Photocatalytic H2 Evolution Research Articles

Organic‐Inorganic Hybrid Material for Photocatalytic H₂ Evolution: Electron Shuttling between Photoresponsive Nanocomposite and Co(II) Redox Mediator

AbstractIn this report, a conductive polymer encapsulated metal oxide photocatalyst is developed through a straightforward insitu synthesis method wherein, polythiophene is incorporated with TiO2 nanoparticles which imparts enhanced visible‐light absorption to the samples and significantly improves the efficiency of charge transfer resulting due to the vacancy defects and high conductivity, ultimately leading to exceptional performance in H2 production. Significantly, the rate of H2 production was enhanced even further through the deposition of simple redox mediator. The introduction of Co2+ facilitates the transfer of photogenerated holes from the valence band by its conversion from +2 to +3 oxidation state which further enables the oxidation mechanism. The recombination rate of excitons has been significantly reduced due to the efficient transfer of photogenerated holes and the rate of photocatalytic H2 production is improved. Interestingly, the valence states and local atomic structure of the Ti species in the synthesized sample were ascertained through the utilization of Ti K‐edge XANES and EXAFS analysis, which validated the energy position.

Joint Electrons and Photons Transfer from Dual‐Functional WO3:Yb,Er to Zn0.5Cd0.5S for Efficient H2 Evolution

AbstractUtilization of the near‐infrared (NIR) light in the solar spectrum is critical for efficiency improvement of photocatalytic H2 evolution. However, common semiconductors have low response to the NIR light and narrow bandgap semiconductors have inappropriate redox potentials. Here, the study presents a new dual‐functional up‐conversion strategy in one sensitizer for promoting photocatalytic hydrogen production reactions by converting NIR light to visible light and high‐energy electrons simultaneously, via photon‐photon conversion and photo‐electronic process, respectively. Using WO3:Yb,Er as the sensitizer and Zn0.5Cd0.5S as the hydrogen evolution reaction catalyst, a photocatalytic hydrogen release rate of 24.3 mmol g−1 h−1 under simulated solar‐light has been achieved without using any co‐catalyst. After loading Ni2P as a co‐catalyst, the photocatalytic hydrogen production performance can be further improved to 41.3 mmol g−1 h−1 at 10 °C and 93.3 mmol g−1 h−1 under non‐temperature‐controlled conditions, exceeding most photocatalysts. This work offers a new strategy to improve the NIR light utilization of the solar‐light for promoting photocatalytic hydrogen generation through synergistic photo‐optical, photo‐electronic, and photo‐thermal effects.

Interfacial coordination bonds accelerate charge separation for unprecedented hydrogen evolution over S-scheme heterojunction

Inspired by natural photosynthesis, fabricating high-performance S-scheme heterojunction is regarded as a successful tactic to address energy and environmental issues. Herein, NH2-MIL-125(Ti)/Zn0.5Cd0.5S/NiS (NMT/ZCS/NiS) S-scheme heterojunction with interfacial coordination bonds is successfully synthesized through in-situ solvothermal strategy. Notably, the optimal NMT/ZCS/NiS S-scheme heterojunction exhibits comparable photocatalytic H2 evolution (PHE) rate of about 14876.7 μmol h−1 g−1 with apparent quantum yield of 24.2% at 420 nm, which is significantly higher than that of recently reported MOFs-based photocatalysts. The interfacial coordination bonds (Zn–N, Cd–N, and Ni–N bonds) accelerate the separation and transfer of photogenerated charges, and the NiS as cocatalyst can provide more catalytically active sites, which synergistically improve the photocatalytic performance. Moreover, theoretical calculation results display that the construction of NMT/ZCS/NiS S-scheme heterojunction also optimize the binding energy of active site-adsorbed hydrogen atoms to enable fast adsorption and desorption. Photoassisted Kelvin probe force microscopy, in-situ irradiation X-ray photoelectron spectroscopy, femtosecond transient absorption spectroscopy, and theoretical calculations provide sufficient evidence of the S-scheme charge migration mechanism. This work offers unique viewpoints for simultaneously accelerating the charge dynamics and optimizing the binding strength between the active sites and hydrogen adsorbates over S-scheme heterojunction.

Dipole polarization modulating of vinylene-linked covalent organic frameworks for efficient photocatalytic hydrogen evolution

Photocatalytic hydrogen (H2) evolution using covalent organic frameworks (COFs) is an attractive and promising avenue for exploration, but one of its big challenges is low photo-induced charge separation. In this study, we present a straightforward and facile dipole polarization engineering strategy to enhance charge separation efficiency, achieved through atomic modulation (O, S, and Se) of the COF monomer. Our findings demonstrate that incorporating atoms with varying electronegativities into the COF matrix significantly influences the local dipole moment, thereby affecting charge separation efficiency and photostability, which in turn affects the rates of photocatalytic H2 evolution. As a result, the newly developed TMT-BO-COF, which contains highly electronegative O atoms, exhibits the lowest exciton binding energy, the highest efficiency in charge separation and transportation, and the longest lifetime of the active charges. This leads to an impressive average H2 production rate of 23.7 mmol g−1 h−1, which is 2.5 and 24.5 times higher than that of TMT-BS-COF (containing S atoms) and TMT-BSe-COF (containing Se atoms), respectively. A novel photocatalytic hydrogen evolution mechanism based on proton-coupled electron transfer on N in the structure of triazine rings in vinylene-linked COFs is proposed by theoretical calculations. Our findings provide new insights into the design of highly photoactive organic framework materials for H2 evolution and beyond.

Novel Inorganic-Organic Dual-Photosensitizing Dinuclear-Metal Self-Assembly System for Efficient Artificial Photosynthesis without Sacrificial Electron Donors.

Owing to the unique synergistic effect, dinuclear-metal-molecule-catalysts (DMCs) show excellent performance in catalytic fields. However, for overall photocatalytic CO2 reaction (CO2RR), it is still a challenge to construct well-matched photosensitizer (PS) components for DMCs-based photocatalysts. Inorganic-quantum-dot PS possesses capacities of multiple exciton generation and catalyzing water oxidation but is incompatible with DMCs. In contrast, organic PS can be covalently linked with DMCs but inescapable of using sacrificial electron donors. For overall photocatalytic CO2RR, organic-inorganic dual-photosensitizing system might be a promising candidate. Herein, we employed covalent-linking and electrostatic-driven approaches to construct the self-assembly of pyrene-sensitized Co2L DMCs (Py-Co2L) and perovskite (PVK) quantum dots, i.e., PVK@[Py-Co2L]. Using H2O as an electron donor, PVK@[Py-Co2L] realized 105.24 μmol·g-1·h-1 CO yield in photocatalytic CO2RR, much higher than PVK (15.44 μmol·g-1·h-1) and PVK@Co2L (32.30 μmol·g-1·h-1), ascribing to the efficient photogenerated charge separation and transfer. The experimental results and theoretical investigations demonstrated that the pyrene linked on Co2L boosted the electron delivery from PVK to DMCs. Besides, this strategy could also be extended to the photocatalytic H2 evolution coupled with alcohol oxidation. As a proof-of-concept, our work lightens the integration of DMCs, organic and inorganic PS components, promoting the development of photocatalysis without sacrificial electron donors.

Boosted photothermal-assisted photocatalytic H2 production by dual heat source-based S-scheme heterojunction

With advances in catalytic research, improvement of catalytic efficiency by using photothermal synergies to strengthen the reaction mechanisms has been focused. In this work, a novel photothermal-assisted photocatalytic H2 production system was constructed by loading Co3O4 nanoparticles on surface of black carbon nitride (BCN) nanosheets, served as the dual thermal source to enhance photothermal effect for synergistically assisting in photocatalytic H2 evolution with optimal H2 production rate reached 3.7 mmol g−1 h−1, significantly higher than that of pure carbon nitride (CN) and BCN. Moreover, the S-scheme heterojunction is also formed between Co3O4 and BCN, leading to the optimization of the charge transfer path, which further promotes the improvement of photothermal-assisted photocatalytic H2 production activity. This study provides the design idea of coupling the multi-heat source effect with the heterojunction electron transport for constructing an efficient photothermal-assisted hydrogen production system.

Rationally designed photothermal-pyroelectric Fe0.9Ni0.1S2/ZnSnO3 Z-scheme heterojunction for promoting electrical charge polarization towards optimized photocatalytic H2 evolution and intermolecular N-N coupling reaction

Developing a photocatalytic composite system that can couple hydrogen (H2) evolution and benzylamine (BA) oxidation is a challenging task, especially while avoiding sacrificial agents and value-added chemicals. Here, a practical approach is reported to develop a photothermal-pyroelectric-Fe0.9Ni0.1S2/ZnSnO3 photocatalytic system with core–shell and Z-scheme heterostructure via hydrothermal and annealing methods. Although Fe0.9Ni0.1S2 nanoparticles (NPs) could convert most of near-infrared (NIR) light energy into heat energy to drive the pyroelectric effect of ZnSnO3, it also results in temperature fluctuations (ΔT) in the system, causing natural polarization and thermoelectric effects under the condensed water circulation. As a result, the as-designed Fe0.9Ni0.1S2/ZnSnO3-2 composites could yield up to 7.194 mmol g-1h−1 with exceptional photocatalytic H2 evolution under simulated sunlight. This result is 5.41 and 4.92-fold those of Fe0.9Ni0.1S2 and ZnSnO3, respectively, with 16.66 % apparent quantum yield (AQY) under 365 nm monochromatic light. At the same time, the composites could also oxidize BA and yield up to 6.640 mmol g-1h-1n-benzylidene benzylamine (NBBA) with a 90.2 % selectivity. Due to the synergistic effect of Z-scheme’s built-in electric field and photothermal-pyroelectric of Fe0.9Ni0.1S2/ZnSnO3, the surface charges released on them could direct the charge transfer pathways and restrain their recombination with accelerated electron transfer kinetics, thus extending the carrier lifetime. This work offers a new perspective for designing electrical charge polarized by the photothermal-pyroelectric effect, which can enhance H2 evolution and BA oxidation concurrently.

ON-OFF switching of Photocatalytic Hydrogen Evolution by Built-in Pt-Nitrogen-Carbon Reticular Heterojunctions.

COF engineering with a built-in, high concentration of defined N-doped sites overcomes the "black-box" of trial-and-error N-doping methods (used in polymeric carbon nitride and graphene), that hamper a directed evolution of functional carbon interfaces. Herein, an ON-OFF gated photocatalytic H2 evolution (PHE) is dictated by the Pt-NPyridine-carbon active sites and probed with a dual COF platform, based on stable β-ketoenamine connectivities made of triformylphloroglucinol (Tp) as the acceptor knots and 1,4-diaminonaphtalene (Naph) or 5,8-diaminoisoquinoline (IsoQ) as donors. Our results showcase two novel COF-Naph-Tp and COF-IsoQ-Tp featuring quasi-identical structural,spectroscopic properties and PEIS response at the surface/water interface (Rct = 16-10 ±4 KΩ), while a divergent behaviour is indeed observed for COF-IsoQ-Tp with record photoelectrochemical outputs (J = -16 μA cm-2, Rt = 3 KΩ at 0.40 V vs RHE) and two orders of magnitude higher rate of PHE (11.3 mmol g-1 h-1, λ > 400 nm, pH 5) compared to the inactive COF-Naph-Tp analogue. It turns out that PHE is regulated by the isoquinoline residues at the COF pores where emergent Pt-NPyridine-carbon functional heterojunctions are formed upon photo-deposition of Pt nanoparticles as co-catalysts, as probed by combined XPS and DFT calculations evidence.

Naphthalene Monoanhydride and Perylene Composites for Efficient Photocatalytic Hydrogen Evolution and Metal-Free Heterogeneous Oxidative Amidation.

This study explores the synthesis of two visible light active organic chromophore-based composites using naphthalene monoanhydride (Np) and 1,7-dibromoperylene monoanhydride diester (PMDE). These chromophores feature favorable optical and electronic properties and polyaromatic skeletons with anhydride functionalities that facilitate π-π interactions between the chromophore and polymeric carbon nitride (CN) or covalent connections of chromophores with NH2 groups of CN. Accordingly, heterogeneous chromophore-CN composite photocatalysts namely, Np/CN(c) and PMDE/CN(c) were prepared by adopting in situ calcination (c) and composites Np/CN(a) and PMDE/CN(a) were prepared by ex situ physical adsorption (a) methods. In situ prepared Np/CN(c) and PMDE/CN(c) composites exhibited H2 evolution rates (HER) of 1069 and 705 μmol h-1 g-1, respectively, which are significantly higher than ex situ Np/CN(a) and PMDE/CN(a) composites with HER of 465 and 252 μmol h-1 g-1, respectively. These rates are 10, 7, 4.8, and 2.5 times higher than the bulk-CN, indicating the potential of these composites for efficient photocatalytic H2 evolution. Surface area normalized HER enhancements were 3.8, 5.3, 6.6, and 4.2 times higher for Np/CN(c), PMDE/CN(c), Np/CN(a), and PMDE/CN(a) respectively compared to bulk-CN. These composite photocatalysts exhibited excellent stabilities under prolonged photoirradiation, with H2 evolution consistently increasing with the light exposure time. Additionally, these metal-free heterogeneous composites demonstrated efficient photocatalytic activities towards oxidative amidation of aromatic aldehydes, with up to 80% product yields, establishing the prospects of combining homogeneous and heterogeneous entities in a metal-free active material in solar energy harvesting.

Elevating photocatalytic H2 evolution over ZnIn2S4@Au@Cd0.7Zn0.3S multilayer nanotubes via Au-mediating H–S antibonding-orbital occupancy

Metal sulfides have been considered as an important category of photocatalysts for photocatalytic hydrogen evolution because of their low cost, simple preparation process and abundance of active sites. However, the atomic hydrogen is generally adsorbed on the sulfide photocatalysts to form strong H–S bond, which impedes the release of generated H2 molecules from the photocatalyst surface, severely limiting the H2 evolution efficiency. To address this issue, herein we have designed an interesting type of ZnIn2S4@Au@Cd0.7Zn0.3S (ZIS@Au@CZS) multilayer nanotubes with Au medium sandwiched between inner CZS layer and outer ZIS layer. The Au medium serves as the electron mediator to provide free electrons to fill the H–S antibonding orbitals in CZS and ZIS; this process decreases the adsorption capability of the S sites towards atomic hydrogen, thus facilitating the release of generated H2 molecules. This study provides an important guidance for modifying the photocatalysts to maximize their photocatalytic H2 evolution.

Elaborate construction of a MOF-derived novel morphology Z-scheme ZnO/ZnCdS heterojunction for enhancing photocatalytic H2 evolution and tetracycline degradation

Elaborate construction of novel Z-scheme heterojunction with exceptional morphology derived from metal-organic framework (MOF) have been attracted greatly interest for improving the photocatalytic ability. Herein, a Z-scheme ZnO/ZnCdS heterojunction of rare morphology with ultrathin-nanosheet assembled hierarchical morphology ZnCdS supporting on rich gap ZnO nanospheres were constructed from Zn-based MOF (namely PZH-139) for the first time. This unique feature increased specific surface area, offered abundant mass transport channels and accessible catalytic active sites, accelerated electron migration, which highly elevated photocatalytic property. Furthermore, electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) calculations confirmed the reservation of strong redox capability owing to Z-scheme electron transfer path and the ΔGH* closer to zero of Z-scheme ZnO/ZnCdS system were another two key factors for boosting the photocatalytic activity. As a result, 3-ZnO-700/ZnCdS-160 with optimal morphology showed the best H2 generation performance of 15.43 mmol h−1 g−1 and degradation tetracycline (TC) efficiency of 98.14 %. This work offered a novel and feasible idea for elaborate synthesis of the high-efficiency Z-scheme ZnO/ZnCdS heterojunction with special morphology derived from Zn-MOF.

Optimizing H-adsorption affinity on electron-enriched Pdδ- active sites for efficient photocatalytic H2 evolution

Noble metal Pd is a promising H2-evolution cocatalyst and has attracted expansive attention in photocatalytic water splitting. However, the present H2-production rate of Pd cocatalysts is still limited due to its strong hydrogen adsorption on Pd active sites, resulting in poor hydrogen evolution kinetics. In this work, an electron-enriched Pdδ- modulation strategy is developed to weaken the hydrogen adsorption on Pd active sites by producing PdAu alloy, resulting in an increased H2-production rate. In this case, the PdAu homogeneous alloy with a particle size of 9–20 nm is uniformly deposited on the TiO2 surface to produce PdAu-modified TiO2 photocatalysts (TiO2/PdAu). It is found that the prepared TiO2/Pd79Au21 sample achieves the maximal photocatalytic H2-production performance of 31.98 mmol g-1 h−1, which is 1.53 times higher than that of TiO2/Pd photocatalyst. Experimental and theoretical studies show that in addition to the promoted transfer of photogenerated carriers, the PdAu alloy can spontaneously induce the electron transfer from Au to Pd to form electron-enriched Pdδ- sites, which prominently weakens the Pd-Hads bonds and thus improve the H2-production efficiency. This study provides further insight into the rational optimization of active sites to facilitate the design of efficient photocatalysts.

Oriented Crystal Polarization Tuning Bulk Charge and Single-Site Chemical State for Exceptional Hydrogen Photo-Production.

Rapid bulk charge recombination and mediocre surface catalytic sites harshly restrict the photocatalytic activities. Herein, the aforementioned concerns are well addressed by coupling macroscopic spontaneous polarization and atomic-site engineering of CdS single-crystal nanorods for superb H2 photo-production. The oriented growth of CdS nanorods along the polar axis, vectorially superimposing substantial polar units with orderly arrangement, renders a strong polarization electric field (20.1 times enhancement), which boosts bulk charge separation with an efficiency up to 72.4% (80.4-fold). Remarkably, polarization electric field alters the chemical state of Pt single sites by orderly reducing the binding energy of Pt atom with stepwise polarization enhancement of CdS substrate, which increases the onsite electron density of Pt from 10.232 to 10.261e- and *H key intermediates, providing preponderant Volmer-Tafel/Volmer-Heyrovsky reaction pathways with significantly decreased energy barriers for H2 production. Thus, highly polarized CdS nanorods with atomically dispersed Pt sites perform an outstanding H2 space-time yield of 118.5mmol g-1 h-1 and apparent quantum efficiency of 57.7% at λ = 420nm, and a record-high H2 turnover frequency of 57798.4 h-1, being one of the best catalysts for photocatalytic H2 evolution. This work highlights the function of polarization in manipulating charge separation and catalytic reaction.

Constructing a Z-scheme heterojunction of oxygen-deficient WO3-x and g-C3N4 for superior photocatalytic evolution of H2

Semiconductor-based photocatalytic water splitting enables the conversion of abundant solar energy to green and renewable hydrogen energy. Graphitic carbon nitride (g-C3N4) is synthesized using a straightforward method, demonstrating stable physicochemical properties and possessing an optimal bandgap, thus positioning it as a promising photocatalyst in the realm of environmental sustainability. Oxygen vacancies are extensively employed to modulate light absorption and surface properties of metal-oxide semiconductors. In this study, g-C3N4 nanosheets were coupled with oxygen-deficient tungsten trioxide (WO3-x) to form heterojunction photocatalysts (X-WOCN). Comprehensive material characterization results demonstrated that the constructed heterojunction extended the visible light absorption range, improved photogenerated electron-hole separation efficiency, and thus augmented photocatalytic activity. Notably, the optimum hydrogen evolution rate of 6%-WOCN was enhanced by 5.4-fold compared to that of g-C3N4. Furthermore, we propose a Z-scheme heterojunction charge separation mechanism mediated by oxygen defects and support this mechanism through detection of surface-active substances •O2− and •OH. This study offers novel propositions into the function of oxygen defects in facilitating charge separation within Z-scheme heterojunction.

Photocatalytic H2 evolution over CuCoSe2 nanoparticles decorated TiO2 nanosheets with S-scheme charge separation route

The construction of S-scheme heterojunctions via exploring semiconductors with suitable energy band structures can effectively improve the photocatalytic performance of TiO2. In this work, CuCoSe2/TiO2 heterojunction were prepared using solvent evaporation strategy by their different surface charge properties. The investigation indicates that rates of H2 evolution (rH2) of the system increases significantly from 138.1 (TiO2) to 3773.8 μmol·g−1·h−1 (CuCoSe2/TiO2). It is found that the incorporation of CuCoSe2 can extend the visible light absorption range of the system, increase the electrochemically active surface area, facilitate charge generation and decrease the transfer resistance, reduce the H2 production overpotential and the water contact angle. Further investigation reveals that a bimetallic selenide CuCoSe2 exhibit superior enhancement activity compared to their monometallic selenides (CuSe2, CoSe2) due to the synergistic effect of Co and Cu. Especially, the charge transfer between CuCoSe2 and TiO2 follows S-scheme charge separation route, which can effectively enhance charge separation/migration, reserve e− with strong reducing ability in TiO2, thereby promoting the H2 evolution kinetics. Moreover, the heterojunction also demonstrates exceptional stability throughout the cycle experiment. The present work establishes an experimental basis for the advancement of highly efficient and stable bimetallic selenides related heterojunctions in the field of photocatalytic H2 evolution.

Enhanced Photothermal-Assisted Hydrogen Production via a Porous Carbon@MoS2/ZnIn2S4 Type II-S-Scheme Tandem Heterostructure.

MoS2/ZnIn2S4 flower-like heterostructures into porous carbon (PC@MoS2/ZIS) are embedded. This ternary heterostructure demonstrates enhanced light absorption across a broad spectral range from 200 to 2500nm. It features both Type-II and S-scheme dual heterojunction interfaces, which facilitate the generation, separation, and transfer of photoinduced carriers. The PC enveloped by MoS2/ZIS composite microspheres serves as a photothermal source, providing additional energy to the carriers. This process accelerates charge separation and migration, enhancing photothermal-assisted photocatalytic H2 evolution. The optimal H2 evolution rate for PC@MoS2/ZIS reaches an impressive 18.79mmolg-1h-1, with an apparent quantum efficiency of 14.1% at 400nm. This work presents a promising approach for effectively integrating multicomponent heterostructures with photothermal effects, offering innovative strategies for efficient solar energy utilization and conversion.

Modulating Schottky barriers and active sites of Ag-Ni bi-metallic cluster on mesoporous carbon nitride for enhanced photocatalytic hydrogen evolution

The advancement of photocatalysis relies on the development of novel hetero-structured materials with unique architectures. In this study, we successfully synthesized a hetero-structured g-C3N4 (GCN) material with a distinctive surface-interface modification. To further enhance its photocatalytic performance, we optimized the Ag and Ni concentration to maximize the visible light absorption and catalytic active sites for hydrogen evolution reactions. By using systematic physicochemical characterizations and density functional theory (DFT) calculations, we elucidated the pivotal role of graphitic carbon nitride (g-C3N4) in facilitating the formation of an efficient charge transfer channel and promoting the effective generation and separation of photo-generated carriers. From the DFT calculations, we also demonstrated that the Ag and Ni nanoparticles provide more efficient visible light absorption and active sites than Ni nanoparticles for water splitting and hydrogen evolution and In-situ TEM exploration. Furthermore, the hetero microstructure consisting of thin g-C3N4 nano scrolls has a crucial role in shortening the migration distance of the carriers, effectively suppressing carrier recombination. Consequently, these extraordinary characteristics resulted in a superior solar light-driven photocatalytic H2 evolution rate of 2507 μmol.h-1.g−1, surpassing the rate achieved by g-C3N4 heterostructures by a remarkable 18.6-folds. Moreover, the apparent quantum efficiency of this hetero-structured material reached an exceptional value of 1.6 % under a 1.5 G air mass filter.

The regular octahedral CdS/K2Nb2O6 core-shell Z-Scheme heterojunction towards enhancing photocatalytic H2 evolution and degradation via synergism of carrier efficiency and light response

The regular octahedral CdS/K2Nb2O6 core-shell Z-Scheme heterojunction is synthesized via an approach of hydrothermal-chemical method. The CdS/K2Nb2O6 nano-heterojunction (CdS/KNO-3) exhibits arresting enhanced photocatalytic HER (∼634.39 μmol g−1 h−1)/degradation (∼0.05428 min−1) than the monomer K2Nb2O6 (∼27.8/14.4 folds) and CdS (∼20.3/10.0 folds), including a decent stability (average HER of ∼621.39 μmol∙g−1 h−1). It can be mainly attributed to the CdS/K2Nb2O6 Z-Scheme heterojunction with appropriate potential gradient can promote the interface carrier driving to optimize carrier efficiency, including increasing carrier transport, extending carrier lifetime and reducing recombination. Additionally, the octahedral core-shell nanostructure can provide numerous active sites for decreasing overpotential and promoting electron diffusion, while improving the solar efficiency (high solar response of CdS), including shorting carrier pathway for photocorrosion optimization and increasing structural stability.

Efficient photocatalytic H2 evolution over CuCo2S4 decorated ZnIn2S4 with S-scheme charge separation way

The construction of an S-scheme heterojunction can facilitate the separation and utilization of photogenerated charges, as well as reserve the reducing power of electrons to induce proton reduction for H2 evolution. In this study, CuCo2S4 nanoparticles and ZnIn2S4 nanoflowers were both synthesized via a hydrothermal method, and then CuCo2S4 was employed to decorate ZnIn2S4 to form CuCo2S4/ZnIn2S4 heterojunction through a simple physical solvent evaporation strategy. The experiment result shows that the rate of photocatalytic H2 evolution (rH2) over 10 wt% CuCo2S4/ZnIn2S4 can reach up to 20421.3 μmol g−1 h−1, which is 4.0 times that of ZnIn2S4 (5062.5 μmol g−1 h−1) and 144.6 times that of CuCo2S4 (141.2 μmol g−1 h−1). The improved activity results from the establishment of an S-scheme charge transfer way between CuCo2S4 and ZnIn2S4, which facilitates efficient charge separation while preserving active e− and h+. Besides, the formation of the heterojunction broadens the range of light absorption, promotes charge carrier generation, reduces charge transfer impedance, and increases electrochemically active surface area, these together lead to faster H2 evolution kinetics. The present study demonstrates the potential of bimetallic sulfides as a promising catalyst for construction ZnIn2S4-based photocatalysts for efficient solar conversion.

Enhanced interfacial electric field via sulfur vacancies modified ZnIn2S4-Vs@NiIn2S4 S-scheme photocatalysts for simultaneous H2 evolution and benzyl alcohol oxidation

Designing and developing efficient photocatalysts for H2 evolution and simultaneous oxidation of benzyl alcohol (BA) in aqueous environments provides a cutting-edge strategy for green synthesis. Nevertheless, the photocatalysts suffer from the low photoconversion efficiency because of the sluggish dynamics and repaid recombination of photogenerated charge carriers, which hindering their widespread applications. To address the limitation, a multifunctionnal sulfur vacancies (SVs) modified ZIS-Vs@NIS S-scheme heterojunction with a strong interfacial electric field effect was synthesized to use photocatalytic H2 production and BA oxidation, simultaneously. Experimental analysis supports that the synergistic effect of SVs and S-scheme heterojunction engineering result in a suitable energy band structure alignment and larger Fermi level potential difference. Those factors can realize effective charge transfer and separation, and enhance the photocatalytic performance. As anticipated, ZIS-Vs@NIS exhibited a superior photocatalytic performance with H2 and benzaldehyde (BAD) yields up to 168.1 and 146.1 μmol under the simulated solar-light irradiation for 1.0 h, respectively, which are approximately 13.3 and 11.8 times higher than pristine ZIS. Moreover, the photocatalytic H2 evolution coupled with BA oxidative dehydrogenation mechanism via S-scheme heterojunction over ZIS-Vs@NIS is also demonstrated in detail.