensional (2D) layered carbon allotrope, graphdiyne (GDY) is rarely studied in the application field of photocatalytic hydrogen production. In addition, the efficient construction of photocatalyst heterostructure is a promising strategy to improve the yield of hydrogen production from photocatalytic split of water. Therefore, it is an excellent method to construct heterostructure photocatalytic system by introducing GDY into semiconductor photocatalytic materials. Herein, it is an excellent method to construct heterostructure photocatalytic system by introducing the cuprous iodide based 2D layered carbon allotrope (GDY) into metallic oxide semiconductor (NiO). Thus, a ternary hybrid photocatalyst (GDY/CuI/NiO) was prepared by in situ ultrasonic agitation method. X-ray diffraction, SEM, transmission electron microscope and x-ray photoelectron spectroscopy results showed that NiO nanosheets were successfully adsorbed by GDY/CuI. In addition, the composite catalyst (GDY/CuI/NiO) showed excellent photocatalytic performance, which performed a high hydrogen production activity of 5955 μmol g−1 and good stability in the 20 h hydrogen production experiment. Amorphous GDY provides more active sites for the process of hydrogen evolution in this photocatalytic system. Most importantly, the construction of S-scheme heterojunction promotes electron transfer and plays an important role in enhancing the hydrogen production activity. These findings provide new ideas for realizing efficient solar hydrogen production system.

Efficient photocatalytic hydrogen evolution through reverse hydrogen spillover on photoactivated copper-doped mesoporous titania spheres

Transition-metal-doped mesoporous TiO2 (M-mTiO2) spheres are highly desired for photocatalysis because of their large specific surface area and extended light absorption. Herein, a universal method is developed for the preparation of M-mTiO2 spheres and their photocatalytic mechanism is unveiled. Fe-mTiO2, Co-mTiO2, Ni-mTiO2, Cu-mTiO2 spheres are successfully prepared by the developed method. Among all M-mTiO2 samples, the Cu-mTiO2 catalyst exhibits reversible photoactivation phenomenon during photocatalysis. The photocatalytic hydrogen evolution rate on photoactivated Cu-mTiO2 can reach 3.31 mmol g−1 h−1, which is much higher than those of other M-mTiO2 and is 28.3 times of that of the mTiO2. Density functional theory (DFT) calculations reveal that the photoactivation of Cu-mTiO2 is associated with the facile formation of oxygen vacancies on Cu-mTiO2. The photoactivation induces the active site change and the light absorption increase of Cu-mTiO2. The active site change has the dominant role for the enhancement of photocatalytic performance. On the photoactivated Cu-mTiO2, the hydrogen production is through a reverse hydrogen spillover process. Our findings not only provide a universal method for the preparation of M-mTiO2 but also deepen the understanding about the photoactivation and the hydrogen production mechanism.

An innovative synthesis strategy for high-efficiency and defects-switchable-hydrogenated TiO2 photocatalysts

Hydrogenated TiO₂ (H-TiO₂) is one of the most promising TiO₂-based photocatalysts. Through effectively narrowing the band gap of TiO₂ and restraining the recombination of photogenerated carriers, in the January issue of <i>Matter</i>, Cui et al. reported a new and facile one-pot wet-chemistry strategy to prepare H-TiO₂ for highly efficient photocatalytic hydrogen (H₂) evolution.¹

2D CeO2 and a Partially Phosphated 2D Ni-Based Metal-Organic Framework Formed an S-Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution.

Here, an S-scheme heterojunction was constructed on the basis of the modification of a Ni-based metal-organic framework (Ni-MOF) by different in situ treatment strategies. First, NiS2, NiO, and Ni2P were derived in situ on the surface of Ni-MOF through surface sulfonation, oxidation, and phosphatizing treatments. They can efficiently accept the electrons from the conduction band of Ni-MOF as the trap centers, thus improving the hydrogen production activity. Additionally, phosphatizing makes the electronegativity of Ni-MOF/P stronger than that of the original Ni-MOF, which can enhance the absorption of protons, thus promoting the hydrogen evolution reaction. Next, the S-scheme heterojunction was successfully built by the coupling of 2D CeO2 with Ni-MOF/P. The maximum hydrogen production rate of the hybrid catalyst (6.337 mmol g-1 h-1) is 14.18 times that of the untreated Ni-MOF due to the full utilization of photo-induced electrons. Finally, the probable hydrogen evolution mechanism was proposed by analyzing a series of characterization results and by the density functional theory (DFT) calculation.

NiO and Co1.29Ni1.71O4 derived from NiCo LDH form S-scheme heterojunction for efficient photocatalytic hydrogen evolution

NiO and Co1.29Ni1.71O4 were generated in situ by oxidizing and calcining NiCo LDH (Layered Double Hydroxide) to erect an S-scheme heterojunction heterogeneous catalyst. After calcination, the lamellar structure of NiCo LDH becomes thinner and part of the lamellar porous, which can provide more active sites for hydrogen precipitation reaction. The amount of hydrogen released by the composite catalyst is 3 times that of NiCo LDH This in-situ generation method will allow NiO and Co1.29Ni1.71O4 to establish a close relationship, form a built-in electric field, and build an S-scheme heterojunction. NiO and Co1.29Ni1.71O4 have good band structure and band gap position matching. S-scheme heterojunction composite catalyst has the best light absorption intensity and photocurrent response, the smallest electronic impedance, and good electron and hole separation efficiency, thereby improving the performance of photocatalytic hydrogen evolution. It was confirmed by a large number of characterization studies.