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.     

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.     

Novel microreactors of polyacrylamide (PAM)CdS microgels for admirable photocatalytic H2 production under visible light

Cadmium sulfide, with its narrow band gap, can be used as a photocatalyst in the visible light region for the splitting of water, but its limited number of active sites and tendency to agglomerate are problematic for producing high yields of hydrogen. Therefore, an inverse emulsion polymerization method was used to fabricate polyacrylamide (PAM) microgels as a substrate to immobilize CdS nanoparticles (PAM-CdS). The PAM microgels not only immobilized the CdS nanoparticles, but also prevented aggregation. NCd bonds in the PAM-CdS microgels facilitated electron transfer from the PAM to the CdS resulting in more electrons participating in the H₂ production process. The electrostatic interactions between the PAM and CdS also hindered the recombination of electron-hole pairs. These PAM-CdS microgels exhibit admirable photocatalytic H₂ production performance with a H₂ production rate of up to 5.21 mmol h⁻¹ g⁻¹.     

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.     

Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

Construction of porous Ni2P cocatalyst and its promotion effect on photocatalytic H2 production reaction and CO2 reduction

Due to superior light absorption abilities, porous materials are suitable to be served in photocatalytic reactions. In this study, porous Ni₂P is target-constructed from porous Ni(OH)₂ nanoflower. Promotion effect of the porous Ni₂P as cocatalyst is confirmed on photocatalytic performance of Ni₂P/CdS composite. The constructed porous Ni₂P/CdS photocatalyst shows much higher photocatalytic H₂ evolution rate (111.3 mmol h⁻¹ g⁻¹) from water and much higher CO (178.0 μmol h⁻¹ g⁻¹) and CH₄ (61.2 μmol h⁻¹ g⁻¹) evolution rates from CO₂ reduction than non-porous Ni₂P/CdS photocatalyst. Characterizations including UV-Vis diffuse reflectance, photoluminescence, transient photocurrent response, electrochemical impedance and electron paramagnetic resonance are conducted to verify the role of porous Ni₂P cocatalyst. The slow photon effect derived from porous structure Ni₂P is found to improve light path and increase the absorption utilization of light. The enhanced photocurrent intensity and the lowered resistance of porous Ni₂P/CdS due to the formed heterojunctions indicate much rapid isolation of photogenerated electron-hole pairs and rapid charge transfer of electrons. The higher signal of ⋅O₂- radicals is detected in porous Ni₂P/CdS than non-porous Ni₂P/CdS, which result in the remarkable photocatalyst activities of porous Ni₂P/CdS. Reaction mechanisms over Ni₂P/CdS photocatalyst are illustrated with a Z-scheme charge transfer path.     

Organic molecule embedded CdS nanocomposite for hydrogen generation from water: Effect of precursors’ concentrations

Organic molecule (Histidine) embedded cadmium sulfide (CdS) nanocomposites are prepared by the solvothermal method. CdS nanocomposite, prepared with 1:1 M ratio of S²⁻ to Cd²⁺, shows the highest crystallinity and highest hydrogen production via water splitting. Optimization of Pt deposition indicates that 5.5 wt% of Pt deposition on CdS nanocomposite produces the highest amount of H₂ gas. Moreover, the contents of histidine in CdS were changed from 0.0 to 2.5 mmol, and the result shows that CdS nanocomposite with 1 mmol of histidine has the highest rate of hydrogen production (21.35 mmol/g/h). This is one of the highest rates of hydrogen production from a single semiconductor photocatalyst system under visible light irradiation. These results indicate that organic molecules embedded CdS nanocomposites could be a promising photocatalyst for hydrogen production via water splitting.     

Hydrogen adsorption properties of in-situ synthesized Pt-decorated porous carbons templated from zeolite EMC-2

To increase the interaction between the adsorbed hydrogen and the adsorbent surface to improve the hydrogen storage capacity at ambient temperature, decorating the sorbents with metal nanoparticles, such as Pd, Ni, and Pt has attracted the most attention. In this work, Pt-decorated porous carbons were in-situ synthesized via CVD method using Pt-impregnated zeolite EMC-2 as template and their hydrogen uptake performance up to 20 bar at 77, 87, 298 and 308 K has been investigated with focus on the interaction between the adsorbed H₂ and the carbon matrix. It is found that the in-situ generated Pt-decorated porous carbons exhibit Pt nanoparticles with size of 2–4 nm homogenously dispersed in the porous carbon, accompanied with observable carbon nanowires on the surface. The calculated H₂ adsorption heats at/near 77 K are similar for both the plain carbon (7.8 kJ mol⁻¹) and the Pt-decorated carbon (8.3 kJ mol⁻¹) at H₂ coverage of 0.08 wt.%, suggesting physisorption is dominated in both cases. However, the calculated H₂ adsorption heat at/near 298 K of Pt-decorated carbon is 72 kJ mol⁻¹ at initial H₂ coverage (close to 0), which decreases dramatically to 20.8 kJ mol⁻¹ at H₂ coverage of 0.014 wt.%, levels to 17.9 at 0.073 wt.%, then gradually decreases to 2.6 kJ mol⁻¹ at 0.13 wt.% and closes to that of the plain carbon at H₂ coverage above 0.13 wt.%. These results suggest that the introduction of Pt particles significantly enhances the interaction between the adsorbed H₂ and the Pt-decorated carbon matrix at lower H₂ coverage, resulting in an adsorption process consisting of chemisorption stage, mixed nature of chemisorption and physisorption stage along with the increase of H₂ coverage (up to 0.13 wt.%). However, this enhancement in the interaction is outperformed by the added weight of the Pt and the blockage and/or occupation of some pores by the Pt nanoparticles, which results in lower H₂ uptake than that of the plain carbon.     

Interfacing CdS particles on Ni foam as a three-dimensional monolithic photocatalyst for efficient visible-light-driven H2 evolution

Solar photocatalytic water splitting using particulate semiconductors has been valued as a potentially scalable way for the production of clean H₂ energy, yet the performances of the powder-suspension systems are constrained by insufficient utilization of light energy and tedious recycling of photocatalyst particles. Here, we present a high-performance photocatalytic H₂ evolution using a visible-light-driven CdS-based monolithic photocatalyst with three-dimensional (3D) heterostructure. The monolithic photocatalyst is fabricated by firmly growing CdS microspheres on a Ni(OH)₂ nanosheet-modified Ni foam (NF) (denoted as CdS-NiS_x/NF) via a simple hydrothermal process. The structure and component synergy endows the monolithic CdS-NiS_x/NF photocatalyst advantageous features including high-density CdS microspheres for visible light harvesting, multiple heterojunction interfaces for efficient electron-hole separation, and abundant interfacial NiS_x active sites for efficient H₂ evolution reaction (HER). Upon visible light irradiation, the monolithic CdS-NiS_x/NF photocatalyst exhibits an outstanding photocatalytic H₂ evolution activity with an enhanced rate of 6.2 mmol·h⁻¹ g⁻¹_CdS, which is 6 times higher than that of the suspended CdS powder. In addition, the structural integrity of the CdS-NiS_x/NF enables a good stability for H₂ evolution over a 30 h reaction. This monolithic photocatalyst is scalable in preparation and compatible for device fabrication, which offers great potentials for applications in solar cells, photoelectrocatalysis, and electrocatalysis.     

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.     

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.^.     

Silicon monoxide assisted synthesis of Ru modified carbon nanocomposites as high mass activity electrocatalysts for hydrogen evolution

Extremely low content of Ruthenium (Ru) nanoparticles were loaded on the carbon black (Ru/C) via reducing Ru ions with silicon monoxide. The obtained Ru/C nanocomposites exhibit an exciting electrochemical catalytic activity for hydrogen evolution reaction (HER) in the oxygen-free 0.5 M H₂SO₄ medium. The optical one (Ru/C-2) with a low Ru amount of 2.34% shows higher activity than previously reported Ru-based catalysts. The overpotential at 10 mA cm⁻² is 114 mV and the Tafel slope is 67 mV·dec⁻¹. Ru/C-2 catalyst also has good stability. The overpotential that afford the current density of 10 mA cm⁻² of 20 wt% Pt/C increased 92 mV while that of Ru/C-2 only increased 50 mV after a 30,000 s chronopotentiometry test. Furthermore, the mass activity of Ru/C-2 catalyst is even better than that of the commercial 20 wt% Pt/C when the overpotential is larger than 0.18 V. This silicon monoxide-mediated strategy may open a new way for the fabrication of high performance electrocatalysts.     

Structure characteristics of CdS/H1.9K0.3La0.5Bi0.1Ta2O7 and photocatalytic activity for hydrogen evolution under visible light

Visible-light-driven CdS/HKLBT photocatalyst was prepared by ion exchange of Cd²⁺ in aqueous Cd(CH₃COO)₂ solutions, then by sulfurization in aqueous N₂H₈S solutions. The characterization by XRD, SEM, HRTEM and XRS revealed that CdS nanoparticles exist both on the surface and in the interlayer of HKLBT. The composite CdS/HKLBT showed higher photocatalytic activity for hydrogen evolution (504.2 μmol/h) than that of pure CdS (187.3 μmol/h), even than that of 0.5 wt%Pt/CdS (496.0 μmol/h) under visible light (λ > 400 nm) in the presence of lactic acid as sacrificial reagent. The enhancement of photocatalytic activity is attributed to the strong contact between CdS and HKLBT in CdS/HKLBT as well as the effective separation of photogenerated carrier in CdS through electron rapid injection into CB of HKLBT.     

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.     

Hydrogen generation by photocatalytic reforming of glucose with heterostructured CdS/MoS2 composites under visible light irradiation

A binary heterostructured CdS/MoS₂ flowerlike composite photocatalysts was synthesized via a simple one-pot hydrothermal method. This photocatalyst demonstrated higher photocatalytic hydrogen production activity than pure MoS₂. The heterojunction formed between MoS₂ and CdS seems to promote interfacial charge transfer (IFCT), suppress the recombination of photogenerated electron–hole pairs, and enhance the hydrogen generation. Based on the good match between the conduction band (CB) edge of CdS and that of MoS₂, electrons in the CB of CdS can be transferred to MoS₂ easily through the heterojunction between them, which prevents the accumulation of electrons in the CB of CdS, inhibiting photocorrosion itself and greatly enhancing stability of catalyst. Hydrogen evolution reaction (HER) using Na₂S/Na₂SO₃ or glucose as sacrificial agents in aqueous solution was investigated. The ratio between CdS and MoS₂ plays an important role in the photocatalytic hydrogen generation. When the ratio between CdS and MoS₂ reaches 40 wt%, the photocatalyst showed a superior H₂ evolution rate of 55.0 mmol g⁻¹ h⁻¹ with glucose as sacrificial agent under visible light, which is 1.2 times higher than using Na₂S/Na₂SO₃ as sacrificial agent. Our experimental results demonstrate that MoS₂-based binary heterostructured composites are promising for photocorrosion inhibition and highly efficient H₂ generation.     

Refined Z-scheme charge transfer in facet-selective BiVO4/Au/CdS heterostructure for solar overall water splitting

Artificial Z-scheme systems that mimic natural photosynthesis are well applicable to photocatalytic overall water splitting for hydrogen (H₂) production free of electricity. However, it commonly confronts low efficiency with huge challenge of steering charge transfer between H₂ evolution photocatalyst (HEP) and oxygen evolution photocatalyst (OEP). Here we report an all-solid-state Z-scheme system with facet-selective construction that favors charge spatial separation toward HEP and OEP for high efficient solar overall water splitting. Based on the spontaneous separation of photogenerated electrons and holes on the different crystal facets of BiVO₄ decahedra, we successively implemented the selective depositions of Au and CdS nanoparticles (NPs) onto the electron-rich {010} facets, to fortify the Z-scheme charge transfer between BiVO₄ and CdS across Au mediators upon two-step photoexcitation. In-situ photoelectron dynamics ascertains Z-scheme model of resultant BiVO₄/Au/CdS, which enables an impressive overall water splitting with stoichiometric H₂ and O₂ evolution rates of 281 and 138 μmol g^?1 h^?1, respectively, under 1 sun irradiation (100 mW cm^?2, AM 1.5G) without using any sacrificial agents and external bias. This work not only presents a refined Z-scheme overall water splitting system, but also gains insights into photo-induced charge transfer dynamics.     

Non-noble-metal Ni nanoparticles modified N-doped g-C3N4 for efficient photocatalytic hydrogen evolution

The use of non-noble-metal to replace precious metal as co-catalyst in solar-driven hydrogen evolution reaction (HER) is important for lowering hydrogen production cost. In this work, nickel metal nanoparticles loaded nitrogen-doped graphite carbon nitride (NiNCN3) was prepared, which significantly enhanced the HER activity of nitrogen-doped graphite carbon nitride. The hydrogen evolution rate of NiNCN3 can reach to 1507 μmol g⁻¹ h⁻¹, much higher than that of 3 wt % Pt/NCN (1055 μmol g⁻¹ h⁻¹). The distinguished photocatalytic performance is due to the accelerated electron transfer efficiency and inhibited photogenerated electron-hole recombination. Our study offers an alternative method to achieve the low-cost and effective noble-metal-free photocatalyst for HER.     

Nanoarchitectonics of CdS/ZnSnO3 heterostructures for Z-Scheme mediated directional transfer of photo-generated charges with enhanced photocatalytic performance

The construction of heterostructure is an effective strategy to synergetically couple wide-band-gap with the narrow-band-gap semiconductor with a mediate optical property and charge transfer capability. Herein, the Z-Scheme CdS/ZnSnO₃ (CdS/ZSO) heterostructures were constructed by anchoring CdS nanoparticles on the surface of double-shell hollow cubic ZnSnO₃ via the hydrothermal method. The direct recombination of excited electrons in the conduction band (CB) of ZSO and holes in the valence band (VB) of CdS via d-p conjugation at the interface greatly accelerated the internal electric field (IEF). The transfer mode follows the Z-Scheme mechanism, where CdS/ZSO synergistically facilitates the efficient charges transfer from CdS to ZnSnO₃ through the intimate interface. Here, ZnSnO₃ and CdS serve as an oxidation photocatalyst (OP) and reduction photocatalyst (RP), respectively. Thus, it can promote synergistically the oxidation half-reaction and reduction half-reaction of H₂ evolution. The density-functional theory (DFT) calculation further confirms the charges transfer from CdS to ZnSnO₃. The hydrogen evolution of 5% CdS/ZSO heterostructure reached 1167.3 μmol g^?1, which was about 8 and 3 folds high compared to pristine ZSO (141.9 μmol g^?1) and CdS (315.5 μmol g^?1), during 3 h of reaction respectively. Furthermore, the CdS/ZSO heterostructures could suppress the photo corrosion of CdS, resulting in its high stability. This work is expected to enlighten the rational design of heterostructure for OP and RP to promote the hybrid heterostructures photocatalytic H₂ evolution.     

Photocatalytic decomposition of H2S to produce H2 over CdS nanoparticles formed in HY-zeolite pore

The H₂ production rate from H₂S photocatalytic decomposition under visible light irradiation (λ > 400 nm) over CdS nanoparticules formed in HY-zeolite pore (named CdS/HY) was much higher compared to the commercial bulk CdS. The CdS/HY photocatalyst was characterized by UV–Vis, XRD, FT-IR, N₂ adsorption, SEM and HRTEM. The blue shift from bulk which confirmed CdS nanoparticles located in the pore of HY-Zeolite (named HY). Photocatalytic activity and surface area were enhanced by such structures.     

Synthesis of Al-substituted mesoporous silica coupled with CdS nanoparticles for photocatalytic generation of hydrogen

Aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS nanoparticles (CdS/Al-HMS) were prepared by template assembly, ion-exchange and sulfuration routes. The XRD and TEM results indicated that the assembly of less than 2 wt% CdS nanoparticles in the porous channels of Al-HMS didn't significantly affect the wormhole-like mesoporous framework structure of Al-HMS, whereas the porous channels of Al-HMS were filled up by CdS nanoparticles after loading of 21 wt% CdS. The diffuse reflectance UV–visible spectra exhibited that the absorption edge was gradually blue-shifted with decrease in CdS content due to the quantum confinement effect. The CdS/Al-HMS sample loaded 0.99 wt% Ru showed the highest H₂ evolution at a rate of 13.23 mL h⁻¹ with an apparent quantum yield of 5.92% at 420 nm by photocatalytic degradation of formic acid under visible light irradiation.