High-efficiency Photocatalytic H2 Research Articles

Optimizing Electronic Density at Active W Sites for Boosting Photocatalytic H2 Evolution.

It is highly desirable but challenging to optimize the electronic structure of an active site to realize moderate active site-Hads bond energies for boosting photocatalytic H2 evolution. Herein, an interfacial engineering strategy is developed to simultaneously concentrate hydrogen species and accelerate the combination of an Hads intermediate to generate free H2 by constructing W-WC-W2C (WCC) cocatalysts. Systematic investigations reveal that hybridizing with W2C creates electron-rich W active sites and effectively induces the downshift of the d-band center of W in WC. Consequently, the strong W-Hads bonds on the surface of WC are weakened, thus promoting the desorption of Hads to rapidly produce free H2. The optimized 40-WCC/CdS photocatalyst exhibits a high hydrogen evolution rate of 63.6 mmol g-1 h-1 under visible light (≥420 nm) with an apparent quantum efficiency of 39.5% at 425 nm monochromatic light, which is about 40-fold of the pristine CdS. This work offers insights into the design of cocatalyst for high-efficiency photocatalytic H2 production.

Novel noble-metal-free NiCo-LDH/CdSe S-type heterojunction with built-in electric field for high-efficiency photocatalytic H2 production

BackgroundConstructing heterojunction is one of the effective strategies for boosting carrier separation. Although CdSe is an excellent photocatalytic material, its activity is still very low. MethodsIn this paper, NiCo-LDH/CdSe (NCCSe) binary heterojunctions were successfully prepared by a two-step hydrothermal method. The results of photocatalytic tests show that 12NCCSe composites have the highest photocatalytic H2 production activity, with an average rate of 2929.4 μmol·g−1·h−1, which is 74 times higher than that of pure CdSe (39.5 μmol·g−1·h−1). Significant findingsThere are two main reasons for the obvious improvement of photocatalytic activity. Firstly, the separation efficiency of photogenerated carriers is greatly improved, which is attributed to the formation of S-type heterojunction with built-in electric field. Secondly, the addition of NiCo-LDH greatly enhances the light absorption intensity of NCCSe composites, providing more photogenerated electrons. In addition, the mechanism of increased photocatalytic activity for NCCSe S-type heterojunction composites was further discussed. This work provides a thought for constructing NiCo-LDH-based S-type heterojunction for efficient photocatalytic H2 production, which could easily extend to other LDHs materials.

Hollow-shell hybrids with regulatable microelectronic structures for boosting photocatalytic H2 evolution via water splitting and isopropanol oxidation under visible light

Herein, a series of heteroatoms doped-NMIL(Ti)/Cd0.5Zn0.5S are synthesized, where the Cd0.5Zn0.5S (CZS) uniformly grows in situ on the surface of NMIL(Ti) encapsulating ultra-trace Cu/Fe/Co atoms to form the mesoporous hollow-shell structures. The microelectronic structures of photocatalysts can be modulated via regulatable band potential of Cu/Fe/Co-doped NMIL(Ti) due to the intense interaction between heteroatoms and −NH2 groups. Moreover, the Ti3+-oxygen vacancy pairs as the photogenerated electron library and the heterojunction effectively facilitate the special separation and migration of carriers. The optimal hybrid (Cu1%-NMIL(Ti)/CZS) has a photocatalytic hydrogen evolution rate of 251.2 μmol g−1 (12,560.12 μmol g−1 h−1) in 0.35 M Na2S/0.25 M Na2SO3 under visible light, which is 4.34 and 1.74 times higher than that of CZS and NMIL(Ti)/CZS, respectively. Moreover, the H2 yield reaches 29,860 μmol g−1 h−1 in 0.35 M Na2S/0.25 M Na2SO3/2 M isopropanol system, which is 2.38 times than before, displaying that isopropanol oxidation not only consumes photo-holes to inhibit carries recombination, but also provides H+ to participate in H2 production. This work provides a new insight for developing a high-efficiency photocatalytic H2 evolution system.

Facile fabrication of NiWO4/ZnIn2S4 p-n heterojunction for enhanced photocatalytic H2 evolution

Construction heterojunction has been demonstrated to be a potential strategy to facilitate the activity of single component photocatalyst due to the enhanced light absorption, accelerated charge separation and so on. Herein, a NiWO4/ZnIn2S4 p-n heterojunction was prepared via a facile physical solvent evaporation method. In the binary system, the p-n heterojunction formed between NiWO4 and ZnIn2S4 can boost the charge separation. Besides, the introduction of NiWO4 can induce more electrochemically active surface area and decrease the overpotential of H2 evolution. In addition, the water angle contact (WAC) of ZnIn2S4 was reduced from 58.6° to 12.1°, suggesting a better hydrophilic surface. The photocatalytic activity tests indicated that the obtained composite exhibited excellent H2 evolution activity than NiWO4 or ZnIn2S4 alone. 10.7 %-NiWO4/ZnIn2S4 has a superior H2 production rate of 30.51 mmol·g−1·h−1, 4.42 folds higher than that of pure ZnIn2S4 (5.63 mmol·g−1·h−1). Meanwhile, the microstructure of 10.7 %-NiWO4/ZnIn2S4 is well preserved after reaction. This work provides experimental basis for the development of ZnIn2S4 based heterojunction for high-efficiency photocatalytic H2 evolution.

C, N-vacancies and Br dopant co-enhanced photocatalytic H2 evolution of g-C3N4 from water and simulated seawater splitting

Introducing defects and heteroatoms on carbon nitride (g-C3N4, CN) framework are effective ways to enhance its photocatalytic activity by regulating light absorption and charge carriers separation. Herein, a mechanochemical method was employed to synthesize Br-doped C, N-deficient CN (CNV-mCN-Br) via ball-milling of N-containing precursor and 6-Bromopyridine-3-carbaldehyde (BrPyCHO) followed by calcining. The ball-milling-evolved mechanical forces and BrPyCHO-derived HBr induced formation of C, N vacancies and C-Br bond in CNV-mCN-Br framework. The CNV-mCN-Br exhibited curled nanosheets morphology and separated electrons-holes distribution. The photocatalytic H2 evolution rates of 1 %Pt-loaded CNV-mCN-Br in distilled water and simulated seawater were 22.21 and 34.41 mmol g–1h−1, respectively with 10% triethanolamine. The corresponding apparent quantum yields were 25.87% and 40.08% at 420 nm. This work provides a facile technique to simultaneously introduce defect and heteroatom in CN for high-efficiency photocatalytic H2 evolution.

Fabrication of Porous Hydrophilic CN/PANI Heterojunction Film for High-Efficiency Photocatalytic H2 Evolution

The modulation of surface wettability and morphology are essential to optimize the photocatalytic H2 evolution activity of graphitic carbon nitride (CN)-based photocatalysts. In this work, the porous hydrophilic CN/PANI heterojunction film was prepared via interfacial polymerization and loaded on a porous PCL substrate. The construction of the type-II CN/PANI heterojunction enabled an overall spectrum response and the efficient separation and transportation of photoexcited charge carriers. The fabricated CN/PANI solid-state film in comparison with its powder counterpart elevated the utilization efficiency and maintained the long-term stability of photocatalyst. The porous morphology and hydrophilic surface increased the surface area and enhanced the surface wettability, favoring water-molecule adsorption and activation. The as-prepared CN/PANI heterojunction film exhibited photocatalytic H2 production activity up to 3164.3 μmol·h−1·g−1, which was nearly 16-fold higher than that of pristine CN (569.1 μmol·h−1·g−1).

Well-Defined Ultrasmall V-NiP2 Nanoparticles Anchored g-C3N4 Nanosheets as Highly Efficient Visible-Light-Driven Photocatalysts for H2 Evolution

Exploring low-cost and highly active, cost-effective cocatalysts is of great significance to improve the hydrogen evolution performance of semiconductor photocatalysts. Herein, a novel ultrasmall V-doped NiP2 nanoparticle, as an efficient cocatalyst, is reported to largely upgrade the photocatalytic hydrogen evolution reaction (HER) of g-C3N4 nanosheets under visible-light irradiation. Experimental results demonstrate that V-NiP2 cocatalyst can enhance the visible-light absorption ability, facilitate the separation of photo-generated electron-hole pairs and boost the transfer ability of electrons of g-C3N4. Moreover, the V-NiP2/g-C3N4 hybrid exhibits prominent photocatalytic HER activity 17 times higher than the pristine g-C3N4 counterpart, even outperforming the 1 wt.% platinum-loaded g-C3N4. This work displays that noble-metal-free V-NiP2 cocatalyst can serve as a promising and efficient alternative to Pt for high-efficiency photocatalytic H2 evolution.

Facile synthesis of mesoporous polymeric carbon nitride nanosheets anchored by Pt with ultralow loading for high-efficiency photocatalytic H2 evolution.

The facile fabrication of low-cost photocatalysts with enhanced activity and high atomic utilization is becoming increasingly necessary for solar energy usage and/or conversion. In this work, a series of mesoporous carbon nitride nanosheets with an enlarged specific surface area was synthesized via an inorganic acid-assisted exfoliation method without any soft or hard templates. An ultralow loading of downsized noble metal Pt was anchored on these porous nanosheets, exhibiting enhanced photocatalytic activity. The formation of mesoporous nanosheets in carbon nitride was expected to boost the mass transfer and shorten the charge carrier transfer route during the photocatalytic reaction. The characterization of samples revealed that the enhanced conductivity and photocurrent of the carbon nitride nanosheets also contributed to the enhanced H2 evolution activity. The maximum H2 production rates of 172.92 μmol h-1 and 321 μmol h-1 were achieved over the nanosheets derived from melamine and urea under visible light irradiation, which are 10.92- and 2.22-fold that of the corresponding bulk carbon nitride, respectively. This exfoliation method was demonstrated to be an efficient and universal method for the preparation of carbon nitride nanosheets with a mesoporous structure and high atom utilization of the co-catalyst for H2 evolution from water.

Synergistic effects of g-C3N4 three-dimensional inverse opals and Ag modification toward high-efficiency photocatalytic H2 evolution

Photocatalytic hydrogen evolution is considered as a sustainable and economical scheme to meet the energy demand and solve the environmental pollution. Herein, we developed a sandwich sintering strategy to improve the production yield and uniformity of g-C3N4 inverse opal (CN IO) nanostructure via SiO2 colloidal crystal template. Based on the highly ordered CN IO nanostructure, novel photocatalysts of silver-modified CN IO (Ag–CN IO) nanocomposites were presented. The formation mechanism, morphology, microstructure, element content and distribution, optical and electrochemical properties were investigated. The photocatalytic performances were evaluated by H2 evolution under visible light irradiating. Also, the effects of Ag content and morphology of the nanostructures on the photocatalytic performances were studied. The results show that the as-developed Ag–CN IO exhibits the best H2 evolution performance among all the tested samples. The enhanced photocatalytic performance of the Ag–CN IO is mainly attributed to the Ag nanoparticles and IO structure, which can synergistically improve the light absorption and charge transfer as well as the surface kinetics. The photocatalytic mechanism of the Ag–CN IO was also proposed.

Spatial carrier separation in cobalt phosphate deposited ZnIn2S4 nanosheets for efficient photocatalytic hydrogen evolution

Developing photocatalyst with effective charge separation and fast surface reaction kinetics is crucial to high-efficiency photocatalytic H2 evolution. Herein we spatially separate the reductive and oxidative reaction sites of ZnIn2S4 nanosheet and accelerate the hole transfer process by simply depositing cobalt phosphate (CoHxPOy, noted as Co-Pi), a non-precious co-catalyst, on its basal plane. Theoretical calculations combined with comprehensive characterizations reveal that Zn vacancies induced deep local energy levels serve as hole trap states to pin the photogenerated holes on (001) surface of ZnIn2S4. Upon Co-Pi deposition, Co atoms preferentially bond with S atoms nearby the Zn vacancies of ZnIn2S4. Taking advantage of the formation of Co-S bonds, Co-Pi acts as a hole receptor to extract the trapped holes effectively. As the photocatalytic activity of ZnIn2S4 is caused by active S atoms on its edge side, deposition of Co-Pi on planar side of nanosheets helps electron-hole migration to different facets. As a result of inert facet activation and spatial carrier separation, Co-Pi/ZnIn2S4 exhibits a superior photocatalytic H2 evolution rate of 10.19 mmol g-1h−1 under visible light, which is superior to most of reported ZnIn2S4-based photocatalysts. This work will provide novel insights into the activation of inert basal planes of two-dimensional photocatalysts.

Sea-urchin-like ReS2 nanosheets with charge edge-collection effect as a novel cocatalyst for high-efficiency photocatalytic H2 evolution

The recombination of charge carriers arriving from the random charge movement in semiconductor photocatalysts greatly limits the practical application of solar-driven H2 evolution. The design of photocatalytic systems with spatially oriented charge-transfer is a promising route to achieve high charge-separation efficiency for photocatalysts. Herein, novel sea-urchin-like ReS2 nanosheet/TiO2 nanoparticle heterojunctions (SURTHs) are constructed. The unique sea-urchin-like structure endows the ReS2 cocatalyst with an unusual charge edge-collection effect, which leads to a significant acceleration of charge separation and transfer, as evidenced by the well-designed selective photodeposition of Pt quantum dots in SURTHs. The markedly improved charge transfer capacity contributes to a high photocatalytic H2 evolution rate of 3.71 mmol h−1 g−1 for SURTHs (an apparent quantum efficiency (AQE) of 16.09%), up to 231.9 times by contrast with that of P25 TiO2. This work would provide a new platform for designing the high-efficiency cocatalyst/photocatalyst system with excellent charge transfer capacity.

Uniformly Dispersed Metal Sulfide Nanodots on g-C3N4 as Bifunctional Catalysts for High-Efficiency Photocatalytic H2 and H2O2 Production under Visible-Light Irradiation

Uniformly Dispersed Metal Sulfide Nanodots on g-C₃N₄ as Bifunctional Catalysts for High-Efficiency Photocatalytic H₂ and H₂O₂ Production under Visible-Light Irradiation

P, S Co-doped g-C3N4 isotype heterojunction composites for high-efficiency photocatalytic H2 evolution

The photocatalytic hydrogen generation, which makes use of metal-free and low-cost graphite carbon nitride as a photocatalyst, is termed as a pivotal and viable strategy for solving the ecological and energy issues. Nevertheless, the key impediment is the agglomeration phenomenon, as a result of the uneven heat and mass transfer during calcination, besides the low utilization rate of photogenic electron holes. In the current work, this issue was overcome by a simple one-step method of copolymerization, combining the codoping and construction of isotype heterojunction. This strategy can overcoming the incidence of agglomeration and effectively optimizing the physical and surface properties of the catalyst as well, thereby enhancing the photocatalytic performance. The changed g-C3N4 manifests the higher surface area, together with broadened the visible-light responsive, improved electron migrate potential and prolonged life time of photogenerated carriers. In addition, these effectively-amended g-C3N4 nanosheets have an improved hydrogen evolution rate, which is 7.47 times that of SCN-1.

RGO Boosts Band Gap Regulates for Constructing Ni2P/RGO/MoO2 Z-Scheme Heterojunction to Achieve High Efficiency Photocatalytic H2 Evolution

A Z-scheme heterojunction composite material Ni2P/RGO/MoO2 with high efficiency HER activity via a simple hydrothermal synthesis method which is one-step for photocatalytic H2 production was synthesized. The composite material which used reduced graphene oxide (RGO) as an electron transport medium and utilized a synergistic action of non-noble metal semiconductors Ni2P and MoO2 to construct Z-scheme heterojunction. Compared with the binary Ni2P/MoO2 composite photocatalyst, the photocatalytic hydrogen evolution activity of RGO assisted ternary composite Ni2P/RGO/MoO2 is significantly improved under visible light (λ > 420 nm) in the dye sensitization system in 5 h. The photocatalyst with optimal ratio reaches 355.34 μmol, which is about two times as much as the one without RGO. The transient photocurrent response, fluorescence test and hydroxyl radical capture experiment show that the type-II heterojunction originally composed of Ni2P and MoO2 is converted to Z-scheme in the presence of RGO. The transformation of the electron transfer mode effectively reduces the composite of photogenerated carriers. In addition, in situ hydrothermal synthesis allows Ni2P and MoO2 to be firmly modified on the RGO surface. This makes the composite photocatalyst exhibit great catalytic stability, and the HER activity of the photocatalyst hardly decrease in the four-cycle experiment. Through the one-step hydrothermal method, RGO assisted non-precious metal semiconductor composite provides a new idea for the synthesis of photocatalytic materials. The composite catalyst via the band gap regulation of MoO2 by Ni2P exhibits great hydrogen production activity in the dye-sensitized system. Subsequently, the GO solution was added during the synthesis to construct a Z-scheme heterojunction with graphene as an electron transporter. The ternary composite catalyst with a Z-scheme heterojunction shows approximately twice the hydrogen production rate of the binary catalyst.

Orderly designed functional phosphide nanoparticles modified g-C3N4 for efficient photocatalytic hydrogen evolution

The synthesis of highly efficient and stable photocatalysts has always been one of the key research objects in the field of photocatalysis. Increasing the efficiency of charge separation is an important aspect of improving photocatalytic activity. In this work, the Co-W-P cocatalysts were loaded on g-C3N4, synthesized for the first time and the electron transport routes were appropriately adjusted, which extremely improved efficiency of photocatalytic decomposition of water for hydrogen evolution. A composite photocatalyst with high-efficiency photocatalytic H2 production performance under visible light was obtained by loading the Co-W-P composites on a g-C3N4 nanosheet. It was ascribed to the efficient interfacial electron transfer routes. This has contributed to the synthesis of high-priority and stable photocatalysts. Besides, the composite catalysts were characterized by SEM, TEM, XRD, XPS, UV-vis, BET, transient photocurrent, and FT-IR etc. And a mechanism of photocatalytic hydrogen production was hypothesized.

Design of cocatalyst loading position for photocatalytic water splitting into hydrogen in electrolyte solutions

Photocatalytic water splitting into hydrogen is a very attractive and desirable technology to realize sustainable and renewable green energy conversion. Up to now, many research results have confirmed that cocatalyst such as Pt is essential for a high efficiency photocatalytic H2 evolution system. In a traditional view, the cocatalyst should be closely combined with the photocatalyst to achieve a high H2 or O2 photo-productive rate. In this work, an unusual point has been put forward that the suitable loading position of cocatalyst Pt for film-type TiO2 catalyst is on the bare Fluorine-doped tin oxide (FTO) substrate instead of on the surface of TiO2 in the electrolyte solutions. Especially, in acidic electrolyte, the hydrogen production rate of this new designed catalyst with Pt loaded on FTO (TiO2-Pt/FTO) reaches 2.4 times that of the common catalyst with Pt loaded on TiO2 (Pt/TiO2-FTO). According to the experiment results, it is supposed that this loading way of cocatalyst on the substrate can construct a self-bias photocatalytic electrochemical cell system, drive electrolyte ions' movement directionally, and obtain high photocatalytic H2 production efficiency. The universality of this innovation has been verified by CdS and CdS@TiO2 film-type catalysts. This study provides a new guide in exploring high-efficiency film-type photocatalytic system for water splitting into hydrogen in the electrolyte solution.

Building surface defects by doping with transition metal on ultrafine TiO2 to enhance the photocatalytic H2 production activity

Inefficient charge separation and limited light absorption are two critical issues associated with high-efficiency photocatalytic H2 production using TiO2. Surface defects within a certain concentration range in photocatalyst materials are beneficial for photocatalytic activity. In this study, surface defects (oxygen vacancies and metal cation replacement defects) were induced with a facile and effective approach by surface doping with low-cost transition metals (Co, Ni, Cu, and Mn) on ultrafine TiO2. The obtained surface-defective TiO2 exhibited a 3–4-fold improved activity compared to that of the original ultrafine TiO2. In addition, a H2 production rate of 3.4 μmol/h was obtained using visible light (λ > 420 nm) irradiation. The apparent quantum yield (AQY) at 365 nm reached 36.9% over TiO2-Cu, significantly more than the commercial P25 TiO2. The enhancement of photocatalytic H2 production activity can be attributed to improved rapid charge separation efficiency and expanded light absorption window. This hydrothermal treatment with transition metal was proven to be a very facile and effective method for obtaining surface defects.

Noble-metal-free Ni3C cocatalysts decorated CdS nanosheets for high-efficiency visible-light-driven photocatalytic H2 evolution

In this work, Ni3C nanoparticles (NPs, 0 D) were for the first time used as H2-evolution cocatalysts to modify CdS nanosheets (NSs, 2 D) to achieve the high-efficiency photocatalytic H2 evolution under visible light irradiation. The photocatalytic H2-evolution activities of the Ni3C/CdS hybrid NSs were tested under 350 W Xe lamp irradiation (λ ≥ 420 nm) with a sacrificial agent. The results proved that Ni3C NPs were efficient cocatalysts for photocatalytic H2 evolution over CdS NSs. The CdS-1% Ni3C hybrid NSs exhibited the highest photocatalytic H2-evolution rates of 357 μmol h−1 in 0.25 M Na2S-Na2SO3 and 450.5 umol h−1 in lactic acid, which were approximately 7.76 and 4.79 times higher than that of bare CdS NSs, corresponding to the apparent quantum yields of 7.58% and 8.72% at 420 nm, respectively. Clearly, the Ni3C NPs serve as H2-evolution electrocatalysts either in acidic or basic media. It is believed that the noble-metal-free Ni3C cocatalyst NPs on the surface of CdS NSs can effectively increase the visible-light absorbance, promote the charge carriers separation and transfer, improve the surface H2-evolution kinetics, thus achieving the obviously boosted hydrogen evolution. It is hoped that this study could contribute to the further investigation in exploiting the low-priced, high efficiency and environmentally friendly noble-metal-free cocatalysts for photocatalytic H2 evolution.

Synergistically enhanced photocatalytic hydrogen evolution performance of ZnCdS by co-loading graphene quantum dots and PdS dual cocatalysts under visible light

Here, we report that the co-loading of graphene quantum dots (GQDs) and PdS dual cocatalysts on ZnCdS surface achieves a high efficiency photocatalytic H2 evolution under visible light (≥420nm). The GQDs/ZnCdS/PdS photocatalyst was prepared by a facile two steps: hydrothermal coupling of GQDs on ZnCdS surface followed by an in-situ chemical deposition of PdS. The resulted GQDs/ZnCdS/PdS exhibits a H2 evolution rate of 517 μmol h−1, which is 15, 7, and 1.7 times higher than that of pure ZnCdS, GQDs/ZnCdS, and ZnCdS/PdS, respectively, demonstrating the synergistic effects of GQDs and PdS dual cocatalysts. A high apparent quantum efficiency (AQE) up to 22.4% can be achieved over GQDs/ZnCdS/PdS at 420nm. GQDs/ZnCdS/PdS also has a relatively good stability. Such a considerable enhancement of photocatalytic activity was attributable to the co-loading of the GQDs and PdS as respective reduction and oxidation cocatalysts, leading to an efficient charge separation and surface reactions.