Photocatalytic H2 Production Performance Research Articles

Enhanced photocatalytic H2 production performance of Au@Cu2O-Ta3N5 discrete ternary core-shell spheres

Ta3N5 owns a theoretical band structure for photocatalytic H2 production. However, the practical production performance is unsatisfactory, which is probably attributed to fast electron-hole recombination. In this study, we design novel Au@Cu2O-Ta3N5 discrete core-shell ternary nanospheres for highly efficient photocatalytic H2 production by splitting water. This catalyst is prepared by coating Cu2O on the Au nanoparticles of Au-Ta3N5 nanospheres via an illumination method. The core-shell structure irradiated for 2 h (Au@Cu2O-Ta3N5 2 h) shows higher photocatalytic H2 production rate (65.78 μmol·g−1·h−1) than Au-Ta3N5 (0.5% Au-Ta3N5, 22.43 μmol·g−1·h−1), Au-Cu2O-Ta3N5 (32.24 μmol·g−1·h−1), and fully covered Au@Cu2O-Ta3N5 5 h sample (51.27 μmol·g−1·h−1). The enhanced performance is attributed to the unique discrete core-shell structure, designed appropriate band structure, low charge transfer resistance, and high electron-hole separation ability. This study provides a novel Ta3N5-based ternary core-shell structure for high-performance H2 production.

Construction of S-scheme Co3O4/g-C3N4 heterojunctions with boosted photocatalytic H2 production performance

The key step of photocatalytic technology using light energy to split water for hydrogen production is to prepare high performance and environmentally friendly stable photocatalysts. In this study, Co3O4 was loaded onto polymeric carbon nitride (PCN) to construct S-scheme heterojunctions by an impregnating method. The successful construction of S-scheme Co3O4/PCN heterojunctions was proved by the various characterizations, the constructed S-scheme Co3O4/PCN heterojunctions have favorable photoelectric effect and exhibit better H2 evolution performance than the single Co3O4 and PCN. Construction of S-scheme Co3O4/PCN heterojunctions can elevate active sites induced by N-deficient formation. Therein, 3% is the optimal molar ratio of Co/PCN, and the corresponding sample (3CoO/CN) exhibits the highest H2 evolution efficiency (105.06 μmol·g − 1·h − 1) via simulated solar light illumination for 4 h, which is about 41 folds higher than the single PCN (2.48 μmol·g − 1·h − 1). In short, the conspicuously boosted water splitting efficiency is mainly due to the strong light responsiveness and rapidly separation and migration of photoexcited charge pairs. The cyclic experiment results show that the S-scheme Co3O4/PCN heterojunction photocatalysts have high stability. The apparent quantum efficiency (AQE) of H2 generation on 3CoO/CN is 0.053% under 420 nm monochromatic light irradiation. This study strongly verifies that construction of S-scheme Co3O4/PCN heterojunctions is a feasible route to boost the photocatalytic activity of g-C3N4, providing an interesting reference for design highly efficient and environmentally friendly C3N4-based photocatalysts.

Effect of synthesis conditions on the photocatalytic behavior of ZnS-ZnO heterojunctions for the H2 generation

In the present work, the synthesis and photocatalytic performance for H2 production of ZnS-ZnO composites at different compositions of cubic sphalerite (ZnS-c), hexagonal wurtzite (ZnS-h) and zincite (ZnO) phases are shown. The synthesis was carried out by the solvothermal method using mono ethylene glycol and thiourea as solvent and sulfur source, respectively, for the partial sulfidation of ZnO at different temperatures (150 °C, 200 °C, and 250 °C). When the temperature is increased in the solvothermal process, the hexagonal phase grows at the expense of the cubic phase. The materials as powders were characterized by X-ray diffraction, scanning and transmission electron microscopy, UV–visible spectroscopy, X-ray photoelectron microscopy, N2 adsorption-desorption isotherms, and photoelectrochemical techniques. These materials were applied in H2 production as an alternative source of clean and sustainable energy generation. It was found that the most photoactive material was the one synthesized at 200 °C, this photocatalyst presented an H2 production rate of 580 µmol h−1 g−1. The enhancement of the photocatalytic activity is due to the optimization of the interfacial properties between ZnS-c/ZnS-h and ZnO as a model system for coupled photocatalysts.

Covalent Organic Framework/g-C3N4 van der Waals Heterojunction toward H2 Production.

Photocatalytic water splitting into H2 is the most economic and environmentally friendly strategy for H2 production, and rationally constructing a heterojunction retains enormous influence on a photocatalytic system. Herein, 2D/2D covalent organic framework/graphitic carbon nitride (COF/CN) van der Waals heterojunctions were readily prepared via an ultrasonic method for high-efficiency visible-light photocatalytic H2 production. The photocatalytic H2 production performance of optimized COF/CN composites can reach up to 449.64 μmol·h-1, which is approximately 5 times that of pure CN (89.08 μmol·h-1). The characterization and experimental studies reveal that the synergistic effect between COF and CN contributes to promoting the interfacial migration and spatial separation of photoinduced e--h+ pairs, further boosting the photocatalytic hydrogen production activity. This work may open a new window to design and fabricate effective heterojunction photocatalysts for photocatalytic energy conversion.

0D/2D/3D ternary Au/Ti3C2/TiO2 photocatalyst based on accelerating charge transfer and enhanced stability for efficiently hydrogen production

The development of multi-components composited photocatalytic materials with strong interaction is a key approach to realize the spatial separation and fast transfer of charge carriers in H2 production. In this study, 2D layered Ti3C2 with –OH group was introduced to stabilize thiolate-protected Au clusters by strong electrostatic interaction and coupled with TiO2 nanoparticles to build a 0D/2D/3D ternary Au/Ti3C2/TiO2 photocatalyst for H2 evolution. In this composited material, Ti3C2 can serve as the electron transfer intermedium accelerating charge transfer from TiO2 to Au clusters. Au/Ti3C2/TiO2 shows excellent photocatalytic performance for H2 production (7989 μmol⋅g-1h−1), approximately 13.7 times higher than that of Au/TiO2. Photoluminescence spectra and photoelectrochemical results confirm that the introducing of layered Ti3C2 into ternary Au/Ti3C2/TiO2 material can markedly suppress the photogenerated charge recombination and thus enhance the charge separation efficiency. Moreover, after several cyclic reactions, Au/Ti3C2/TiO2 maintained a high stability and durability, indicating the strong interaction of Ti3C2 with Au and TiO2. This work not only highlights the significant role of MXene for the enhancement of photogenerated electron transfer, but also demonstrates a clearly objective to construct a suitable composited photocatalyst for H2 production.

Framework Ti-rich titanium silicalite-1 zeolite nanoplates for enhanced photocatalytic H2 production from CH3OH

As a successful industrial catalyst, titanium silicalite-1 zeolite (TS-1) also possesses unique photocatalytic activity, but still challenging due to the unsatisfactory activity and unclear photocatalytic mechanism. Here, we achieved the optimization of TS-1 in both the morphology and content of framework Ti by a facile dual-structure directing agent method. The Ti-rich TS-1 nanoplates exhibit enhanced photocatalytic H2 production performance from methanol. The structure-activity relationship was revealed that the nanoplate-like morphology is beneficial to the photocatalytic activity, owing to the largely retainment of photogenerated electrons. Combined with in-situ DRIFTS and theoretical calculations, it is proposed that Ti−O group would function as a whole to serve as the active site, rather than separated Ti and O sites for reduction and oxidation half reactions respectively. The formation of hydroxylated Ti can also promote the photocatalytic performance. These insights into the mechanisms suggest the great potential of Ti-rich TS-1 nanoplates as commercial photocatalytic materials.

Structural Distortion of g-C3N4 Induced by N-Defects for Enhanced Photocatalytic Hydrogen Evolution

Hydrogen evolution by photocatalytic technology has been one of the most promising and attractive solutions, and can harvest and convert the abundant solar energy into green, renewable hydrogen energy. As a new kind of photocatalytic material, graphitic carbon nitride (g-C3N4) has drawn much attention in photocataluytic H2 production due to its visible light response, ease of preparation and good stability. For a higher photocatalyic performance, N defects were introduced in to the traditional g-C3N4 in this work. The existence of N defects was proved by adequate material characterization. Significantly, a new absorption region at around 500 nm of N-deficient g-C3N4 appeared, revealing the exciting n-π* transition of lone pair electrons. The photocatalytic H2 production performance of N-deficient g-C3N4 was increased by 5.8 times. The enhanced photocatalytic performance of N-deficient g-C3N4 was attributed to the enhanced visible light absorption, as well as the promoted separation of photo-generated carries and increased specific surface area.

Photothermal effect of carbon dots for boosted photothermal-assisted photocatalytic water/seawater splitting into hydrogen

Herein, carbon dots were loaded on the surface of hollow tubular carbon nitride (CDs/TCN) via a two-step route of hydrothermal and calcination processes for photothermal-assisted photocatalytic water/seawater splitting into hydrogen full spectrum light irradiation. The introduction of CDs promotes the separation and transfer rate of photogenerated carriers, and provides active sites for the hydrogen precipitation reaction. Most importantly, with the assistance of the thermal insulation effect of TCN, the photothermal effect of CDs can greatly increase the surface temperature of CDs/TCN composite system, thus enhancing the photocatalytic H2 production performance. All the synthesized CDs/TCN composites exhibited efficient photocatalytic H2 production rates, the highest of which reached 12.94 mmol h−1 g−1 and 11.92 mmol h−1 g−1 from water and seawater splitting, respectively. This study provides a new idea for enhancing the photothermal-assisted photocatalytic water splitting into hydrogen using CDs with photothermal effect.

Controllable construction of alkynyl defective dibenzo[b,d]thiophene-sulfone-based conjugated microporous polymers for enhanced photocatalytic performance

Defect engineering is a versatile approach to modulate band and electronic structures as well as materials performance. Nowadays, more research has been performed for enhancing catalytic performance of organic photocatalysts via the regulation of structure defect. Herein, we constructed the dibenzo[b,d]thiophene-sulfone-based conjugated microporous polymers (CMPs) with alkynyl defects via the molecular design. The effects of the concentration of alkynyl defects on the optical band gap, energy level structure, charge separation and photoactivity of the as-prepared samples were further explored. Combination of the first-principle density functional theory (DFT) calculations and experimental results, the incorporation of alkynyl defects accelerated the separation of photogenerated charge carriers. Furthermore, the concentration of alkynyl defects in CMPs can be adjusted by the dosage of 1,3-diethynylbenzene (MEB), thereby modulating the electronic structure and charge carrier separation properties. At appropriate alkynyl defect concentration, the prepared Defect-TD-2 shows higher visible-light photocatalytic performance for H2 production and pollutants degradation. The work therefore shows an efficient self-modification strategy for improving the photoactivity of CMPs.

Rational Construction of Z‐Scheme Charge Transfer Based on 2D Graphdiyne (g‐CnH2n−2) Coupling with Amorphous Co3O4 Quantum Dots for Efficient Photocatalytic Hydrogen Generation

AbstractA novel Co3O4 quantum dots (CQDs)/2D graphdiyne (GDY) Z‐scheme heterojunction is fabricated by cross‐coupling reaction and electrostatic self‐assembly methods. GDY with the features of 2D porous structures has not only conducted the adsorption of dye molecules but also CQDs is facile to be anchored on the surface. Additionally, the construction of Z‐scheme heterojunction is conductive to conquer the shortcomings of easy agglomeration and poor dispersion for CQDs. The maximum photocatalytic hydrogen generation rate of 1500.85 µmol h−1 g−1 is gained for 30% GDY/CQDs and display an apparent quantum efficiency of 1.37% at 475 nm, which is roughly 11‐fold and 2.8‐fold higher than the pristine GDY and CQDs, respectively. The superior photocatalytic H2 production performance would be put down to the intense synergy of Z‐scheme heterostructure and the size effect of CQDs. They dramatically enhance the separation and transport of photogenerated charge carriers. Besides, the Z‐scheme charge transfer mechanism is further verified through the results of photoluminescence. This work offers new insight into the design of GDY‐based Z‐scheme heterojunction for photocatalysis.

An electron-hole separation mechanism caused by the pseudo-gap formed at the interfacial Co-N bond between cobalt porphyrin metal organic framework and boron-doped g-C3N4 for boosting photocatalytic H2 production

Photocatalytic hydrogen evolution from water splitting presents an attractive prospect in dealing with the energy crisis, but the low efficiency of charge separation and migration still seriously hinders its further practical application. Here, an acidified boron-doped g-C3N4 (HBCNN) and cobalt porphyrin metal organic frameworks (CoPMOF) self-assembled two-dimensional and two-dimensional (2D/2D) hybrid photocatalyst is fabricated successfully. The resultant HBCNN/CoPMOF with optimum ratio exhibits a superior H2 evolution rate of 33.17 mmol g−1 h−1, which is 3.04 and 100.50 times higher than the single HBCNN and CoPMOF, respectively. It is found that a coordination connection has formed between CoPMOF and HBCNN through Co-N bond, and the interfacial Co-N bond then forms a pseudo-gap in the up-spin channel of electronic states, establishing an electron-hole separation mechanism. It is this electron-hole separation mechanism that contributes to a Z-scheme transport mode of photogenerated carriers, which greatly promotes the photocatalytic H2 production performance of HBCNN/CoPMOF heterostructure. This work may provide an idea for the design of heterojunction to improve the photocatalytic performance by constructing electron-hole separation through interfacial bond.

Photodeposition Synthesis of CdS@Ni2P Composites for Efficacious Photocatalytic Hydrogen Evolution

Noble-metal-free semiconductor composites are very valuable for efficient water splitting driven by visible light. In this paper, CdS@Ni2P was successfully prepared by a simple hydrothermal method followed by in situ photodeposition. The results showed that the best photocatalytic hydrogen production rate of the composite is 287 μmol h–1, which is about 98.3 times that of pure CdS. The high activity of the material may be attributed to the intimate interface between the Ni2P cocatalyst and CdS nanorods for accelerating the separation and transport of photoelectrons. Further UV and PL tests found that Ni2P significantly extends the lifetime of photogenerated charge carriers and reduces charge recombination rates, resulting in improved photocatalytic H2 production performance. The potential mechanism of photocatalytic enhancement of CdS@Ni2P composite samples was proposed based on the experimental results and DFT calculation, which could lead to a neoteric approach for the efficient preparation of other photocatalytic materials.

Interfacial microenvironment-regulated cascade charge transport in Co6Mo6C2-MoO2-CoNC@ZnIn2S4 photocatalyst for efficient hydrogen evolution

High-quality interfacial coupling can effectively boost photogenerated charge separation/transfer efficiency. Herein, we develop a multicomponent photocatalyst, Co6Mo6C2-MoO2-CoNC@ZnIn2S4 (CMN@Z), featuring directional and swift carrier transfer ability through interfacial microenvironment modulation. The distinctive CMN@Z displays a ten-times enhanced photocatalytic H2-production performance of 4728 μmol·g−1·h−1 than pure ZIS, accompanied by optimized apparent quantum efficiency of 25.06 % at 420 nm. Typically, the well-tuned Schottky barrier readily balances its bifunctionality in rectifying effect and powerful photogenerated electron extraction impetus. Moreover, the gradient work function variation enables the interfacial potential as a robust driving force to expedite charge transfer. Therefore, the resulting cascade charge channel and intimate interfacial contact endow CMN@Z photocatalyst with optimized H2-production performance by virtue of high-efficiency carrier spatial separation and utilization. Our work deeply explores the role of multiple interfacial in coupling photocatalytic systems, which offers new insight into the rational design of cascade photocatalysts.

Surface modulation of MoS2/O-ZnIn2S4 to boost photocatalytic H2 evolution

To realize the continuous production of hydrogen energy, the efficient photocatalysts are required in the heterogeneous reaction for water splitting. Herein, we reported a surface modulation strategy, via doping oxygen atoms to tune the surface state of ZnIn2S4 nanosheets with cocatalyst MoS2 modification, to enhance water adsorption and surface catalytic reaction for boosting the photocatalytic activity. Consequently, MoS2/O-ZnIn2S4 photocatalysts showed a remarkably superior photocatalytic H2 production performance of 4.002 mmol g−1 h−1 and an apparent quantum yield (AQY) of ∼2.53%, 5.4 folds higher than ZnIn2S4. Using operando infrared spectroscopy and DFT calculation, we revealed the dynamic structural evolution, as well as the active sites for water adsorption and the catalytic reaction at the MoS2/O-ZnIn2S4 interface. This work reveals the effect of surface modulation on the photocatalytic activity for MoS2/O-ZnIn2S4 and offers a feasible method to devise excellent nanomaterial photocatalysts for H2 production.

An S-scheme photocatalyst constructed by modifying Ni-doped Sn3O4 micro-flowers on g-C3N4 nanosheets for enhanced visible-light-driven hydrogen evolution

Carbon nitrides (g-C3N4) is considered to be the prospective semiconductor photocatalyst for photocatalytic H2 evolution. Nevertheless, it suffers from low charge transfer efficiency and fewer metal active sites. Thereby, Ni-Sn3O4/g-C3N4 photocatalysts were constructed by anchoring Ni-doped Sn3O4 micro-flowers on g-C3N4 via a feasible and straightforward solvothermal treatment. The prepared Ni-Sn3O4/g-C3N4 S-scheme heterojunction could improve the transfer and separation efficiency of photo-generated electron-hole pairs by facilitating the electrons transfer from Ni-Sn3O4 to g-C3N4. Moreover, the photocatalytic H2 production performance was ameliorated due to the established internal electric field and the energy band bending in Ni-Sn3O4/g-C3N4 S-scheme heterojunction. Meanwhile, the doping Ni in Sn3O4 exposed more active sites in Ni-Sn3O4/g-C3N4 heterojunction for producing H2. As a result, Ni-Sn3O4/g-C3N4-5 photocatalyst exhibited outstanding H2 yields of 1961 µmol h−1 g−1 under visible light irradiation in comparison with pure Ni-Sn3O4 (12 µmol h−1 g−1) and bared g-C3N4 (1391 µmol h−1 g−1). Furthermore, the S-scheme mechanism in Ni-Sn3O4/g-C3N4 heterojunction for producing H2 by oxidizing H2O was proposed. This study provides helpful guide for developing efficient g-C3N4-based photocatalytic systems.

Photo-inactive ZIF-8 is applied to significantly enhance the photocatalytic water reduction by forming a built-in electric field with g-C3N4 and the mechanism analysis

It has been found in this study that the combination of ZIF-8 and g-C3N4 turns the photo-inactive ZIF-8 into “active” and significantly enhances the photocatalytic performance for H2 production. The experimental results such as contact potential difference (CPD) and photodeposition analysis suggest that a built-in electric field exists at the interface of g-C3N4 and ZIF-8, and the direction is from ZIF-8 to g-C3N4. Furthermore, the theoretical calculation of charge density difference and work functions uncover the potential forming mechanism of the built-in electric field. The mechanism analysis exhibits that the built-in electric field is conducive to promote the directional transfer of photo-induced electrons from g-C3N4 to ZIF-8, which significantly boosts the catalytic ability. Hence, the construction of a built-in electric field is considered to be an effective strategy to synthesize robust photocatalysts, and the strategy can be extended to prepare a range of advanced catalysts needing directional charge transfer.

Synthesis of ternary Ni2P@UiO-66-NH2/Zn0.5Cd0.5S composite materials with significantly improved photocatalytic H2 production performance

The design and construction of low-cost and high-performance hybrid materials for the photocatalytic hydrogen production reaction (HER) are extremely important for the large-scale application of hydrogen energy. Metal-organic frameworks (MOFs) are considered to be potential photocatalytic materials. Herein, monodisperse, small size, non-precious metal transition metal phosphide Ni2P is encapsulated into a typical MOF (UiO-66-NH2) as a hybrid core-shell cocatalyst to modify Zn0.5Cd0.5S for photocatalytic hydrogen production. Ni2P is wrapped in UiO-66-NH2 via an in situ solvothermal method, and Zn0.5Cd0.5S sulfide is decorated with a core-shell Ni2[email protected]2 cocatalyst to obtain ternary Ni2[email protected]2/Zn0.5Cd0.5S composite materials. Photoelectric and chemical characterization confirms that the ternary composites have good kinetic hydrogen production performance. The hydrogen production rate of 10% 10 mg Ni2[email protected]2/Zn0.5Cd0.5S reaches 40.91 mmol·g–1·h–1 with an apparent quantum efficiency at 420 nm of 13.57%. The addition of 10 mg Ni2[email protected]2 increases the surface area of the ternary material, providing abundant reaction sites and forming an efficient charge transfer channel, which is conducive to efficient hydrogen production by the ternary photocatalysts. It is shown that the formation of a ternary composite system is beneficial to the occurrence of an efficient catalytic reaction. This study provides a new perspective for the construction of high-performance photocatalytic materials.

Facilely coupling CaTiO3 nanorods with Cu nanoparticles for enhanced photocatalytic hydrogen evolution through efficient charge separation

Photocatalytically splitting water to hydrogen production is a great potential for addressing the issue of energy crisis and environmental pollution. Metal-semiconductor hybrid photocatalyst has attracted increasing attention, and especially non-noble metal decoration is one of promising strategies to promote photoinduced electron-hole pairs separation for an efficient solar-to-hydrogen evolution. Herein, a facile solvothermal approach was successfully employed to prepare calcium titanate (CaTiO3) nanorods with decoration of copper particles. The composition and morphology characterization showed that the Cu particle was deposited on the surface of CaTiO3 nanorod. The as-synthesized CaTiO3/Cu composites exhibited promoted solar-to-hydrogen performance and their activities varied from copper loading amounts. The optimized CaTiO3/Cu-0.05 achieved a hydrogen evolution rate of 251 µmol g−1 h−1 , which was much higher than that of bare CaTiO3. Based on the photoluminescence spectra and photocurrent density measurements, it was proposed that efficient separation of photogenerated charges was achieved between the CaTiO3 nanorod and Cu nanoparticles, which promoted water splitting for H2 production. This work further confirms that metallic Cu decoration is an efficient approach to promote photocatalytic H2 production performance of semiconductor photocatalysts.

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.

An excellent H2 production photoelectrode based on mixed valence Sn3O4 nanoflake arrays treated by H2O2 hydrothermal reaction

To design nanostructured photoelectrodes with unique morphology and suitable band structure is a crucial step for potential photoelectrochemical application. For above purpose, the compact Sn3O4 nanoflakes with the smooth surface have been directly grown on carbon paper substrate by a simple hydrothermal method. It is found that the molar ratio of Sn2+ and Sn4+ ions in Sn3O4 nanoflakes can be modulated by the subsequent H2O2-assisted hydrothermal treatment. The effect of different molar ratio on the energy band has been investigated systematically, together with the evolution of the surface morphology of nanoflakes. Finally, a highly efficient photoelectrode based on Sn3O4 nanoflake has been prepared by the H2O2-assisted hydrothermal process, which is of larger active surface area and suitable band structure, and therefore exhibits the excellent photocurrent response and photocatalytic performance for H2 production. The photoelectrode based on Sn3O4 nanoflake displays enhanced photocurrent with 40 μA cm−1 at a basis of 0 V and higher H2 generation rate with 1.43 × 104 μmol h−1 g−1, much better than those of the original sample. Such superior performance can be probably attributed to the combined effect of unique porous nanoflake-structured, higher active surface area and suitable band structure.