Efficient Photocatalysts For Hydrogen Evolution Research Articles

Construction of Z‐scheme heterojunction g‐C3N4/CQDs/InVO4 with broad‐spectrum response for efficient rhodamine B degradation and H2 evolution under visible light

AbstractBACKGROUNDA Z‐scheme structured photocatalyst is a highly efficient photocatalyst for hydrogen evolution and degradation of pollutants.RESULTSAn indirect Z‐scheme heterojunction g‐C3N4/CQDs/InVO4 with carbon quantum dots (CQDs) as electron mediator was constructed and was successfully synthesized using a facile hydrothermal method. The photocatalytic activity of the as‐prepared composite was evaluated in terms of hydrogen generation and degradation of rhodamine B (RhB) dye. The as‐prepared sample CV20/CQDs2 (g‐C3N4/2 wt% CQDs/20 wt% InVO4) exhibits the best photocatalytic activity towards hydrogen production and RhB degradation. Within 90 min, 99.6% of RhB is removed, and the degradation rate constant of RhB over CV20/CQDs2 is 0.06491 min−1, which is 43.9, 6.64 and 3.3 times as high as that of InVO4, g‐C3N4 and binary composite g‐C3N4/InVO4. CV20/CQDs2 exhibits H2 evolution rate of 2.169 mmol g−1 h−1, which is 26.07, 2.65 and 1.6 times as high as that of InVO4, g‐C3N4 and g‐C3N4/InVO4.CONCLUSIONSThe enhanced photocatalytic activity is attributed to two aspects. First, CQDs, as electron mediator, promote the effective separation of photogenerated electrons and holes through Z‐scheme charge transfer pathway, preserving the high redox ability of electrons and holes. Second, g‐C3N4/CQDs/InVO4 shows strong optical absorption in the full visible‐light region. © 2021 Society of Chemical Industry (SCI).

Sustainable synthesis of low-cost nitrogen-doped-carbon coated Co3W3C@g-C3N4 composite photocatalyst for efficient hydrogen evolution

The availability of low-cost noble-metal-free photocatalyst is vital for sustainable and large-scale hydrogen production. Herein, N-doped-carbon coated Co3W3C nanocrystallines (NC-Co3W3C), a novel cocatalyst, are anchored onto g-C3N4, forming a (NC-Co3W3C@g-C3N4) composite photocatalyst for application in photocatalytic hydrogen evolution reaction (HER). Under visible light irradiation, NC-Co3W3C@g-C3N4 photocatalyst shows a remarkable photocatalytic HER rate of 1332 μmol h−1 g−1, achieving 148 times higher than pristine g-C3N4 photocatalyst and 89.22% as high as Pt/g-C3N4 photocatalyst (the expensive noble-metal-based catalyst). The mechanism investigation via systematic experimental and theoretical analysis (Density Functional Theory (DFT) calculation) suggests that the high photocatalytic efficiency could be attributed to boosted light absorption and accelerated HER kinetic that is resulted from the enhanced conducitity, reinforced stability, and the suitable H adsorption free energy introduced by the cocatalyst. This work suggests the construction of highly efficient catalyst for photocatalytic hydrogen evolution is chemically and economically viable for the green hydrogen economy.

Interfacial chemical bond and internal electric field modulated Z-scheme Sv-ZnIn2S4/MoSe2 photocatalyst for efficient hydrogen evolution

Construction of Z-scheme heterostructure is of great significance for realizing efficient photocatalytic water splitting. However, the conscious modulation of Z-scheme charge transfer is still a great challenge. Herein, interfacial Mo-S bond and internal electric field modulated Z-scheme heterostructure composed by sulfur vacancies-rich ZnIn2S4 and MoSe2 was rationally fabricated for efficient photocatalytic hydrogen evolution. Systematic investigations reveal that Mo-S bond and internal electric field induce the Z-scheme charge transfer mechanism as confirmed by the surface photovoltage spectra, DMPO spin-trapping electron paramagnetic resonance spectra and density functional theory calculations. Under the intense synergy among the Mo-S bond, internal electric field and S-vacancies, the optimized photocatalyst exhibits high hydrogen evolution rate of 63.21 mmol∙g−1·h−1 with an apparent quantum yield of 76.48% at 420 nm monochromatic light, which is about 18.8-fold of the pristine ZIS. This work affords a useful inspiration on consciously modulating Z-scheme charge transfer by atomic-level interface control and internal electric field to signally promote the photocatalytic performance.

Ultra-Thin Red Phosphor Nanosheets as an Efficient Photocatalyst for Hydrogen Evolution Under Visible Light

Ultra-Thin Red Phosphor Nanosheets as an Efficient Photocatalyst for Hydrogen Evolution Under Visible Light

Metal-free Synthesis of Pyridyl Conjugated Microporous Polymers for Photocatalytic Hydrogen Evolution

Developing efficient, stable and sustainable photocatalysts for water splitting is one of the most significant methods for generating hydrogen. Conjugated microporous polymers, as a new type of organic semiconductor photocatalyst, have adjustable bandgaps and high specific surface areas, and can be synthesized using diverse methods. In this work, we report the design and synthesis of a series of pyridyl conjugated microporous polymers (PCMPs) utilizing polycondensation of aromatic aldehydes and aromatic ketones in the presence of ammonium acetate. PCMPs with different chemical structures were synthesized via adjusting monomers with different geometries and contents of nitrogen element, which could adjust the bandgap and photocatalytic performance. Photocatalytic hydrogen evolution rate (HER) up to 1198.9 μmol·h−1·g−1 was achieved on the optimized polymer with a specific surface area of 312 m2·g−1 under UV-Vis light irradiation (λ>320 nm). This metal-free synthetic method provides a new avenue to preparing an efficient photocatalyst for hydrogen evolution.

Formation of noble-metal-free 2D/2D ZnmIn2Sm+3 (m = 1, 2, 3)/MXene Schottky heterojunction as an efficient photocatalyst for hydrogen evolution

Ternary chalcogenides ZnmIn2S3+m (m = 1–3) has great potential in photocatalytic hydrogen evolution reaction if their low solar-to-hydrogen conversion efficiency and expensive co-catalyst assistance can be overcome. Herein, we adopt MXene (Ti3C2Tx) nanosheets as the noble-metal-free cocatalyst substrate to support the in situ growth of ultrathin ZnmIn2S3+m nanosheets, expediting charge separation and mobility, large surface area surface and hydrophilicity. Particularly, the Schottky junction formed at ZnmIn2S3+m/MXene interface induces the electrons transfer to MXene nanosheets timely and inhibits the backflow, further promote the separation of photogenerated charge carriers. This mechanism of the photocatalytic H2 evolution was further evidenced by the DFT calculations and experimental results. As a result, 2D/2D ZnmIn2S3+m/MXene exhibits good stability and an outstanding H2 yield under visible light irradiation, especially for Zn2In2S5/MXene (2.5 wt% of MXene), which is 2.67 times higher than that of pristine Zn2In2S5.

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.

Mixed Metal-Metal Organic Frameworks (MM-MOFs) and Their Use as Efficient Photocatalysts for Hydrogen Evolution from Water Splitting Reactions

Mixed Metal-Metal Organic Frameworks (MM-MOFs) and Their Use as Efficient Photocatalysts for Hydrogen Evolution from Water Splitting Reactions

Polyoxometalate Template-Based Synthetic Strategy to Prepare Ni, Mo Co-Doped CdS for Efficient Photocatalytic Hydrogen Evolution from Water Splitting

In this work, a novel polyoxometalate template-based strategy was applied to construct the bi-metal-doped CdS photocatalysts. NiMo6 polyoxometalate template precursor was applied for the preparation of Ni, Mo co-doped CdS photocatalysts (NiMo-CdS). The structures of the materials were explored by XRD, SEM, HRTEM, HAADF, element mapping, XPS, Raman spectrum and UV-vis DRS. Moreover, the results of the UV-vis spectrum showed that NiMo-CdS exhibited an enhanced performance on light absorption. The results of photocatalytic hydrogen evolution from water splitting demonstrated that the NiMo-CdS showed higher efficiency on hydrogen evolution than noble-metal Pt-doped CdS. The reason could be ascribed to the enhanced light absorption ability and charge separation after Ni and Mo were introduced, which could also act as co-catalysts. The apparent quantum yield (AQY) efficiency could reach 42% at 365 nm. This work proposed a novel and inexpensive method to synthesize the bi-metal (Ni, Mo) decorated CdS photocatalysts for efficient hydrogen evolution from water splitting.

Novel Aggregation-Induced Emission Materials/Cadmium Sulfide Composite Photocatalyst for Efficient Hydrogen Evolution in Absence of Sacrificial Reagent.

This work focuses on the development of a novel organic–inorganic photoactive material composited by aggregation-induced emission luminogens (AIE) and CdS. Tetraphenylethene-based AIE (TPE-Ca) is synthesized on CdS to form CdS/TPE-Ca electrode, due to its suitable band structure and potential capability of renewable energy production. The CdS/TPE-Ca electrode presents over three-fold improved photocurrent density and dramatically reduced interfacial resistance, compared with the pure CdS electrode. In addition, the engineering of the band alignment allows the holes to accumulate on the valance band of TPE-Ca, which would partially prevent the CdS from photo-corrosion, thus improving the stability of the sacrificial-free electrolyte photoelectrochemical cell.

Direct observation of dynamic interfacial bonding and charge transfer in metal-free photocatalysts for efficient hydrogen evolution

Herein, we employed a simple approach for incorporating covalent triazine frameworks (CTF) with ultrathin black phosphorus (BP) nanosheets, resulting in one of the highest hydrogen evolution activities (17.1 mmol h−1 g−1) among all reported metal-free photocatalysts. More importantly, a detailed mechanistic study on dynamic charge transfer and interfacial bonding was conducted by an in-situ irradiation X-ray photoelectron spectroscopy (SI-XPS). The related results clearly reveal that the interfacial PC bonding between ultrathin BP and CTFs is crucial for promoting both photocatalytic activity and stability. More specifically, under light irradiation, the interfacial PC bonds were remarkably enhanced, which efficiently accelerate the photo-generated electron transfer from CTF to BP surfaces for hydrogen evolution reactions. Moreover, owing to the electron enrichments on BP for effectively restraining surface oxidation, the photocatalytic stability of BP/CTF has also been significantly improved. This work not only reported an effective way for fabricating highly efficient metal-free photocatalysts, but also provided the unique insights into the fundamental understanding of the intrinsic mechanisms during photocatalytic reactions.

Heterojunction of CdS Nanocapsules–WO3 Nanosheets Composite as a Stable and Efficient Photocatalyst for Hydrogen Evolution

CdS based nanocomposites are well reported for photocatalytic hydrogen evolution reactions because of their favorable band edge potentials. The preparation of well dispersed photocatalyst plays an ...

CdS Nanospheres Decorated with NiS Quantum Dots as Nobel-Metal-Free Photocatalysts for Efficient Hydrogen Evolution

Noble-metal-free photocatalysts have attracted tremendous interest in recent years. Among them, cadmium sulfide (CdS) has been considered as one of the most important photocatalysts with potential ...

In-situ construction of ternary Ti3C2 MXene@TiO2/ZnIn2S4 composites for highly efficient photocatalytic hydrogen evolution

Facing the demand of cleaning energy, the development of efficient photocatalysts for hydrogen evolution is a promising way to realize solar-to-chemical energy conversion for solving energy crisis. Hence, a novel hierarchical Ti3C2 MXene@TiO2/ZnIn2S4 photocatalyst with rapid charge transfer channels was constructed by two-step hydrothermal for efficient hydrogen production, adopting hydrothermal oxidation to in-situ synthesize Ti3C2 MXene embedded with TiO2 nanosheets (M@TiO2), which was applied to load ZnIn2S4 (ZIS). The hybridized photocatalyst with optimized ZIS amount had a hydrogen generation rate of 1185.8 μmol/g/h, which was higher than that of M@TiO2 and pure ZIS. That was originated from the outstanding light harvesting of ZIS and Ti3C2, sufficient active sites of Ti3C2, intimate interfacial contact, and efficient separation and transfer of photogenerated charges via heterojunction. The favorable and rapid charge transfer routes included type-II heterojunction between ZIS and TiO2 nanosheets, Schottky junction of Ti3C2/semiconductor, and metallic Ti3C2 with high conductivity. This work revealed the Schottky junction forming between ZIS and Ti3C2, and hierarchical M@TiO2 could be served as advantageous platform and efficient cocatalyst to construct MXene-based photocatalyst.

Mesoporous Pt/La0.02Na0.98TaO3 nanocomposites as efficient photocatalyst for hydrogen evolution

Mesoporous La0.02Na0.98TaO3 and Pt/La0.02Na0.98TaO3 at various Pt concentration (0.5–2 %) were synthesized through Pluronic F-127 Assisted sol-gel approach and the as-made materials were calcinated at 700 °C for 8 h. The obtained photocatalysts have been employed for the photocatalytic H2 evolution in the existence of glycerol as an electron donor. The TEM image of the mesoporous Pt/La0.02Na0.98TaO3 was well orderly orthorhombic-shaped morphology with smooth crystal surfaces with small particle size about 20−30 nm. XRD findings revealed that mesoporous La0.02Na0.98TaO3 and Pt/La0.02Na0.98TaO3 nanocomposites were properly indexed for structural orthorhombic. The surface area of mesoporous La0.02Na0.98TaO3 was determined around 220 m2 g−1; which reduced to 198 m2 g-1 with the introduction of 2%Pt into the pores. The H2 evolution over 1.5 % Pt/La0.02Na0.98TaO3 nanocomposite was greater 1350 times that mesoporous La0.02Na0.98TaO3 nanocomposite. The maximum H2 evolution rate over the 1.5 %Pt/La0.02Na0.98TaO3 nanocomposite was nearly 1094-fold higher than that the La0.02Na0.98TaO3 photocatalyst. The fabrication of mesoporous Pt/La0.02Na0.98TaO3 nanocomposites through a sol-gel assisted Pluronic F-127 template approach with small particle sizes, high crystallinity and large surface area are an efficient approach to promote H2 evolution. The enhancement of photocatalytic H2 evolution over mesoporous Pt/La0.02Na0.98TaO3 compared with La0.02Na0.98TaO3 were confirmed by photoelectrochemical and photoluminescence measurements. The reducibility and stability of the mesoporous Pt/La0.02Na0.98TaO3 nanocomposites can be employed as excellent photocatalysts in potential applications for H2 evolution.

Flexible self-supporting bifunctional [TiO2/C]//[Bi2WO6/C] carbon-based Janus nanofiber heterojunction photocatalysts for efficient hydrogen evolution and degradation of organic pollutant

A novel [TiO2/C]//[Bi2WO6/C] carbon-based Janus nanofiber heterojunction photocatalyst (denoted as JNHP) was designed and constructed via conjugate electrospinning combined with subsequent calcination process. The JNHP with unique Janus structure has two sides: one side is TiO2/C nanofiber which responds to ultraviolet light, the other side is Bi2WO6/C nanofiber responding to visible light, thus effectively utilizing sunlight. JNHP possesses excellent bi-functionality of photocatalytic hydrogen production and methylene blue (MB) degradation. Hydrogen production rates of JNHP reach respectively as high as 11.58 and 16.32 mmol h−1 g−1 under visible light and simulated sunlight irradiation, and no noble metal is needed to add as cocatalyst in the process of hydrogen production, and further the photo-degradation rates of MB respectively are 93.3% (160 min) and 97.9% (140 min). Compared with counterpart TiO2/C and Bi2WO6/C carbon-based nanofiber photocatalysts, enhanced photocatalytic performance of JNHP mainly results from the synergistic effect of unique heterojunctions between TiO2 and Bi2WO6 and one-dimensional conductive carbon nanofiber (CNFs). Furthermore, JNHP with one-dimensional flexible self-supporting structure can be easily separated from the solution and has excellent recyclable stability. The proposed designing philosophy and preparation approach have guiding significance for the development of other one-dimensional bifunctional nanofiber photocatalysts.

Fabrication of antennae-like nanoheterostructure attached by porphyrin for increased photocatalytic hydrogen generation and electron transfer mechanism

In order to obtain a highly efficient photocatalyst for hydrogen evolution, an excellent photo active molecule, tetra (p-carboxylphenyl) porphyrin (TCPP) was introduced and orientedly attached on an antennae-like Cu2O/NiO heterostructure. Subsequently, heterogeneous Cu2O/NiO/TCPP nanocomposites were achieved. Assembly mechanism of the nanocomposites was investigated in detail. The results showed that, by coordination interaction and hydrogen bond, TCPP molecules can be strongly assembled onto the NiO-riveted Cu2O. Because of strong interaction among Cu2O, NiO and TCPP, and the enhanced light absorption, quick transfer of more photo-generated electrons can be achieved. Furthermore, the nanocomposite displayed a higher photocatalytic activity compared with other contrast materials (Cu2O/NiO/NiTCPP, Cu2O/NiO, Cu2O et al.). It was attributed to the improved separation of charges as well as light absorption, which was originated from the well-matched band structure and special heterogeneous interface. This study will open up new perspectives for the fabrication and application of heterojunction photocatalysts.

Covalent-organic framework based Z-scheme heterostructured noble-metal-free photocatalysts for visible-light-driven hydrogen evolution

A COF-based Z-scheme heterostructure hybrids (α-Fe2O3/TpPa-2-COF) for noble-metal-free photocatalytic hydrogen evolution.

Nickel-decorated g-C3N4 hollow spheres as an efficient photocatalyst for hydrogen evolution and oxidation of amines to imines

Photocatalysts composed of earth-abundant elements are highly desired for photocatalytic hydrogen evolution as well as oxidation of amines to imines without the requirement of precious metals.

A novel hierarchical Bi2MoO6/Mn0.2Cd0.8S Heterostructured Nanocomposite for Efficient Visible-light hydrogen production

In this work, a series of MnxCd1-xS solid solutions as efficient photocatalysts for hydrogen evolution with visible light response were synthesized via a co-precipitation method firstly. Then, the hierarchical Bi2MoO6/Mn0.2Cd0.8S heterostructured composite was prepared by combining Mn0.2Cd0.8S composite with Bi2MoO6 nanocrystalline through a hydrothermal process. The optimized Mn0.2Cd0.8S composite's photocatalytic activity is more than 3 times of pristine CdS and the prepared Bi2MoO6/Mn0.2Cd0.8S nanocomposites exhibited a significantly improved photocatalytic activity for hydrogen evolution from water with visible light response comparing with single Mn0.2Cd0.8S composite. The optimized photocatalytic activity of Bi2MoO6/Mn0.2Cd0.8S composite is around 10 times of pristine CdS. The excellent photocatalytic activity of Bi2MoO6/Mn0.2Cd0.8S composite might be ascribed to the well-matched energy band structures of the Bi2MoO6 and Mn0.2Cd0.8S. Furthermore, the heterojunctions in Bi2MoO6/Mn0.2Cd0.8S composite might also do some contributions to improve its photocatalytic activities to some extent. A possible photocatalytic mechanism was proposed. Due to its excellent photocatalytic activity and good stability for hydrogen evolution from water, the obtained hierarchical Bi2MoO6/Mn0.2Cd0.8S composite has potential application in photocatalytic hydrogen evolution from water by using solar power.