H2 Production Activity Research Articles

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.

Accelerating Nickel-Based Molecular Construction via DFT Guidance for Advanced Photocatalytic Hydrogen Production.

Understanding the nickel-based molecular catalyst structure and functional relationship is crucial for catalytic hydrogen production in aqueous solutions. Density functional theory (DFT) provides mature theoretical knowledge for efficient catalyst design, significantly reducing catalyst synthesis time and energy consumption. In the present work, three molecular catalysts, Ni(qbz)(pys)2 (qbz = 2-quinoline benzimidazole) (NQP 1), Ni(qbo)(pys)2 (qbo = 2-quinoline benzothiazole) (NQP 2), and Ni(pbz)(pys)2 (pbz = 4-chloro-2,2-pyridylbenzimidazole) (NQP 3) (pys = 2-mercaptopyridine), were designed and synthesized and exhibit a high performance for H2 generation in aqueous solution with a lamp (λ ≥ 400 nm) under visible light irradiation. Under the optimal conditions, a H2 evolution rate as high as 1190 μmol h-1 can be obtained over 25 mg of NQP 1 with the best catalytic performance. DFT has been adopted in this study to unveil the relationship between the ligand qbz and catalyst NQP 1─an efficient step in the design of catalysts with an excellent catalytic performance. We show that, in addition to the presence of the triphenyl ring increasing the overall electron density, rapid electron transfer (ET) from excited fluorescein (Fl) to NQP 1 significantly improves the chance of photogenerated electrons transferring to the active site, ultimately increasing the catalytic activity for H2 production. This work on understanding the correlation between structures and properties of complexes provides a new idea for manufacturing high-performance photocatalysts.

Morphologies dependence of hydrogen evolution over CeO2 via ultrasonic triggering

Ultrasonic field can lead to cavitation bubbles explosion, which rises a high-frequency oscillation and generates a high-frequency current in semiconductor nanoparticles in suspension. However, the effect of nanoparticle morphology on ultrasonic-triggered H2 production is still unclear. To this end, herein, nanorods CeO2 (nrCeO2), CeO2 nanocubes (ncCeO2), and CeO2 nanospheres (nsCeO2) were successfully synthesized. Among them, one-dimensional nrCeO2 had the most abundant O-vacancies. As revealed by the COMSOL simulation, nanoparticle deformation was easier in nanorods compared with nanocubes and nanospheres, resulting in more efficient charge separation and facilitating H2 production reaction in nrCeO2. In detail, within a 5 h’ period, nrCeO2 presented the highest H2 production activity of 983.1 μmol g−1 h−1 with the positive charge (q+) trapping agent of CH3OH, and that of 278.1 μmol g−1 h−1 in pure water. This work presents a new understanding about the relationship between nanoparticle morphology and H2 production activity, and provides a promising, efficient, and clean H2 production approach, which can be further extended to multi-field coupling reactor.

Few-Layered MoS2/ZnCdS/ZnS Heterostructures with an Enhanced Photocatalytic Hydrogen Evolution

Studies on highly efficient noble-metal-free catalysts are regarded as an important task for H2 production by water-splitting. MoS2/ZnCdS/ZnS dual heterostructures were successfully prepared with respective supernatant MoS2 colloidal solutions (called M/ZC/Z) and MoS2 precipitates (M(p)/ZC/Z). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the M/ZC/Z sample showed that ZnS nanosheets were decorated with ZnCdS nanorods and few-layered MoS2. Then, photocatalytic hydrogen production study was performed and the results showed that the M/ZC/Z sample has a H2 evolution rate of up to 79.3 mmol g–1 h–1 under visible light irradiation with an apparent quantum efficiency of 47.9% at 420 nm with noble-metal-free catalysts, which is nearly 5 times that of the M(p)/ZC/Z sample (15.7 mmol g–1 h–1) and approximately 9 times that of the ZC/Z sample (8.98 mmol g–1 h–1). Cycle tests showed that M/ZC/Z is stable and reusable. Without sacrificial agents, the production rates for hydrogen and oxygen evolution were obtained as 3.15 and 1.55 mmol g–1 h–1, respectively. Time-resolved photoluminescence spectra revealed that the well-matched structure is effective in the separation and transfer of photogenerated electron and hole pairs, leading to the enhancement of the photocatalytic H2 production activity.

Growing ZnIn2S4 nanosheets on FeWO4 flowers with p-n heterojunction structure for efficient photocatalytic H2 production

Constructing heterojunction structure can efficiently accelerate the separation and transfer of charge carriers and improve the photoactivity. Herein, a high-performance FeWO4/ZnIn2S4 composite with abundant and tight 2D/2D hetero-interfaces was rational designed and prepared. ZnIn2S4 nanosheets as hydrogen evolution species uniformly grow on the surface of FeWO4 flower, constructing a unique face-to-face hierarchical architecture. A maximum H2 production rate of 3531.2 μmol h−1 g−1 was obtained at the optimal mass ratio of FeWO4 to ZnIn2S4, which was 35 times higher than pure ZnIn2S4. Based on the experimental results and the Density Functional Theoretical calculation results, a possible p-n heterojunction mechanism and the transfer route of photoinduced charges toward the improved H2 production were proposed. The p-n heterojunction between FeWO4 and ZnIn2S4 nanosheets plays a key role in enhancing photocatalytic H2 production activity. Moreover, the intimate interface between two components and the preferable hydrophilic property favors the improved H2 evolution rate.

Band Structure Engineering and Defect Passivation of Cu x Ag1-x InS2/ZnS Quantum Dots to Enhance Photoelectrochemical Hydrogen Evolution.

The AgInS2 colloidal quantum dot (CQD) is a promising photoanode material with a relatively wide band gap for photoelectrochemical (PEC) solar-driven hydrogen (H2) evolution. However, the unsuitable energy band structure still forms undesired energy barriers and leads to serious charge carrier recombination with low solar to hydrogen conversion efficiency. Here, we propose to use the ZnS shell for defect passivation and Cu ion doping for band structure engineering to design and synthesize a series of CuxAg1–xInS2/ZnS CQDs. ZnS shell-assisted defect passivation suppresses charge carrier recombination because of the formation of the core/shell heterojunction interface, enhancing the performance of PEC devices with better charge separation and stability. More importantly, the tunable Cu doping concentration in AgInS2 CQDs leads to the shift of the quantum dot band alignment, which greatly promotes the interfacial charge separation and transfer. As a result, CuxAg1–xInS2/ZnS CQD photoanodes for PEC cells exhibit an enhanced photocurrent of 5.8 mA cm–2 at 0.8 V versus the RHE, showing excellent photoelectrocatalytic activity for H2 production with greater chemical-/photostability.

Facile synthesis of three-dimensional hollow porous carbon doped polymeric carbon nitride with highly efficient photocatalytic performance

Developing a high photocatalytic performance metal-free catalyst with both a fast H2 evolution rate and efficient pollutant degradation efficiency is an urgent requirement to solve the challenges associated with water pollution and energy crises. Herein, we first report a novel and feasible strategy to develop a highly efficient three-dimensional (3D) hollow porous C-doped polymeric carbon nitride (CPCN) catalyst based on the combination of morphological controls and in situ C doping. The as-synthesized CPCN catalysts show outstanding H2 production activity (16.69 mmol g−1h−1) as well as a high degradation rate (20.3 × 10−3 min−1) of diclofenac under visible light. The characterization and density functional theory calculation results indicate that the 3D hollow porous structure can not only endow the CPCN catalyst with a large surface area and countless exposed active sites but also promote the substrate adsorption reaction and maintain its structural stability. Simultaneously, in situ C doping can also enhance the light absorption and promote the charge transfer and separation of the CPCN sample. Consequently, excellent photocatalytic performance was achieved and the proposed enhanced mechanism of photocatalytic activity was also elucidated. This work may shed light on the development of highly efficient metal-free catalysts.

Binary Type-II Heterojunction K7HNb6O19/g-C3N4: An Effective Photocatalyst for Hydrogen Evolution without a Co-Catalyst.

The binary type-II heterojunction photocatalyst containing g-C3N4 and polyoxoniobate (PONb, K7HNb6O19) with excellent H2 production activity was synthesized by decorating via a facile hydrothermal method for the first time. The as-fabricated Nb–CN-0.4 composite displayed a maximum hydrogen evolution rate of 359.89 µmol g−1 h−1 without a co-catalyst under the irradiation of a 300 W Xenon Lamp, which is the highest among those of the binary PONb-based photocatalytic materials reported. The photophysical and photochemistry analyses indicated that the hydrogen evolution performance could be attributed to the formation of a type-II heterojunction, which could not only accelerate the transfer of photoinduced interfacial charges, but also effectively inhibit the recombination of electrons and holes. This work could provide a useful reference to develop an inexpensive and efficient photocatalytic system based on PONb towards H2 production.

Sorption-enhanced steam gasification of woody biomass assisted by Ca/Na/FS (fine slag) composite sorbents

In this research, composite sorbents with high activity in promoting H2 production during sorption-enhanced steam gasification of pine sawdust (PS) were developed by doping coal gasification fine slag (FS) and NaOH into calcined conch shell (CS). The tests performed in a laboratory-scale fixed bed reactor demonstrated that the composite sorbents greatly improved H2 concentration and yield over that achieved with CHCS (CS after hydration and calcination), reaching 73.5% and 600.7 mL/g-PS, respectively. This promotion effect on H2 production was not influenced by the unburned carbon in FS. To obtain high H2 concentration and yield with as little NaOH and as much FS as possible, the optimum sorbent was found to be 3CS-2FS-0.32Na (in mass ratio of CS:FS:NaOH = 3:2:0.32). Under this condition, the H2 concentration and yield reached 74.3% and 572.3 mL/g-PS, respectively. In five cycles of experiment, although the H2 yield of 3CS-2FS-0.32Na decreased from 572.3 mL/g-PS to 416.6 mL/g-PS, it was always higher than with CHCS alone by at least 28%. The results in this study indicate that FS has potential to be an effective inert support material that endows CaO with high activity in H2 production during sorption-enhanced steam gasification. This might help to provide a new approach to minimizing the negative environmental impact of FS.

Rational design of interfacial energy level matching for CuGaS2 based photocatalysts over hydrogen evolution reaction

CuGaS2(CGS) is effectively synthesized by a one-step solid-phase sintering method. The conduction band maximum, valence band maximum and flat band potential of the obtained CGS are −1.14, 1.21 and 0.33 V vs RHE, respectively. When the Cu to Ga atom ratio is 1: 1.4 in the raw material, the prepared CuGaS2 exhibits the highest visible-light (λ˃420 nm) H2 production activity. The hydrogen production rate of CuGaS2 reaches 1.12 mmol g−1 h−1 under visible-light radiation. When Ruthenium is loaded as cocatalyst, the H2 production rate of CuGaS2@Ru is promoted to 3.38 mmol g−1 h−1. At the same, the interior component of photo-induced carries transfer among photoharvestor and cocatalyst has been revealed. This research provides a facile strategy to fabricate CuGaS2 with excellent photocatalytic performance for H2 production.

Switching on photocatalytic NO oxidation and proton reduction of NH2-MIL-125(Ti) by convenient linker defect engineering

Photocatalysis technology has been widely adopted to abate typical air pollutants. Nevertheless, developing photocatalysts aimed at improving photocatalytic efficiency is a challenge. Herein, the linker-defect NH2-MIL-125(Ti) photocatalyst was synthesized through a convenient one-step heating-stirring method (just adjusting multiple temperatures) to firstly realize efficient photocatalytic performances of NO removal and hydrogen evolution. The optimal sample (named 65-NMIL) with a linker-defect content of 32.08% exhibited a NO removal ratio of 65.49%, which was 37.57% higher than that of pristine NH2-MIL-125(Ti), and displayed better H2-production activity. Through ESR, it was confirmed that 65-NMIL can generate more •O2- and •OH under visible light, and the radical trapping experiment further proved that •O2- played a more important role in photocatalytic activity. Moreover, the photocatalytic NO oxidation process was also monitored by in situ DRIFTS, it was found that the defective samples could promote the oxidation of NO and intermediates to the final product (NO3-). On the basis of the above-mentioned photocatalytic experimental results and characterization, a possible mechanism or pathway was proposed and illustrated. This work can provide a new strategy for the subsequent defect engineering for photocatalytic MOFs materials to further solve environmental and energy crises.

Crystalline C3N4/CeO2 composites as photocatalyst for hydrogen production in visible light

Crystalline carbon nitride (C-C3N4) doped with cerium oxide (CeO2) was synthesized using ionothermal method to increase the photocatalytic activity for H2 production. Graphitic carbon nitride (g-C3N4) obtained from direct pyrolysis of urea at 550°C was subsequently annealed with a mixture of KCl and LiCl to obtain C-C3N4. CeO2 was doped onto C-C3N4 and g-C3N4 via calcination at 550°C. XRD analysis showed the formation of high intensity C3N4 and CeO2 peaks in C-C3N4/CeO2, meanwhile g-C3N4/CeO2 only showed CeO2 peaks. FTIR analysis confirmed all the samples contained C3N4 polymeric structure. The specific surface area of g-C3N4 was measured at 61 m2/g. The surface area increased to 92 m2/g when g-C3N4 transformed into C-C3N4, and further increased to 106 m2/g on C-C3N4/CeO2. The photocatalytic activity for H2 gas production showed significant increase of H2 rate on C-C3N4/CeO2 compared to g-C3N4/CeO2 and g-C3N4. The high crystallinity and high surface area were suggested to enhance photocatalytic activity of C-C3N4/CeO2 in visible light presumably due to the increase of electron and hole lifetimes.

Atomically dispersed Pt sites on porous metal–organic frameworks to enable dual reaction mechanisms for enhanced photocatalytic hydrogen conversion

We report a porous metal–organic framework loaded with single Pt atoms, namely PCN-222(Pt) nanorods, which are prepared by the self-assembly of Pt-metalized tetrakis(4-carboxyphenyl)porphyrin ligand with a Zr6 cluster. The mass-loading of Pt in the synthesized PCN-222(Pt) is up to 4.67%, and can be accurately controlled by using an in-situ reaction strategy. Remarkably, the PCN-222(Pt) exhibits a highly efficient photocatalytic hydrogen production rate of 614 μmol g-1h−1, which is 7.4 times higher than that of PCN-222 (an isostructural sample to PCN-222(Pt) without coordinated Pt ions in the porphyrin rings). The apparent quantum efficiency of PCN-222(Pt) reaches up to 1.049% at 420 nm. Electron paramagnetic resonance spectra confirm the as-formed intermediate ZrIII, obtained from the reduction of ZrIV species, participates in the photocatalytic reaction. Density functional theory calculations demonstrate the positive role that single Pt atoms in PCN-222(Pt) play in optimizing the corresponding hydrogen binding energy. The existence of this dual reaction mechanism in PCN-222(Pt) greatly and synergistically boosts the photocatalytic H2 production activity.

In-situ formation of nanosized 1T-phase MoS2 in B-doped carbon nitride for high efficient visible-light-driven H2 production

The high photogenerated carrier recombination rate and the low visible light utilization limit the development of graphitic carbon nitride (CN) in industrial photocatalytic H2 generation. Herein, 1T-phase MoS2 nanoparticles with high conductivity and more active sites are in-situ grown on B-doped carbon nitride (CNB) nanosheets through a one-step hydrothermal method. The doping of boron element effectively improves the harvesting visible light ability by tuning the energy gap, while the introduction of 1T-phase MoS2 successfully increases the carrier transfer rate by suppressing charge trapping. An optimized H2 production activity of 5334 μmol h−1 g−1 with the apparent quantum efficiency of 10.2% is achieved by 1T-MoS2/CNB sample, which is 167 times higher than that of pure CN. The mechanism is systematically illustrated by the combination of DFT calculations and transient absorption measurements. This work provides a new way for the construction of transition metal-derived co-catalysts in photocatalytic hydrogen energy storage.

Vertically grown CeO2 and TiO2 nanoparticles over the MIL53Fe MOF as proper band alignments for efficient H2 generation and 2,4-DCP degradation.

The design of highly efficient photoca talysts for clean energy production and environmental remediation are the grand challenges of scientific research. Herein, TiO2@MIL53Fe and CeO2@MIL53Fe composite photocatalysts are synthesized via solvothermal technique. The SEM and TEM micrographs reveal that TiO2 and CeO2 nanoparticles are vertically grown onto the surface of MIL53Fe MOF. Further, HRTEM micrograph confirmed the formation of heterojunction. It has been investigated that the resultant TiO2@MIL53Fe and CeO2@MIL53Fe photocatalysts exhibit remarkably improved visible light activities for H2 production and 2,4-dichlorophenol (2,4-DCP) degradation in comparison to the bare MIL53Fe photocatalyst. The enhanced photoactivities of the fabricated TiO2@MIL53Fe and CeO2@MIL53Fe photocatalysts are attributed to significantly promoted charge separation as confirmed via the surface photo voltage (SPV) and photoluminescence (PL) results. Further, the photocatalysts exhibit high stability and reusability as confirmed via the recyclable tests. This work will promote the design of MOF-based efficient photocatalysts for clean energy production and environment purification.

MOFs-derived MoS2/C3N4 composites with highly efficient charge separation for photocatalytic H2 evolution

Photocatalytic hydrogen (H2) production utilizing metal organic frameworks (MOFs) as catalysts is one of the most promising methods for production of H2. However, pure MOFs have poor mechanical and chemical stability. Preparing MOF-derived materials with MOFs as templates is an effective method to improve their stability. MOFs were used as precursors to synthesise MoS2/CN by a solvothermal method. The results show that under visible-light irradiation, the material exhibits significant photocatalytic H2 production activity. Modification of CN by MOF-derived MoS2 increases the light absorption capacity and further improves photogenerated charge separation. The optimal production rate for H2 evolution was 1695.76 μmol g−1 (4 h). MoS2 and CN are uniformly dispersed and firmly connected in the catalyst, which is conducive to charge transfer. In addition, the MoS2/CN catalyst exhibited better stability for H2 production. This study provides a reference for the preparation of noble-metal-free sulfide cocatalysts using metal MOFs as self-sacrificing templates.

Linker engineering in metal-organic frameworks for dark photocatalysis.

Dark reactions featuring continuous activity under light off conditions play a critical role in natural photosynthesis. However, most artificial photocatalysts are inactive upon the removal of the light source, and the artificial photocatalysts with dark photocatalysis abilities have been rarely explored. Herein, we report a Ti-based metal–organic framework (MOF), MIL-125, exhibiting the capability of dark photocatalytic hydrogen production. Remarkably, the introduction of different functional groups onto the linkers enables distinctly different activities of the resulting MOFs (MIL-125-X, X = NH2, NO2, Br). Dynamic and thermodynamic investigations indicate that the production and lifetime of the Ti3+ intermediate are the key factors, due to the electron-donating/-withdrawing effect of the functional groups. As far as we know, this is the first report on dark photocatalysis over MOFs, providing new insights into the storage of irradiation energy and demonstrating their great potential in dark photocatalysis due to the great MOF diversity.

The doping of B in ZnO/CdS for enhanced visible-light H2 production

A B-ZnO/CdS heterojunction composite was prepared and its H2 production activity was enhanced up to 13 100 μmol h−1 g−1.

A bio-inspired heterodinuclear hydrogenase CoFe complex.

Herein, a new heterobimetallic CoFe complex is reported with the aim of comparing its performance in terms of H2 production within a series of related MFe complexes (M = Ni, Fe). The fully oxidized [(LN2S2)CoII(CO)FeIICp]+ complex (CoIIFeII, LN2S2 2- = 2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1'-diphenylethanethiolate), Cp- = cyclopentadienyl anion) can be (electro)chemically reduced to its CoIFeII form, and both complexes have been isolated and fully characterized by means of classic spectroscopic techniques and theoretical calculations. The redox properties of CoIIFeII have been investigated in DMF, revealing that this complex is the easiest to reduce by one-electron among the analogous MFe complexes (M = Ni, Fe, Co). Nevertheless, it displays no electrocatalytic activity for H2 production, contrary to the FeFe and NiFe analogs, which have proven remarkable performance.

Hydrogen production activity of MoS2-ZnIn2S4 nanocomposite under visible light irradiation

In this manuscript, we report the synthesis of MoS2-ZnIn2S4 nanocomposite by using methods including hydrothermal and chemical aqueous method under low temperature. The prepared MoS2-ZnIn2S4 composite sample was characterized by X-ray powder diffraction(XRDfield emission scanning electron microscopy (FESEM). The photocatalytic activities for H2 production were investigated under the visible light of MoS2-ZnIn2S4 nanocomposite. The result indicates that H2 production rate of ZnIn2S4 increase by adding of MoS2 as co-catalyst and MoS2-ZnIn2S4 nanocomposite show higher rate of hydrogen production under. pure ZnIn2S4 sample shows a very low rate of H2 production activity (30 μ mol. g-1h−1) however MoS2/ZnIn2S4 composite shows approximately 3 times higher rate of H2 production activity (97.36 μ mol. g-1h−1. The synergistic combination of increased specific surface area, efficient electron hole pair separation, and amplified catalytic active sites is primarily responsible for the increased rate of H2 production activity. This work contributes a high potential of developing of low cost and low temperature or template free synthesised semiconductor for hydrogen production.