Photocatalysts For Hydrogen Production Research Articles

Coal-based carbon quantum dots modified Ni-MOF and Co/Zr-MOF heterojunctions for efficient photocatalytic hydrogen evolution

NS-CQDs were synthesized by a hydrothermal method using high-sulfur lignite as the carbon source. Modification of Ni-MOF and Co/Zr-MOF using NS-CQDs to explore the performance of composite photocatalysts for hydrogen production. It was found that NS-CQDs significantly enhanced the hydrogen precipitation performance of the composite photocatalysts compared with the MOFs catalysts alone, and the highest hydrogen precipitation rate of the novel composite photocatalyst 5%NS-CQDs/NCZ2 reached 3662.68 μmol·g-1·h-1. It can be inferred from the conduction band and valence band positions of Ni-MOF, Co/Zr-MOF and NS-CQDs that a double S-type heterojunction is formed. The presence of thiophene and pyrrole nitrogen in NS-CQDs can promote electron transport, reduce the rate of electron-hole pair complexation, and improve the hydrogen evolution activity of the 5%NS-CQDs/NCZ2.

Π‐Bridge Modulations in D–π–A Conjugated Microporous Polymers to Facilitate Charge Separation and Transfer Kinetics for Efficient Photocatalysis

AbstractThe burgeoning field of conjugated microporous polymers (CMPs) has generated widespread interest due to their potential as photocatalysts for hydrogen production from water. Nevertheless, their photocatalytic performance is sometimes hindered by inadequate charge separation and transfer, coupled with rapid charge recombination. Herein, a strategy to enhance photocatalytic performance via the customization of π‐bridges through the modulation of heteroatoms in a series of donor‐π‐acceptor (D‐π‐A) CMPs is proposed. This affords optimized energy levels and improved charge separation and transfer, thus boosting photocatalytic efficiency. Among various heteroatom substitutions, S‐doped CMP (10 mg) demonstrates the highest photocatalytic hydrogen evolution rate of 203 µmol h−1 (AQY450nm = 7.4%) under visible light irradiation. Subsequent experimental analysis reveals its superior photocatalytic performance can be largely related to its minimized exciton binding energy, facilitated charge transfer efficiency, and impeded charge recombination among these heteroatom‐doped D‐π‐A CMPs. This research paves the way for the rational design and modification of organic semiconductors for advanced solar‐driven photocatalysis by promoting charge separation and transfer.

High‐Performance Microfluidic Techniques toward Nanostructuration of BODIPY and BOPHY Based CPPs Hybrid Photocatalyst for Hydrogen Production

AbstractHere, the use of high‐performance microfluidic techniques (HPMT) is reportedto afford conjugated porous polymer (CPPs) with smaller particle size and narrower particle size dispersion than the obtained by miniemulsion methodology. Specifically, polymers based on BODIPY or BOPHY dyes are synthesized by HPMT conditions and conventional miniemulsion conditions. The polymer textural properties from HPMT are notably improved, giving rise to high‐quality thin films that are photoelectrochemically characterized. Furthermore, hybrid materials of CPPs synthesized by HPMT and TiO2 inorganic semiconductor revealed enhanced photocatalytic activity in the hydrogen evolution reaction (HER). The most active hybrid UN_IEP‐7@T‐10 photocatalyst, containing 10 wt% polymer loading, achieved a hydrogen evolution rate of 3.10 mmol g−1 h−1 (ƺ = 1.13%), which is threefold higher than that of its non‐nanostructured from bulk synthesis, two‐times greater than its nanostructured by conventional miniemulsion techniques and even surpassed by 39‐times the performance of bare TiO2. It is noteworthy that both photoluminescence lifetime (τPL) and transient lifetime (τT) are not affected by the nanoestructuration of CPPs, which agrees with the preservation of the chemical structure by both synthetic methodologies. The employment of HPMT as nanostructuration strategy clearly supports the obtaining of more processable polymers for a wide range of energy applications.

Boosting intimate contact and charge transfer between carotenoid dye and Ti3C2Tx MXene for photocatalytic hydrogen production

Developing efficient heterojunction photocatalysts with improved light-harvesting capacity and high charge carrier separation rates for photocatalytic hydrogen production remains a challenge in the field of energy conversion. In this study, we synthesized two-dimensional Ti3C2Tx nanosheets through HF etching of Ti3AlC2 and combined them with carotenoid dyes (Car) with different structural characteristics using a solvent spontaneous volatilization method to construct novel Car@Ti3C2Tx Schottky heterojunctions. The intimate interface contacts between the two-dimensional Ti3C2Tx MXene and Car enhanced the light-harvesting capacity of the photocatalysts and promoted charge separation rates. The optimal sample, Car-3@Ti3C2Tx nanocomposite, exhibited excellent photocatalytic activity of 84.4 µmol h−1 g−1 for H2 production under visible light illumination. This work demonstrates the potential of earth-abundant organic Car dyes in constructing high-efficiency and low-cost photocatalysts for hydrogen production.

Harnessing intrinsic electric fields in 2D Janus MoOX (X=S, Se, and Te) monolayers for enhanced photocatalytic hydrogen evolution

Two-dimensional (2D) Janus monolayers, distinguished by their intrinsic vertical electric fields, emerge as highly efficient and eco-friendly materials for advancing the field of hydrogen evolution reactions (HER). In this study, we explore, for the first time, the potential viability of the oxygenation phase of two-dimensional Janus transition metal dichalcogenides MoOX (X = S, Se, and Te) monolayers as an exceptionally efficient photocatalyst for hydrogen production. Based on first-principles computations, we demonstrate that all three monolayers exhibit semiconductor behavior, characterized by a band gap ranging from 0.66 to 1.55 eV. This narrow band gap renders the proposed materials highly efficient at absorbing light within the visible region. Excitingly, the introduction of an electrostatic potential difference ΔΦ has granted us the ability to surpass the conventional bandgap limit (Eg≥1.23). Consequently, all monolayers exhibit favorable band alignment with respect to the vacuum level. Moreover, the calculated solar-to-hydrogen efficiency for the envisaged monolayer exceeds the established theoretical limit. Particularly, the MoOTe monolayer emerges as an infrared-light-driven photocatalyst, demonstrating a remarkable solar-to-hydrogen efficiency limit of up to 25,21% when considering the entire solar spectrum. A thorough examination of the Gibbs free energy differences across these monolayers has revealed that the values during the oxygenation phase are significantly smaller and approach the optimum, in contrast to the parental two-dimensional Janus transition metal dichalcogenides. Our results conclusively establish that the proposed materials exhibit exceptional efficiency as photocatalysts for hydrogen evolution reactions. Notably, their efficacy is demonstrated even in the lack of co-catalysts or sacrificial agents.

Unraveling the solar and visible light-induced deactivation mechanism of Pt-decorated carbon/TiO2 nanocomposite in photocatalytic hydrogen production

Photocatalytic water splitting presents an attractive and environmentally friendly method for generation of "green" hydrogen. However, the most widely used photocatalyst for hydrogen production, Pt-doped TiO2, has low stability, thus limiting its application for long term performance. In this study, the deactivation mechanism of Pt-decorated carbon TiO2 nanocomposite photocatalysts during photocatalytic hydrogen production was thoroughly investigated under solar and visible light irradiation. Solar light irradiation promoted markedly higher H2 production activity, however with lower catalyst stability. Deactivation studies using fresh catalysts/deactivated solutions and deactivated catalysts/fresh solutions point out the effect of the light used on the catalyst stability through changes on the catalyst surface as well as by the kinetics of intermediate/products formation during the reaction course. The present study revealed the importance of charge transport direction between TiO2, carbon and Pt on catalyst activity and stability and highlights the difference in visible and solar light-induced hydrogen production.

Photothermal ReO2/ReS2/Zn2In2S5 heterojunction for enhanced photocatalytic hydrogen evolution

Converting solar energy into hydrogen production is a promising strategy to alleviate the energy crisis. In this study, we developed a system for the study of photocatalytic hydrogen production performance by coupling ReO2/ReS2 community and 3D Zn2In2S5 nanoflowers. The combination of experimental results and Density functional theory (DFT) calculations show that ReO2/ReS2 not only endows the composites with photothermal properties, but also acts as a step for electron transport, enabling accelerated photocatalytic charge separation and transfer. Among them, 0.75-ReO2/ReS2/Zn2In2S5 (up to 6.75 mmol•g−1•h−1) can achieve the highest hydrogen production with Triethanolamine (TEOA) as substrate, which is 23.28 times higher than that of pure Zn2In2S5 (0.29 mmol•g−1•h−1). In addition, 0.75-ReO2/ReS2/Zn2In2S5 also exhibited certain hydrogen production performance when some representative biomasses (lactic acid, glycerol, glucose, and xylose) were used as substrates. This work provides a feasible strategy for the design of new photothermal hydrogen production photocatalysts.

Recent advances on metal-organic frameworks (MOFs) and their applications in energy conversion devices: Comprehensive review

Metal-organic frameworks (MOFs) have enticed huge interest over the years in a wide range of applications, including electrochemical energy storage/conversion devices, due to their controllable porous structure, tuneable composition, excellent thermal/chemical stabilities, and facile synthesis. However, conductivity enhancement and synthesis of redox-active MOFs are two key challenges hindering their large-scale applications in electrochemistry. Redox-active MOFs can be prepared using redox-active ligands and metal ions, which in turn leads to an additional benefit of π-stacking interactions. Conductivity improvements through favourable overlap of energy and orientation of both metal and ligand, π-π stacking, and the incorporation of a guest molecule to induce free charge carriers and reduce band gaps are key strategies. This review provides a detailed assessment of various synthesis techniques followed by post-production treatments to improve MOF's conductivity. Advancements in computational methods & machine learning for MOFs as well as the econmics of MOF's production are introduced. The use of MOFs and MOF-based nanomaterials in batteries, supercapacitors, and fuel cells, as well as the progress in using MOF and MOF-based catalysts for CO2 reduction and as a photocatalyst for hydrogen production, have been scrutinized by highlighting their benefits and shortcomings. Finally, the challenges MOFs and MOF-based materials face and their prospects when adopted as active materials in energy storage/conversion devices, as well as CO2 reduction and green hydrogen production, have also been elaborated.

Oxygen vacancy-rich high-pressure rocksalt phase of zinc oxide for enhanced photocatalytic hydrogen evolution

The generation of hydrogen as a clean energy carrier by photocatalysis, as a zero-emission technology, is of significant scientific and industrial interest. However, the main drawback of photocatalytic hydrogen generation from water splitting is its low efficiency compared to traditional chemical or electrochemical methods. Zinc oxide (ZnO) with the wurtzite phase is one of the most investigated photocatalysts for hydrogen production, but its activity still needs to be improved. In this study, an oxygen-deficient high-pressure ZnO rocksalt phase is stabilized using a high-pressure torsion (HPT) method, and the product is used for photocatalysis under ambient pressure. The simultaneous introduction of oxygen vacancies and the rocksalt phase effectively improved photocatalytic hydrogen production to levels comparable to benchmark P25 TiO2, due to improving light absorbance and providing active sites for photocatalysis without any negative effect on electron-hole recombination. These results confirm the high potential of high-pressure phases for photocatalytic hydrogen generation.

Boosting Hydrogen Production through Water Splitting: N, Ni, and N-Ni Doped ZnO Photocatalysts

This work investigates the potential of N, Ni, and N-Ni-doped ZnO as photocatalysts for hydrogen production through water splitting. Sonochemical techniques were used to synthesize these materials. In contrast to undoped or singly-doped ZnO, N-Ni-double-doped ZnO demonstrated a significantly narrower band gap (2.89 eV) and smaller crystallites (21.60 nm). This led to a remarkable doubling in the hydrogen production rate under UV-visible light irradiation. The combined effect of N and Ni doping effectively promotes efficient charge separation and enhanced light absorption, resulting in significantly increased photocatalytic activity. Furthermore, N-Ni-ZnO demonstrates exceptional stability, retaining over 95% of its initial activity after five cycles. This work paves the way for the development of cost-effective and scalable photocatalysts for sustainable solar hydrogen production.

Probing charge transfer of NiCo2O4/g-C3N4 photocatalyst for hydrogen production

Quantum dots/two-dimensional (0D/2D) semiconductor photocatalysts demonstrate wide solar light absorption region and high charge transfer efficiency. However, the relation between the interfacial electric field and the charge transfer during the photocatalytic hydrogen production process is still unclear. Here, we construct NiCo2O4 quantum dots (QDs) and NiCo2O4 nanoparticles (NPs) anchored with 2D g-C3N4 (CN) to form NiCo2O4-QDs/CN and NiCo2O4-NPs/CN heterojunctions. The hydrogen production rate of CN loaded with NiCo2O4 QDs is about 3 times higher than that of CN loaded with NiCo2O4 NPs. The electric field intensity at the NiCo2O4-QDs/CN interface is calculated to be about 15,600 V cm−2, about 9 times higher than that of NiCo2O4-NPs/CN, which could effectively drive the electrons of CN to flow toward NiCo2O4 QDs, promoting photocarriers separation and hence greatly improving the photocatalytic performance. This work provides a method to understand the relationship between interfacial electric field strength and photogenerated charges of heterostructure photocatalysts.

Interface-induced charge transfer pathway switching of a Cu2O-TiO2 photocatalyst from p-n to S-scheme heterojunction for effective photocatalytic H2 evolution

Photocatalytic hydrogen evolution from water splitting is an appealing method for producing clean chemical fuels. Cu2O, with a suitable bandgap, holds promise as a semiconductor for this process. However, the strong photo-corrosion and rapid charge recombination of Cu2O strongly limit its application in the photocatalytic fields. Herein, an S-scheme heterojunction photocatalyst composed of TiO2 and Cu2O was rationally designed to effectively avoid the photo-corrosion of Cu2O. The introduction of an interfacial nitrogen-doped carbon (NC) layer switches the heterojunction interfacial charge transfer pathway from the p-n to S-scheme heterojunction, which avoids excessive accumulation of photogenerated holes on the surface of Cu2O. Meanwhile, the hybrid structure shows a broad spectral response (300–800 nm) and efficient charge separation and transfer efficiency. Interestingly, the highest photocatalytic hydrogen evolution rate of TiO2-NC-3%Cu2O-3%Ni is 13521.9 μmol g−1 h−1, which is approximately 664.1 times higher than that of pure Cu2O. In-situ X-ray photoelectron spectroscopy and Kelvin probe confirm the charge transfer mechanism of S-scheme heterojunction. The formation of S-scheme heterojunctions effectively accelerates the separation of photogenerated electron-hole pairs and enhances redox capacity, thereby improving the photocatalytic performance and stability of Cu2O. This study provides valuable insights into the rational design of highly efficient Cu2O-based heterojunction photocatalysts for hydrogen production.

Simple Functionalization of a Donor Monomer to Enhance Charge Transfer in Porous Polymer Networks for Photocatalytic Hydrogen Evolution.

Porous polymer networks (PPNs) are promising candidates as photocatalysts for hydrogen production. Constructing a donor-acceptor structure is known to be an effective approach for improving photocatalytic activity. However, the process of how a functional group of a monomer can ensure photoexcited charges transfer and improve the hydrogen evolution rate (HER) has not yet been studied on the molecular level. Herein, we design and synthesize two kinds of triazatruxene (TAT)-based PPNs: TATR-PPN with a hexyl (R) group and TAT-PPN without the hexyl group, to understand the relationship between the presence of the functional group and charge transfer. The hexyl group on the TAT unit was found to ensure the transfer of photoexcited electrons from a donor unit to an acceptor unit and endowed the TATR-PPN with stable hydrogen production.

PbBi2Se4 monolayer: A new 2D material with outstanding electronic, photocatalytic, and optical properties

Two-dimensional layered PbBi2Se4 nanosheets were recently successfully produced [Chatterjee et al., Phys. Chem. Chem. Phys., 2014,16, 14,635–14639]. Inspired by these promising experimental findings, herein we examine the electronic and photocatalytic properties of the PbBi2Se4 monolayer by density functional calculations. The phonon dispersion of the designed monolayer validated that the PbBi2Se4 is dynamically and thermally stable. Our results showed that the PbBi2Se4 has a bandgap of 1.211/1.650 eV according to the PBE/HSE06 hybrid functional. In addition, the optoelectronic properties are altered by the application of electric field and strain, but the band gap is more significantly modified by strain than by electric field, which reduces the energy gap. Interestingly, the results of photocatalytic properties revealed that PbBi2Se4 is an effective photocatalyst for hydrogen production. Under the application of a biaxial strain of −8%, the superior absorption coefficient of PbBi2Se4 is 20.1×104cm−1, consequently, the application of strain resulted in an improvement in the absorption of light in the visible and ultraviolet ranges. Furthermore, the greatest value of the conductivity is due to the compressive strain, which is about 8.14×1015 at 3.23 eV for −8%. These results suggest that the PbBi2Se4 monolayer has potential uses in the development of sensors, solar cells, and photocatalysts.

Photocatalytic Hydrogen Evolution of TiZrNbHfTaOx High-Entropy Oxide Synthesized by Mechano-Thermal Method.

One of the most promising solutions to slow down CO2 emissions is the use of photocatalysis to produce hydrogen as a clean fuel. However, the efficiency of the photocatalysts is not at the desired level, and they usually need precious metal co-catalysts for reactions. In this study, to achieve efficient photocatalytic hydrogen production, a high-entropy oxide was synthesized by a mechano-thermal method. The synthesized high-entropy oxide had a bandgap of 2.45 eV, which coincided with both UV and visible light regions. The material could successfully produce hydrogen from water under light, but the main difference to conventional photocatalysts was that the photocatalysis proceeded without a co-catalyst addition. Hydrogen production increased with increasing time, and at the end of the 3 h period, 134.76 µmol/m2 h of hydrogen was produced. These findings not only introduce a new method for producing high-entropy photocatalysts but also confirm the high potential of high-entropy photocatalysts for hydrogen production without the need for precious metal co-catalysts.

Au decorated chemically exfoliated g-C3N4 as highly efficient visible light catalyst for hydrogen production

The demand for photocatalytic hydrogen production through water splitting is continuously increasing as the world is seeking cleaner and sustainable energy solutions. Herein, we report a comparative study of the as-fabricated Bulk g-C3N4 (BCN), chemically exfoliated g-C3N4 (ECN) and Au-decorated chemically exfoliated g-C3N4 (Au/ECN) photocatalysts for visible light-driven catalytic hydrogen production. To understand the structural, morphological, chemical, and electronic properties of the as-fabricated photocatalysts, XRD, TEM, Raman, PL, XPS, FTIR, UV and EPR analysis was performed. The as-prepared Au/ECN photocatalyst revealed exceptional visible light catalytic performance by producing 410 μmol·g−1 of hydrogen, which is 27.3- and 9.3-fold enhanced compared to those of the CN (15 μmol·g−1) and ECN (44 μmol·g−1) photocatalysts, respectively. This improved visible light-driven catalytic performance of the Au/ECN photocatalyst for hydrogen production is due to the enhanced specific surface area via the chemically exfoliated layered sheets, promoted light absorption due to the decrease in band gap via the effect of surface plasmon resonance attributable to decorated Au nanoparticles, and efficient separation of charge carriers at the interfacial contact. The photocatalytic recyclable experiments indicate excellent stability of the Au/ECN photocatalyst for H2 evolution. These findings reveal the effect of chemical exfoliation and Au decorating on the catalytic efficiency of g-C3N4-based photocatalysts, revealing potential functions for green hydrogen production under the standard visible light illumination.

S and N codoped graphene quantum dots decorated on (001)TiO2 to boost surface reaction for photocatalytic hydrogen production

Titanium dioxide (TiO2) composites are popular photocatalysts for hydrogen production from water. Here we report a composite consisting of S and N co-doped graphene quantum dots (SN-GQDs) with (001)TiO2 for photocatalytic hydrogen production. In addition to traditional advantages like light absorption promotion and charge transfer improvement, the as-prepared SN-GQDs/(001)TiO2 composite could significantly enhance the surface reaction by promotion of the formation of hydroxyl radicals, which results in the increase of the hydrogen production activity by 40 times. This work reveals the importance of surface reaction promotion by GQDs for hydrogen production, which will help researchers understand relevant systems comprehensively.

Probing Intra-Gap States Mediated Charge Dynamics of Rh-Doped Rutile TiO2 Photocatalyst by Light-Modulated Photocurrent Spectroscopies.

The intra-gap states that are introduced into a semiconducting photocatalyst via dopants and other defects have significant implications on the transport dynamics of photoexcited electrons and holes during an aqueous light-driven reaction. In this work, mechanistic understanding of Rh-doped rutile, a promising photocatalyst for hydrogen production from water, is gained by systematic assessment combining intensity-modulated photocurrent spectroscopy with sub-gap excitations and alternating-current photocurrent spectroscopy. These operando techniques not only help in discovering a new electronic transport path in Rh-rutile via surface Rh4+ species and elucidating complex interaction between electrolyte molecules and semiconductors, but also underscore the potential of utilizing multiple sub-gap excitations synergistically. This combination offers a powerful tool for acquiring insight into photo-physical and photo-chemical behaviors of photo(electro)catalysts with intra-gap states.

Green and sustainable synthesis of TPD-based donor–acceptor-type conjugated polymer photocatalysts for hydrogen production under visible light

The conjugated polymers are synthesized via greener direct C–H/C–H cross-coupling polycondensation for application in photocatalytic hydrogen production.

Accelerating photocatalytic hydrogen production by anchoring Pt single atoms on few-layer g-C3N4 nanosheets with Pt–N coordination

g-C3N4 nanosheets are modified with Pt single atoms at 1.5 at% through a low-temperature incipient wetness impregnation method followed by high-temperature pyrolysis, increasing the photocatalytic H2 production rate by two orders of magnitude.