Efficient Photocatalytic Hydrogen Production Research Articles

Ni/Co-bimetallic organic framework-derived NiS/Co3S4/ZnCdS heterojunction for efficient photocatalytic hydrogen production

Heterojunctions can effectively separate electrons (e−) and holes (h+) and achieve efficient photocatalytic water splitting to produce H2. Here, a simple strategy for the synthesis of a sulfide/solid solution heterojunction denoted by NiS/Co3S4/ZnCdS is proposed using a Ni/Co-bimetallic organic framework as a template. The heterostructure formed between ZnCdS and NiS/Co3S4 shortens the electron transport distance and greatly reduces the recombination of e− and h+. The resulting composites show excellent photocatalytic activity, with the highest H2 rate reaching 98.6 mmol h−1 g−1 in the presence of Na2SO3-Na2S as a sacrificial agent. The improvement in the photocatalytic ability of the composites can be attributed to the synergy between ZnCdS and NiS/Co3S4, which inhibits the agglomeration of ZnCdS nanoparticles to expose more active sites. This work offers a new strategy for the preparation of efficient photocatalysts for the utilization of clean energy.

Highly efficient visible-light photocatalytic hydrogen production using ZIF-derived Co9S8/N, S-CNTs-ZnIn2S4 composite

A hierarchical Co9S8/N, S-CNTs-ZnIn2S4 (CSCNs-ZIS) composite was reasonably constructed by grafting ZnIn2S4 nanosheets on the ZIF (67) derived Co9S8/N, S-doped carbon nanotubes for effective photocatalytic hydrogen production. The aggregated ZnIn2S4 nanosheets were uniformly wrapped on the surface of CSCNs, forming a hierarchical core–shell configuration, which effective inhibition of charge-carrier recombination. The CSCNs was adopted as an effective multi-component co-catalyst and further promoted photocatalytic hydrogen production performance. The H2 production rate of optimized CSCNs-ZIS composite reached 2409.2 μmol·h−1·g−1 and has high stability after three cycles. This work may inspire the design of a new noble-metal-free multi-component co-catalyst for sustainable H2 production.

Long-range electron synergy over Pt1-Co1/CN bimetallic single-atom catalyst in enhancing charge separation for photocatalytic hydrogen production

The development of novel single-atom catalysts with optimal electron configuration and economical noble-metal cocatalyst for efficient photocatalytic hydrogen production is of great importance, but still challenging. Herein, we fabricate Pt and Co single-atom sites successively on polymeric carbon nitride (CN). In this Pt1-Co1/CN bimetallic single-atom catalyst, the noble-metal active sites are maximized, and the single-atomic Co1N4 sites are tuned to Co1N3 sites by photogenerated electrons arising from the introduced single-atomic Pt1N4 sites. Mechanism studies and density functional theory (DFT) calculations reveal that the 3d orbitals of Co1N3 single sites are filled with unpaired d-electrons, which lead to the improved visible-light response, carrier separation and charge migration for CN photocatalysts. Thereafter, the protons adsorption and activation are promoted. Taking this advantage of long-range electron synergy in bimetallic single atomic sites, the photocatalytic hydrogen evolution activity over Pt1-Co1/CN achieves 915.8 mmol·g-1Pt·h−1, which is 19.8 times higher than Co1/CN and 3.5 times higher to Pt1/CN. While this electron-synergistic effect is not so efficient for Pt nanoclusters. These results demonstrate the synergistic effect at electron-level and provide electron-level guidance for the design of efficient photocatalysts.

Ceria-based quantum dots/nanorods supported metallic cobalt for efficient photocatalytic hydrogen production

The concentration of photogenerated electrons on support surface has a significant impact on the photocatalytic performance of the corresponding catalyst. Herein, the CeO2-based homojunction support consisted of quantum dots/nanorods (QDs/NRs) was fabricated by two-step calcination with assistance of KCI and NaCl. Based on CeO2-QDs/NRs support, the Co-based catalyst exhibited excellent catalytic performance for photocatalytic hydrogen evolution from Ammonia Borane (NH3BH3). The catalysts exhibited the highest activity with TOF 96.15 min−1 under optimized conditions, which was significantly improved compared Co/CeO2 NRs (68.5 min−1). Detailed structure characterizations revealed that the QDs with size range from 2 to 5 nm grow on the surface of NRs, which had capacity to transfer more photogenerated electrons from the bulk to surface compared with pristine CeO2 NRs. Meanwhile, work function was upshifted from CeO2 NRs to CeO2-QDs/NRs. The synergy of two factors drove more electrons transfer from CeO2-QDs/NRs to active metal Co, accelerating the adsorption and activation of NH3BH3. In addition, the forming mechanization QDs by inducing the morphological evolution of CeO2 nanoparticles was also investigated. This work not only provides efficient photocatalyst for H2 evolution from NH3BH3 but also provides new insights into the design and preparation efficient QDs-based homojunction catalyst.

Dual Defective K-Doping and Cyano Group Sites on Carbon Nitride Nanotubes for Improved Hydrogen Photo-Production

In this work, dual defective potassium (K) doping and cyano group sites have been introduced into carbon nitride (CN) with various morphologies by a co-condensation method for highly efficient photocatalytic hydrogen production. The photocatalysts with potassium doping and inserted cyano groups display higher photocatalytic activity of hydrogen evolution under visible light irradiation in contrast to undoped bulk CN, CN nanosheets, and CN nanotubes. Potassium-doped CN nanotubes present the greatest hydrogen generation yield of 2.11 mmol g–1 h–1 with an apparent quantum efficiency of 5.28% at 420 nm, which is about 2.0 and 40 times that of K-incorporated bulk CN and the bare CN nanotubes, respectively. Benefiting from uniformly distributed potassium ions, the introduction of cyano groups, and the one-dimensional tubular structure of CN nanotubes, the resultant K-doped CN nanotubes have new charge transfer paths between potassium ions and adjacent heptazine units, accelerating photogenerated carrier transfer and enhanced photoreduction ability, thereby improving the photocatalytic performance. This study presents a reliable method for element doping of CN with various morphologies to photocatalytic hydrogen evolution through water splitting.

Vinylene-linked covalent organic frameworks with manipulated electronic structures for efficient solar-driven photocatalytic hydrogen production

Vinylene-linked covalent organic frameworks with manipulated electronic structures for efficient solar-driven photocatalytic hydrogen production

Hydrogen Production from Formic Acid by In Situ Generated Ni/CdS Photocatalytic System under Visible Light Irradiation.

Simple and practical noble-metal-free catalyzed hydrogen production from sustainable resources, such as renewable formic acid, is highly desirable. Herein, the development of an efficient photocatalytic hydrogen production from aqueous solution of formic acid using in situ generated Ni/CdS photocatalytic system was described. CdS-Cys (Cys=l-cysteine) quantum dots (QDs) acting as photocatalyst with Ni(OAc)2 as H2 production catalyst precursor, a 94 % yield was obtained within 5 h under visible light irradiation at 50 °C. The average rate of H2 production reached up to 282 μmol mg-1 h-1 with 99.8 % H2 selectivity. Mechanistic studies indicate cooperation of dynamic quenching and static quenching of CdS-Cys QDs by Ni(OAc)2 . Especially, Ni0 , generated in the dynamic quenching, accelerated the electron transfer by acting as an electron outlet and enhancing the stability of CdS to slow down the photocorrosion distinctly, delivering efficient H2 production with high selectivity. Our study will inspire exploration of various efficient non-noble-metal catalysts for practical H2 production from bio-based formic acid.

Graphdiyne (CnH2n–2) based CuI-GDY/ZnAl LDH double S-scheme heterojunction proved with in situ XPS for efficient photocatalytic hydrogen production

The photocatalytic performance can be significantly improved by constructing suitable heterojunction photocatalysts. It is well known that graphdiyne possesses a unique conjugated carbon network nanostructure, which gives it ample active sites on its surface and facilitates the reduction of protons. In this study, a unique new double S-scheme heterojunction photocatalyst was constructed by simple self-assembly of GDY prepared via organic synthesis methods and ZnAl-LDH. According to the study, an internal electric field controlling the transfer direction of the electron hole is formed between the interface of CuI-GDY and ZnAl-LDH, which broadens the light absorption range of the catalyst and improves the redox ability of the photocatalytic system. CuI-GDY and ZnAl-LDH are tightly bound together, which helps to separate the photogenerated carriers while preserving the strong reduction electrons in the GDY conduction band and the strong oxidation holes in the ZnAl-LDH valence band so that they can fully participate in the redox reaction. The charge-transfer paths on the S-scheme heterojunction interface were analyzed by in situ irradiation XPS. This work provides an effective strategy for the construction of double S-scheme heterojunction photocatalysts.

CdxZn1-xS with bulk-twinned homojunctions and rich sulfur vacancies for efficient photocatalytic hydrogen production

Utilizing photocatalysts devoid of noble metals for solar hydrogen production is a viable option in resolving the rising energy crisis. However, the current photocatalytic performance is inadequate due to the insufficient conversion of solar energy into storable chemical energy. Photocatalysts with bulk-twinned homojunction for enhanced photocatalytic performance have received attention in recent years. In addition, it has been demonstrated that introducing sulfur vacancies is an effective approach to improving the photocatalytic performance of metal sulphides. A key factor in increasing photocatalyzed solar hydrogen production is the charge separation and limiting their recombination using stacking fault. Herein, we synthesized novel nanocrystal solid solutions of twinned wurtzite/zinc blende, CdxZn1-xS (x = 0.1, 0.3, 0.5, 0.7 and 0.9), having rich sulfur vacancies. The solid solutions were prepared via a facile alkaline-assisted hydrothermal pathway, and then the activity, morphology, and surface properties were correlated using extensive characterization techniques. It was found that the Cd0·5Zn0·5S solid solution with twinned homojunction and rich sulfur vacancies exhibited a higher solar hydrogen production activity and stability than the bare Cd0·5Zn0·5S solid solution.

Ultrathin Pd metallenes as novel co-catalysts for efficient photocatalytic hydrogen production

Photocatalytic hydrogen production as a green and pollution-free technology plays an important role in alleviating the fossil fuel crisis, but remains a great challenge. Herein, an ultrathin two-dimensional (2D) palladium metallene (Pd-ene) is first developed as hydrogen evolution co-catalysts for g-C3N4 nanosheets. The Pd-ene and Pd-ene/g-C3N4 photocatalysts were fabricated by a hydrothermal method and deposition method using acetylacetonate palladium as Pd source, and the Pd-ene with a size of 100 nm uniformly distributed on the surface of g-C3N4 nanosheets forming a 2D/2D structure. The Pd-ene/g-C3N4 with 2 wt% Pd-ene showed the highest photocatalytic hydrogen production rate with 31,292 μmol/h/ g, which was>98 times that of the pure g-C3N4 and superior to the PdNC/g-C3N4 loading with Pd nanocluster. The unique 2D/2D structure of the Pd-ene/g-C3N4 catalyst, which promotes the transfer and separation of photogenerated charge carriers, is credited with the improved photocatalytic performance. In additions, the 2D structure of Pd-ene makes it expose more reaction sites for the photocatalytic reduction reaction, promoting the hydrogen production of the photocatalysts. This study demonstrates that the development of structurally matched 2D metallene co-catalysts for 2D photocatalysts is a promising strategy to obtain the photocatalysts with high hydrogen production performance.

Covalent organic framework films grown on spongy g-C3N4 for efficient photocatalytic hydrogen production

Photocatalytic hydrogen production promisingly mitigates and ameliorates the status quo of energy shortage and decarbonization of the energy supply. Given this, a photocatalyst was prepared by modifying spongy g-C3N4 with covalent organic frameworks (COFs). As an electron acceptor with a large specific surface, COFs can trap more transition electrons, leading to an increase in the photogenerated carriers involved in the surface reaction and increasing the active sites of the photocatalyst. The S-scheme heterojunction structure formed in g-C3N4/COFs composite catalyst triggers a decrease in the recombination rate of photogenerated electron-hole pairs as well as an increase in photogenerated electrons. The photocatalytic hydrogen production rate reached the maximum value of 7788.10 μmol·h−1·g−1, almost 7 times that of g-C3N4. The AQE of the catalyst reached 29.6 %. The electron transfer path from g-C3N4 to COFs was verified by density functional theory (DFT) calculation.

N-doped C-coated MoO2/ZnIn2S4 heterojunction for efficient photocatalytic hydrogen production

N-doped C-coated MoO2/ZnIn2S4 heterojunction for efficient photocatalytic hydrogen production

Construction of graphdiyne (CnH2n-2) based Co-S-P/CuI double S-scheme heterojunctions proved with in situ XPS characterization for efficient photocatalytic hydrogen production

Graphdiyne (GDY) is a novel two-dimensional carbon isomeric material with a high π⁃conjugation and good electrical conductivity, a tunable natural band gap. Here, the promotion of GDY on the photocatalytic system is investigated by preparing Co-S-P/CuI double S-scheme heterojunctions based on graphdiyne (CnH2n-2). The Co-S-P rough nanosheet structure provides a large number of aiming points for CuI nanoblocks, which effectively prevents the aggregation of CuI nanoblocks. It not only provides a large number of active sites for the reaction, but also facilitates the visible light injection. When GDY is introduced, the three-dimensional structure of GDY/CuI is tightly attached to the Co-S-P surface. On the one hand, the unique two-dimensional/three-dimensional structure is beneficial to promote the mass transfer properties between Co-S-P, GDY and CuI and improve the absorption of visible light. On the other hand, the unique lamellar structure of GDY is like a “tape” connecting Co-S-P and CuI, which not only makes the bond between Co-S-P and CuI tighter, but also serves as a “fabric” to isolate the oxidation sites on the surface of Co-S-P. As a result, the ternary catalyst exhibits excellent hydrogen precipitation stability and photocorrosion resistance. Under 5 W (λ > 420 nm) LED light, CSPGC-20 (135.49 μmol) exhibited the best hydrogen precipitation activity, which is 26.22, 9.2 and 1.6 times higher than that of GDY/CuI (5.32 μmol), Co-S-P (14.72 μmol) and CSPC-20 (85.08 μmol), respectively. This experiment demonstrates the promising potential of Graphdiyne (GDY) for photocatalytic water splitting.

Bi-doped twin crystal Zn0.5Cd0.5S photocatalyst for highly efficient photocatalytic hydrogen production from water

Bi doped twin crystal Zn0.5Cd0.5S (Bi/ZCS) was prepared for the first time via a facile hydrothermal method and used as a highly efficient hydrogen production photocatalyst. Our study found that Bi doping in ZCS could significantly enhance the light absorption and promote the photogenerated carrier separation and transport owing to the formation of Bi impurity level inside the bandgap of ZCS. Accordingly, the photocatalytic hydrogen production performance of ZCS was greatly improved. The optimal Bi/ZCS photocatalyst showed a very high photocatalytic hydrogen evolution rate up to 1.09 mmol h−1 (10 mg catalyst was used) and a very high apparent quantum efficiency of 31.5% at the wavelength of 420 nm. Moreover, Bi/ZCS photocatalyst also demonstrated its practical application towards photocatalytic hydrogen production from seawater, realizing a superior hydrogen evolution rate which was nearly 4 times higher than the pristine ZCS, providing an effective and low-cost way to design high-efficiency solar hydrogen production photocatalysts.

Facile construction of a sulfur vacancy defect-decorated CoSx@In2S3 core/shell heterojunction for efficient visible-light-driven photocatalytic hydrogen evolution.

Photoinduced electron-separation and -transport processes are two independent crucial factors for determining the efficiency of photocatalytic hydrogen production. Herein, a sulfur vacancy defect-decorated CoSx@In2S3 (CoSx@VS-In2S3) core/shell heterojunction photocatalyst was synthesized via an in situ sulfidation method followed by a liquid-phase corrosion process. Photocatalytic hydrogen evolution experiments showed that the CoSx@VS-In2S3 nanohybrids delivered an attractive photocatalytic activity of 4.136 mmol h-1 g-1 under visible-light irradiation, which was 8.23 times higher than that of the pristine In2S3 samples. As expected, VS could enhance the charge-separation efficiency of In2S3 through rearranging the electrons of the In2S3 basal plane, in addition to improving the electron-transfer efficiency, as visually verified by transient absorption spectroscopy. Mechanism studies based on density functional theory calculations confirmed that the In atoms adjacent to VS played a key role in the translation, rotation, and transformation of electrons for water reduction. This scalable strategy focused on defect engineering paves a new avenue for the design and assembly of 2D core/shell heterostructures for efficient and robust water-splitting photocatalysts.

Phosphorus doped and defect modified graphitic carbon nitride for boosting photocatalytic hydrogen production.

The enhancement of photogenerated carrier separation efficiency is a significant factor in the improvement of photocatalyst performance in photocatalytic hydrogen evolution. Heteroatom doping and defect construction have been considered valid methods to boost the photocatalytic activity of graphitic carbon nitride. Herein, we report graphitic carbon nitride modified with P doping and N defects (PCNx), and the effects of doping and defects were investigated in photocatalytic H2 evolution. Its hydrogen evolution rate can reach up to about 59.1 μmol h-1, which is more than 123.1 times higher than pristine graphitic carbon nitride under visible light irradiation. Importantly, the apparent quantum efficiency reaches 8.73% at 420 nm. The excellent performance of the PCNx photocatalyst was attributed to the following aspects: (I) the large BET surface area of PCNx affords more active sites for H2 production and (II) the introduction of P and N defects can accelerate the charge carrier separation and transfer efficiency, leading to more efficient photocatalytic hydrogen production. The photocatalyst showed obviously enhanced activities.

Efficient photocatalytic hydrogen production over ZnIn2S4 by producing sulfur vacancies and coupling with nickel-based polyoxometalate.

A composite catalytic system using sulfur-vacancy-containing ZnIn2S4-Sv as a light-harvesting material and nickel-based polyoxometalate Na6K4[Ni4(H2O)2(PW9O34)2] (Ni4POM) as a co-catalyst was developed. The Ni4POM/ZnIn2S4-Sv composite gave a good hydrogen production rate of 337.5 μmol h-1, a value 11.8 times higher than that of ZnIn2S4-Sv. The direction of electron transfer, from ZnIn2S4-Sv to Ni4POM, was verified using surface photovoltage spectra.

Recent progress in metal halide perovskite photocatalysts for hydrogen evolution

The basic design principles and recent progress in halide perovskite-based photocatalysts are summarized, aiming to achieve efficient and stable photocatalytic hydrogen production.

Phosphating core–shell graphdiyne/CuI/Cu3P S-scheme heterojunction confirmed with in situ XPS characterization for efficient photocatalytic hydrogen production

The core–shell encapsulated ternary catalyst graphdiyne/CuI/Cu3P was obtained by phosphating the CuI on the outer surface to Cu3P, substantially improving its hydrogen evolution efficiency.

Synergetic microstructure engineering by induced ZB/WZ twin boundaries and S vacancies in a Zn0.5Cd0.5S-based S-scheme photocatalyst for highly efficient photocatalytic hydrogen production

Development of structurally unique Zn0.5Cd0.5S (with twin structure and S vacancies) and a Zn0.5Cd0.5S-based metal–organic framework for photocatalytic applications.