Photocatalytic Hydrogen Production Performance Research Articles

Ni-doped CdS porous cubes prepared from prussian blue nanoarchitectonics with enhanced photocatalytic hydrogen evolution performance

In this paper, NixCdyS composite photocatalysts were synthesized by using Ni-doped Cd–Co PBA as the precursor, which retains the advantages of PBA such as porous structure, large specific surface and highly dispersed metal active sites. The photocatalytic hydrogen production performance over NixCdyS is three times higher than that of pure CdS with H2 yield of 8.45 mmol g−1 h−1. The catalyst was analyzed by the UV/Vis absorption spectra, photoluminescence spectra, time-resolved photoluminescence spectra, transient photocurrent responses, electrochemical impedance spectra, Mott-Schottky test, etc. A series of characterization results prove that the electron-hole recombination rate, electrochemical resistance and band gap of nickel-doped CdS composites are obviously smaller than CdS, which are important factors to improve the photocatalytic hydrogen production performance. This work may provide some reference value for the fabrication of other functional materials using PBA as precursors.

Boosting the photocatalytic hydrogen production performance of graphitic carbon nitride nanosheets by tailoring the cyano groups

Graphitic carbon nitride (g-C3N4) is a promising visible light responsive photocatalyst for solar hydrogen production. However, pristine g-C3N4 suffers from severe charge recombination, resulting in a poor photocatalytic activity. Herein, a facile KOH-assisted sealed heating process is designed to tailor the electronic structure of g-C3N4, leading to a significantly enhanced and stable photocatalytic hydrogen production rate of 225.1 µmol h−1 using only 50 mg of the photocatalyst. An excellent apparent quantum efficiency of 16.82% is achieved at 420 nm. Systematic studies reveal that KOH-assisted sealed heating can generate more cyano groups onto the framework of g-C3N4, which can increase the charge carrier density and reduce the surface charge transfer resistance, promoting charge separation and transfer. The new findings demonstrated in this work provide a facile strategy for the design of low-cost and efficient photocatalyst for solar fuel production.

Creating triazine units to bridge carbon nitride with titania for enhanced hydrogen evolution performance

In this work, a wealth of triazine units was created in carbon nitride through a facile molten salt method to bridge titania and carbon nitride for accelerating charge transportation and enhancing hydrogen production performance. The doping of triazine ring into C3N4 framework results in more exposure of − CN − and − CN bond and forms a homojunction (MCN), which favors photocatalysis by acting as photoresponse and active centers, respectively. Moreover, the triazine units can bridge the hybridized C3N4 and TiO2, forming a stable MCN/TiO2 homo-heterojunction. Attributed to the matched band energy structure of MCN and TiO2 and the structural characteristics of triazine/heptazine heterocyclic, the light response, charge separation and transfer as well as the lifetime of carriers on MCN/TiO2 hybrid are improved significantly. As a result, the MCN/TiO2 homo-heterojunction exhibits excellent activity and stability for photocatalytic hydrogen production performance, up to 2594 μmol∙g−1∙h−1 under simulated solar irradiation, which is 5.5 times higher than that of the bare g-C3N4.

Rational design of direct Z-scheme heterostructure NiCoP/ZIS for highly efficient photocatalytic hydrogen evolution under visible light irradiation

• Direct Z-scheme catalyst of NiCoP/ZIS was prepared through hydrothermal method. • The 37.5% Ni 0.7 Co 0.3 P/ZnIn 2 S 4 showed the best H 2 evolution rate of 3.84 mmol g −1 h −1 . • The charge transfer pathway of NiCoP/ZIS followed the Z-scheme mechanism. Construction of Z-scheme heterojunctions has been recognized as one of the most efficient strategies to significantly improve the charge-separation efficiency and achieve highly efficient solar energy conversion in photochemical reactions. Herein, a novel direct Z-scheme catalyst of NiCoP/ZIS was rational designed and prepared by dispersing ternary metal phosphide NiCoP in ZnIn 2 S 4 (ZIS) nanoflowers under solvothermal method. The compact heterojunction structural characteristic of NiCoP/ZIS afford the composite prominent enhanced photocatalytic hydrogen (H 2 ) production performance. The relative quantities of Ni and Co in NiCoP/ZIS composite can significantly influence the photocatalytic activities of the material, and the 37.5% Ni 0.7 Co 0.3 P/ZIS composite with a Ni/Co mole ratio of 0.7: 0.3 had the best hydrogen production efficiency with a hydrogen evolution rate of 3.84 mmol g −1 h −1 , which is approximately 8 times higher than that of single ZIS. The apparent quantum efficiency (AQE) for 37.5% Ni 0.7 Co 0.3 P/ZIS is about 5.14% under the incident monochromatic light of 405 nm. The subsequent electrochemical analyses proved the significant roles of the direct Z-scheme heterojunction in accumulating the electrons at the conduction bands of ZIS with more negative potential, which contributed to the stronger reduction activity in the promoted hydrogen generation for Ni 0.7 Co 0.3 P/ZIS. This work not only reported a a novel direct Z-scheme catalyst of NiCoP/ZIS heterostructure with enhanced photocatalytic hydrogen generation performance, but also provided a promising approach to rational design and construct efficient visible-light-driven photocatalysts for solar energy utilization.

Promotion effect of rhenium on MoS2/ReS2@CdS nanostructures for photocatalytic hydrogen production

Photocatalytic hydrogen generation is a promising way for clean energy and efficient photocatalysts are essential. Transition metal disulfides of both ReS2 and MoS2 are explored as cocatalysts for CdS photocatalyst. Ternary MoS2/ReS2@CdS photocatalysts are provided with the superior photocatalytic activity for hydrogen production as 171.9 mmol•g-1•h-1. The dual cocatalysts form the heterojunctions with CdS, which accelerate the transfer of photo-induced carriers and improve photo-responsive and photo-electrochemical properties of MoS2/ReS2@CdS. Promotion effect of rhenium on the photocatalytic activity of MoS2/ReS2@CdS is confirmed and optimized. The introduce of a small amount of rhenium brings the remarkable enhancement of photocatalytic activity. It is attributed to the dual Z-scheme electron transfer pathway in MoS2/ReS2@CdS photocatalyst. The aid of rhenium is an efficient strategy to tune photocatalytic performance for hydrogen production, which would be applicable in other kinds of photocatalysts.

The electronegativity modulation of rutile TiO2 nanorods by phosphate and its photocatalytic hydrogen production performance

In this paper, PO was grafted on the surface of rutile TiO2 by one-step hydrothermal method. Due to the presence of the highly electronegative oxygen element, the surface of TiO2 often presented an electron-deficient state, which limited its application in reduction reactions. Herein, the low electronegativity element P from the phosphate was grafted on the surface of TiO2 to form a PO structure, which changes the electronic equilibrium state of the TiO2 and provide a new channel for electron migration. The surface of TiO2 presented an electron-enrich structure, which promoted the best hydrogen production performance around 28 mmol·g−1·h−1 on TiO2-P-0.01.

Preparation of TiO2/MoSe2 heterostructure composites by a solvothermal method and their photocatalytic hydrogen production performance

TiO2/MoSe2 composite photocatalysts were prepared by a solvothermal method using different MoSe2 loadings on the surface of TiO2 to improve the catalytic activity. Upon increasing the MoSe2 loading, the fluorescence intensity of the catalyst gradually decreased, indicating that the MoSe2 loading increased the utilization of photogenerated carriers in TiO2 and improved the catalytic activity. The formic acid produced by the oxidation of lactic acid and methanol dissociated into oxygen-containing anions that were electrostatically adsorbed on the catalyst surfaces. During photocatalysis, the photogenerated electrons on TiO2 were transferred to MoSe2, which separated the photogenerated electrons and holes and increased the quantum efficiency. Therefore, the hydrogen production rate of the composite catalyst was higher than that of pure TiO2, with a quantum efficiency of about 36.8%.

Enhanced photocatalytic hydrogen production performance of pillararene-doped mesoporous TiO2 with extended visible-light response

Pillararenes are a new type of supramolecular hosts, and they have been widely applied in drug delivery, catalysis, separation process, and sensors. However, they have rarely been used to produce hydrogen. Here, we report that pillararenes were used as functional molecules to explore photocatalysts and efficiently promoted hydrogen production from water. The most common and easily synthesized p-dimethoxy pillar[5]arene (PI-OMe) was employed to form an organic-inorganic hybrid material with titanium dioxide (TiO2), denoted as PI-OMe-TiO2, using a convenient sol-gel method. When the material was loaded with Pt nanoparticles, the resulting Pt/PI-OMe-TiO2 had a good activity and stability in catalyzing water splitting to produce hydrogen under visible light. The optimized catalyst Pt/PI-OMe-TiO2(5.2 wt%) had a photocatalytic hydrogen production rate of 1736 µmol g−1 h−1 under visible light (λ > 420 nm) irradiation. The catalyst with a Pt loading of 0.5 wt% and a PI-OMe content of 5.2 wt% also showed good long-term durability after 10 cycles of 50 h testing. The total amount of hydrogen produced was 65.01 mmol/g, and the corresponding turnover number (TON) value was 2084. Our findings suggest that pillararene derivatives are promising functional molecules to make efficient and stable hybrid photocatalysts with TiO2 and open a new door to hydrogen production using visible light.

Hollow CdS nanotubes with ZIF-8 as co-catalyst for enhanced photocatalytic activity

Designing high-efficiency heterojunction photocatalysts for water splitting is an intriguing prospect in energy conversion. Herein, we successfully fabricated a CdS/ZIF-8 heterojunction system through a facile wet-chemically method, in which ZIF-8 nanoparticles were in-situ adhered on hollow CdS nanotubes. Due to the well-matched band structure and intimate interface contact in CdS/ZIF-8 hybrid structure, the interfacial charge separation in the established system was tremendously boosted. As a consequence, the established CdS/ZIF-8 heterojunction exhibited the optimal photocatalytic hydrogen production performance (2.10 mmol·g−1 L−1), which was 35 times higher than pristine CdS (0.06 mmol·g−1·L−1). We believe this strategy will endow new insights for the development of novel photocatalysts.

Preparation of TiO2-Based Photocatalysts Synergistically Modified with Fe3+–Graphene and Their Visible-Light-Catalyzed Hydrogen Production from Ammonia Borane

TiO2-based photocatalysts are promising materials that show great potential in the field of catalysis due to their excellent properties including nontoxicity, high photocatalytic performance, and outstanding thermal and chemical stability. However, several challenges exist regarding TiO2 applications for catalytic hydrogen production. In this work, Fe- and graphene-comodified TiO2 (Fe–rGO/TiO2) was synthesized via a two-step solvothermal method. In addition, the effect of Fe3+ and graphene addition upon the catalytic performance of TiO2 was investigated based on the ammonia borane hydrogen production reaction, and the catalysts were characterized by SEM, XRD, XPS, UV–vis, FT-IR, and Raman methods. Batch experiments showed that the synthesized Fe–rGO/TiO2 composites exhibited high photocatalytic performance for hydrogen production from ammonia borane under visible-light irradiation. Moreover, the highest photocatalytic hydrogen production rate (1235.32 μmol·min–1·gcat–1) of 2%Fe–1%rGO/TiO2 was observed under visible-light irradiation at 25 °C, and the photocatalytic activity of the sample remained almost unchanged after the fifth cycle. The XRD, XPS, FT-IR, and Raman analyses showed that Fe and graphene successfully modified TiO2 and the presence of Ti4+. In addition, the extended visible-light absorption range and a reduction of the band gap of Fe–rGO/TiO2 were demonstrated by UV–vis diffuse reflectance spectra and calculation of the band gap. Also, the preparation of hydrogen from the hydrolysis of ammonia borane photocatalyzed by TiO2 composites was discussed. These findings are crucial for designing TiO2-based photocatalysts with high performance for photocatalytic hydrogen production.

Electron-extracting system with enhanced photocatalytic hydrogen production performance: Synergistic utilization of Z-scheme and Ohmic heterojunctions

Low utilization of photogenerated electrons is usually caused by severe carrier recombination, being one of bottlenecks towards acquiring highly efficient photocatalytic hydrogen production system. Here, an artificial Z-scheme CuWO4/ZnIn2S4 heterojunction is integrated with NixP/ZnIn2S4 Ohmic contact to form a fascinating ternary-component system. The Z-scheme heterojunction can not only preserve excellent carrier separation and sunlight harvesting capability, but also markedly eliminate the photogenerated holes and improve the long-term photostability of ZnIn2S4. Additionally, the electrons can be further extracted from ZnIn2S4 to NixP due to the Ohmic contact, finally enhancing the utilization of photogenerated electrons, inhibiting the electron/hole recombination and prolonging the lifetime of photogenerated electrons. Benefiting from the synergistic effect of Z-scheme structure and Ohmic contact, the ternary system with excellent electron-extracting capacity exhibits 14-folds enhanced photocatalytic hydrogen evolution activity, compared to pure ZnIn2S4. This work may provide a valuable guideline in preparing highly efficient photocatalytic hydrogen production system.

CTAB-melamine molecular crystals as precursor for synthesis of layered carbon nitride porous nanostructures with enhanced photocatalytic activity for hydrogen production

It is still a great challenge to enhance the photocatalytic hydrogen production performance of photocatalysts. Herein, we used a simple two-step method to prepare layered graphitic carbon nitride (g-C3N4) porous nanostructures with much higher surface area by calcination of molecular crystals precursor assembled by hexadecyl trimethyl ammonium bromide (CTAB) and melamine. CTAB was found to act as the soft template and pore forming agent. CTAB and melamine firstly assembled together to form molecular crystals in hydrothermal conditions via electrostatic interaction. Then, after calcination, layered g-C3N4 porous nanostructures were formed. The as-prepared product exhibited almost 27.5-fold higher photocatalytic hydrogen generation than g-C3N4, which may be caused by the much higher surface area, faster separation rate of photogenerated hole-electron pairs and the narrowed band gap due to the carbon doping induced by the CTAB. This work provides a facile method for improving the performance of the hydrogen production of g-C3N4.

Rational design of all-solid-state TiO2-x/Cu/ZnO Z-scheme heterojunction via ALD-assistance for enhanced photocatalytic activity

Poor visible light utilization and charge separation efficiency of TiO2 restrict its extensive application in the photocatalytic field. Herein, a specific Z-scheme TiO2-x/Cu/ZnO heterojunction was successfully constructed by atomic layer deposition (ALD) technique and spray pyrolysis technology. Benefited from the surface plasmon resonance (SPR) effect of Cu and Z-scheme heterojunction, the visible light absorption capacity was greatly enhanced. Meanwhile, ZnO nanolayer coating, prepared by ALD technique, protects Cu element to hinder its oxidation, thus enhancing the separation efficiency of photogenerated carriers. Therefore, the photocatalytic hydrogen production performance was significant improved, exhibiting a maximum value of 342.0 µmol·g−1·h−1 for the optimal B-T-0.1C-10Z (black TiO2/0.1Cu/10 nm ZnO) sample without any noble-metal cocatalyst, which is higher than pure TiO2 (310.7 µmol·g−1·h−1, with 3 wt% Pt) synthesized by spray pyrolysis method under equal conditions. In addition, a possible mechanism for the enhanced performance was briefly discussed based on the experimental results.

Metal-Organic-Frameworks-driven hollow core-shell C03O4/TiO2 Heterojunction for Enhancement of Photocatalytic Hydrogen generation

In recent years, how to further enhance the efficiency of photocatalytic hydrogen generation has become a research hotspot. At present, the metal-organic-frameworks (MOF) has attracted much attention in the field of catalysis due to its special physical and chemical properties. Herein, the hollow core-shell Co3O4/TiO2 heterojunction is prepared by deposition and annealing method with ZIF-67 as self-sacrificial templates and metal precurous. The characterzation of XRD, SEM, and TEM indicate that the hollow core-shell Co3O4/TiO2 heterojunction is synthesized successfully. The characterzation of UV, PL indicate that the Co3O4/TiO2 show superior photoelectric performance. By evaluation, the Co3O4/TiO2 heterogeneous catalyst exhibits a remarkable photocatalytic hydrogen production performance, which is ∼11 and ∼14 times higher than that of pure Co3O4 and TiO2. Studies prove that the formation of heterojunction can promote charge carriers separation, the hollow structure can raise the solar efficiency, offer more surface areas and active sites, all these are beneficial for photocatalytic performance.

Synthesis of CdS/CoP hollow nanocages with improved photocatalytic water splitting performance for hydrogen evolution

Photocatalysts with hollow structure have obvious advantages in photocatalytic hydrogen production. Herein, CoP was modified on the surface of CdS by sacrificial template method to prepare CdS/CoP composite photocatalyst with hollow structures. Compared with pure CdS, CdS/CoP nanocage has improved photocatalytic hydrogen production performance due to its hollow structure, excellent light absorption capacity, and electron-hole pair separation and transfer efficiency. The hydrogen production rate of CdS/CoP can reach to 15.74 mmol g−1 h−1, which is about 9 times than that of pure CdS. It is found that the formation of a p-n heterojunction between CdS and CoP is the key factor to improve the photocatalytic performance of the composites. This study provides a simple strategy for the construction of more hollow nanocomposite catalysts with excellent photocatalytic performance.

Defect-rich cobalt pyrophosphate hybrids decorated Cd0.5Zn0.5S for efficient photocatalytic hydrogen evolution: Defect and interface engineering

Photocatalysts with highly efficient charge separation are of critical significance for improving photocatalytic hydrogen production performance. Herein, a cost-effective and high-performance composite photocatalyst, cobalt-phosphonate-derived defect-rich cobalt pyrophosphate hybrids (CoPPi-M) modified Cd0.5Zn0.5S is rationally devised via defect and interface engineering, in which the co-catalyst CoPPi-M delivers a strong interaction with host photocatalyst Cd0.5Zn0.5S, rendering Cd0.5Zn0.5S/CoPPi-M with a remarkably improved efficiency of charge separation and migration. Besides, Cd0.5Zn0.5S/CoPPi-M exhibits a hydrophilic surface with ample access to electrons and a strong reduction ability of electrons. Benefiting from these advantages, the integration of defect-rich cobalt pyrophosphate and Cd0.5Zn0.5S enables Cd0.5Zn0.5S/CoPPi-M−5% with high photocatalytic H2 production rate of 6.87 mmol g−1h−1, which is 2.46 times higher than that of pristine Cd0.5Zn0.5S, and the notable apparent quantum efficiency (AQE) is 20.7% at 420 nm. This work provides a promising route for promoting the photocatalytic performance of non-precious hybrid photocatalyst via defect and interface engineering, and advances energy-generation and environment-restoration devices.

Surface-Engineered Ni(OH)2/PtNi Nanocubes as Cocatalysts for Photocatalytic Hydrogen Production

Exposure of specific crystallographic planes as catalyst surfaces has been reported to effectively affect the performance of noble metal cocatalysts used for photocatalytic hydrogen production via water splitting. However, the performance of noble metals for hydrogen production in alkaline solutions is usually 2 orders of magnitude lower than that in acidic media because of the weak dissociative adsorption ability of noble metals to water molecules, which may greatly limit their applications in photocatalytic hydrogen production. In this research we report a Pt-based composite cocatalyst (Ni(OH)2/PtNi nanocubes), designed by separating the dissociative sites of water molecules from active sites for photocatalytic hydrogen production. Compared with PtNi nanocube-loaded CdS, Ni(OH)2/PtNi nanocube-modified CdS exhibits a much higher photocatalytic performance for hydrogen production in alkaline solutions. This study provides a method for synthesizing highly active water-splitting/reducing photocatalysts under alkaline conditions.

EDTA-assisted synthesis of amorphous BiSx nanodots for improving photocatalytic hydrogen-evolution rate of TiO2

Compared with crystalline metal sulfides, amorphous metal sulfides can expose more unsaturated S atoms as hydrogen-production active centers to enhance photocatalytic hydrogen-evolution activity of photocatalysts. Therefore, it is of great significance to explore simple and mild strategies to fabricate new amorphous metal sulfides for improving H2-production performance. In this work, the amorphous BiSx nanodots with the size of 0.5–2 nm as a novel and effective H2-evolution cocatalyst were successfully and homogeneously loaded on TiO2 surface to extremely facilitate the photocatalytic H2-production performance. The BiSx/TiO2 photocatalyst was obtained by an EDTA-assisted two-step process, which was including the adsorption of the Bi(Ш)-EDTA ions on TiO2 and the in-situ formation of amorphous BiSx nanodots. It is found that the BiSx/TiO2(1.0 wt%) photocatalyst achieved the maximum photocatalytic hydrogen-production performance (803.2 μmol h−1 g−1, AQE= 3.86%), which was 83.6 and 1.6 folds of the blank TiO2 and crystalline Bi2S3-modified TiO2 (c-Bi2S3/TiO2), respectively. Importantly, the above amorphous BiSx nanodots can serve as a general cocatalyst to promote the H2-generation activity of other typical photocatalysts (g-C3N4 and CdS). The boosted photocatalytic H2-production performances are attributed to that the amorphous BiSx nanodots can provide more unsaturated active S atoms as the efficient H2-evolution active sites for promoting H2-evolution rate. This study provides a new insight for exploiting novel metal sulfide cocatalyst in the field of photocatalytic hydrogen evolution.

Enhanced photocatalytic hydrogen production under visible light of an organic-inorganic hybrid material based on enzo[1,2-b:4,5-b']dithiophene polymer and TiO2

Titanium dioxide (TiO2) has been limited in photocatalysis due to its wide band gap (3.2 eV) and limited absorption in the ultraviolet range. Therefore, organic components have been introduced to hybrid with TiO2 for enhanced photocatalytic efficiency under visible light. Here, we report that benzo[1,2-b:4,5-b']dithiophene polymer was an ideal organic material for the preparation of a hybrid material with TiO2. The energy band gap of the resulting hybrid material decreased to 2.9 eV and the photocatalytic hydrogen production performance reached 745.0 µmol g−1 h−1 under visible light irradiation. Meanwhile, the material still maintained the stability of hydrogen production performance after 40 h of photocatalytic cycles. The analysis of the transient current response and electrochemical impedance revealed that the main reasons for the enhanced water splitting of the hybrid materials were the faster separation of electron hole pairs and the lower recombination of photocarrier ions. Our findings suggest that polythiophene is a promising organic material for exploring hybrid materials with enhanced photocatalytic hydrogen production.

Strategy of Graphdiyne (g-Cn H2n-2 ) Preparation Coupling with the Flower-Like NiAl-LDH Heterojunctions for Efficient Photocatalytic Hydrogen Evolution*.

Graphdiyne (g-Cn H2n-2 ), a novel two-dimension carbon allotrope material composed of a sp- and sp2 -hybrid carbon network, has been widely explored since it was synthesized for the first time by Li's group in 2010. A series distinct and excellent properties bestow graphdiyne excellent performance in many fields. Here, an innovative progress for preparing graphdiyne by using Cu+ contained material as catalyst is reported and the composite CuI-GD is coupled with flower-like NiAl-LDH to produce H2 from photocatalytic water splitting. The results of FTIR and Raman spectroscopy together reveal that graphdiyne nanosheets are synthesized successfully by employing a cross-coupling method. Photocatalytic hydrogen evolution performance shows that the hydrogen production activity of CuI-GD/NiAl-LDH has a 15- and 216-fold enhancement compared with CuI-GD and NiAl-LDH, respectively. A series of characterizations are carried out to expound the underlying reasons in the enhancement of the photocatalytic hydrogen production performance of CuI-GD/NiAl-LDH. Meanwhile, a possible mechanism for the photocatalytic hydrogen evolution process was proposed to understand the interaction among these materials.