Photocatalytic Hydrogen Production System Research Articles

Enhancing catalytic activity of TiO2 nanoparticles through acid treatment in Eosin-Y sensitized photohydrogen evolution reaction system

Light-driven water splitting has gained increasing attention as an eco-friendly method for hydrogen production. There is a pressing need to enhance the performance of catalysts for the commercial viability of this reaction. Many methods have been proposed to improve catalyst performance; however, an economical and straightforward approach remains a priority. This paper presents an uncomplicated technique called acid treatment, which augments the catalytic performance of nanoparticles. The method promotes a change in the catalytic reactivity by causing a deficit in electron density of Ti and O on the surface of TiO2 nanoparticles without altering their size, morphology, or crystal structure. In the Eosin Y sensitized photocatalytic hydrogen production system, nitric acid treated TiO2 (16.95 μmol/g) exhibited 1.5 times the hydrogen production compared to bare TiO2 (11.15 μmol/g).

Perovskite-based Z-scheme photocatalytic system for hydrogen production

Photocatalytic hydrogen production is recognized as a promising approach to produce greener hydrogen. The development of next-generation photocatalytic materials aims to enhance photocatalysis efficiency. Perovskite, a third-generation photocatalytic material, has gained interest in photocatalytic water splitting due to its optical stability, structural flexibility, bandgap tunability, and charge transfer efficiency. However, the perovskites are not able to achieve the targeted efficiency. Perovskite-based Z-scheme heterojunction photocatalysts can enhance efficiency. This review gives special attention to types and the formation of Z-schemes. In particular, photocatalysts involved in all-solid-state and direct Z-scheme for photocatalytic hydrogen production have been discussed.

Type-II CoMoO4/Graphdiyne heterojunction promotes visible-light-driven photocatalytic hydrogen production activity

Photocatalytic hydrogen production technology has great challenges in designing and synthesizing stable photocatalyst and inhibiting high recombination rate of carriers. In this paper, CoMoO4/GDY type-II heterojunctions were successfully constructed by coupling a new two-dimensional layered carbon material graphdiyne (GDY) with molybdate (CoMoO4), and the positive effect of GDY on photocatalytic hydrogen production system was studied. The introduction of GDY provides a large number of reaction sites for the reaction. Moreover, due to the strong light absorption and excellent electrical conductivity of GDY, the photoelectrochemical properties of molybdate (CoMoO4) are enhanced. The construction of type-II heterojunctions effectively promotes the spatial separation of photogenerated electrons and holes. The electron transfer mechanism of the photocatalyst was verified based on DFT and in-situ irradiation X-ray photoelectron spectroscopy. The experimental results show that the photocatalytic performance of CoMoO4/GDY photocatalyst is the best (121 μmol), which is 2 times and 45 times that of CoMoO4 and GDY, respectively. This study provides a unique idea for the application of GDY in the field of photocatalysis.

Nanoscale photocatalytic hydrogen production system mitigates inflammation by harnessing glycolysis waste

During tissue infection, immune cells undergo glycolysis, generating lactate that intensifies inflammation and contributes to the excessive production of reactive oxygen species (ROS) and pro-inflammatory cytokines. TiO2 serves as a photocatalyst capable of splitting water and producing H2 when activated by UV light. The study proposes the clinical application of TiO2 to combat tissue inflammation, building upon the antioxidative properties of H2. To address the limited tissue penetration depth of UV light, a TiO2-based photocatalytic H2 production system is developed, utilizing upconversion nanoparticles (UCNPs) coated with a double-shell structure of SiO2 and TiO2 (UST NPs). The efficiency of the UST NPs relies on the utilization of tissue-penetrating near-infrared (NIR) light, which is converted to UV light by the UCNP core. Additionally, the SiO2@TiO2 double-shell enhances light absorbance efficiency and photocatalytic activity. When exposed to NIR light, the UST NPs have the potential to effectively enhance H2 production by utilizing lactate as a sacrificial agent in inflamed tissues, while also facilitating the photocatalytic water splitting process. Consequently, UST NPs + NIR efficiently deplete accumulated lactate in inflamed tissues, reducing inflammation by utilizing the produced H2 to scavenge ROS and pro-inflammatory cytokines. The study explores the innovative application of TiO2-based materials as a photocatalyst, providing fresh perspectives on enhancing H2 production efficiency through the utilization of UCNPs, NIR light, and glycolysis-generated waste (lactate) in inflammation, and examining its relevance in the medical field.

Facilitating methane conversion and hydrogen evolution on platinized gallium oxide photocatalyst through liquid-like water nanofilm formation

The dehydrogenative coupling of methane, an approach aimed at converting methane into valuable chemicals like ethane and hydrogen, can be facilitated under ambient thermal conditions using semiconductor photocatalysts. Herein, we present an efficient continuous-flow photocatalytic system for methane conversion by inducing the formation of physically adsorbed water nanofilms on the surface of a Pt-loaded Ga2O3 photocatalyst. The microscopic properties of the adsorbed water were examined by diffuse reflectance infrared (IR) spectroscopy and ab initio molecular dynamics (AIMD) calculations. In comparison to the photocatalytic non-oxidative coupling of methane operated in the absence of water vapor, the presence of the interfacial water resulted in a 90-fold and 500-fold enhancement in the production rate of hydrogen and ethane, respectively. The rate of ethane formation significantly increased with increasing water vapor pressure (PH2O) under a high methane pressure (PCH4) of 200 kPa. The selectivity for ethane reached 65 % based on carbon content at PH2O = 3 kPa and PCH4 = 200 kPa. Through diffuse reflectance IR spectroscopy, volumetric water vapor adsorption analysis, and AIMD calculations conducted under the reaction conditions, we observed the formation of a liquid-like water nanolayer on the Ga2O3 surface at 300 K. Thus, this strategy of inducing water nanofilms affords a highly efficient photocatalytic system for hydrogen and ethane production.

A floatable hydrogel-based photocatalytic system for large-scale solar hydrogen production

The effectiveness of scaling up photocatalysis is constrained by the agglomeration of photocatalysts. A floatable hydrogel-based photocatalytic system at the air-water interface reported by Hyeon et al. in the current issue of Nature Nanotechnology offers benefits for scaling up solar H2 production with effective light delivery and fast gas separation.

Synergistic effect of internal electric field and ligand-to-metal charge transfer in Z-scheme CuPc/ZnIn2S4 for boosting photocatalytic hydrogen evolution

The construction of an efficient and stable photocatalytic water splitting system is the critical path and arduous challenge to convert solar energy into green hydrogen energy. Herein, a novel CuPc/ZnIn2S4 organic–inorganic hybrid photocatalyst was designed and used for photocatalytic hydrogen production from water. The separation of photogenerated electrons and holes was greatly enhanced due to the formation of the compact organic–inorganic heterointerface and the Z-scheme charge transport mechanism between CuPc and ZnIn2S4. Meanwhile, CuPc can broaden the light absorption of CuPc/ZnIn2S4 to the near infrared region, which enhances the utilization of sunlight. Moreover, the Cu metal center of CuPc could serve as the electron acceptor to accumulate photogenerated electrons via the ligand-to-metal charge transfer pathway, which further accelerates the separation of photogenerated charge carriers and enhances the photocatalytic hydrogen production efficiency. The optimal CuPc/ZnIn2S4 photocatalyst exhibited a hydrogen production rate of 151.2 μmol h−1, which was 8.1 times higher than that of pristine ZnIn2S4 under visible light irradiation. This work provides an idea for the construction of an organic–inorganic photocatalytic system for solar hydrogen production.

Fabrication of Co3O4@ZnIn2S4 for photocatalytic hydrogen evolution: Insights into the synergistic mechanism of photothermal effect and heterojunction

Integration of photothermal materials and photocatalysts can effectively improve photocatalytic hydrogen production. However, the synergistic mechanism of photothermal effect and heterojunction still need to be deeply investigated. Herein, Co3O4@ZnIn2S4 (ZIS) core–shell heterojunction was constructed as a photothermal/ photocatalytic integrated system for photocatalytic hydrogen production. The photothermal effect induced by Co3O4 boosts the surface reaction kinetic of hydrogen evolution with an apparent activation energy decrease from 42.0 kJ⋅mol−1 to 33.5 kJ⋅mol−1. The photothermal effect also increases the charge concentrations of Co3O4@ZIS, which ameliorates the conductivity of Co3O4@ZIS and thus benefits to charge transfer. In addition, a p-n junction forms between Co3O4 and ZIS and provides a built-in electric field to enhance charge separate and prolong charge life time. Benefiting from the synergy of photothermal effect and heterojunction, the photocatalytic performance of Co3O4@ZIS is significantly improved with a highest hydrogen evolution rate of 4515 μmol⋅g−1⋅h−1, which is about 3.5 times higher than that of pure ZIS. This work offers a full perspective to understand the photothermal/photocatalytic integrated conception for solar hydrogen production.

Significantly enhanced photocatalytic hydrogen production performance of MoS2/CNTs/CdS with carbon nanotubes as the charge mediators

Photocatalysis technology can efficiently produce hydrogen, which is essential for the sustainable development of clean energy. Herein, molybdenum sulfide/carbon nanotubes/cadmium sulfide (MoS2/CNTs/CdS) ternary composites are designed as catalysts to obtain an efficient photocatalytic hydrogen production system. In particular, the in-situ growth of CdS on the surface of MoS2/CNTs improves the dispersion of CdS nanoparticles, reduces the size of CdS particles, and increases the active site of photocatalytic reaction. A built-in electric field is formed between the interface between CdS and MoS2, which causes photogenerated electrons in conduction band (CB) of CdS and photogenerated holes in valence band (VB) of MoS2 to move in Z-type conduction mechanism. The excellent charge-conducting ability of CNTs reduces the recombination of photogenerated electrons and holes in CdS, further improving the hydrogen production efficiency and the stability of photocatalytic performance. Experiments showed that MoS2/CNTs/CdS (15%) have the highest hydrogen production rate (101.18 mmol h−1 g−1), which was 253 times higher than that of pure CdS. This study is expected to provide new ideas for the design and preparation of ternary hybrid photocatalysts for hydrogen production by photolysis of water.

Strategies for Improving the Photocatalytic Hydrogen Evolution Reaction of Carbon Nitride-Based Catalysts.

Due to the depletion of fossil fuels and their-related environmental issues, sustainable, clean, and renewable energy is urgently needed to replace fossil fuel as the primary energy resource. Hydrogen is considered as one of the cleanest energies. Among the approaches to hydrogen production, photocatalysis is the most sustainable and renewable solar energy technique. Considering the low cost of fabrication, earth abundance, appropriate bandgap, and high performance, carbon nitride has attracted extensive attention as the catalyst for photocatalytic hydrogen production in the last two decades. In this review, the carbon nitride-based photocatalytic hydrogen production system, including the catalytic mechanism and the strategies for improving the photocatalytic performance is discussed. According to the photocatalytic processes, the strengthened mechanism of carbon nitride-based catalysts is particularly described in terms of boosting the excitation of electrons and holes, suppressing carriers recombination, and enhancing the utilization efficiency of photon-excited electron-hole. Finally, the current trends related to the screening design of superior photocatalytic hydrogen production systems are outlined, and the development direction of carbon nitride for hydrogen production is clarified.

A highly efficient and recyclable Pt/TiO2 thin film photocatalytic system for sustainable hydrogen production

Powder samples (P) of TiO2 and Pt/TiO2 were prepared using conventional methods. Then, thin films (TF) incorporating these powders onto SiO2 films were prepared via dip coating. The powder and thin film samples were characterized by Raman spectroscopy, FESEM, elemental mapping, ICP-OES, HRTEM, UV–vis DRS, and XPS. The samples were then tested in a water-splitting reaction to generate hydrogen, using a water/methanol mixture with a 1:1 volume ratio, and two purple lamps as the radiation sources. The results suggest that incorporating the powder photocatalyst into the thin film resulted in a significant improvement in photocatalytic performance. Furthermore, the thin film samples were more stable during three consecutive runs.

Novel interfacial lateral electron migration pathway formed by constructing metallized CoP2/CdS interface for excellent photocatalytic hydrogen production

Promoting photo-induced electron transfer is one of the most efficient approaches for improving photocatalytic hydrogen production performance. Herein, we construct a novel interfacial lateral electron migration path by introducing CoP2 into CdS photocatalytic system as cocatalyst for the first time. This peculiar migration path can be attributed to two aspects: 1) the built-in electric field between CoP2 and CdS could drive carrier separation effectively; 2) the “metallized” interface serves as a special electron trap to accumulate electrons and promote them transfer along it instead of diffusion into cocatalyst. The energy-efficient interface shortens the electron migration distance and make more hot electrons participate in the reaction at the active sites with lower activation energy. As expected, the optimal hydrogen production rate of CoP2/CdS reaches up to 1071 mmol h−1 g−1, which is one of the most robust photocatalytic hydrogen production systems.

Conceptualization and application of an environmental dashboard to benchmark technical aspects in photocatalytic hydrogen production

There is a growing interest in direct solar-to-hydrogen conversion, for which photocatalysis is often considered a promising option. Although environmental advantages can be expected for such systems, several aspects should be considered when evaluating its environmental suitability. In this sense, while a complete life-cycle assessment of photocatalytic systems typically involves concerns linked to the low maturity of these technologies and its associated lack of data, this article proposes a novel methodological approach, in the form of a scoring dashboard, to environmentally benchmark technical aspects in photocatalytic hydrogen production. It is based on the identification and quantification of technical and environmental hotspots and thresholds for photocatalytic technologies targeted at producing green hydrogen. In order to illustrate the proposed approach, a case study with alternative process configurations is implemented in the methodological framework. Through this case study, the proposed configurations are assessed in terms of carbon footprint by focusing on three key aspects: sacrificial agent, power consumption, and direct CO2 emissions. In particular, two options for methanol as the sacrificial agent and two options for electricity as energy required for pumping and hydrogen compression are explored. The results show a relevant influence of the sacrificial agent source on the carbon footprint of the produced hydrogen, for which its bio-based origin would be key for the produced hydrogen to be deemed green. The proposed methodological approach is concluded to be a practical solution to benchmark photocatalytic hydrogen production systems, representing a straightforward way to define technical objectives and guide research efforts.

Photocatalytic Hydrogen Production Activity and Mechanism of New Nickel-Based Sulfur Complexes in Aqueous Solution.

The development of industry and the increase in population have caused energy shortages and environmental pollution problems. Developing clean and storable new energy is identified as a key way to solve the problems above. Hydrogen is viewed as the most potential energy carrier due to its high calorific value and pollution-free. To convert solar energy into hydrogen energy, three nickel-based catalysts, Ni(aps)(pys)2 (aps=2-amino-2-phenylacetic salicylaldehyde) (1), Ni(ads)(pys)2 (ads=aniline salicylaldehyde, pys=pyridine-2-thiolate) (2), Ni(acs)(pys)2 (acs=aniline 5-chlorosalicylaldehyde) (3), were synthesized and explored as photocatalysts for hydrogen production. A three-component photocatalytic system for hydrogen production was constructed using target complex as photocatalyst, triethanolamine (TEOA) as electron sacrificial agent and fluorescein (FL) as photosensitizer. Under the optimum conditions, about 1504 μmol of H2 can be obtained with 25 mg catalyst 2 after 3 hours of irradiation. Finally, the hydrogen-production mechanism was discussed by experimental and theoretical methods.

A novel graphdiyne (CnH2n−2) synthesis strategy: design and application of an organic/inorganic conjugated system for photocatalytic hydrogen production

The GDY/CN-EDA composite photocatalyst was constructed according to the solvent-coordination molecular template mechanism. The synergistic interaction of EDA as a hole fixator and GDY as a hole inducer enhanced the H+reduction reaction.

Promotion of photocatalytic hydrogen production by utilization of triplet excited states of organic dyes and adjustment of π–π interactions

Dye–dye and dye–PCN interactions were well-tuned by alkyl chain engineering to solve the unmatched electronic transitions in photocatalytic hydrogen production systems.

The Side-chain design of rhodamine dye and the performance research of photocatalytic hydrogen production system by the first principles

It is very important to seek visible light photosensitizers with high catalytic activity and continuous reaction stability to promote the development of the homogeneous photocatalytic hydrogen production. The study shows that the hydrogen production activity of organic dyes is higher than that of noble metal complexes under the same experimental conditions, so the pure organic dyes can effectively reduce the hydrogen production reaction cost under the premise of ensuring the photocatalytic activity. In this work, we take rhodamine photosensitizers S150 to replace S in the xanthene ring as the prototype and modify its structure by extending side chain. We further comprehensively study the electronic and optical properties of newly designed photosensitizer molecules by density functional theory (DFT). The results indicate that both S156 and S162 molecules exhibit excellent light absorption properties, such as wide range of absorption spectrum and good visible light response. The molar extinction coefficient of S156 molecule is as high as2.65×104M-1·cm-1. And the molecules that are screened out have a larger photoinduced electron transfer drive and more negative reduction potential. The reduction potential of S162 (-0.76 V vs SCE) is 22.6 % higher than that of S150, which suggests that S162 has more outstanding photocatalytic performance of hydrogen production than S150. So the dyes extended by the 3-(methoxymethyl) Heptane side chain are very promising candidates for homogeneous photocatalytic hydrogen production photosensitizer systems.

Tailoring of efficient electron-extracting system: S-scheme g-C3N4/CoTiO3 heterojunction modified with Co3O4 quantum dots for photocatalytic hydrogen evolution

• g-C 3 N 4 /CoTiO 3 S-scheme heterojunction was successfully designed and prepared. • Co 3 O 4 quantum dots were uniformly and tightly attached to the surface of the heterojunction. • The integration of S-scheme/promoter realized an efficient electronic-extracting system. • The hydrogen evolution performance of the ternary nanoreactor exceeds the binary system. Enhancing the utilization rate of photogenerated electrons has been considered as one of the bottlenecks in obtaining efficient photocatalytic hydrogen production system. This work deals with Co 3 O 4 quantum dots (CDs) modified S-scheme g-C 3 N 4 /CoTiO 3 (CN/CTO) heterojunction as a photocatalyst for water splitting. The S-scheme heterojunction retains a good carrier separation, and the built-in electric field also endows vigorous driving force for charge transport. CDs can be used as the electron acceptor, providing more active sites and achieving rapid capture of photogenerated electrons. The synergistic utilization of S-scheme structure and promoter considerably optimizes the electron transfer path, with enhanced spatial charge separation leading to more useful electrons with higher reducing capacity to participate in hydrogen evolution reaction. Using triethanolamine solution as sacrificial agent and eosin-Y as photosensitizer, the average H 2 evolution rate of optimized CN/CTO/CDs within 5 h of visible light irradiation was 1971.7 μmol g -1 h −1 , which was 102.7, 2.5 and 2.3 times higher than that of pure CN, CN/CTO and CN/CDs, respectively, with a corresponding apparent quantum efficiency was 3.39 %. Additionally, the charge transfer mechanism of S-scheme and the co-catalytic properties of CDs were further verified by the results of photoluminescence and photoelectrochemistry. This research contributes a valuable opinion for the integration of multicomponent photocatalytic systems.

Visible light – driven photocatalytic hydrogen production using Cu2O/TiO2 composites prepared by facile mechanochemical synthesis

A visible light – driven photocatalytic hydrogen production system was evaluated for methanol as a sacrificial agent using a Cu2O/TiO2 composite material. A simple ball – milling method was proposed to prepare the Cu2O/TiO2 photocatalyst, focusing on those factors influencing the photocatalytic system through a two-level 3-factorial design approach. The effect of the Cu2O loading and the operating conditions (milling time and rotation rate) for the preparation method were analysed. 1% wt. of Cu2O over TiO2 was identified as the best formulation for the composite catalyst, achieving a maximum hydrogen production of about 1 mmol/g after 5 h of irradiation. The quantum yield and the light to chemical conversion under visible light conditions for the best performing photocatalyst were 1.51% and 0.6%, respectively, which was about 1.5 – fold higher than that obtained in the presence of a simple mixture of the pure starting powders.

Synergistic effect of oxygen defect and doping engineering on S-scheme O-ZnIn2S4/TiO2-x heterojunction for effective photocatalytic hydrogen production by water reduction coupled with oxidative dehydrogenation

Aiming to the unwanted photocatalytic hydrogen production systems using sacrifice agents, a well-design S-scheme O-ZnIn2S4/TiO2-x heterojunction was fabricated to realize photocatalytic hydrogen production via water reduction coupled with organic oxidative dehydrogenation. As supported by DFT calculations and experimental analysis, owing to the synergistic effect of oxygen defect and doping engineering, a tailored energy band structure alignment with higher redox potentials and larger Fermi level potential difference are achieved, resulting in more efficient S-scheme interface charge transfer and separation efficiency, thus improving the photocatalytic activity of O-ZnIn2S4/TiO2-x. The optimal O-ZnIn2S4/TiO2-x photocatalyst shows remarkable H2 and benzaldehyde production rate of 2584.9 μmol g-1h−1 and 2880.5 μmol g-1h−1 under visible light, which are 52.5 and 66.4 times as high as those over blank TiO2. Interestingly, this coupled reaction system also displays superior H2 evolution activity compared to sacrificial reagent systems of Na2SO3/Na2S and triethanolamine. Further quenching and EPR experiments reveal that both water and organic molecules provide protons for H2 production.