Photocatalytic Water Splitting Research Articles

MOF-derived hollow octahedral CoxP/MOF-801 p-n heterojunction for efficient photocatalytic hydrogen production

Hydrogen energy produced through photocatalytic water splitting is widely recognized as a viable solution to the depletion of non-renewable energy resources and ecological contamination concerns. This work designed and synthesized the MOF-derived hollow octahedral CoxP/MOF-801 p-n heterojunction photocatalyst. According to the result of hydrogen production test, the hydrogen production amount of CoxP/MOF-801-2 could reach 25.31 mmol g−1 under light irradiation for 5 h. The hollow octahedral structure and p-n heterojunction of the photocatalyst helped to enhance the light trapping ability and promote carrier transfer, resulting in improved performance of photocatalytic hydrogen production. To sum up, the design of hollow octahedral CoxP/MOF-801 photocatalyst effectively improved the photocatalytic hydrogen production performance.

Efficient Holes Abstraction by Precisely Decorating Ruthenium Single Atoms and RuOx Clusters on ZnIn2S4 for Photocatalytic Pure Water Splitting.

Developing efficient photocatalysts for two-electron water splitting with simultaneous H2O2 and H2 generation shows great promise for practical application. Currently, the efficiency of two-electron water splitting is still restricted by the low utilization of photogenerated charges, especially holes, of which the transfer rate is much slower than that of electrons. Herein, Ru single atoms and RuOx clusters are co-decorated on ZnIn2S4 (RuOx/Ru-ZIS) to employ as multifunctional sites for efficient photocatalytic pure water splitting. Doping of Ru single atoms in the ZIS basal plane enhances holes abstraction from bulk ZIS by regulating the electronic structure, and RuOx clusters offer a strong interfacial electric field to remarkably promote the out-of-plane migration of holes from ZIS. Moreover, Ru single atoms and RuOx clusters also serve as active sites for boosting surface water oxidation. As a result, an excellent H2 and H2O2 evolution rates of 581.9 µmolg-1h-1 and 464.4 µmolg-1h-1 is achieved over RuOx/Ru-ZIS under visible light irradiation, respectively, with an apparent quantum efficiency (AQE) of 4.36% at 400nm. This work paves a new way to increase charge utilization by manipulating photocatalyst using single atom and clusters.

Two-Dimensional High-Entropy Selenides for Boosting Visible-Light-Driven Photocatalytic Performance.

High-entropy materials (HEMs) have garnered extensive attention owing to their diverse and captivating physicochemical properties. Yet, fine-tuning morphological properties of HEMs remains a formidable challenge, constraining their potential applications. To address this, we present a rapid, low-energy consumption diethylenetriamine (DETA)-assisted microwave hydrothermal method for synthesizing a series of two-dimensional high-entropy selenides (HESes). Subsequently, the obtained HESes are harnessed for photocatalytic water splitting. Noteworthy is the optimized HESes, Cd0.9Zn1.2Mn0.4Cu1.8Cr1.2Se4.5, showcasing an output rate of hydrogen of 16.08 mmol h-1 g-1 and a quantum efficiency of ca. 30% under 420 nm monochromatic LED irradiation. It is revealed that the photocatalytic performance of these HESes stems not only from the enlarged specific surface area and enhanced photogenerated charge carrier utilization efficiency but also from the promoted formation of the Cd-Hads bond, influenced by multiple principal elements on the Cd. These findings provide a guide for the design of HEMs tailored for various applications.

Lattice Distortion Induced Ta‐doped BaTiO3 for Efficient Photocatalytic Water Splitting for Hydrogen Production

AbstractBaTiO3, as a perovskite type material with excellent chemical stability and suitable conduction, has been widely studied in the field of photocatalysis. However, it can only absorb ultraviolet light because of its wide band gap. Herein, the lifetime of photogenerated electrons of BaTiO3 doped with Ta5+ can be enhanced. To study the band structure and photocatalytic performance of Ta‐doped BaTiO3, sol‐gel assisted solid‐phase method was employed to prepare BaTiO3 doped with varying Ta5+ doping amounts, and the structure characteristic and formation mechanism of the Ta‐doped BaTiO3 were analyzed. The results showed that the heat treatment temperature reached 1052.7 °C, sufficient thermodynamic conditions were obtained for Ta5+ to dope into the BaTiO3 lattice, and lattice distortion occurred in BaTiO3. Meanwhile, the particle size after doping decreased with the increase of Ta5+ doping amount. The 1.25 mol %Ta5+‐doped BaTiO3 had the lowest band gap (3.077 eV), and the photocatalytic water splitting had the best hydrogen evolution activity, which was 2.4 times that of BaTiO3. Furthermore, the conductance potential of 1.25 mol %Ta5+‐doped BaTiO3 was more negative than that of BaTiO3, which improved the thermodynamic advantage of the photocatalytic water splitting, and it had higher and more stable photoresponse and photogenerated carrier migration rate.

Interfacial B-O bonding modulated S-scheme B-doped N-deficient C3N4/O-doped-C3N5 for efficient photocatalytic overall water splitting

Photocatalytic overall pure water splitting is a promising method for generating green hydrogen energy under mild conditions. However, this process is often hindered by sluggish electron-hole separation and transport. To address this, a step-scheme (S-scheme) B-doped N-deficient C3N4/O-doped C3N5 (BN-C3N4/O-C3N5) heterojunction with interfacial B-O bonds has been constructed. Utilizing Pt and Co(OH)2 as co-catalysts, BN-C3N4/O-C3N5 S-scheme heterojunction demonstrates significantly enhanced photocatalytic activity for overall pure water splitting under visible light, achieving H2 and O2 evolution rates of 40.12 and 19.62 µmol/h, respectively. Systematic characterizations and experiments revealed the performance-enhancing effects of the enhanced built-in electric field and the interfacial B-O bonding. Firstly, the strengthened built-in electric field provides sufficient force for rapid interfacial electron transport. Secondly, by reducing the transport energy barrier and transfer distance, the interfacial B-O bonds facilitate rapid recombination of electrons and holes with relatively low redox potential via the S-scheme charge-transfer route, leaving the high-potential electrons and holes available for H+ reduction and OH− oxidation reactions. Overall, the photocatalytic efficiency of BN-C3N4/O-C3N5 S-scheme heterojunction was significantly improved, making it a promising approach for green hydrogen production through overall pure water splitting.

Graphitic Carbon Nitride Enters the Scene: A Promising Versatile Tool for Biomedical Applications.

Graphitic carbon nitride (g-C3N4), since the pioneering work on visible-light photocatalytic water splitting in 2009, has emerged as a highly promising advanced material for environmental and energetic applications, including photocatalytic degradation of pollutants, photocatalytic hydrogen generation, and carbon dioxide reduction. Due to its distinctive two-dimensional structure, excellent chemical stability, and distinctive optical and electrical properties, g-C3N4 has garnered a considerable amount of interest in the field of biomedicine in recent years. This review focuses on the fundamental properties of g-C3N4, highlighting the synthesis and modification strategies associated with the interfacial structures of g-C3N4-based materials, including heterojunction, band gap engineering, doping, and nanocomposite hybridization. Furthermore, the biomedical applications of these materials in various domains, including biosensors, antimicrobial applications, and photocatalytic degradation of medical pollutants, are also described with the objective of spotlighting the unique advantages of g-C3N4. A summary of the challenges faced and future prospects for the advancement of g-C3N4-based materials is presented, and it is hoped that this review will inspire readers to seek further new applications for this material in biomedical and other fields.

First-Principles Investigation on the Tunable Electronic Structures and Photocatalytic Properties of AlN/Sc2CF2 and GaN/Sc2CF2 Heterostructures.

Heterostructure catalysts are highly anticipated in the field of photocatalytic water splitting. AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures are proposed in this work, and the electronic structures were revealed with the first-principles method to explore their photocatalytic properties for water splitting. The results found that the thermodynamically stable AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures are indirect semiconductors with reduced band gaps of 1.75 eV and 1.84 eV, respectively. These two heterostructures have been confirmed to have type-Ⅰ band alignments, with both VBM and CBM contributed to by the Sc2CF2 layer. AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures exhibit the potential for photocatalytic water splitting as their VBM and CBM stride over the redox potential of water. Gibbs free energy changes in HER occurring on AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures are as low as -0.31 eV and -0.59 eV, respectively. The Gibbs free energy change in HER on the AlN (GaN) layer is much lower than that on the Sc2CF2 surface, owing to the stronger adsorption of H on AlN (GaN). The AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures possess significant improvements in absorption range and intensity compared to monolayered AlN, GaN, and Sc2CF2. In addition, the band gaps, edge positions, and absorption properties of AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures can be effectively tuned with strains. All the results indicate that AlN/Sc2CF2 and GaN/Sc2CF2 heterostructures are suitable catalysts for photocatalytic water splitting.

Piezoelectric Materials and Pyroelectric Materials:High Efficient Catalysts for Photoelectrochemical Water Splitting.

Directly transforming solar energy into chemical compounds via photocatalytic water splitting can continually producing hydrogen, regarded as one of the ultimate sustainable energy sources. The key point of achieving high photoelectrochemical (PEC) water splitting performance depends on the successful design and synthesis of high-efficient photocatalysts. However, the slow separation and fast recombination of photo generated charge carriers greatly limit the utilization of solar energy, resulting in low PEC water splitting efficiency. Recently, piezoelectric/pyroelectric effect assisted PEC water splitting brings new sight on improving charger separate and transfer behaviors. In this review, the recent advancements and state-of-the-art progress in piezoelectric/pyroelectric effect assisted PEC water splitting are summarized and discussed. Different types of photocatalysts are classified according to their chemical constitutions and the corresponding advantages of each type are also discussed. Furthermore, the progress of coupling piezoelectric effect and pyroelectric effect in one PEC water splitting system is also introduced. Finally, the prospects, critical challenges and promising strategies for the application of piezoelectric/pyroelectric materials in PEC water splitting are highlighted.

Solar-driven water splitting: Theoretical insights into M2Te5 (M=Al, In) monolayer photocatalysts

Two-dimensional (2D) semiconducting optical absorbers for photocatalytic applications have gained significant attention due to their unique physicochemical properties. Using density functional theory simulations, this study explores the M2Te5 (M = Al, In) monolayer, highlighting its potential as a robust optical absorber semiconductor for overall water splitting. Detailed analysis of the structural and electronic characteristics of these materials offers crucial insights into their photocatalytic potential. The study reveals that M2Te5 has an optimal band gap, favorable band edge positions, and high charge carrier mobility and transfer efficiency, essential for effective photocatalytic water splitting. The material also shows sufficient driving forces for the photoexcited carriers, particularly in facilitating the hydrogen evolution reaction under acidic conditions. Additionally, these monolayers exhibit impressive mechanical, dynamical, and thermal stabilities, with notable corrosion-resistant properties of In2Te5 against photoinduced effects.

Positive and Negative Impacts of Interfacial Hydrogen Bonds on Photocatalytic Hydrogen Evolution.

Understanding the behavior of water molecules at solid-liquid interfaces is crucial for various applications such as photocatalytic water splitting, a key technology for sustainable fuel production and chemical transformations. Despite extensive studies conducted in the past, the impact of the microscopic structure of interfacial water molecules on photocatalytic reactivity has not been directly examined. In this study, using real-time mass spectrometry and Fourier-transform infrared spectroscopy, we demonstrated the crucial role of hydrogen bond (H-bond) networks on the photocatalytic hydrogen evolution in thickness-controlled water adsorption layers on various TiO2 photocatalysts. Under controlled water vapor environments with relative humidity (RH) below 70%, we observed a monotonic increase in the H2 formation rate with increasing RH, indicating that reactive water molecules were present not only in the first adsorbed layer but also in several overlying layers. In contrast, at RH > 70%, when more than three water layers covered the catalyst surface, the H2 formation rate turned to decrease dramatically because of the structural rearrangement and hardening of the interfacial H-bond network induced during further water adsorption. This unique many-body effect of interfacial water was consistently observed for various TiO2 particles with different crystalline structures, including brookite, anatase, and a mixture of anatase and rutile. Our results demonstrated that depositing several water layers in a water vapor environment with RH ∼ 70% is optimal for photocatalytic hydrogen evolution rather than liquid-phase reaction conditions in aqueous solutions. This study provides molecular-level insights into designing interfacial water conditions to enhance photocatalytic performance.

Energy and mass flow in photocatalytic water splitting by coupling photothermal effect

Solar photocatalytic water splitting for hydrogen production represents an ideal approach to address the current energy and environmental challenges, while also achieving “carbon peak and carbon neutrality” goals. The incorporation of photothermal effect into photocatalysis enables dual utilization of both light and heat energies, resulting in improved solar-to-hydrogen efficiency. In this review, we first discussed the behavior of energy flow and mass flow, and the characteristics of photogenerated carrier throughout the photocatalytic water splitting process, with particular focus on the behaviors induced by photothermal effect. Subsequently, we elaborate on strategies for designing high-efficiency photothermal catalytic systems and novel photothermal–photocatalytic integrated systems based upon concentrating-photothermal coupling effects. We then illustrate the development and large-scale demonstrations that utilize concentrated solar irradiation. Finally, we outline the challenges and highlight the future research directions of photothermal catalysis toward hydrogen production from water. This review aims to provide fundamental references and principal strategies for efficient utilization of solar energy in photothermal catalytic processes.

Rational Design of Covalent Organic Frameworks as Photocatalysts for Water Splitting

AbstractPhotocatalytic water splitting for hydrogen production represents a crucial approach for obtaining green energy through artificial solar energy utilization, offering a sustainable method for energy generation that helps mitigate energy shortages and protect the environment. Among the numerous photocatalytic materials, covalent organic frameworks (COFs) have garnered significant attention and intensive study from researchers due to their distinctive benefits, such as porosity, pre‐design capability, and tunability at the atomic level. Significant advancements are made in the development of materials, enhancement of performance, and comprehension of mechanisms. In this review, recent advancements in COF‐based photocatalytic water splitting are spotlighted, both in half‐reactions and overall reactions, with a particular emphasis on the rational design of COF structures to regulate the materials' optical and electrical properties, as well as the fundamental processes of photocatalysis. Drawing from current research in this field, the existing challenges, and potential opportunities are also discussed for future development.

Dye-sensitized sepiolite clay as natural scaffolds for visible light driven photocatalytic hydrogen evolution

Natural clay minerals are increasingly used as superior support materials for various photocatalysts due to their excellent adsorption capacity, negative surface charge, suitable thermal/chemical stability, large specific surface area, and strong surface reactivity, resulting in low agglomeration and suppression of charge recombination. However, they are still insufficient for photocatalysis due to their low efficiency. Therefore, sensitization of clay minerals with dyes to improve the efficiency and specificity of catalysts is considered a promising route for photocatalytic applications. In this work, the effect of dye sensitization on visible light-driven photocatalytic water splitting of microfibrous sepiolite scaffolds as natural photocatalyst supports was investigated for the first time by using various xanthene dyes (eosin Y, rhodamine B and eryhtrosine B (ErB)) and triethanolamine as photosensitizers and sacrificial agents, respectively, in the absence and presence of platinum as a co-catalyst. The clay/dye system was characterized using various techniques such as X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy and energy dispersive X-rays. Sep/ErB photocatalysts produced the highest amount of hydrogen among the other Sep/dye scaffold systems because they act as an effective matrix by preventing nanoparticle aggregation and promoting electron transfer due to their excellent crystal structures and physicochemical properties.

Constructing multifunctional novel noble-metal free NiS/ZnS/g-C3N4 ternary nanocomposites for highly active superior photocatalytic water splitting

Ultrasound-assisted wet-impregnation approach and cation-exchange hydrothermal method are employed effectively to develop the ternary nanocomposites NiS/ZnS/g-C3N4 (NZ-CN) with promising photocatalytic hydrogen (H2) generation activity. Several analytical techniques are utilized to characterize the as-synthesized NiS/ZnS/g-C3N4 nanocomposites to study their physical and chemical characteristics. The H2 production activity of the synthesized photocatalysts was tested using a 250 W halogen lamp with Na2S (0.25 M) and Na2SO3 (0.35 M) as sacrificial reagents. The optimized NZ-CN7.5% (3% NiS/ZnS/7.5% g-C3N4) catalyst displayed an exceptional H₂ generation rate of 8624 μmol h⁻1 g⁻1, exceeding both, pristine g-C3N4 (by 22.1 times) and 3% NiS/ZnS (by 3 times). This represents the highest reported rate of H₂ evolution for a graphitic carbon nitride (g-C3N4) based ternary nanocomposite under simulated solar radiation. By reusing the used NZ-CN7.5% (3% NiS/ZnS/7.5% g-C3N4) photocatalyst in four consecutive runs, the stability of the catalyst was investigated, and their individual activity in the H2 production activity was assessed. This study provides valuable insights for designing efficient noble metal-free g–C3N4–based photocatalysts, which can significantly contribute to the transition to solar-driven hydrogen generation. Further, we proposed a plausible mechanism for the photocatalytic H2 generation process over the NiS/ZnS/g-C3N4 photocatalyst.

Innovative 2D materials for efficient photocatalysis: A comparative study for WSi2N4, WGe2N4, and their janus counterpart WSiGeN4 monolayers

In pursuit of environmentally friendly and effective photocatalytic materials for water splitting, this research paper presents a thorough evaluation of WSi2N4, WGe2N4, and their Janus counterpart WSiGeN4 monolayers through the application of Density Functional Theory. The study elucidates the optical, electronic, and structural characteristics of these monolayers, thereby demonstrating their potential as highly favorable contenders for applications involving photocatalytic water splitting. By means of comprehensive optimization and analysis, it is shown that these monolayers possess advantageous characteristics, such as favorable band gaps, stable work functions, and stability over a broad pH range. These attributes are of utmost importance in ensuring the effectiveness of hydrogen evolution reaction (HER). The inclusion of Janus WSiGeN4, which possesses an intrinsic mirror asymmetry, significantly improves the photocatalytic efficacy of the material. This is achieved by meeting the demands of optimal redox reaction levels in both the conduction and valence bands. In conjunction with machine learning force fields, ab initio molecular dynamics (AIMD) simulations validate the thermal stability of these monolayers at 300 K. In addition, our analysis of the optical properties reveals substantial absorption in the visible spectrum - vital for photocatalytic applications powered by solar energy. In summary, the research highlights the potential of Janus WSiGeN4, WGe2N4, and WSi2N4 monolayers as multifunctional and effective substances for forthcoming photocatalytic water-splitting systems. This advancement indicates of a significant stride in the direction of sustainable energy solution development.

A density functional theory study on the photocatalytic performance of PtS2 nanotubes with high carrier mobility for photocatalytic water splitting

In this paper, the electronic and photocatalytic properties of PtS2 nanotubes have been further investigated by means of first-principles approach. We observed that the band gap of PtS2 nanotubes increases with the increase of the radius, while the strain energy decreases with the increase of the radius. Significantly, the electron mobility of PtS2 nanotubes was 1.34 × 103cm2V-1S-1, while the hole mobility was only 15.95 cm2V-1S-1. The band edge positions of PtS2 nanotubes at pH=0 can satisfy the requirement of the water splitting redox potential. Moreover, the band gap is decreased by strain regulation which should expand the light absorption range. Based on these important findings, we expect that PtS2 nanotubes will have great potential in photocatalytic material applications.

Best practices for photocatalytic water splitting

Best practices for photocatalytic water splitting

Highly efficient Bi2Fe4O9-ZnIn2S4 Z-scheme heterojunction for piezo-photocatalytic overall water splitting under near-infrared light up to 1200 nm

Photocatalytic overall water splitting is considered as a sustainable and appealing strategy to solve the issues of energy supply and conversion. However, a critical hurdle to applying photocatalytic overall water splitting is the restricted light absorption and sluggish mobility of light-induced charge carriers in catalysts. Herein, a near-infrared light-responsive Bi2Fe4O9-ZnIn2S4 Z-scheme piezoelectric photocatalyst with a Fe-S bonded interface is constructed. This ingenious design synergistically utilizes the advantages of the Z-scheme, strong coupling interfaces, and piezoelectric field. The Bi2Fe4O9-ZnIn2S4 Z-scheme heterojunction significantly suppresses photogenerated carriers' recombine and extends photocatalytic response to the infrared light region, achieving highly efficient piezo-photocatalytic activity. Consequently, the optimized Bi2Fe4O9-ZnIn2S4 heterojunction displays an unprecedented piezo-photocatalytic H2 and O2 generation rate of 1862 and 927 μmol h−1 g−1 under sunlight illumination. This rate is approximately 4.9 and 10.0 times greater than that of photocatalysis and piezocatalysis alone. This study lays novel groundwork for developing future heterojunctions for photocatalytic water splitting.

Kinetic analysis of TiO2-based photocatalysts sensitized with chlorophyll-derived dimers for light-driven hydrogen evolution

This study focuses on the kinetic analysis of chlorophyll-based dimer photosensitizers adsorbed on Pt/TiO2 photocatalyst for light-driven hydrogen evolution. To elucidate the detailed mechanism, four photosensitizers, a carboxylated chlorin (Chl) and its dimer derivatives connecting an accessory pigment of chlorin (Chl-PPa), porphyrin (Chl-Por), and bacteriochlorin (Chl-BPPa) were synthesized and their kinetic processes in photocatalytic hydrogen evolution were investigated. The results indicate that Chl-PPa possesses the highest ability to produce photogenerated carriers, with an appropriate excited state lifetime, lowest propensity for charge recombination, and longest charge transfer lifetime. These favorable characteristics contribute to its exceptional photocatalytic activity compared with other photosensitizers. Specifically, the Chl-PPa-sensitized Pt/TiO2 photocatalyst exhibits a remarkable hydrogen generation rate of 5.36 mmol/g/h. Moreover, these photosensitizers demonstrate excellent stability and multiple-experimental consistency. This study provides significant insights into the development of dyad photosensitizers and highlights their practical significance in the field of photocatalysis. By harnessing chlorophyll, we have successfully harnessed efficient and controlled hydrogen fuel generation through photocatalytic water splitting, thus paving the way for future advancements in clean and sustainable energy production.

Emerging trends in water splitting innovations for solar hydrogen production: Analysis, comparison, and economical insights

The generation of solar H2 emerges as a promising avenue for leveraging solar energy, contributing to mitigating climate change and restricting fossil fuel combustion. The advancement of the hydrogen economy significantly pivots on the production of hydrogen as a fundamental cornerstone. This article furnishes an overview of the available water-splitting technologies for harnessing solar energy as the primary source for hydrogen production, emphasizing the significant solar-to-hydrogen (STH) conversion efficiency. Photocatalytic water splitting, Photoelectrochemical water splitting, and Photovoltaic electrochemical water splitting have been thoroughly addressed over the past five-year period. A comprehensive assessment involves the evaluation and scrutiny of these solar technologies, acknowledging their commercial viability by analyzing key indicators like STH efficiency, robustness, economic likelihood, ecological sustainability, and other innovative attributes.