Editorial

2 pages, 144 KiB

Open AccessEditorial

by Vignesh Kumaravel and Misook Kang

Catalysts 2020, 10(5), 492; https://doi.org/10.3390/catal10050492 - 01 May 2020

Cited by 6 | Viewed by 1722

Solar energy conversion is one of the sustainable technologies that tackles the global warming and energy crisis [...] Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

Research

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12 pages, 3193 KiB

Open AccessArticle

Photoelectrochemical Hydrogen Evolution and CO₂ Reduction over MoS₂/Si and MoSe₂/Si Nanostructures by Combined Photoelectrochemical Deposition and Rapid-Thermal Annealing Process

by Sungmin Hong, Choong Kyun Rhee and Youngku Sohn

Catalysts 2019, 9(6), 494; https://doi.org/10.3390/catal9060494 - 28 May 2019

Cited by 19 | Viewed by 5108

Abstract

Diverse methods have been employed to synthesize MoS₂ and MoSe₂ catalyst systems. Herein, a combined photoelectrochemical (PEC) deposition and rapid-thermal annealing process has first been employed to fabricate MoS₂ and MoSe₂ thin films on Si substrates. The newly developed [...] Read more.

Diverse methods have been employed to synthesize MoS₂ and MoSe₂ catalyst systems. Herein, a combined photoelectrochemical (PEC) deposition and rapid-thermal annealing process has first been employed to fabricate MoS₂ and MoSe₂ thin films on Si substrates. The newly developed transition-metal dichalcogenides were characterized by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. PEC hydrogen evolution reaction (HER) was demonstrated in an acidic condition to show a PEC catalytic performance order of MoO_x/Si < MoS₂/Si << MoSe₂/Si under the visible light-on condition. The HER activity (4.5 mA/cm² at −1.0 V vs Ag/AgCl) of MoSe₂/Si was increased by 4.8× compared with that under the dark condition. For CO₂ reduction, the PEC activity was observed to be in the order of MoS₂/Si < MoO_x/Si << MoSe₂/Si under the visible light-on condition. The reduction activity (0.127 mA/cm²) of MoSe₂/Si was increased by 9.3× compared with that under the dark condition. The combined electrochemical deposition and rapid-thermal annealing method could be a very useful method for fabricating a thin film state catalytic system perusing hydrogen production and CO₂ energy conversion. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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14 pages, 8792 KiB

Open AccessArticle

Synthesis of Spherical TiO₂ Particles with Disordered Rutile Surface for Photocatalytic Hydrogen Production

by Na Yeon Kim, Hyeon Kyeong Lee, Jong Tae Moon and Ji Bong Joo

Catalysts 2019, 9(6), 491; https://doi.org/10.3390/catal9060491 - 28 May 2019

Cited by 17 | Viewed by 5798

Abstract

One of the most important issues in photocatalysis research has been the development of TiO₂-based photocatalysts that work efficiently under visible light conditions. Here, we report the monodispersed, spherical TiO₂ particles with disordered rutile surface for use as visible-light photocatalysts. [...] Read more.

One of the most important issues in photocatalysis research has been the development of TiO₂-based photocatalysts that work efficiently under visible light conditions. Here, we report the monodispersed, spherical TiO₂ particles with disordered rutile surface for use as visible-light photocatalysts. The spherical TiO₂ particles with disordered surface were synthesized by sol-gel synthesis, followed by sequential calcination, and chemical reduction process using Li/Ethylenediamine (Li/EDA) solution. Variation of the calcination temperature allowed the crystalline properties of the calcined TiO₂ samples, such as the ratio of anatase and rutile, to be finely controlled. The content ratios of anatase phase to rutile phase leads to different degrees of disorder of the rutile surface, which is closely related to the photocatalysis activity. Chemical reduction using the Li/EDA solution enables selective reduction of the rutile surface of the calcined TiO₂, resulting in enhanced light absorption. As a result, we were able to synthesize spherical TiO₂ photocatalysts having a disordered rutile surface in a mixed crystalline phase, which is beneficial during photocatalysis in terms of light absorption and charge separation. When used as photocatalysts for hydrogen production under solar light conditions, the chemically-reduced TiO₂ particles with both the disordered rutile surface and mixed crystalline phase showed significantly enhanced catalytic activity. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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35 pages, 2989 KiB

Open AccessEditor’s ChoiceArticle

Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts

by Vignesh Kumaravel, Muhammad Danyal Imam, Ahmed Badreldin, Rama Krishna Chava, Jeong Yeon Do, Misook Kang and Ahmed Abdel-Wahab

Catalysts 2019, 9(3), 276; https://doi.org/10.3390/catal9030276 - 18 Mar 2019

Cited by 212 | Viewed by 16995

Abstract

Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H₂). In the present study, hydrogen (H₂) production efficiency of three promising photocatalysts (titania (TiO₂-P25), graphitic carbon nitride (g [...] Read more.

Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H₂). In the present study, hydrogen (H₂) production efficiency of three promising photocatalysts (titania (TiO₂-P25), graphitic carbon nitride (g-C₃N₄), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO₂-P25, g-C₃N₄, and CdS. H₂ production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H₂ generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H₂ was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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16 pages, 5315 KiB

Open AccessEditor’s ChoiceArticle

In-Situ Synthesis of Nb₂O₅/g-C₃N₄ Heterostructures as Highly Efficient Photocatalysts for Molecular H₂ Evolution under Solar Illumination

by Faryal Idrees, Ralf Dillert, Detlef Bahnemann, Faheem K. Butt and Muhammad Tahir

Catalysts 2019, 9(2), 169; https://doi.org/10.3390/catal9020169 - 11 Feb 2019

Cited by 41 | Viewed by 5718

Abstract

This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H₂). In particular, 3-dimensional Nb₂O₅/g-C₃N₄ heterostructures with suitable band [...] Read more.

This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H₂). In particular, 3-dimensional Nb₂O₅/g-C₃N₄ heterostructures with suitable band positions and high surface area have been synthesized employing a hydrothermal method. The combination of a Nb₂O₅ with a low charge carrier recombination rate and a g-C₃N₄ exhibiting high visible light absorption resulted in remarkable photocatalytic activity under simulated solar irradiation in the presence of various hole scavengers (triethanolamine (TEOA) and methanol). The following aspects of the novel material have been studied systematically: the influence of different molar ratios of Nb₂O₅ to g-C₃N₄ on the heterostructure properties, the role of the employed hole scavengers, and the impact of the co-catalyst and the charge carrier densities affecting the band alignment. The separation/transfer efficiency of the photogenerated electron-hole pairs is found to increase significantly as compared to that of pure Nb₂O₅ and g-C₃N₄, respectively, with the highest molecular H₂ production of 110 mmol/g·h being obtained for 10 wt % of g-C₃N₄ over Nb₂O₅ as compared with that of g-C₃N₄ (33.46 mmol/g·h) and Nb₂O₅ (41.20 mmol/g·h). This enhanced photocatalytic activity is attributed to a sufficient interfacial interaction thus favouring the fast photogeneration of electron-hole pairs at the Nb₂O₅/g-C₃N₄ interface through a direct Z-scheme. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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9 pages, 1901 KiB

Open AccessArticle

Band Gap Modulation of Tantalum(V) Perovskite Semiconductors by Anion Control

by Young-Il Kim and Patrick M. Woodward

Catalysts 2019, 9(2), 161; https://doi.org/10.3390/catal9020161 - 07 Feb 2019

Cited by 10 | Viewed by 4411

Abstract

Band gap magnitudes and valence band energies of Ta⁵⁺ containing simple perovskites (BaTaO₂N, SrTaO₂N, CaTaO₂N, KTaO₃, NaTaO₃, and TaO₂F) were studied by diffuse reflection absorbance measurements, density-functional theoretical calculations, and [...] Read more.

Band gap magnitudes and valence band energies of Ta⁵⁺ containing simple perovskites (BaTaO₂N, SrTaO₂N, CaTaO₂N, KTaO₃, NaTaO₃, and TaO₂F) were studied by diffuse reflection absorbance measurements, density-functional theoretical calculations, and X-ray photoelectron spectroscopy. As a universal trend, the oxynitrides have wider valence bands and narrower band gaps than isostructural oxides, owing to the N 2p contribution to the electronic structure. Visible light-driven water splitting was achieved by using Pt-loaded CaTaO₂N, together with a sacrificial agent CH₃OH. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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15 pages, 3675 KiB

Open AccessArticle

Enhancement of Hydrogen Productions by Accelerating Electron-Transfers of Sulfur Defects in the CuS@CuGaS₂ Heterojunction Photocatalysts

by Namgyu Son, Jun Neoung Heo, Young-Sang Youn, Youngsoo Kim, Jeong Yeon Do and Misook Kang

Catalysts 2019, 9(1), 41; https://doi.org/10.3390/catal9010041 - 04 Jan 2019

Cited by 12 | Viewed by 3237

Abstract

CuS and CuGaS₂ heterojunction catalysts were used to improve hydrogen production performance by photo splitting of methanol aqueous solution in the visible region in this study. CuGaS₂, which is a chalcogenide structure, can form structural defects to promote separation of [...] Read more.

CuS and CuGaS₂ heterojunction catalysts were used to improve hydrogen production performance by photo splitting of methanol aqueous solution in the visible region in this study. CuGaS₂, which is a chalcogenide structure, can form structural defects to promote separation of electrons and holes and improve visible light absorbing ability. The optimum catalytic activity of CuGaS₂ was investigated by varying the heterojunction ratio of CuGaS₂ with CuS. Physicochemical properties of CuS, CuGaS₂ and CuS@CuGaS₂ nanoparticles were confirmed by X-ray diffraction, ultraviolet visible spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Compared with pure CuS, the hydrogen production performance of CuGaS₂ doped with Ga dopant was improved by methanol photolysis, and the photoactivity of the heterogeneous CuS@CuGaS₂ catalyst was increased remarkably. Moreover, the [email protected]₂ catalyst produced 3250 μmol of hydrogen through photolysis of aqueous methanol solution under 10 h UV light irradiation. According to the intensity modulated photovoltage spectroscopy (IMVS) results, the high photoactivity of the CuS@CuGaS₂ catalyst is attributed to the inhibition of recombination between electron-hole pairs, accelerating electron-transfer by acting as a trap site at the interface between CuGaS₂ structural defects and the heterojunction. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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Review

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19 pages, 5693 KiB

Open AccessReview

Photocatalytic Hydrogen Evolution via Water Splitting: A Short Review

by Yifan Zhang, Young-Jung Heo, Ji-Won Lee, Jong-Hoon Lee, Johny Bajgai, Kyu-Jae Lee and Soo-Jin Park

Catalysts 2018, 8(12), 655; https://doi.org/10.3390/catal8120655 - 12 Dec 2018

Cited by 45 | Viewed by 13185

Abstract

Photocatalytic H₂ generation via water splitting is increasingly gaining attention as a viable alternative for improving the performance of H₂ production for solar energy conversion. Many methods were developed to enhance photocatalyst efficiency, primarily by modifying its morphology, crystallization, and electrical [...] Read more.

Photocatalytic H₂ generation via water splitting is increasingly gaining attention as a viable alternative for improving the performance of H₂ production for solar energy conversion. Many methods were developed to enhance photocatalyst efficiency, primarily by modifying its morphology, crystallization, and electrical properties. Here, we summarize recent achievements in the synthesis and application of various photocatalysts. The rational design of novel photocatalysts was achieved using various strategies, and the applications of novel materials for H₂ production are displayed herein. Meanwhile, the challenges and prospects for the future development of H₂-producing photocatalysts are also summarized. Full article

(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

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