Photocatalyst For Hydrogen Evolution Research Articles

New insights on photocatalytic hydrogen evolution of ZnFe2−xGaxO4 (0 ≤ x ≤ 2) solid solutions: Role of oxygen vacancy and ZnO segregated phase

The exponential increase in global energy and clean energy demands lead to the necessity for development of efficient photocatalyst for hydrogen evolution. Herein, photocatalytic hydrogen evolution activity with nano-structured ZnFe2-xGaxO4 (0 ≤x ≤ 2) solid solution samples synthesized by citrate-gel method at 550 °C is reported. The prepared materials have been characterized for their structure and optical properties. The formation of solid solution with spinel type structure in the complete range of composition and a systematically decreasing trend of unit cell parameters with increasing Ga3+ concentration is observed from powder XRD studies. The band gap of these solid solutions could be tuned from 1.9 to 3.1 eV by increasing the Ga3+ concentration. Without any co-catalyst, ZnFe2O4 shows poor catalytic activity (378μmolh−1g−1) for photocatalytic hydrogen evolution from water. Whereas its activity enhances with loading of co-catalyst and touches a maximum activity of 3089μmolh−1g−1 with loading 1 wt% of Pt. The catalytic activity increases systematically with increasing Ga concentration in the solid solutions and reaches to 3989μmolh−1g−1 for ZnGa2O4 nanomaterials. Electrochemical impedance spectroscopic and transient photocurrent measurements also support the observed increasing trend. The lower catalytic activity of ZnFe2O4 has been attributed to the faster e-h recombination due to lower band gap and inherent oxygen vacancies. A smaller amount of oxygen vacancies and segregated ZnO phase observed in Ga substituted ZnFe2O4 samples favor the e-h pair separation and that facilitate the hydrogen generation from water.

Carrier engineering of carbon nitride boosts visible-light photocatalytic hydrogen evolution

Carbon nitride, as one of the metal-free photocatalysts, has aroused wide attention due to its low cost, easy preparation, and excellent optical response. However, challenges of the high recombination rate of electron-hole pair hindered their potential applications. Here, boron-doped carbon nitride nanotubes were designed and prepared by a simple hydrothermal and calcination route. Compared with the bulk carbon nitride, the control strategy forms the ordered nanotube structure, which greatly improved their specific surface area, exposed more active sites, and enhanced the graphitization degree. The transient fluorescence lifetime of tubular carbon nitride is twice as long as that of pure carbon nitride. Furthermore, boron doping carbon nitride nanotubes exhibited a 1.5-fold increase in a lifetime over tubular carbon nitride, which acts a synergistic role with nanotube architecture to further increases the carrier concentration and hinder the recombination of photogenerated electron-hole. Under the irradiation of visible light, the amount of hydrogen evolution of the optimum photocatalyst has achieved 22.1 mmol g−1 h−1, which was 64 times that of the bulk carbon nitride and exhibited excellent stability. This work provides a promising strategy for the development of non-metallic doped carbon nitride nanotube photocatalysts for hydrogen evolution.

Fibrous Phase Red Phosphorene as a New Photocatalyst for Carbon Dioxide Reduction and Hydrogen Evolution.

2D photocatalysts are one of the hottest issues in energy and material science. In the field of photocatalysis, a 2D material with an appropriate bandgap of 1.3 to 2.0eV is desirable. Herein, a new kind of fibrous phase red phosphorene with a bandgap between 1.43 to 1.54eV is obtained. This is much better than black phosphorus because the bandgap of black P depends of its layer number. The black P needs to be as thin as 1-2 layers for suitable band diagram, which is difficult to control. The fibrous red phosphorene is first used for photocatalytic CO2 reduction, and its activity is superior to the majority of mainstream photocatalysts and reaches a record-high value among phosphorus. Besides, its activity in hydrogen evolution is higher than most of the phosphorus photocatalysts. The intralayer charge transfer is much easier than interlayer transfer. The mobility of electron and hole along the phosphorene plane is about 20 times higher than that perpendicular to different layers. The activity sites is at region between the two P[21] chains. These regions are easy to be exposed for fibrous phase phosphorene, making it to exhibit high activity.

Confined Synthesis: From Layered Titanate to Highly Efficient and Durable Mesoporous Cu/TiO2 Hydrogen Evolution Photocatalysts

Highly efficient, durable, and earth-abundant photocatalysts are of great interest toward practical photocatalytic conversion reactions, such as hydrogen generation and CO2 reduction. In this work,...

Novel B-N-Co surface bonding states constructed on hollow tubular boron doped g-C3N4/CoP for enhanced photocatalytic H2 evolution

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for water hydrogen evolution. Nonetheless, fast recombination of photogenerated electron-hole pairs and the slow kinetics of hydrogen production result in the unsatisfactory efficiency of solar hydrogen production. we address this issue by anchoring the cobalt phosphide (CoP) cocatalyst onto the one-dimensional boron doped g-C3N4 nanotube (B-CNNT) to construct B-N-Co surface bonding states in the B-CNNT/CoP photocatalyst. Spectroscopic measurement and density functional theory (DFT) calculations demonstrated that the B-N-Co bonds optimize the local electronic distribution of bonded Co and adjacent P atoms, strengthen the electrons’ delocalization capacity of Co atoms for high electrical conductivity and accelerate the photogenerated carrier transfer between B-CNNT and CoP, which lead to the enhanced photocatalytic activity of the B-CNNT/CoP photocatalyst for hydrogen evolution. B-CNNT/CoP-2.45% achieved a remarkable photocatalytic hydrogen production rate of 784 μmol g-1h−1 with an apparent quantum efficiency of 5.32% at 420 nm, which is significantly higher than demonstrated by CNNT/CoP-2.45% (153 μmol g-1h−1). Our findings provide insights into as well as establish theoretical and practical grounds for the development of low-cost, high-performance photocatalytic materials for hydrogen evolution.

Recent advances in bismuth-based multimetal oxide photocatalysts for hydrogen production from water splitting: Competitiveness, challenges, and future perspectives

The efficient utilization of photocatalytic technology is essential for clean energy. Bismuth-based multimetal oxides (Bi2WO6, Bi2MoO6, BiVO4 and Bi4Ti3O12) have aroused widespread attention as a visible light responsive photocatalyst for hydrogen evolution due to their low cost, nontoxicity, modifiable morphology, and outstanding optical and chemical properties. Nevertheless, the photocatalytic activities of pure materials are unsatisfactory because of their relative small specific surface area, poor quantum yield, and the rapid recombination of photogenerated carriers. Therefore, some modification strategies, including morphological control, semiconductor combination, doping, and defect engineering, have been systematically studied to enhance photocatalytic H2 evolution activity in the past few years. Herein, we summarize the recent research progress on bismuth-based photocatalysts, pointing out the prospects, opportunities and challenges of bismuth-based photocatalysts. Eventually, we aims to put forward valuable suggestions for designing of bismuth-based photocatalysts applied in hydrogen production on the premise of consolidating the existing theoretical basis of photocatalysis.

Phosphorus-doped Carbon Nitride Nanosheets as Efficient White-LED-Light-Driven Photocatalyst for Hydrogen Evolution and Tetracycline Degradation

g-C3N4 has received much attention due to its role in photocatalytic hydrogen evolution and contaminants degradation. Nevertheless, the photocatalytic property of bulk g-C3N4 (BCN) is seriously restricted owing to its short photo-generated carrier lifetime, small specific surface area and low visible light utilization rate, etc. In this study, nanosheet constructing and heteroatom phosphorus (P) doping, as two important strategies, are synergistically adopted to co-enhance its activity. The controllable P atoms were successfully doped into the framework of g-C3N4 nanosheet (NCN-P) through forming P-N bond. The optimized NCN-P sample displays an excellent H2 production rate (3263.99 µmol·g−1·h−1) under white LED light irradiation, which is more than 11.6 times that of the BCN. Moreover, it also exhibits excellent photocatalytic degradation ratio of tetracycline reached 80% in 1 h. Furthermore, the optimized NCN-P sample still maintains robust photocatalytic performance after recycling tests, making it as a bright prospect photocatalyst for solar energy utilization and contaminants removal.

Single-atomic Pt sites anchored on defective TiO2 nanosheets as a superior photocatalyst for hydrogen evolution

Single-atomic site catalysts have drawn considerable attention because of their maximum atom-utilization efficiency and excellent catalytic activity. In this work, a highly active single-atomic Pt site photocatalyst was synthesized through employing defective TiO2 nanosheets as solid support for photocatalytic water splitting. It indicated that the surface oxygen vacancies on defective TiO2 nanosheets could effectively stabilize the single-atomic Pt sites through constructing a three-center Ti–Pt–Ti structure. The Ti–Pt–Ti structure can hold the stability of isolated single-atomic Pt sites and facilitate the separation and transfer of photoinduced charge carriers, thereby greatly improving the photocatalytic H2 evolution. Notably, our synthesized photocatalyst exhibited a remarkably enhanced H2 evolution performance, and the H2 production rate is up to 13460.7 μmol·h−1·g−1, which is up to around 29.0 and 4.7 times higher than those of TiO2 nanosheets and Pt nanoparticles-TiO2. In addition, a plausible enhanced reaction mechanism was also proposed combining with photo-electrochemical characterizations and density functional theory (DFT) calculation results. Ultimately, it is believed that this work highlights the benefits of a single-site catalyst and paves the way to rationally design the highly active and stable single-atomic site photocatalysts on metal oxide support.

Synthesis of graphitic carbon nitride-based photocatalysts for hydrogen evolution under visible light

The optimal conditions for the synthesis of platinized graphitic carbon nitride (Pt/g-C3N4) have been found. It was investigated as a catalyst for the production of hydrogen from aqueous solutions of triethanolamine (TEOA) under irradiation with visible light. The highest photocatalytic activity of 450 μmol h−1 g−1 and an apparent quantum efficiency of 1.1% were demonstrated by the 1% Pt/g-C3N4 sample prepared from melamine by calcining at 600 °C for 2 h.

NiS/Pt nanoparticles co-decorated black mesoporous TiO2 hollow nanotube assemblies as efficient hydrogen evolution photocatalysts

A novel mesoporous Pt/NiS/black TiO2 hollow nanotubes (P-NBTNs) is assembled by a facile synthesize route based on hollow black TiO2 nanotubes with 2D mesoporous TiO2 nanosheets. This unique structure increases the specific surface area of the material, exposes more photocatalytic reaction active sites, and reduces the bandgap to about 2.87 eV, thereby improving its light absorption capacity in the visible light region. At the same time, the surface plasmon resonance effect of the noble metal Pt is employed to further improve the absorption and utilization of visible light. The strong electron-withdrawing ability of Pt nanoparticles and the synergistic catalytic between NiS and Pt, and the formation of built-in electric field at the interface all promote the separation and transmission of photo-generated charge carriers, leading to significant improvement of photocatalytic performance. Under AM 1.5 G irradiation, the hydrogen production rate of P-NBTNs is up to 4.70 mmol h−1g−1, which is more than 4 times higher than that of pristine TiO2 nanotubes (TNs) (~0.94 mmol h−1g−1). The photocatalytic performance nearly keeps constant after more than 10 cycles, indicating the high stability of P-NBTNs, which favors the practical applications.

In situ constructing Ni foam supported ZnO-CdS nanorod arrays for enhanced photocatalytic and photoelectrochemical activity

Abstract Constructing sustainable and efficient photocatalyst for solar hydrogen evolution via photocatalytic (PC) or photoelectrocatalytic (PEC) water splitting is considered as one of the most potential solutions for the contemporary energy crisis. In this study, we synthesized a film-like photocatalyst ZnO-CdS(Ar)@Ni with one-dimensional (1D) nanorod arrays of ZnO-CdS heterojunction anchoring on three-dimensional (3D) Ni foam. The ZnO-CdS(Ar)@Ni photocatalyst not only exhibited higher PC hydrogen generation rate (16.31 µmol cm−2 h−1) than that of precursor samples, but could also be used as a photoelectrode to achieve efficient PEC water splitting on the basis of the applied bias photo-to-current conversion efficiency (ABPE) of 2.0% (at −0.6 V vs. Ag/AgCl) and the incident photo-to-current efficiency (IPCE) of 35% (at 450 nm), respectively. Such enhanced performances relate to the cohesive combination of ZnO-CdS heterojunction via calcination, more active areas in the 1D nanorod structure combining with 3D Ni foam substrate, and the collection and rapid transfer of electrons within Ni foam. This study demonstrates such a strategy of film-like photocatalyst construction has great potential for practical utilization in both PC and PEC systems for renewable energy generation.

Oxygen vacancy stimulated direct Z-scheme of mesoporous Cu2O/TiO2 for enhanced photocatalytic hydrogen production from water and seawater

Abstract Oxygen vacancy stimulated direct Z-scheme Cu2O/TiO2 hybrid photocatalysts were designed and constructed through a Cu2+ ions adsorption-reduction strategy with Cu2O nanospecies decorated on/within mesoporous TiO2 microspheres. Narrow band gap of Cu2O favors visible light absorption. The mesoporous structure stabilizes Cu2O nanospecies and benefits the efficient charge carrier mobility and light harvest. The high specific surface area provides more photocatalytic active sites for both Cu2O and TiO2 components. Oxygen vacancy stimulated all-solid direct Z-scheme electron transport mechanism was proposed to explain the high activity and stability of the hybrid catalyst. The catalyst behaves enhanced hydrogen evolution rate of 11 mmol h−1 g−1 in water and 5.1 mmol h−1 g−1 in seawater, respectively. The highest AQY of hydrogen production is 15.1% in water (and 8.4% in seawater) at 365 nm. The work will provide new insight for controllable creation of Z-scheme photocatalysts for practical hydrogen evolution from water and seawater splitting.

Hierarchical bismuth vanadate/reduced graphene oxide composite photocatalyst for hydrogen evolution and bisphenol A degradation

Bismuth vanadate (BiVO4) is a widely studied photocatalyst for the depollution of contaminated wastewater, production of hydrogen by water splitting, and organic synthesis. The photophysical properties of BiVO4 are sensitive to morphology and quantum confinement effects, and can exhibit enhanced photocatalytic performance in nanocomposites with graphene. Synthesis of hierarchical BiVO4 plates decorated by nanoparticles (h-BiVO4) in contact with reduced graphene oxide (RGO) is reported via a facile one-pot solution phase approach using ethanolamine and a polyethylene glycol stabilizer. The resulting h-BiVO4/RGO photocatalyst exhibited superior photoactivity for bisphenol A (BPA) degradation and hydrogen evolution under visible light irradiation compared to single component h-BiVO4 or a μm-sized block-like BiVO4 morphology. Rates of BPA photocatalytic degradation and apparent quantum efficiency (AQE) decreased in the order h-BiVO4/RGO (4.5 × 10−2 mmol.g−1.min−1; 15.1% AQE) > h-BiVO4 (3.5 × 10−2 mmol.g−1.min−1; 11.7% AQE) > BiVO4 (1 × 10−2 mmol.g−1.min−1; 3.4% AQE), representing a 4.5 fold enhancement for h-BiVO4/RGO versus BiVO4. Liquid phase photodegradation products included benzene-1,4-diol, cyclohexa-2,5-diene-1,4-dione and (2Z)-but-2-enedioic acid. The rate of photocatalytic hydrogen production under visible light was 11.5 µmol.g−1.h−1 for h-BiVO4/RGO, ~383.3 times greater than for BiVO4 (0.03µmol.g−1.h−1). The superior photocatalytic performance of h-BiVO4/RGO is largely attributed to its higher surface area, aided by enhanced visible light absorption and charge separation across the semiconductor-RGO interface, which together confer a higher density and lifetime of photoexcited charge carriers.

Defect-engineered 2D/2D hBN/g-C3N4 Z-scheme heterojunctions with full visible-light absorption: Efficient metal-free photocatalysts for hydrogen evolution

2D/2D hBN/g-C3N4 nanocomposites with good photocatalytic activity have been successfully prepared, and fortunately defected 2D material heterojunction opens up new possibilities for high-efficiency photocatalysts. However, its photocatalytic performance and mechanism in splitting water have not been thoroughly explored. Herein, using the state-of-theart TDHF-HSE06 method, 2D/2D hBN/g-C3N4 nanocomposites with different defected types were discussed in detail, including C atoms doping and natural point vacancies. We demonstrate that the defect-induced Z-scheme vdW heterojunction is a key for excellent photocatalytic performance. Compared to perfect hBN/g-C3N4, the defected hBN/g-C3N4 heterojunctions have stronger interfacial interaction with more than 20 times of charge transfer. And it even has full visible-light response due to the suitable band gap width. More importantly, the Z-scheme band edge potentials have perfect redox capacity for water splitting at both PH = 0 and 7. The findings not only explain the existing experimental phenomena, but also provide new insights into the design of high-efficiency metal-free photocatalysts.

Stable core–shell ZIF-8@ZIF-67 MOFs photocatalyst for highly efficient degradation of organic pollutant and hydrogen evolution

Compared to single metal–organic framework (MOF), core–shell MOF crystals are more promising due to their special structure and unique properties. Herein, since ZIF-8 and ZIF-67 have the same topology, crystal growth method is used to synthesize core–shell crystals ZIF-8@ZIF-67, which exhibit far superior light adsorption, charge separation capabilities, and excellent stability than ZIF-8 and ZIF-67. The photocatalytic H2 generation rate for ZIF-8@ZIF-67 (1:1) is about 17 times higher than that of pure ZIF-67 without cocatalyst loading under same reaction conditions. Through a series of characterizations, two connection modes between ZIF-8 and ZIF-67 frames in core–shell contact interface are proposed, and the corresponding photocatalytic mechanism is elucidated. Transient photovoltaic curve reveals the unique transfer paths of electrons through contact interface, which leads to efficient charge separation compared with other ZIF materials. This study provides a novel and simple strategy to synthesis high effective and stable core–shell ZIF photocatalyst for photodegradation and hydrogen evolution.

CoB/C3N4 photocatalyst for rapid hydrogen evolution from hydrolysis of sodium borohydride under light irradiation

For practical application of sodium borohydride (NaBH[Formula: see text] hydrolysis to generate hydrogen, metallic catalysts with low cost but excellent activity are highly desired. However, it remains a big challenge to further improve the activity of non-noble metal catalysts. In this work, photocatalysis technology was successfully introduced to enhance the catalyst activity for NaBH4 hydrolysis. By means of conventional impregnation-reduction method, CoB nanocatalyst was evenly deposited on graphitic carbon nitride surface, resulting in a Schottky-type photocatalyst (CoB/CN). As expected, hydrogen generation rate was greatly boosted owing to light irradiation. According to the results of capture experiments, photoexcited electron from g-C3N4 could enrich the electron density of CoB surface, which leads to the improvement of catalyst activity. Additionally, the light irradiation facilitates the remarkable decrease of apparent activation energy. Compared with some reported noble metal catalysts, the CoB/CN presents higher activity, especially under light irradiation.

C-Rich Graphitic Carbon Nitride with Cross Pore Channels: A Visible-Light-Driven Photocatalyst for Water Splitting

Carbon nitride is found to be an outstanding metal-free photocatalyst for photocatalytic hydrogen evolution. However, carbon nitride suffers from insufficient light absorption and wide band gap, wh...

BiOI Particles Confined into Metal-Organic Framework NU-1000 for Valid Photocatalytic Hydrogen Evolution under Visible-Light Irradiation.

Herein, a surface site engineering strategy is used to construct a porous Z-scheme heterojunction photocatalyst for photocatalytic hydrogen evolution (PHE) by integration of BiOI in a mesoporous Zr-based metal-organic framework (MOF) NU-1000. Three high-quality and highly dispersed BiOI@NU-1000 heterojunction materials are synthesized, and a set of methods is used to characterize these materials, indicating that the BiOI@NU-1000 heterojunction can retain high porosity and crystallinity of the parent NU-1000. Furthermore, the built-in electric field of the BiOI@NU-1000 composite can effectively tune the band gap, promote the separation of photoinduced charge carriers, improve photocurrent intensity, and reduce photoelectric impedance. Under visible-light irradiation, BiOI@NU-1000-2 showed the best photocatalytic performance in the field of MOF-based photocatalysts for PHE, with a hydrogen production rate of up to 610 μmol h-1 g-1. This study will open up opportunities for the construction of Z-scheme photocatalysts based on the highly porous MOF materials to inspire the development of innovative photocatalysts.

Towards Green, Enhanced Photocatalysts for Hydrogen Evolution

The constant growth of energy demand joined with the adverse effects on the global environment induced by use of fossil fuels is increasingly requiring new routes to obtain clean and renewable energy sources [...]

Ga2OSe monolayer: A promising hydrogen evolution photocatalyst screened from two-dimensional gallium chalcogenides and the derived janus

Using first-principles calculations, hydrogen evolution reaction (HER) activity on two-dimensional (2D) gallium chalcogenides monolayers GaX (X = O, S, Se, and Te) as well as the derived Janus monolayers Ga2XY (X≠Y, X/Y = O, S, Se, and Te) were systematically examined. It was found that Ga2OSe Janus monolayer with a 0.3% strain has the lowest ΔGH∗ of 0.19 eV (modified to −0.01 eV including the solvation effect) because (i) O is the most electronegative among X/Y atoms, (ii) the Ga2OSe monolayer has a larger lattice parameter with respect to GaO monolayer, and (iii) the built-in electric field is enhanced after H adsorption. The enhanced H adsorption with the lattice stretching is a result of the weaker Ga–O bond strength before H adsorption and the reduced electron fillings of anti-bonding molecular orbital formed by H 1s and O 2pz orbitals after H adsorption. The O-pz band center can be served as a descriptor to describe the HER activity trend for these p-block materials. Moreover, Ga2OSe monolayer has appropriate band alignment, distinguished optical absorption coefficient (105 cm−1), low exciton binding energy (0.71 eV), and the spontaneous HER process, indicating that it is a highly potential candidate for near-infrared photocatalyst for hydrogen production. Our research provides a novel paradigm that forming Janus structure can effectively tune the HER activity, which would guide the searching for excellent HER photocatalysts for clean hydrogen production.