Highly exposed (001) facets Ni(OH)2 induced formation of nickle phosphide over cadmium sulfide nanorods for efficient photocatalytic hydrogen evolution

An efficient Ni₂P–CdS photocatalyst for photocatalytic hydrogen evolution was synthesized by phosphorizing β-Ni(OH)₂ nanosheet with exposed (001) facets on CdS nanorods. The obtained Ni₂P–CdS composite displays an outstanding and stable photocatalytic hydrogen generation rate of 68.47 mmol g⁻¹ h⁻¹ in 10 vol% lactic acid under visible light irradiation, more than 17 times higher than that for pure CdS nanorods. The transient photocurrent response, EIS measurement, Mott-Schottky plots, acidic LSV measurement, and PL spectra have proved that Ni₂P loading can significantly improve the separation of photo-excited electron-hole pairs in CdS nanorods and enhance the hydrogen evolution capability for CdS. These improvements are achieved by features of Ni₂P such as the high capability of trapping photo-generated electrons from CdS, lifting the total Fermi level and lowering the hydrogen evolution overpotential of the composite. The results show that β-Ni(OH)₂ precursor with a high exposure degree of (001) facet is contributed to the epitaxial formation of (001)-facet-exposed Ni₂P co-catalyst on CdS nanorods, resulting in that the Fermi level and the hydrogen evolution overpotential of the composite can be further lifted and lowered. This study has provided a novel precursor-derived route to fabricate high-performance co-catalysts with highly exposed active facets on CdS nanorods for effective photocatalytic hydrogen evolution.     

A novel pathway toward efficient improvement of the photocatalytic activity and stability of CdS-based photocatalyst for light driven H2 evolution: The synergistic effect between CdS and SrWO4

It has been a research hot spot how to efficiently heighten the photocatalytic activity and stability of CdS-based photocatalysts for H₂ evolution. Here, SrWO₄/CdS nanoparticles which contained CdS/SrWO₄ heterojunctions were prepared. Meanwhile, their photocatalytic performance and stability were investigated in detail for H₂ evolution. At last, the photocatalytic mechanism of the SrWO₄/CdS nanoparticles was discussed roughly. The results show that the photocatalytic performance of CdS can be heightened significantly due to introduction of SrWO₄. The fastest evolution rate of H₂ over the SrWO₄/CdS nanoparticles is 392.5 μmol g⁻¹ h⁻¹, which is 5.8 times as high as that over the pure CdS nanomaterial. More interestingly, the SrWO₄/CdS nanoparticles possess excellent stability. The evolution rate of H₂ over the photocatalyst used 10 times can be up to 473 μmol g⁻¹ h⁻¹, which is the same as that over the once used sample, even is 37% higher than that over of the fresh one. In contrast, after used five times, the photocatalytic activity of the pure CdS nanomaterial is only 57% of that of the fresh sample. This study will supply a new idea for the design and development of highly stable and efficient CdS-based photocatalysts for H₂ evolution in the future.     

Noble-metal-free CuS/CdS composites for photocatalytic H2 evolution and its photogenerated charge transfer properties

CuS/CdS composites have been successfully prepared by a simple hydrothermal and cation exchange method. Even without noble-metal cocatalyst, the prepared CuS/CdS composites exhibited enhanced photocatalytic H₂ evolution activity. CuS content had a great influence on photocatalytic activity and an optimum amount of CuS was determined to be ca. 3 mol%, at which the CuS/CdS displayed the highest photocatalytic activity, giving an H₂ evolution rate of 332 μmol g⁻¹ h⁻¹, exceeding that of pure CdS by 3.5 times. The results of SPV (surface photovoltage) and SPC (surface photocurrent) revealed that photogenerated electrons were captured by CuS loaded. TPV (transient photovoltage techniques) indicated that photogenerated charges lifetime in CdS, was prolonged with CuS loaded. Those are the main reasons for the improvement of photocatalytic H₂ evolution.     

Synergistic enhancement of photocatalytic H2 production by Ni decorated 2D bubble-like carbon nitride

In this paper, a novel 2D bubble-like g-C₃N₄ (B–CN) with a highly porous and crosslinked structure is successfully synthesized via a cost-effective bottom-up process. The as-prepared B–CN photocatalyst delivers a considerably expanded specific surface area and increased active sites. Moreover, the 2D bubble-like structure can afford shortened diffusion paths for both photogenerated charge carriers and reactants. As a result, the photocatalytic H₂ evolution rate of B–CN reached 268.9 μmol g^?1 h^?1, over 5 times more than that of bulk C₃N₄. The Ni ions were further deposited on B–CN as a cocatalyst to enhance the photocatalytic activity. Benefit from the synergy of 2D bubble-like structure and Ni species cocatalyst, recombination of photoinduced charges was greatly inhibited and the hydrogen evolution reaction (HER) was significantly accelerated. The resulted catalyst achieved a dramatically high H₂ evolution rate of 1291 μmol g^?1 h^?1. This work provides an alternative way to synthesize novel porous carbon nitride together with non-noble metal cocatalysts toward enhanced photocatalytic activity for H₂ production.     

Highly active FexCo1-xP cocatalysts modified CdS for photocatalytic hydrogen production

In this paper, we report a ternary Fe_xCo_1−xP co-catalyst, which can greatly improve the photocatalytic performance of CdS photocatalyst for hydrogen production under visible light irradiation. The high efficiency of ternary Fe_xCo_1-xP loaded CdS is mainly due to the high electrochemical activity and efficient charge transfer between Fe_xCo_1-xP cocatalyst and CdS. Experimental results have shown that the substitution of Fe ions for some Co ions in CoP can change the electrochemical properties of Fe_xCo_1-xP. The electrocatalytic performance of Fe_xCo_1-xP and the photocatalytic activity of Fe_xCo_1-xP/CdS are both dependent on the molar concentration x of Fe. When x = 0.4 the hydrogen generation rate (18.27 mmol h⁻¹ g⁻¹) and the quantum efficiency (50.6% at 420 nm) for 0.5 wt% Fe_0.4Co_0.6P/CdS photocatalyst is 5.85 times higher than that of pure CdS and 1.35 times higher than that of 0.5 wt% CoP/CdS. This new noble-metal-free Fe_xCo_1-xP cocatalyst is beneficial for the solar hydrogen economy.     

Facile fabrication of nickel/porous g-C3N4 by using carbon dot as template for enhanced photocatalytic hydrogen production

Ni/porous g-C₃N₄ was prepared by high temperature thermal polymerization process using carbon dots as soft template and photodeposition. With nickel nanoparticles supported as co-catalyst, the hydrogen evolution reaction (HER) activity of the photocatalyst has been significantly enhanced under visible light, which is up to 1273.58 μmol g⁻¹ h⁻¹, superior to pristine g-C₃N₄ (4.12 μmol g⁻¹ h⁻¹). This is attributed to the inhibited recombination of photogenerated electron-hole pairs and the much better electron transport efficiency. The formed porous structure of carbon nitride could facilitate light utilization and together with nickel nanoparticles, better charge separation can be realized which are proved by the photoluminescence, time-resolved photoluminescence spectra, transient photocurrent measurements and electrochemical impendence spectroscopy. This work provides a useful route to obtain less expensive and efficient photocatalyst containing no noble metals for hydrogen production.     

Decoration of nicale phosphide nanoparticles on CdS nanorods for enhanced photocatalytic hydrogen evolution

Manipulation of the co-catalyst plays an important role in charge separation and reactant activation to enhance the activity of CdS based photocatalysts. Transition-metal phosphides have aroused widespread interest in catalysis owing to their special structure and catalytic behavior. Herein, Ni₂P as a cocatalyst coupled with CdS for efficient photocatalytic hydrogen evolution with a rate of 483.25 mmol g^?1.h^?1, which was nearly 525 and 1.92 times higher than that of CdS (0.92 mmol g^?1.h^?1) and 1 wt% noble metal Pt modified CdS (251.29 mmol g^?1.h^?1), respectively. Its apparent quantum yield reaches 70% at 420 nm. Based on data analysis, Schottky heterostructure was constructed by combining Ni₂P with CdS. The Schottky junction provides a convenient way for photoinduced electrons to transfer and promotes the effective separation of photoinduced carriers.     

Fabrication of CdS/Zn2GeO4 heterojunction with enhanced visible-light photocatalytic H2 evolution activity

CdS/Zn₂GeO₄ (CG) composites were synthesized through the simple hydrothermal process. The crystal structure, morphology and light absorption property of the products were studied in detail. The CG composites showed excellent photocatalytic hydrogen production performance upon visible light illumination. Especially, the CG-3 composite displayed the highest H₂ evolution rate of 1719.8 μmol h⁻¹ g⁻¹, which was about 3.80 and 4.28 times higher than the pure CdS and Zn₂GeO₄. Besides, the cyclic stability of the CG-3 composite was also excellent. The PL, photocurrent response and EIS spectra results testified that the efficient separation and transfer of photoinduced charge carriers achieved between CdS and Zn₂GeO₄, which could result in the promotion of photocatalytic performance. Moreover, a possible mechanism of H₂ generation over CdS/Zn₂GeO₄ heterojunction was discussed. The practicable way to construct heterojunction composites would be helpful for the design of other systems with excellent photocatalytic property.     

Vanadium diboride as an efficient cocatalyst coupled with CdS for enhanced visible light photocatalytic H2 evolution

Exploiting active, stable, and cost-efficient cocatalysts is crucial to enhance the photocatalytic performance of semiconductor-based photocatalysts for H₂ evolution from water splitting. Herein, we report on using vanadium diboride (VB₂) as an efficient cocatalyst to enhance the photocatalytic H₂ evolution performance of CdS nanoparticles under visible light irradiation (λ ≥ 420 nm). The CdS/VB₂ composites prepared by a facile solution-mixing method exhibit much improved H₂ evolution activities in 10 vol% lactic acid (LA) solution relative to pristine CdS. The most efficient CdS/VB₂ composite with 20 wt% VB₂ (CB20) exhibits a H₂ evolution rate as high as 12.1 mmol h⁻¹ g⁻¹, which is about 11 times higher than that of CdS alone (1.1 mmol h⁻¹ g⁻¹). Moreover, the highest apparent quantum efficiency (AQE) of 4.4% is recorded on CB20 at 420 nm. The improved photocatalytic activity of CdS/VB₂ composite can be attributed to the excellent cocatalytic effect of VB₂, which can not only enhance the charge separation on CdS but also accelerate the H₂ evolution kinetics. This work demonstrates the great potential of using transition metal brodies (TMBs) as efficient cocatalysts for developing noble-metal-free and stable photocatalysts for solar photocatalytic H₂ evolution.     

Mesoporous g-C3N4 decorated by Ni2P nanoparticles and CdS nanorods together for enhancing photocatalytic hydrogen evolution

Ni₂P nanoparticles and CdS nanorods were grew together on a mesoporous g-C₃N₄ through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni₂P composite displays a high H₂ evolution rate with 2905.86 μmol g^?1 h^?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni₂P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni₂P. Meanwhile, Ni₂P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni₂P composite exerts good stability in 12-h cycles.     

Cd0.5Zn0.5S/Ni2P noble-metal-free photocatalyst for high-efficient photocatalytic hydrogen production: Ni2P boosting separation of photocarriers

Establishing efficient co-catalytic loaded semiconductors for efficient charge separation is a hopeful way for enhance photocatalytic water splitting hydrogen evolution. Herein, we successfully constructed the Cd_0.5Zn_0.5S/Ni₂P (CZS/Ni₂P) nanocomposites via two-step hydrothermal method. The CZS/Ni₂P composites show much improved activity than the origin CZS for photocatalytic H₂ generation. When the content of Ni₂P loaded on the Cd_0.5Zn_0.5S (CZS) is 0.3 mol%, the photocatalyst achieves the highest photocatalytic hydrogen generation rate of 41.26 mmol g⁻¹ h⁻¹ under visible light. The Ni–S bonds on the close contact interface between CZS and Ni₂P can be act as electron-bridge to provide a channel for electron transfer. During the photocatalysis processing, Ni₂P can be used as electron traps to attract electrons from CZS, resulting in the improvement of the photocatalytic performance.     

Nanoflower-like Ti3CN@TiO2/CdS heterojunction photocatalyst for efficient photocatalytic water splitting

Solar energy to hydrogen production is an effective way to solve the energy crisis. Here, we report a Ti₃CN@TiO₂/CdS photocatalyst with highly efficient photocatalytic performance. Ti₃CN@TiO₂ materials with nanoflower morphology or lamellar morphology were obtained from Ti₃AlCN by controlling the etching time, and then loaded CdS nanoparticles to improve the photocatalytic efficiency. The physical and chemical properties of the catalyst were characterized by various characterization techniques. Ti₃CN@TiO₂/CdS photocatalyst shows an enhanced photocatalytic activity of 3393.4 μmol g^?1h^?1, much higher than that of CdS and Ti₃CN@TiO₂.^.     

Separation of hot electrons and holes in Au/LaFeO3 to boost the photocatalytic activities both for water reduction and oxidation

Construction of plasmon-based nanostructures is an effective way to enhance the photocatalytic activities of semiconductor photocatalysts for water-splitting. However, the synergistic effect of plasmon-related hot electrons and holes for water splitting in the plasmon-hybrid photocatalyst is rarely considered. Herein, we construct a plasmon-based Au/LaFeO₃ composite photocatalyst to investigate the complex roles of hot electrons and holes for solar water splitting. Benefiting from the formation of Schottky junction and surface plasmon resonance effect of the Au nanoparticles, the synthesized photocatalyst exhibits an excellent photocatalytic activity for each half-reaction of water splitting, and the rates for H₂ and O₂ generation are obtained as high as 202 μmol g⁻¹ h⁻¹ and 23 μmol g⁻¹ h⁻¹, respectively. Moreover, an in-depth investigation reveals that the improved hydrogen evolution is caused by the hot electron injection from Au to LaFeO₃, and the hot holes in Au induced by the separation of hot charges can initiate the water oxidation directly on the surface of gold. Thus, this work provides a new insight into the synergistic effect of plasmon-related hot electrons and holes for boosting the photocatalytic reactions.     

Well-dispersed CoSx nanoparticles modified tubular sulfur doped carbon nitride for enhanced photocatalytic H2 production activity

Appropriate dispersion of cocatalyst on semiconductor for improving photocatalytic H₂ production efficiency is a challenging work in semiconductor photocatalysis. Herein, we constructed the noble-metal-free CoS_x modified tubular sulfur doped carbon nitride (SCN) photocatalysts by chemical precipitation process. The amorphous CoS_x well dispersed on SCN served as H₂ production sites, which reduced the overpotential and inhibited the recombination of photogenerated carriers by interfacial charge transfer. Maximized H₂ production rate of 573.06 μmol g⁻¹ h⁻¹ under visible light irradiation was obtained by optimizing the CoS_x loading proportion to 2.4%, which was higher than that of 0.75 wt% Pt/SCN. In addition, a possible mechanism for improved H₂ production activity was proposed based on the experiments and discussion. This work provides a new strategy to design rational structure of non-noble metal cocatalyst modified photocatalyst to further improve H₂ production performance.     

Enhanced photocatalytic hydrogen evolution over semi-crystalline tungsten phosphide

Increasing the separation efficiency and transfer rate of photogenerated charges is the dominant factor for improving photocatalytic activity. Herein, we successfully prepared semi-crystalline WP (SC-WP) with good optical properties and as a cocatalyst to modify CdS nanorods (CdS NRs) to construct SC-WP/CdS (PD) composite catalyst by simple electrostatic self-assembly method for photocatalytic hydrogen evolution. Two high-efficiency and stable photocatalytic hydrogen evolution systems were constructed with 1.0 M ammonium sulfite solution and 10 vol% lactic acid solution as sacrificial agents, respectively. Surprisingly, the maximum photocatalytic H₂ production rate of 15446.21 μmol h⁻¹ g⁻¹ is obtained over 10PD composite, which is 10.58 times greater than that of pure CdS. The improved photocatalytic activity can be attributed to the fact that the SC-WP nanoparticles provides a large number of exposed active sites on the surface of CdS for hydrogen evolution reaction, which can efficiently capture photogenerated electrons from CdS nanorods and promotes the transport and separation of light-induced charges. And the introduction of SC-WP nanoparticles with excellent optical properties can efficiently improve the visible light absorption range and the utilization rate of the absorbed light of the PD composite. In addition, the SC-WP nanoparticles show semi-crystalline state, which is also conducive to enhancing the photocatalytic activity.     

(In,Cu) Co-doped ZnS nanoparticles for photoelectrochemical hydrogen production

In and Cu co-doped ZnS nanoparticles were successfully synthesized in DI water and ethanol solvent by a sonochemical approach using citric acid as surfactants in aqueous medium. FESEM micrographs show that In and Cu co-doped ZnS crystallites have a rough surface nanostructure and the as-synthesized photocatalysts were tested for the photocatalytic hydrogen evolution from water splitting via the irradiation of simulated sunlight. Among In and Cu co-doped ZnS products, 4In4CuZnS photocatalyst can achieve the maximum hydrogen production rate (752.7 μmol h⁻¹ g⁻¹) in 360 min under simulated sunlight illumination. Meanwhile, we separated the hydrogen and oxygen cells using an ion exchange membrane. Both electrodes (working electrode and Pt electrode) are dipped into each cell containing an aqueous solution containing 0.1 M Na₂S at pH 3 to convert water into hydrogen and oxygen under solar irradiation. As expected, the photoelectrochemical water splitting cells could significantly improve the photocatalytic activity, where the 4In4CuZnS nanoparticles shows the photoelectrochemical performance with photocurrent density of 12.2 mA cm⁻² at 1.1 V and hydrogen evolution rate of 1189.4 μmol h⁻¹ g⁻¹.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

Efficient photocatalytic hydrogen evolution with high-crystallinity and noble metal-free red phosphorus-CdS nanorods

The photocatalytic production of H₂ by low-cost semiconductors is a promising approach to store solar energy. Photocatalysts with heterojunctions convert visible light into H₂ faster because of more efficient charge separation. The morphology, the structure, and the crystallinity are additional factors to consider when developing a photocatalyst. Here, highly-crystalline CdS nanorod (NR) were synthesized by a facile one-pot process. Under visible light, pure CdS NR produced H₂ 2.1 times faster than conventional CdS nanoparticles (NP). CdS NR were then combined with the semiconductor red phosphorus (RPh). A CdS NR-based heterojunction photocatalyst with RPh_5% had an excellent photocatalytic H₂ evolution rate of 11.72 mmol g⁻¹ h⁻¹, which was 3.6 times higher than pure CdS NR. The apparent quantum efficiency of RPh_5%/CdS NR was 19.57%. Furthermore, RPh_5%/CdS NR exhibited a superior photogenerated charge separation efficiency and was stable with little photocorrosion compared to CdS NP showing the high potential of this heterojunction photocatalyst.     

Fabricating NixCo1−xO@C cocatalysts sensitized by CdS through electrostatic interaction for efficient photocatalytic H2 evolution

Exploiting efficient and stable noble metal-free hydrogen evolution catalysts for water splitting is of great importance. In this work, Ni_xCo_1-xO@C/CdS hybrid is successfully fabricated through an electrostatic interaction of oppositely charged nanoparticles on their surfaces. The resulting Ni_xCo_1-xO@C nanoboxes cocatalysts which were derived from NiCo-LDH@ZIF-67 with Ni–Co layered double hydroxides (LDH) decorated with ZIF-67 precursor exhibited improved hydrogen production rate compared with bare CdS semiconductor from 0.7 mmol g⁻¹ h⁻¹ to 56 mmol g⁻¹ h⁻¹. It is demonstrated that the electrostatic interaction between the two surface charged nanoparticles of Ni_xCo_1-xO@C and CdS play an important role in migrating and separating of photogenerated charge carriers. The synthesized Ni_xCo_1-xO@C as excellent candidates for cost-effective cocatalysts is aimed to substitute for noble metals in photocatalytic H₂ evolution.     

Effect of tri-doping on H2 evolution under visible light irradiation on SrTiO3:Ni/Ta/La prepared by spray pyrolysis from polymeric precursor

Tri-doped photocatalyst, SrTiO₃:Ni/Ta/La, was prepared by spray pyrolysis from aqueous and polymeric precursor solutions. The third dopant, La³⁺, contributed to the BET surface area and porous morphology by preventing crystal growth, and increased the Ni²⁺/Ni³⁺ ratio by affecting the electron configuration in the lattice structure, which is closely related to the hydrogen evolution rate. The hydrogen evolution rate of the tri-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%)/La(0.3 mol%), was increased by about 60%–895.2 μmol g⁻¹ h⁻¹ from the value of 561.2 μmol g⁻¹ h⁻¹ for the co-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%), and was further enhanced to 2305.7 μmol g⁻¹ h⁻¹ when a polymeric precursor was used instead of an aqueous precursor in spray pyrolysis. The optimum additive content for polymeric precursor solution was 300 mol%.