High-efficiency Photocatalytic Hydrogen Evolution Research Articles

Preparation and Application of a Novel S-Scheme Nanoheterojunction Photocatalyst (LaNi0.6Fe0.4O3/g-C3N4).

Rapid recombination of photogenerated electrons and holes affects the performance of a semiconductor device and limits the efficiency of photocatalytic water splitting for hydrogen production. The use of an S-scheme nanoscale heterojunction catalyst for the separation of photogenerated charge carriers is a feasible approach to achieve high-efficiency photocatalytic hydrogen evolution. Therefore, we synthesized a three-dimensional S-scheme nanoscale heterojunction catalyst (LaNi0.6Fe0.4O3/g-C3N4) and investigated its activity in photocatalytic water splitting. An analysis of the band structure (XPS, UPS, and Mott-Schottky) indicated effective interfacial charge transfer in an S-scheme nanoscale heterojunction composed of two n-type semiconductors. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy confirmed that the light-induced charge transfer followed the S-scheme mechanism. Based on the capture test (EPR) of •OH free radicals, it can be seen that the enhanced activity is attributed to the S-scheme carrier migration mechanism in heterojunction, which promotes the rapid adsorption of H+ by the abundant amino sites in g-C3N4, thus effectively generating H2. The 2D/2D LaNi0.6Fe0.4O3/g-C3N4 heterojunction has a good interface and produces a built-in electric field, improving the separation of e- and h+ while increasing the oxygen vacancy. The synergistic effect of the heterostructure and oxygen vacancy makes the photocatalyst significantly better than LaNi0.6Fe0.4O3 and g-C3N4 in visible light. The hydrogen evolution rate of the composite catalyst (LaNi0.6Fe0.4O3/g-C3N4-70 wt %) was 34.50 mmol·h-1·g-1, which was 40.6 times and 9.2 times higher than that of the catalysts (LaNiO3 and g-C3N4), respectively. After 25 h of cyclic testing, the catalyst (LaNi0.6Fe0.4O3/g-C3N4-70 wt %) composite material still exhibited excellent hydrogen evolution performance and photostability. It was confirmed that the synergistic effect between abundant active sites, enriched oxygen vacancies, and 2D/2D heterojunctions improved the photoinduced carrier separation and the light absorption efficiency of visible light. This study opens up new possibilities for the logical design of efficient photodecomposition using 2D/2D heterojunctions combined with oxygen vacancies.

A high-efficiency photocatalytic hydrogen evolution system based on nickel-quinoxaline dithiolate complexes and water-soluble CdSe quantum dots

Photocatalytic water splitting of water for hydrogen evolution is one of the effective methods to obtain clean hydrogen energy. In the present work, the following materials were synthesized: two nickel quinoxaline thiolate complexes [NBu4]2 [Ni(qdt)2] (1, Bu = n-butyl, qdt = quinoxaline-dithiol), [NBu4]2 [Ni(qdt)2(NO2)2] (2) and water-soluble MPA-CdSe quantum dots (MPA-CdSe QDs, MPA = 3-mercaptopropionic acid). Subsequently, an efficient three-component photocatalytic hybrid system for hydrogen evolution was developed and tested under visible light irradiation, in which one of the target complex 1 or 2 was used as the catalyst, triethylamine (TEA) was used as the sacrificial electron donor, and MPA-CdSe QDs were used as the light harvesting reagent. The turnover numbers (TON) for H2 evolution of 8974 (vs. complex 1) and 6532 (vs. complex 2) were obtained under the optimal conditions with TEA concentration of 5 %, pH = 12, and concentration of complex 1 or 2 of 1 × 10−5 mol L−1 after 13 h of irradiation (λ > 420 nm) in pure water. The mechanism investigation indicated that critical steps of hydrogen production was formation of hydride intermediates Ni(II)-H and Ni(I)-H spices, followed by the reaction of two Ni(II)-H or Ni(I)-H species with protons generating H2 molecules and regenerating the catalyst Ni(II).

The Z-scheme of 2D structured BCN and Ti MOF heterojunctions for high-efficiency photocatalytic hydrogen evolution

Element doping and construction of heterojunction composites are the most common ways to enhance g-C3N4, which are very attractive in achieving high photocatalytic activity.

Sulfurized Ru constructed enhanced carrier separation heterojunction RuS2/Bi2WO6 for high-efficiency photocatalytic hydrogen evolution

In this paper, a new type of heterojunction photocatalyst RuS2/Bi2WO6 was prepared. The H2 yield of the RuS2/Bi2WO6 sample is up to 18.72 mmolg−1 after 4 h, which is almost five times of Bi2WO6 (4.51 mmolg−1). The structure and performance were analyzed by XRD, SEM, XPS, PL and photocatalytic experiments. It was found that the RuS2/Bi2WO6 heterojunction can not only accelerate the separation and transfer of photogenerated carriers, but also broaden their absorption band. The low-cost Ru is sulfurized to form a heterojunction with Bi2WO6, which offers a new perspective for synthesizing photocatalysts, and improves the capability of hydrogen evolution.

Perovskite-like Oxide KCuTa3O9 Decorated with Ultra-Thin Carbon Layers as a Visible-Light-Response Photocatalyst for Hydrogen Evolution

Development of a perovskite-like metal oxide (PLMO) photocatalyst with a visible light response has long been pursued in the field of photocatalysis. Herein, a PLMO KCuTa3O9 (KCTO) photocatalyst with a narrow band gap of 2.68 eV and a suitable energetic position that straddles the water redox potential has been developed. Subsequently, a 3 nm-thick carbon layer was coated uniformly on the surface of KCuTa3O9 (KCTO@C). The optimized KCTO@C-10 photocatalyst exhibits an excellent photocatalytic hydrogen evolution rate under visible light irradiation (λ > 420 nm), which is 2.87 times higher than that of pure KCTO. Systematic investigations reveal that carbon layer coating on the surface of KCTO not only expands visible light absorption but also promotes electron transfer, facilitating photoinduced electron–hole separation. In addition, an unobvious structural change of the KCTO@C-10 photocatalyst after four cycle tests demonstrates its good photochemical stability. This work offers a perspective for exploiting carbon-coated perovskite-like metal oxide photocatalysts to achieve high-efficiency photocatalytic hydrogen evolution.

Recent Advances in Cadmium Sulfide-Based Photocatalysts for Photocatalytic Hydrogen Evolution

High-efficiency photocatalytic hydrogen evolution (PHE) relies on the development of inexpensive, stable, and efficient photocatalysts. Cadmium sulfide (CdS), as a typical binary metal sulfide, has attracted considerable research attention due to its negative conduction band position, narrow band gap for visible-light response, and strong driving force for PHE. However, the construction of CdS-based photocatalysts and the PHE rate still require improvement for practical applications. In this review, recent advances in CdS-based photocatalysts for PHE via water splitting are systematically summarized. First, the semiconductor properties of CdS, including the crystal and band structures, are briefly introduced. Afterward, the fundamental mechanisms of PHE using semiconductor photocatalysts via water splitting are discussed. Subsequently, the photoactivity of bare CdS with different morphologies and structures, CdS with cocatalyst loading, and CdS-based heterojunction photocatalysts are reviewed and discussed in detail. Finally, the challenges and prospects for exploring advanced CdS-based photocatalysts are provided.

3D nanorod-like Mn0.2Cd0.8S modified by amorphous NiCo2S4 was used for high efficiency photocatalytic hydrogen evolution

The Mn0.2Cd0.8S/NiCo2S4 was prepared using an electrostatic self-assembly method.

Electron-rich pyrimidine rings enabling crystalline carbon nitride for high-efficiency photocatalytic hydrogen evolution coupled with benzyl alcohol selective oxidation

With electron-rich pyrimidine rings introduced, the obtained crystalline PCN is favored with rationally modulated band and electronic structures, resulting in efficient photocatalytic hydrogen evolution and benzyl alcohol selective oxidation.

Two-Dimensional Ultrathin Graphic Carbon Nitrides with Extended π-Conjugation as Extraordinary Efficient Hydrogen Evolution Photocatalyst.

Construction of 2D graphic carbon nitrides (g-CNx ) with wide visible light adsorption range and high charge separation efficiency concurrently is of great urgent demand and still very challenging for developing highly efficient photocatalysts for hydrogen evolution. To achieve this goal, a two-step pyrolytic strategy has been applied here to create ultrathin 2D g-CNx with extended the π-conjugation. It is experimentally proven that the extension of π-conjugation in g-CNx is not only beneficial to narrowing the bandgap, but also improving the charge separation efficiency of the g-CNx . As an integral result, extraordinary apparent quantum efficiencies (AQEs) of 57.3% and 7.0% at short (380nm) and long (520nm) wavelength, respectively, are achieved. The formation process of the extended π-conjugated structures in the ultrathin 2D g-CNx has been investigated using XRD, FT-IR, Raman, XPS, and EPR. Additionally, it has been illustrated that the two-step pyrolytic strategy is critical for creating ultrathin g-CNx nanosheets with extended π-conjugation by control experiments. This work shows a feasible and effective strategy to simultaneously expand the light adsorption range, enhance charge carrier mobility and depress electron-hole recombination of g-CNx for high-efficient photocatalytic hydrogen evolution.

High-efficiency charge separation of Z-scheme 2D/2D C3N4/C3N5 nonmetal VdW heterojunction photocatalyst with enhanced hydrogen evolution activity and stability

The interfacial charge transfer control is a key and arduous issue for propelling the migration/separation of photogenerated carriers for heterojunction photocatalysts. Here, a new 2D/2D C3N4/C3N5 nonmetal van der Waals (VdW) heterojunction is fabricated by the simple self-assembly technique in acidic medium, whose charge separation efficiency is promoted dramatically, thus being endowed with the high-efficiency photocatalytic hydrogen evolution (PHE) performance. The PHE rate reaches up to 3.33 mmol h−1 g−1 under the visible light and the apparent quantum efficiency (AQE) of 20.6% is achieved at 420 nm on the optimal 2D/2D C3N4/C3N5-5% sample. Furthermore, the 2D/2D C3N4/C3N5 nonmetal VdW heterojunction also exhibits the desired stability because there was no significant decrease after PHE reaction of 10 cycles with total 40 h. Such outstanding PHE activity and stability originate from the impelled separation of photoinduced charge carriers and the powerful interfacial interaction through forming Z-Scheme charge transfer path and π-π coupling effect between C3N4 and C3N5 nanosheets. This work takes a significant guiding and demonstration for designing and exploiting other novel nonmetallic polymer-based VdW heterojunctions in the photocatalytic application field.

Enhanced visible light response of Ag/SnO2 nanostructure enables high-efficiency photocatalytic hydrogen evolution

Construction of synergistic photocatalysis system is regarded as an important concept for effectively utilizing solar energy. Herein, Ag nanoparticles decorated SnO2 flower-like structure is designed and fabricated to synergistically realize efficient hydrogen production from water splitting. According to the results of density functional theory simulations and corresponding experimental analyses, it is identified that interfacial charge coupling of composite system intrinsically facilitate the efficient interfacial charge migration and separation. Moreover, introducing Ag nanoparticles not only expands response range of incident light for SnO2 through LSPR effect but also reduces the hydrogen adsorption free energy in the catalytic process. Eventually, contributed by the enhanced interaction between reactants and catalysts and optimized carrier behavior, Ag/SnO2 exhibits a faster hydrogen production rate than SnO2. The research method designed in this paper may provide a new idea for research of photocatalyst for photocatalytic hydrogen evolution.

Interesting molecular adsorption strategy induced surface charge redistribution of commercial TiO2: Boosting 9 times photocatalytic hydrogen production performance

A higher conduction band position and more photogenerated electrons are distinctly important for the high-efficiency photocatalytic hydrogen evolution performance. However, raising conduction band position will enlarge the band gap and reduce the production of photogenerated electrons. Herein, a super simple and efficient ammonia molecular adsorption strategy was proposed and designed to promote efficient hydrogen production by a simple ammonia molecules adsorption on commercial TiO2 surface. The experimental and theoretical calculation results indicated that aniline can be successfully adsorbed on TiO2 surface by a straightforward mechanical grinding method, and the photocatalytic hydrogen production performance of TiO2 can be improved by more than 9 times after the adsorption of aniline. This is because the adsorbed aniline can provide electrons to the TiO2 surface and lead to a charge redistribution and accumulation on the surface of TiO2. Excessive electrons make the conduction band of TiO2 bend upward, thus improving the photogenerated electron reduction ability and the photocatalytic performance of TiO2. In addition, the adsorption of aniline enables TiO2 to show light absorption in the visible region, generating more photogenerated electrons to participate in the photocatalytic water splitting reaction. In this work, the molecular adsorption strategy is not only simple to operate, but also can improve the photoreduction ability and surface charge quantity of materials. It provides a simple and efficient new method for photocatalyst modification in addition to the traditional modification methods such as doping compounds.

In situ growth of highly dispersed Ni2P quantum dots on nitrogen-vacancy g-C3N4 nanosheets for high-efficient photocatalytic hydrogen evolution

In situ growth of highly dispersed Ni2P quantum dots on nitrogen-vacancy g-C3N4 nanosheets for high-efficient photocatalytic hydrogen evolution

Hierarchically Grown Ni–Mo–S Modified 2D CeO2 for High-Efficiency Photocatalytic Hydrogen Evolution

Hierarchically Grown Ni–Mo–S Modified 2D CeO2 for High-Efficiency Photocatalytic Hydrogen Evolution

Molecular Engineering of Fully Conjugated sp2 Carbon-Linked Polymers for High-Efficiency Photocatalytic Hydrogen Evolution.

The diverse nature of organic precursors offers a versatile platform for precisely tailoring the electronic properties of semiconducting polymers. In this study, three fully conjugated sp2 carbon-linked polymers have been designed and synthesized for photocatalytic hydrogen evolution under visible-light illumination, by copolymerizing different C3 -symmetric aromatic aldehydes as knots with the 1,4-phenylene diacetonitrile (PDAN) linker through a C=C condensation reaction. The hydrogen evolution (HER) is achieved at a maximum rate of 30.2 mmol g-1 h-1 over a polymer based on 2,4,6-triphenyl-1,3,5-triazine units linked by cyano-substituted phenylene, with an apparent quantum yield (AQY) of 7.20 % at 420 nm. Increasing the degree of conjugation and planarity not only extends visible-light absorption, but also stabilizes the fully conjugated sp2 -carbon-linked donor-acceptor (D-A) polymer. Incorporating additional electron-withdrawing triazine units into the D-A polymer to form multiple electron donors and acceptors can greatly promote exciton separation and charge transfer, thus significantly enhancing the photocatalytic activity.

An all-organic TPA-3CN/2D-C3N4 heterostructure for high efficiency photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution has emerged as a promising technology to alleviate energy and environmental issues. Numerous inorganic semiconductors have been designed for efficient photocatalytic hydrogen evolution, but which are generally limited by the heavy metal contamination. All-organic semiconductors have attracted great interest due to the low cost, stable properties and tunable chemical structures. In our paper, TPA-3CN, with the superior donor-acceptor (D-A) structure, was synthesized via the molecular engineering of triphenylamine (TPA) and (3-cyano-4,5,5-trimethyl-2(5H)-furanylidene) malononitrile (3-CN). Then an all-organic TPA-3CN/2D-C3N4 heterostructure is formed by linking the TPA-3CN of stronger electron-withdrawing property with two-dimension graphitic carbon nitride (2D-C3N4), which realizes the broader solar absorption compared to the pristine CNS, as well as the quicker electron transfer rate. Significantly, the TPA-3CN/2D-C3N4 shows superior photocatalytic performance of 1558.6 μmol (twice as 2D-C3N4) under 5 h visible light irradiation (λ > 400 nm) and its apparent quantum efficiency (AQE) reaches 9.3% at 420 nm. This work offers an innovative opinion for rational development of efficient all-organic photocatalysts for solar energy utilization.

Merging Single-Atom-Dispersed Iron and Graphitic Carbon Nitride to a Joint Electronic System for High-Efficiency Photocatalytic Hydrogen Evolution.

Scalable and sustainable solar hydrogen production via photocatalytic water splitting requires extremely active and stable light-harvesting semiconductors to fulfill the stringent requirements of suitable energy band position and rapid interfacial charge transfer process. Motivated by this point, increasing attention has been given to the development of photocatalysts comprising intimately interfaced photoabsorbers and cocatalysts. Herein, a simple one-step approach is reported to fabricate a high-efficiency photocatalytic system, in which single-site dispersed iron atoms are rationally integrated on the intrinsic structure of the porous crimped graphitic carbon nitride (g-C3 N4 ) polymer. A detailed analysis of the formation process shows that a stable complex is generated by spontaneously coordinating dicyandiamidine nitrate with iron ions in isopropanol, thus leading to a relatively complicated polycondensation reaction upon thermal treatment. The correlation of experimental and computational results confirms that optimized electronic structures of Fe@g-C3 N4 with an appropriate d-band position and negatively shifting Fermi level can be achieved, which effectively gains the reducibility of electrons and creates more active sites for the photocatalytic reactions. As a result, the Fe@g-C3 N4 exhibits a highlighted intramolecular synergistic effect, performing greatly enhanced solar-photon-driven activities, including excellent photocatalytic hydrogen evolution rate (3390 µmol h-1 g-1 , λ > 420 nm) and a reliable apparent quantum efficiency value of 6.89% at 420 nm.

Ni doped noble-metal-free CdZnNiS photocatalyst for high-efficient photocatalytic hydrogen evolution reduction by visible light driving

In this paper, we report a method that the transition element nickel is doped into the interstitial position of CdZnS (CZS) nanoparticles for their photocatalytic hydrogen evolution activity boosting. It is demonstrated that CdZnNiS nanocrystalline materials (with 0.5 wt% of Ni) could achieve the highest photocatalytic H2-evolution activity of 25.4 mmol·g−1·h−1 in sulfide and sulfite solution under visible light which value is 1.16 times higher than that of Pt modified CdZnS particles (with 3 wt% of Pt). This work evidences the possibility of substitution of noble metal cocatalyst by adding a suitable inexpensive Ni to achieve high-efficient visible light driven water splitting hydrogen production.

Generated gas molecules-modified carbon nitride nanosheets with nitrogen vacancies and high efficient photocatalytic hydrogen evolution

Reaction atmosphere of preparing g-C3N4 can affect the photocatalytic activity in the electronic structure and the separation efficiency of photo-induced charge carriers. However, in the process of preparing graphitic carbon nitride, it is still a challenge to introduce an atmosphere by a simple and economic thermal-treatment method. Herein, a simple approach to preparing g-C3N4 nanosheets under generated gas molecules in a one-step calcination (CN-A) was reported. Such a one-step calcination method not only saved energy consumption, but also provided an economical way to combine a variety of favorable gases. The CN-A with more nitrogen vacancies significantly improved the separation efficiency of photo-induced electron-hole pairs. Furthermore, it formed small grain and high porosity with large surface areas. As expected, the CN-A exhibited a hydrogen evolution rate of 1198 µmol g−1 h−1 under visible-light irradiation, which was 2.5 times higher activity than the g-C3N4 calcined under nitrogen atmosphere (CN-N), as well as higher than most of the reported bulk g-C3N4. Our research provides a new insight into the reaction atmosphere employed in g-C3N4 materials in modifying chemical structure, grain size, porosity and photophysical properties.

In-situ construction of coral-like porous P-doped g-C3N4 tubes with hybrid 1D/2D architecture and high efficient photocatalytic hydrogen evolution

Developing novel methods to prepare hollow one-dimensional (1D) carbon nitride (g-C3N4) nanostructure is highly attractive in photocatalytic water splitting for hydrogen production. Herein, a simple, self-assembly synthesis of coral-like 3D porous P-doped g-C3N4 tubes (PCNT) by the combination of pyrolysis and freeze-drying method was reported. Attributed to the integrated merits of 1D tubular structure, 2D nanosheets and phosphorus doping, the as-prepared hollow PCNT exhibits superior photocatalytic activity under visible light irradiation. Owing to their higher specific surface area, enhanced light absorption, and better charge carrier separation and transfer, the maximum apparent photocatalytic hydrogen evolution rate of PCNT is 2020 μmol g−1 h−1, which is about 4.7 folds and 22.4 folds than that of g-C3N4 tubes and pristine bulk g-C3N4, respectively. Moreover, a possible photocatalytic mechanism and nanostructure formation process based on the experimental results are proposed. The novel growth strategy developed here may offer a new avenue for the rational design and synthesis of potentially efficient photocatalyst with 1D/2D integrated nanoarchitecture.