Photocatalytic H2 Evolution Activity Research Articles

Supercritical CH3OH-Triggered Isotype Heterojunction and Groups in g-C3N4 for Enhanced Photocatalytic H2 Evolution.

The structure tuning of bulk graphitic carbon nitride (g-C3N4) is a critical way to promote the charge carriers dynamics for enhancing photocatalytic H2-evolution activity. Exploring feasible post-treatment strategies can lead to effective structure tuning, but it still remains a great challenge. Herein, a supercritical CH3OH (ScMeOH) post-treatment strategy (250-300 °C, 8.1-11.8 MPa) is developed for the structure tuning of bulk g-C3N4. This strategy presented advantages of time-saving (less than 10 min), high yield (over 80%), and scalability due to the enhanced mass transfer and high reactivity of ScMeOH. During the ScMeOH post-treatment process, CH3OH molecules diffused into the interlayers of g-C3N4 and subsequently participated in N-methylation and hydroxylation reactions with the intralayers, resulting in a partial phase transformation from g-C3N4 into carbon nitride with a poly(heptazine imide)-like structure (Q-PHI) as well as abundant methyl and hydroxyl groups. The modified g-C3N4 showed enhanced photocatalytic activity with an H2-evolution rate 7.2 times that of pristine g-C3N4, which was attributed to the synergistic effects of the g-C3N4/Q-PHI isotype heterojunction construction, group modulation, and surface area increase. This work presents a post-treatment strategy for structure tuning of bulk g-C3N4 and serves as a case for the application of supercritical fluid technology in photocatalyst synthesis.

Homogeneous distribution of highly dispersed Pt species over O and P co-doped g-C3N4 and its superior photocatalytic H2 evolution activity

In this study, we synthesized O and P co-doped graphitic C3N4 (OPCN) materials by a one-step calcination method and prepared Pt/OPCN photocatalysts for the photocatalytic H2 evolution reaction. Among the Pt/OPCN catalysts with various O and P contents, Pt/OPCN2 exhibited the highest H2 evolution rate of 2198 μmol·g−1 (AQE = 7.33%), which was 1.65 times higher than that of Pt/CN (1330 μmol·g−1). Moreover, Pt/OPCN2 demonstrated excellent photocatalytic properties, such as suitable band gap (2.50eV) for visible light and efficient charge separation of photoexcited electron–hole pairs, which was confirmed by ultraviolet-visible spectroscopy, electrochemical impedance spectroscopy, photoluminescence spectroscopy, and time-resolved photoluminescence measurements. Fundamentally, the Pt species effectively interacted with neighboring P=O and C=O functional groups that optimally located defective OPCN2, resulting in a homogeneous formation of highly dispersed PtO evenly distributed over Pt/OPCN2, as confirmed by X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and density functional theory calculations. However, excessive O and P contents of OPCN3 damaged the morphological structure of g-C3N4, inducing a poor interaction between the Pt species and OPCN3 and forming isolated Pt nanoparticles, resulting in the low photocatalytic activity of Pt/OPCN3.

Ternary Cocrystal with Long‐Lived Charge‐Transfer State for Efficient Light Conversion Applications

AbstractCharge‐transfer (CT) cocrystals have attracted continuous interest for their promising optical and optoelectronic applications. To improve the performance of this class of material, a CT cocrystal with long‐lived CT excitons is highly desired. Herein, the development of a pyrene‐doped trans‐1,2‐diphenylethylene‐1,2,4,5‐tetracyanobenzene ternary cocrystal (named P‐TS‐TC) is reported. Compared to the undoped binary cocrystals (without pyrene), P‐TS‐TC exhibits a two times longer CT exciton lifetime (≈60.2 ns), and thus 8.8‐ and 16.6‐times improvement in photocurrent response and photocatalytic H2 evolution activity. By using transient photoluminescence spectroscopy, it is uncovered that the absorbed photon energy in P‐TS‐TC is localized to a lower energy CT state through an efficient energy transfer process (≈389.8 ps) between two co‐existing CT states. The CT exciton lifetime is prolonged due to the weakened CT coupling strength, as a result of the enlarged donor‐acceptor distance and the change of geometric structure. The result is expected to inspire the design of cocrystals with manipulatable CT exciton properties and to promote the potential application of multi‐component CT cocrystals.

Reconstructing delocalized π electron structure of C3N4 nanosheets for enhanced visible light photocatalytic hydrogen evolution

For improving the essential photocatalytic H2 evolution activity of C3N4, strategies via simultaneously modulating the delocalized π electron structure and defects are feasible but challenging. Herein, a C3N4 nanosheets material defined as C3N4-NS-RN with expansive delocalized π electron structure and enriched N vacancies was synthesized successfully via a facile post heat treatment. Firstly, a precursor of C3N4 nanosheets defined as C3N4-NS-PN with corrugate tri-s-triazine basal plane and abundant NHx groups in aromatic conjugate system was prepared. Fourier transform infrared spectra, X-ray photoelectron spectroscopy and nuclear magnetic resonance demonstrated C3N4-NS-PN had an enhanced delocalized π electron configuration via van der Waals coupling effect. However, the delocalization of π electrons across the basal plane was disturbed due to the corrugate conjugate plane. For further reconstructing delocalized π electron structure of C3N4-NS-PN, C3N4-NS-RN was synthesized via eliminating NHx groups and introducing enriched N vacancies in the conjugate system. Photoluminescence spectroscopy and electron paramagnetic resonance verified C3N4-NS-RN had an enhanced delocalized π electrons structure than C3N4-NS-PN. The photocatalytic H2 evolution activity of C3N4-NS-RN was steady and was about 1.8 and 6.1 times of C3N4-NS-PN and the bulk C3N4, respectively.

One-Dimensional Tubular Carbon Nitride Embedded in Ni2P for Enhanced Photocatalytic Activity of H2 Evolution

Graphitic carbon nitride is considered as an ideal semiconductor material for photocatalytic hydrogen evolution due to its suitable energy band structure, durability and environmental friendliness. To further improve the catalytic performance of g-C3N4, nickel phosphide-loaded one-dimensional tubular carbon nitride (Ni2P/TCN) was prepared by thermal polymerization and photo deposition. The beneficial effect of the one-dimensional tubular structure on hydrogen generation was mainly attributed to its larger specific surface area (increased light absorption) as well as the linear movement of the carriers, which reduced their diffusion distance to the surface and facilitated the separation of photogenerated carriers. The loading of Ni2P co-catalyst improved the visible light utilization efficiency and enabled the migration of photogenerated electrons towards Ni2P, which ultimately reacted with the enhanced adsorbed H+ on the Ni2P surface to facilitate the photocatalytic hydrogen evolution process. This study provides new clues for the further development of efficient, environmentally friendly and low-cost g-C3N4 catalysts.

MoB2 modified g-C3N4: A Schottky junction with enhanced interfacial redox activity and charge separation for efficient photocatalytic H2 evolution

The g-C3N4 material, which exhibits a sensitivity to visible light and has a band position that is appropriate for the photoreduction of H2, has garnered significant interest. However, the ability of g-C3N4 to use light for photocatalysis is restricted due to its insufficient capacity to absorb light and its poor reaction kinetics on the surface. The researchers opted for the metallic MoB2 to create a Schottky junction coupled with g-C3N4. The incorporation of MoB2 nanoparticles onto g-C3N4 enhances its light absorption capacity and promotes the efficient separation and transfer of photogenerated charge. In addition, MoB2 nanoparticles served as active sites to accelerate H2 evolution. Compared to g-C3N4, the MoB2@g-C3N4 composite exhibited a nearly 51-fold increase in H2 production rate, indicating a significant improvement in photocatalytic activity. The present investigation demonstrated the potential of metallic MoB2 as a modified material during a photocatalytic H2 evolution reaction.

Hierarchical LaTiO2N/Sn3O4 heterojunction with intimate interface contact for enhanced photocatalytic water splitting

LaTiO2N/Sn3O4 heterojunction with type-II band structure and hierarchical microstructure was constructed by decorating Sn3O4 nanoflowers and nanoflakes intimately on the surface of LaTiO2N nanosheets via a facile hydrothermal method. Compared with pure Sn3O4 and bare LaTiO2N, the photocatalytic H2 evolution activity for LaTiO2N/Sn3O4 heterostructure was boosted by ∼3 and ∼52 times, respectively, reaching 887 μmol·h−1·gcat−1. The mechanism for the elevated photocatalytic performance was systematically disclosed on the basis of comprehensive characterizations. Specifically, the introduced LaTiO2N extended the visible light absorption range to ∼600 nm, endowing Sn3O4 with more photogenerated charge carriers. Subsequently, the type-II band structure expedited the separation and migration of charge carriers, diminishing the internal recombination, thereby enhancing the photocatalytic activity. This work affords a new avenue for designing tin oxide-based and oxynitrides-based heterojunction.

Boosting the internal electron transfer of two-dimensional hybrid perovskites via fluorination of organic cation towards enhanced photocatalytic hydrogen production

Two-dimensional (2D) organic-inorganic hybrid perovskites have emerged as promising candidates for photocatalytic hydrogen production due to their unique optoelectronic properties. However, the organic cations in the interlayer of 2D perovskites generally retard the internal charge transfer due to the large interlayer van der Waals barrier for electron transfer, which defines the imperative to engineering the organic entity. Herein, taking phenethylammonium lead iodide (PEA2PbI4) as a typical example, we show that by substituting the hydrogen with fluorine atom in the para-position of the phenyl group, the internal electron transfer was promoted remarkably. The improved electron transfer is ascribed to the introduction of fluorine with strong electronegativity, which leads to interlayer polarization and almost zero-potential barrier between the organic layers. Consequently, 4-FPEA2PbI4 exhibits ca. 8.2 times higher photocatalytic H2 evolution activity than PEA2PbI4. This work establishes a paradigm for optimizing the photocatalytic properties of 2D hybrid perovskites by engineering the organic cations.

Electron‐Deficient Boron‐Doped g‐C3N4 as an Efficient and Robust Photocatalyst for Visible‐Light Driven Hydrogen Evolution from Water Splitting

AbstractElemental doping is considered to be a promising approach for altering the electronic structure, optical absorbance, and charge separation characteristics of graphitic carbon nitride (g‐C3N4, termed as CN), thus boosting its photocatalytic performance for practical applications. Herein, a series of boron (B) doped g‐C3N4 (named as BCN) photocatalysts are developed via one‐step pyrolysis of a mixture of urea and 3‐methoxycarbonyl‐5‐nitriophenylboronic acid (MCNPBA). The results show that B‐atoms have been successfully incorporated into the g‐C3N4 network. The as‐synthesized BCN‐x (x shows the weight content of MCNPBA) photocatalysts are evaluated in photocatalytic hydrogen (H2) evolution from water splitting under visible‐light (λ ≥ 420 nm). The optimized BCN‐10 sample shows a maximum H2 evolution rate of 1789.93 µmol h─1 g─1, which is 6.2 times higher than that of g‐C3N4 (289.73 µmol h─1 g─1). This is attributed to the fact that the electron‐deficient B‐atoms are lewis acids that trap electrons, which in turn expands visible‐light absorption, narrows the bandgap, and prevents the recombination of photogenerated charge carriers. Moreover, B‐doping can readily modify the valence and conduction band positions of g‐C3N4, therefore augmenting the photocatalytic H2 evolution activity. This paper presents a unique rational framework for developing other functionalized electron‐deficient elemental‐doping g‐C3N4‐based photocatalysts for practical applications in solar‐to‐fuel conversion.

Composite of formamidinium lead bromide perovskite FAPbBr3 with reduced graphene oxide (rGO) for efficient H2 evolution from HBr splitting

Solar hydrobromic acid (HBr) splitting using perovskite photocatalysts provides an attractive avenue to store solar energy into hydrogen (H2) and bromine (Br2), while an efficient photocatalytic system is still demanded. As for the semiconductor photocatalyst, formamidinium perovskites show some superiorities in structural stability, light adsorption and charge dynamics compared to their methylammonium counterparts, which are fitter for the photocatalysis process. Herein, the composite of formamidinium lead bromide perovskite (FAPbBr3) with reduced graphene oxide (rGO) is prepared using a facile photoreduction method. Under simulated sunlight irradiation (AM1.5G, 100 mW cm−2), this FAPbBr3/rGO composite (100 mg) demonstrates a noteworthy enhancement in photocatalytic H2 evolution activity of 386.7 μmol h−1, and it exhibits a notable stability with no significant decrease after 50 h of repeated tests. The single particle PL (photoluminescence) microscope is employed to study the charge dynamics, revealing that rGO in the composite effectively promotes the carrier separation. This work provides a highly efficient and stable photocatalyst for HBr splitting, and offers an effective modification strategy on lead bromide perovskites.

Co-optimization of g-C3N4 with prolonging exciton lifetime strategy and co-catalyst strategy for enhanced photocatalytic H2 evolution activity

In this work, the photocatalytic activity of g-C3N4 is co-optimized for the first time using a strategy of prolonging exciton lifetime and a co-catalyst strategy. Amorphous CoB nanoparticles are loaded on OCN-K-CN, which is an O, K doped g-C3N4 material with van der Waals heterojunctions inside. The optimized OCN-K-CN-CoB sample, containing 12 wt% CoB and 1.25% K2SO4 in precursors, show photocatalytic H2 evolution rate approximately 27 times higher than that of GCN. The mechanism of co-optimization is detailedly investigated through comparative experiments on light absorption, charge separation performance, and HER activity, with optimization strategy and CoB loading ratio as controlled variables. New roles of the two strategies have been revealed: "flux-limited reduction activity sites" for CoB and ''buffer-enhancer'' for OCN-K-CN. These new roles illustrate a hidden relationship between the optimizing effects of the two strategies and can explain a surprising advantage of this co-optimization: achieving near-optimal hydrogen evolution activity with significantly reduced co-catalyst loading ratio.

Enhanced Spin-Polarized Electric Field Modulating p-Band Center on Ni-Doped CdS for Boosting Photocatalytic Hydrogen Evolution.

It is a challenge to regulate charge separation dynamics and redox reaction kinetics at the atomic level to synergistically boost photocatalytic hydrogen (H2 ) evolution. Herein, a robust Ni-doped CdS (Ni-CdS) photocatalyst is synthesized by incorporating highly dispersed Ni atoms into the CdS lattice in substitution for Cd atoms. Combined characterizations with theoretical analysis indicate that local lattice distortion and S-vacancy of Ni-CdS induced by Ni incorporation lead to an increased dipole moment and enhanced spin-polarized electric field, which promotes the separation and transfer of photoinduced carriers. In this contribution, charge redistribution caused by enhanced internal electric field results in the downshift of the S p-band center, which is conducive to the desorption of intermediate H* for boosting the H2 evolution reaction. Accordingly, the Ni-CdS photocatalyst shows a remarkably improved photocatalytic performance with an H2 evolution rate of 20.28mmolg-1 h-1 under visible-light irradiation, which is 5.58 times higher than that of pristine CdS. This work supplied an insightful understanding that the enhanced polarization electric field governs the p-band center for efficient photocatalytic H2 evolution activity.

Construction of 1D/3D Co9S8/Mn0.3Cd0.7S Schottky heterojunction for dramatically boosted photocatalytic H2 evolution performance

One of the most crucial strategies for transforming solar energy into sustainable hydrogen energy is photocatalytic H2 evolution, and constructing an effective and durable photocatalyst remains a difficult task. Herein, a 1D/3D Co9S8/Mn0.3Cd0.7S Schottky heterojunctions were successfully fabricated by three-step hydrothermal procedure, in which 3D Mn0.3Cd0.7S solid solution particles were immobilized on the 1D tube-like Co9S8 surface, allowing for extremely effective charge separation and transfer. Through coupling Co9S8 with Mn0.3Cd0.7S, the photocatalytic H2 evolution activity and stability were significantly boosted. The 7 % Co9S8/Mn0.3Cd0.7S heterojunction possessed the highest photocatalytic activity with the H2 evolution rate of 1586.4 μmol⋅h−1, which was 3.73 times larger than that of pristine Mn0.3Cd0.7S, corresponding to 21.8 % apparent quantum efficiency (AQE) at 420 nm monochromatic light. The Schottky heterojunction mechanism between Co9S8 and Mn0.3Cd0.7S could plausibly explain the enhanced photocatalytic H2 evolution performance, according to density functional theory (DFT) calculations and ultraviolet photoelectron spectroscopy (UPS) measurements. This investigation would offer the useful insights to develop Co9S8 cocatalyst for application in photocatalytic H2 evolution.

Sulfur-doped g-C3N4 photocatalyst for significantly steered visible light photocatalytic H2 evolution from water splitting

The introduction of sulfur atoms as electron donors can effectively improve the activity of photocatalytic H2 evolution.

Multifunctional MgAl LDH/Zn-MOF S-scheme heterojunction: efficient hydrogen production, methyl red removal, and CO2 adsorption

MgAl LDH/Zn-MOF S-scheme heterojunction exhibits superior photocatalytic activity for H2 evolution, methyl red dye removal and CO2 adsorption due to increased light absorption, high surface area, good stability and recyclability.

Enwrapping ZnIn2S4 on vacancy-rich Nb2O5 nanoplates for enhanced photocatalytic hydrogen evolution

Effective separation of photogenerated charge carriers, enhanced reduction ability of conduction band electrons, and improved light harvesting ability are crucial for the significant improvement of photocatalytic H2 evolution activity over Z-scheme ZnIn2S4/v-Nb2O5 heterojunction.

Noble metal-free 0D-1D CoOx/Mn0.3Cd0.7S nanocomposites for efficient visible-light hydrogen production

Here, a series of MnxCd1-xS sosoloid composite photocatalysts with visible-light activity were first prepared by a solvothermal process. The element ratio of Cd2+ to Mn2+ was optimized to be Mn0.3Cd0.7S in MnxCd1-xS sosoloid on account of its photocatalytic activity for H2 evolution from H2O in response to visible light excitation. And on this basis, the CoOx nanopariticles were loaded on the surface of Mn0.3Cd0.7S sosoloid composite to obtain a binary p-n heterojunction of CoOx/Mn0.3Cd0.7S composite through a facile impregnation process and a high temperature sintering procedure. Benefitting from the synergistic effect of the built-in electric field, binary p-n heterojunction structure, and rearrange of the Fermi level equilibrium, the as-synthesized CoOx/Mn0.3Cd0.7S composite presents a highly enhanced photocatalytic activity for hydrogen production from H2O in response to visible light excitation, which is demonstrated to be 53.4 and 4.0 times higher than that of the primitive CdS and Mn0.3Cd0.7S, respectively. Furthermore, after 4 times circles of photocatalytic H2 production tests, the CoOx/Mn0.3Cd0.7S composite still keeps 92.0 % of the original photocatalytic activity. Considering its reasonable photochemistry stability and excellent photocatalytic activity for hydrogen evolution from H2O under with visible light excitation, the as-synthesized CoOx/Mn0.3Cd0.7S composite has potential applications in solar hydrogen production areas.

Construction novel highly active photocatalytic H2 evolution over noble-metal-free trifunctional Cu3P/CdS nanosphere decorated g-C3N4 nanosheet

Hydrogen energy possesses immense potential in developing a green renewable energy system. However, a significant problem still exists in improving the photocatalytic H2 production activity of metal-free graphitic carbon nitride (g-C3N4) based photocatalysts. Here is a novel Cu3P/CdS/g-C3N4 ternary nanocomposite for increasing photocatalytic H2 evolution activity. In this study, systematic characterizations have been carried out using techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), Raman spectra, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area analysis (BET), electrochemical impedance (EIS), and transient photocurrent response measurements. Surprisingly, the improved 3CP/Cd-6.25CN photocatalyst displays a high H2 evolution rate of 125721 μmol h−1 g−1. The value obtained exceeds pristine g-C3N4 and Cu3P/CdS by 339.8 and 7.6 times, respectively. This could be the maximum rate of hydrogen generation for a g–C3N4–based ternary nanocomposite ever seen when exposed to whole solar spectrum and visible light (λ > 420 nm). This research provides fresh perspectives on the rational manufacture of metal-free g-C3N4 based photocatalysts that will increase the conversion of solar energy. By reusing the used 3CP/Cd/g-C3N4 photocatalyst in five consecutive runs, the stability of the catalyst was investigated, and their individual activity in the H2 production activity was assessed. To comprehend the reaction mechanisms and emphasise the value of synergy between the three components, several comparison systems are built.

MoO2-C@MoS2: A unique cocatalyst with LSPR effect for enhanced quasi-full-spectrum photocatalytic hydrogen evolution of CdS

A well-designed cocatalyst structure can improve the light-harvesting and quantum efficiency of photocatalysis. A multidimensional MoO2-C@MoS2 (MOCS) cocatalyst was successfully synthesized by post-sulfidation of MoO2-C nanorods. This controlled sulfidation process effectively inhibits the undesired oxidation of MoO2, stabilizing its metallicity and creating a synergistic effect for H2 evolution. Firstly, the highly dispersed metallic MoO2 nanoparticles induce localized surface plasmon resonance effects, expanding the light-harvesting range and generating abundant hot electrons. Secondly, the build-in electrostatic field and highly conductive carbon framework facilitates efficient interfacial electrons transfer. Thirdly, the amorphous MoOx and fragmented few-layers MoS2 in MOCS provide dual active sites with superior intrinsic activity for H2 evolution. Moreover, the unique multi-interface structure of MOCS optimizes the separation and reaction of charge carriers. As a result, the 20 wt% MOCS/CdS system show an excellent quasi-full-spectrum driven photocatalytic H2 evolution activity of 48.41 mmol/h·g, with 4.03 mmol/h·g in near-infrared region (> 800 nm).

Intermediate products driven one-pot in-situ synthesis of BiOCl/WO3 heterojunction with enhanced photocatalytic hydrogen and oxygen evolution for potential industrial applications

One-pot in-situ method was one of crucial industrial techniques to construct heterojunctions, while some intermediate reaction mechanisms of photocatalysts in this procedure were not specific enough. Herein, a new intermediate products driven one-pot in-situ method was investigated for construction of BiOCl/WO3 that applied in photocatalytic water splitting. According to some characterizations, the hydrochloric acid and water were recognized as important intermediates controlling on growth of BiOCl/WO3 heterojunction. Under significant effects of Z-scheme structure and internal electric fields, the BiOCl/WO3 showed enlarged light absorption and enhanced photo-induced carriers separation ability that its O2 and H2 evolution rates were improved effectively, in which the optimal photocatalytic O2 (994.5 µmol/g∙h) and H2 evolution activity (83.4 µmol/g∙h) were ∼2.5 and 4.5 times higher than that of the single BiOCl, respectively. Due to compact interfacial connection between BiOCl and WO3 after in-situ synthesis, the heterojunction showed a high stability and recyclability for potential industrial applications. We believe that the facile synthetic method was essential for more researches on heterojunction materials and their industrial applications.