Photocatalyst For Hydrogen Evolution Research Articles

Facile synthesis of bimodal porous graphitic carbon nitride nanosheets as efficient photocatalysts for hydrogen evolution

A novel, facile, and cost-effective approach has been developed for the preparation of hierarchically bimodal porous graphitic carbon nitride nanosheets (BP-g-C3N4) by KOH activation and thermal oxidation simultaneously. The BP-g-C3N4 demonstrates a high surface area of 219 m2 g−1, high porosity and hierarchically bimodal porous structure, which enhances the electron transport ability and photoreaction activity, enlarges the band gap, and prolongs the lifetime of the photoexcited charge carriers. Consequently, the BP-g-C3N4 exhibits a highly improved photocatalytic activity of 1900 µmol h−1 g−1 (8.6 times higher than that of bulk g-C3N4) towards hydrogen evolution and excellent cycling stability.

Co3O4/Ni-based MOFs on carbon cloth for flexible alkaline battery-supercapacitor hybrid devices and near-infrared photocatalytic hydrogen evolution

Metal-organic frameworks (MOFs) appear as interesting candidates for various applications. Herein, we report the growth of Ni-based MOF nanosheets on a flexible carbon cloth substrate as a binder-free anode. Furthermore, unique core-shell Co3O4/Ni-based MOFs are successfully anchored on a carbon cloth substrate by a facile two-step hydrothermal method. The as-prepared hybrid materials are directly used as electrode materials without adding any nonelectroactive components such as the insulating binders or conductive additive, which exhibit an excellent specific capacity (209 mAh g−1 at 1.0 A g−1) and a good cycling stability (90% retention after 3000 cycles). In addition, triethanolamine (TEOA)-assisted Ni-based MOF can be used as a photocatalyst for hydrogen evolution from water splitting under the near-infrared irradiation (λ > 800 nm). The present results reveal a potential prospect for the Co3O4/Ni-based MOFs in the field of energy storage and the near-infrared driven photocatalyst.

Effects of Se Incorporation in La5Ti2CuS5O7 by Annealing on Physical Properties and Photocatalytic H2 Evolution Activity.

Oxysulfoselenide semiconductor photocatalysts absorb light at longer wavelengths than the corresponding oxysulfides. However, the synthesis of oxysulfoselenides is challenging due to excessive particle growth and the limited availability of metal selenide precursors. In this study, a La5Ti2CuS5O7 (LTCSO) oxysulfide was annealed with Se powder in sealed, evacuated quartz tubes to obtain LTCSO:Se photocatalysts, and the properties of these materials were investigated. Se was found to be incorporated into the LTCSO upon heating at 973 K or higher, and the Se/(S + Se) ratio was increased to a maximum of 0.3 upon repeating the heat treatment twice. The addition of Se extended the absorption edge of the LTCSO and thus increased its photocatalytic H2 evolution activity at longer wavelength. Even so, the apparent quantum yield at shorter wavelengths was reduced, which is similar to the results obtained for La5Ti2Cu(S1- xSe x)5O7 (LTCS1- xSe xO) solid solutions. Overall water splitting was achieved by constructing photocatalyst sheets using LTCSO:Se and LTCS1- xSe xO as hydrogen evolution photocatalysts and BiVO4 as an oxygen evolution photocatalyst. Heat treatment with Se is evidently an effective method for the transformation of oxysulfide photocatalysts to oxysulfoselenides that promote photocatalytic H2 evolution and have longer absorption edge wavelengths.

Carbon Nitride Nanocomposites with Layered Niobates as Photocatalysts for Hydrogen Evolution from Aqueous Solutions of Organic Acids by the Action of Visible Light

The efficiency of H2 evolution from aqueous solutions of organic acids using composite photocatalysts derived from layered KNb3O8 and C3N4 was found to be much higher than for individual C3N4. This enhanced photocatalytic activity may be attributed to better separation of the photogenerated charges between the composite components and suppression of unwanted electron–hole recombination.

(Invited) Particulate Photocatalyst Systems for Sunlight-Driven Water Splitting

Sunlight-driven water splitting has been studied actively for production of renewable solar hydrogen as a storable and transportable energy carrier [1-3]. Both the efficiency and the scalability of water-splitting systems are important factors for practical utilization of renewable solar hydrogen because of the low areal density of solar energy. Particulate photocatalyst systems do not involve any secure electric circuit and thus can be spread over a wide area by inexpensive processes potentially. In this regard, activation of particulate photocatalysts and development of their reaction systems are important subjects. A semiconductor photocatalyst can split water into hydrogen and oxygen thermodynamically when the band gap straddles the potentials of the hydrogen evolution reaction (0 V vs. RHE) and the oxygen evolution reaction (+1.23 V vs. RHE). In addition, it is generally necessary to modify photocatalysts with appropriate cocatalysts in order to facilitate charge separation and surface redox reactions. The authors’ group has studied various semiconducting materials including oxides, (oxy)nitrides, and (oxy)chalcogenides for photocatalytic water splitting [1]. Recently, we have found that doping Al into SrTiO3 boosts the water splitting activity by two orders of magnitude [4]. The resultant Al-doped SrTiO3 achieved an apparent quantum yield (AQY) of 30% at 360 nm. Through the optimization of the preparation and modification methods of Al-doped SrTiO3, the AQY of photocatalytic water splitting has been upgraded to 56% and higher at 365 nm. Processing of such particulate photocatalysts into potentially extensible forms is to be presented [5]. Two different photocatalysts can also be combined so that hydrogen and oxygen are generated on the different photocatalysts [1,3]. Recently, the authors’ group has developed particulate photocatalyst sheets consisting of the hydrogen evolution photocatalyst (HEP) and the oxygen evolution photocatalyst (OEP) embedded into conductive layers by particle transfer [6-11]. A photocatalyst sheet consisting of La- and Rh-codoped SrTiO3 as the HEP and Mo-doped BiVO4 as the OEP embedded into a carbon conductor exhibits a solar-to-hydrogen energy conversion efficiency of 1.0% at ambient pressure [10]. The photocatalyst sheet shows significantly higher water splitting activity than the corresponding powder suspension systems, because the conductor layer transfers photogenerated electrons between photocatalyst particles effectively. In addition, evolution of hydrogen and oxygen in close proximity allows to prevent generation of pH gradient during the water splitting reaction. Therefore, the photocatalyst sheet is scalable directly without sacrificing the high activity. However, the absorption edge wavelengths of La- and Rh-codoped SrTiO3 and Mo-doped BiVO4 are 520 nm at most. It is necessary to utilize photocatalysts with longer absorption edge wavelengths to pursuit higher STH values. We have found that some (oxy)chalcogenides and (oxy)nitrides with narrower band gap energies are applicable as the HEP and the OEP of particulate photocatalyst sheets. In this talk, recent progress and future challenges in photocatalytic water splitting and system development will be presented. Hisatomi et al., Chem. Soc. Rev. 2014, 43, 7520.Hisatomi et al., Catal. Lett. 2015, 145, 95.Hisatomi et al., Faraday Discuss. 2017, 198, 11.Ham et al., J. Mater. Chem. A 2016, 4, 3027.Xiong et al., Catal. Sci. Technol. 2014, 4, 325.Minegishi et al., Chem. Sci. 2013, 4, 1120.Wang et al., J. Catal. 2015, 328, 308Wang et al., Nat. Mater. 2016, 15, 611Wang et al., Faraday Discuss. 2017, 197, 491Wang et al., J. Am. Chem. Soc. 2017, 139, 1675.Hisatomi et al., Curr. Opin. Electrochem. 2017, 2, 148.

(Invited) High Surface Area, Amorphous Titania with Reactive Ti3+ through a Photo-Assisted Synthesis Method for Photocatalytic H2 Generation

Amorphous titania-based photocatalysts are synthesized using a facile, UV-light mediated method and evaluated as photocatalysts for hydrogen evolution from water/methanol mixtures. The photocatalysts are prepared through the direct injection of a titanium alkoxide precursor into a water/methanol mixture, with subsequent hydrolysis, condensation, and polycondensation to form TiOx(OH)y species under UV-irradiation. The resulting amorphous titania materials exhibit an overall higher hydrogen evolution rate compared to a crystalline TiO2 reference (P25) on a molar basis of photocatalyst due to the highly porous structure and high surface area (~500 m2/g). The employed titanium alkoxide precursor did not play a major role in affecting the hydrogen evolution rate or the catalyst surface and morphology. A blue coloration, which is associated with the formation of Ti3+ species, was observed in the amorphous titania but not in P25 upon light irradiation and is enabled by the porous and disordered structure of the amorphous photocatalyst. The Ti3+ species are also used to reduce protons to H2 in the absence of light irradiation or reduce Pt2+ to form Pt nanoparticles. These Pt nanoparticles are smaller and better dispersed on the photocatalyst compared to particles prepared using conventional photodeposition, leading to higher H2 evolution rates. The results show that the direct injection method is a facile approach for the preparation of high surface area titania photocatalysts containing Ti3+ species with good photocatalytic activity for production of H2.

SWCNT Photocatalysts for Hydrogen Evolution from Water

Visible and near-infrared (NIR) light-induced water splitting has received considerable attention in terms of solar energy conversion and hydrogen energy storage. Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption wavelengths between 500 and 1350 nm depending on their chiral indices (n,m). However, their application for solar energy conversion is difficult because of the large binding energy (> 100 meV) of excitons. In order to make SWCNTs act as a H2-evolving photocatalyst, we have developed coaxial p-n heterojunction systems consisting of a SWCNT and fullerodendrons, such as SWCNT/fullerodendron, SWCNT/fullerodendron/SiO2, SWCNT/fullerodendron/Pt(II), SWCNT/fullerodendron/TiOx. This paper describes fabrication of several SWCNT photocatalysts and their photocatalytic activity for H2 evolution from water by the use of a three-component system and an interconnecting system including Z-scheme (Figure 1). Figure 1

Construction of network-like and flower-like 2H-MoSe2 nanostructures coupled with porous g-C3N4 for noble-metal-free photocatalytic H2 evolution under visible light

Colloidally synthesized flower-like and network-like MoSe2 nanostructures are coupled with porous g-C3N4 nanosheets through a facile solution-phase route. Herein, two distinct morphological structures of MoSe2/g-C3N4 hybrid nanocomposites are applied as noble-metal-free photocatalysts for hydrogen (H2) evolution. In the resulting optimally-designed hybrid systems, the optimal flower-like and network-like MoSe2 nanostructures loading is determined to be 5 wt%, attaining a maximum H2 evolution rate of 114.5 μmol h−1 g−1 and 136.8 μmol h−1 g−1, respectively. In comparison with flower-like MoSe2 cocatalysts, the network-like MoSe2 hybridized with g-C3N4 endows excellent photocatalytic H2 evolution activity. This phenomenon stems from the intimate formation of unique sheet-on-sheet nanoarchitecture, which is auspicious for the absorption of light and high-efficiency separation of photoexcited electron-hole pairs to hamper the charge recombination. The present studies elucidate the prevailing role of MoSe2 nanostructures as active catalytic sites for H2 evolution, and importantly, the hybrid systems exhibit high photocatalytic stability. Collectively, the work opens up new insights for the utilization of low-cost MoSe2 nanomaterials as remarkable noble-metal-free cocatalysts for effective photocatalytic H2 generation.

P-doped ZnxCd1−xS solid solutions as photocatalysts for hydrogen evolution from water splitting coupled with photocatalytic oxidation of 5-hydroxymethylfurfural

Photocatalytic water splitting over semiconductors without using of any electron sacrificial agents is essential to the conversion of solar energy into chemical energy. Herein, we report remarkable photocatalytic hydrogen production from pure water without the assistance of electron sacrificial agents by using P-doped ZnxCd1−xS with rich S vacancies (ZnxCd1−xS-P) as the photocatalyst. It is found that interstitial P doping in ZnxCd1−xS solid solutions with rich S vacancies can prolong the lifetime of charge carriers and enhance the generation and separation of photogenerated electrons-holes, resulting in a H2 evolution rate of up to 419 μmol h−1 g−1, which is 72 and 7.5 times higher than those of ZnS-P (5.8 μmol h−1 g−1) and CdS-P (56 μmol h−1 g−1), respectively. Furthermore, the introduction of biomass-derived compound 5-hydroxymethylfurfural (HMF) into this system further promotes the photocatalytic hydorgen evolution reaction and simultaneously obtains value-added HMF oxidation products.

Facile bottom-up synthesis of partially oxidized black phosphorus nanosheets as metal-free photocatalyst for hydrogen evolution

Few-layer black phosphorus (BP) nanosheets were first reported as a 2D material for the application of field-effect transistors in 2014 and have stimulated intense activity among physicists, chemists, and material and biomedical scientists, driving research into novel synthetic techniques to produce BP nanosheets. At present, exfoliation is the main route toward few-layer BP nanosheets via employing bulk BP as raw material. However, this is a complicated and time-consuming process, which is difficult for the large-scale synthesis of BP nanosheets. Moreover, BP degrades rapidly when exfoliated to nanoscale dimensions, resulting in the rapid loss of semiconducting properties. Here, we report the direct wet-chemical synthesis of few-layer BP nanosheets in gram-scale quantities in a bottom-up approach based on common laboratory reagents at low temperature, showing excellent stability due to partial oxidation of surface. Solvent and temperature are two critical factors, controlling not only the formation of BP nanosheets but also the thickness. The as-prepared BP nanosheets can extract hydrogen from pure water (pH = 6.8), exhibiting more than 24-fold higher activity than the well-known C3N4 nanosheets. Our results reporting the ability to prepare few-layer BP nanosheets with a facile, scalable, low-cost approach take us a step closer to real-world applications of phosphorene including next-generation metal-free photocatalysts for photosynthesis.

Molybdenum disulfide quantum dots decorated bismuth sulfide as a superior noble-metal-free photocatalyst for hydrogen evolution through harnessing a broad solar spectrum

Molybdenum disulfide quantum dots (MoS2QDs) decorated bismuth sulfide (Bi2S3) photocatalyst was synthesized. Photoluminescence characterization showed that the as-developed MoS2QDs possessed intriguing up-conversion and down-conversion properties, indicating their capability to harness energy from the light spectrum ranging from ultraviolet (UV) to near-infrared (NIR). In this study, the highest hydrogen yield of 17.7 mmol/g.h was achieved by 0.14MoS2QD/Bi2S3, which was almost 4.5 folds higher than that of undoped Bi2S3 under stimulated solar light irradiation. Furthermore, examination of the 0.14MoS2QD/Bi2S3 photocatalysts under NIR irradiation showed a significant photocurrent response and an accumulative H2 yield of 53.6 μmol/g after 6 h reaction. This is a major breakthrough as most photocatalysts can only be activated under UV and/or visible light irradiation. This work provides new insights into the design of MoS2QD/Bi2S3 for harnessing energy from a broad solar spectrum to photocatalytically split water to produce hydrogen.

Photodeposition of amorphous MoSx cocatalyst on TiO2 nanosheets with {001} facets exposed for highly efficient photocatalytic hydrogen evolution

Semiconductor-based photocatalytic hydrogen production is a promising approach to convert solar energy to renewable and clean hydrogen energy. However, development of cheap and efficient hydrogen evolution cocatalyst to replace noble metal based cocatalysts remains a challenge. Here, we report a MoSx/TiO2 nanohybrid prepared by a facile photo-assisted deposition method. The amorphous MoSx grows intimately on the single-crystalline TiO2 nanosheet with {001} facets exposed to form a heterojunction, which can not only facilitate the charge separation and transfer, but also provide plenty of active sites for hydrogen evolution reaction owing to abundant unsaturated S atoms on amorphous MoSx. As a result, the MoSx/TiO2 nanohybrid shows a remarkable enhancement in photocatalytic hydrogen evolution performance in comparison to bare TiO2 nanosheet. The best 0.5%-MoSx/TiO2 nanohybrid exhibits a hydrogen production rate at 1835.7 μmol g−1 h−1 under Xenon light irradiation, which is about 177 times higher than that of bare TiO2 nanosheet. This work paves a way for the design and construction of low-cost and noble-metal-free photocatalysts for efficient photocatalytic hydrogen evolution.

One-Step Synthesis of Nb2 O5 /C/Nb2 C (MXene) Composites and Their Use as Photocatalysts for Hydrogen Evolution.

Hydrogen production through facile photocatalytic water splitting is regarded as a promising strategy to solve global energy problems. Transition-metal carbides (MXenes) have recently drawn attention as potential co-catalyst candidates for photocatalysts. Here, we report niobium pentoxide/carbon/niobium carbide (MXene) hybrid materials (Nb2 O5 /C/Nb2 C) as photocatalysts for hydrogen evolution from water splitting. The Nb2 O5 /C/Nb2 C composites were synthesized by one-step CO2 oxidation of Nb2 CTx . Nb2 O5 grew homogeneously on Nb2 C after mild oxidation, during which some amorphous carbon was also formed. With an optimized oxidation time of 1.0 h, Nb2 O5 /C/Nb2 C showed the highest hydrogen generation rate (7.81 μmol h-1 gcat-1 ), a value that was four times higher than that of pure Nb2 O5 . The enhanced performance of Nb2 O5 /C/Nb2 C was attributed to intimate contact between Nb2 O5 and conductive Nb2 C and the separation of photogenerated charge carriers at the Nb2 O5 /Nb2 C interface; the results presented herein show that transition-metal carbide are promising co-catalysts for photocatalytic hydrogen production.

Efficient Redox-Mediator-Free Z-Scheme Water Splitting Employing Oxysulfide Photocatalysts under Visible Light

Oxysulfides, which exhibit intense visible light absorption and high photocatalytic activity during hydrogen evolution, are promising photocatalysts for Z-scheme water splitting. However, the realization of efficient Z-scheme water splitting using oxysulfides as hydrogen evolution photocatalysts (HEPs) has been hampered by backward reactions involving reversible redox couples, the low efficiency of interparticle electron transfer, and a lack of knowledge regarding the means of promoting hydrogen evolution activity under nonsacrificial conditions. In this study, La5Ti2CuS5O7 was found to realize water splitting without any redox mediator by constructing Z-scheme-type photocatalyst sheets with BiVO4 as the oxygen evolution photocatalyst. It is also demonstrated that p-type doping and the formation of a La5Ti2Cu0.9Ag0.1S5O7 solid solution effectively enhance the water-splitting activity of the photocatalyst sheet. An apparent quantum yield of 4.9% at 420 nm and a solar to hydrogen energy conversion efficienc...

Across the Board: Xinchen Wang.

In this series of articles, the board members of ChemSusChem discuss recent research that they consider of exceptional quality and importance for sustainability. In this entry, Prof. Xinchen Wang discusses the investigations of a printable Z-scheme system for photocatalytic water splitting by the pioneer, Prof. Kazunari Domen, who has been constantly contributing to this field for about 40 years. The recent achievement of an overall water splitting system has exceeded the solar-to-hydrogen energy efficiency of 1% by integrating efficient hydrogen and oxygen evolution photocatalysts with charge-transport channel.

Hydrogen-interstitial CuWO4 nanomesh: A single-component full spectrum-active photocatalyst for hydrogen evolution

It is of practical and theoretical significance to realize full spectrum-active photocatalytic hydrogen (H2) evolution using a single-component photocatalyst. The bottleneck is the utilization of near infrared (NIR) light with 52% of the energy in solar spectrum due to the mismatch between its low single photon energy and the large bandgaps of many photocatalysts. In fact, except for the intrinsic inter-band transition, charge-transfer transition is another strategy to produce hot electrons as a result of light excitation. Herein, charge-transfer transition is achieved in hydrogen-interstitial CuWO4 nanomesh (H-CuWO4) by introducing low-valence Cu+ and W5+. The resulting polaron absorption produces abundant free electrons upon NIR irradiation. Meanwhile, the intrinsic inter-band transition supplies more electrons upon ultraviolet and visible (UV and Vis) irradiations. The mesh structure induced by the self-assembled orientated attachment facilitates the electron transport in the photocatalytic process. Further, the lattice stress resulting from the H intercalation raises the conduction band (CB) above the H+/H2 potential level. CuWO4, incapable of realizing photocatalytic H2 evolution, is therefore activated to be a single-component full spectrum-active photocatalyst based on the dual-channel mechanism without any assistance of cocatalysts. It exhibits an excellent H2 evolution rate and high stability. This advance may have great potential in the future environmental and energy engineering applications.

Composite of CH3 NH3 PbI3 with Reduced Graphene Oxide as a Highly Efficient and Stable Visible-Light Photocatalyst for Hydrogen Evolution in Aqueous HI Solution.

A facile and efficient photoreduction method is employed to synthesize the composite of methylammonium lead iodide perovskite (MAPbI3 ) with reduced graphene oxide (rGO). This MAPbI3 /rGO composite is shown to be an outstanding visible-light photocatalyst for H2 evolution in aqueous HI solution saturated with MAPbI3 . Powder samples of MAPbI3 /rGO (100 mg) show a H2 evolution rate of 93.9 µmol h-1 , which is 67 times faster than that of pristine MAPbI3 , under 120 mW cm-2 visible-light (λ ≥ 420 nm) illumination, and the composite is highly stable showing no significant decrease in the catalytic activity after 200 h (i.e., 20 cycles) of repeated H2 evolution experiments. The electrochemiluminescence performance of MAPbI3 is investigated to explore the charge transfer process, to find that the photogenerated electrons in MAPbI3 are transferred to the rGO sites, where protons are reduced to H2 .

Engineering an effective noble-metal-free photocatalyst for hydrogen evolution: hollow hexagonal porous micro-rods assembled from In2O3@carbon core–shell nanoparticles

It is desirable but challenging to design noble-metal-free photocatalysts with improved activity for hydrogen (H2) evolution.

Facile synthesis of a red light-inducible overall water-splitting photocatalyst using gold as a solid-state electron mediator.

We facilely prepared a solid-state heterojunction photocatalyst in which zinc rhodium oxide (ZnRh2O4) and bismuth vanadium oxide (Bi4V2O11) as hydrogen (H2) and oxygen (O2) evolution photocatalysts, respectively, were connected with gold (Au) to generate ZnRh2O4/Au/Bi4V2O11. ZnRh2O4/Au/Bi4V2O11 photocatalyzed the overall pure-water splitting under irradiation with red light at wavelengths of up to 740 nm.

Constructing a novel TiO2/γ-graphyne heterojunction for enhanced photocatalytic hydrogen evolution

TiO2/γ-graphyne nanocomposites were successfully synthesizedviaa simple hydrothermal method, and demonstrated as a promising photocatalyst for hydrogen evolution.