Activity For Hydrogen Generation Research Articles

Encapsulation Strategy on All Inorganic Perovskites for Stable and Efficient Photoelectrocatalytic Water Splitting

AbstractAll inorganic perovskite CsPbBr3 nanocrystals are a promising candidate as photocathode for efficient photoelectrocatalytic (PEC) water splitting. However, the poor chemical stability severely limits its practical applications. The exploration of perovskite‐based ideal photocathode materials with efficient and highly stable PEC performance is still an ambitious and meaningful challenge. Herein, under guidance of theoretical calculations, an encapsulation strategy is proposed to prepare the CsPbBr3/Ni2P core/shell nanostructures. Compared with the pristine CsPbBr3 nanocrystals, the CsPbBr3/Ni2P nanostructures show a significant improvement of photocurrent density up to 10 000 folds with long‐term stability in aqueous solution, and present superior PEC activity for hydrogen generation with nearly 100% faradic efficiency. The encapsulation strategy opens up an avenue for rational design of perovskite‐based photocathodes for efficient and stable PEC water reduction.

Preparation of double-vacancy modified carbon nitride to greatly improve the activity of photocatalytic hydrogen generation

Vacancy engineering has been a very active research area in the field of photocatalysis. The electronic/band structure of carbon nitride can be tuned by introducing vacancies. However, the hydrogen production rate of carbon nitride modified only by a single defect is not significant. Therefore, we have constructed nitrogen-oxygen double vacancy modified carbon nitride by a simple two-step method. Especially, the photocatalytic performance of DACN-2 was 11.7 times and 5.8 times better than that of carbon nitride and oxygen-doped carbon nitride, respectively. The increase of specific surface area along with more available active sites, the pull-up of conduction band position and more efficient separation of photogenerated electron-hole pairs accounted for the improvement of hydrogen evolution performance. Moreover, the double vacancy was the separation center of the photogenerated charges, which accelerated the separation of photogenerated electrons and holes. This research provided a new concept for the design of defective carbon nitride and laid the foundation for the development of more effective photocatalysts in the future.

Core-shell structure of sulphur vacancies-CdS@CuS: Enhanced photocatalytic hydrogen generation activity based on photoinduced interfacial charge transfer

To regulate the charge flow of the photocatalyst in photocatalytic hydrogen reactions is highly desirable. In this study, a highly efficient sulphur vacancies-CdS@CuS core–shell heterostructure photocatalyst (denoted CdS-SV@CuS) was developed through the surface modification of CdS-sulphur vacancies (SV) nanoparticles by CuS based on photoinduced interfacial charge transfer (IFCT). This novel photocatalyst with modulated charge transfer was prepared by hydrothermal treatment and subsequent cation-exchange reactions. The SV confined in CdS and the IFCT facilitate the charge carrier’s efficient spatial separation. The optimized CdS-SV@CuS(5%) catalyst exhibited a remarkably higher H2 production rate of 1654.53 μmol/g/h, approximately 6.7 and 4.0 times higher than those of pure CdS and CdS-SV, respectively. The high photocatalytic performance is attributed to the rapid charge separation, caused by the intimate interactions between CdS-SV and CuS in the core–shell heterostructure. This is the first time that a straightforward method is adopted to construct a metal sulphide core–shell structure for superior H2-production activity by IFCT.

Water Splitting with a Single-Atom Cu/TiO2 Photocatalyst: Atomistic Origin of High Efficiency and Proposed Enhancement by Spin Selection.

Anatase TiO2 is an intensely investigated photocatalytic material due to its abundance and chemical stability. However, it suffers from weak light harvesting and low photocatalytic efficiency. Experiments show that light absorption and photocatalytic properties can be enhanced simultaneously by TiO2 doping with well-dispersed Cu atoms, forming a single-atom catalyst (Cu/TiO2) that can be used for solar water splitting and other applications. By performing ab initio nonadiabatic molecular dynamics simulations, we demonstrate that Cu/TiO2 is inactive before light irradiation due to rapid electron–hole recombination via both shallow and deep traps. Surprisingly, the shallow trap is more detrimental to the Cu/TiO2 performance than the deep trap because it couples better to free carriers. After light irradiation, leading to electron transfer and Cu/TiO2 protonation, the shallow trap is eliminated, and a local distortion around the Cu atom stabilizes the deep trap state on the Cu d-orbital, decoupling it from free charges and giving rise to high photocatalytic hydrogen generation activity. We further demonstrate that the photocatalytic performance of Cu/TiO2 can be enhanced by spin selection, achievable experimentally via optical intersite spin transfer or chiral semiconductor coating. Both H adsorption and spin selection enhance charge carrier lifetimes by an order of magnitude. The spin selection mechanism does not require formation of the H species, which necessitates concurrent sources of electrons and protons and which is intrinsically unstable because water splitting involves frequent proton shuffling. Our results rationalize the experimental observations at the atomistic level, provide mechanistic insights into operation of single atom photocatalysis, and demonstrate that spin selection can be used to develop advanced and efficient systems for solar energy conversion.

The distinct role of non-noble metal Cu NPs deposition in boosting the overall photocatalytic performance over a ternary Zn-based photocatalyst system

Metal nanoparticles (NPs) deposition is an effective strategy to enhance the photocatalytic performance. Here, we developed a non-noble Cu NPs deposition strategy to largely boost the overall photocatalytic performance of a ternary Zn-based composite photocatalyst (ZnTiO3/Zn2Ti3O8/ZnO, ZTO). The physicochemical properties of copper-deposited ZTO were extensively analyzed by a series of techniques such as XRD, BET, FT-IR, XPS, TEM, PL, and photoelectrochemical tests. And the free radical and light absorption properties of copper-deposited ZTO were examined by ESR and UV–vis DRS, respectively. The photocatalytic performance for hexavalent chromium reduction removal, dye decomposition, and water splitting for hydrogen production without noble metal cocatalyst were investigated. The results show that with suitable Cu content (3%~ 4.7%), the Cu-ZTO samples showed high activity for Cr(VI) reduction (3.2 times reduction rate of ZTO), dye decomposition(5.3 times degradation rate of ZTO), and hydrogen generation (19 times of the H2 production rate of ZTO). The synergistic effect between the plasma effect of Cu NPs and single Z-scheme mechanism over ternary ZTO results in a strong visible light absorption and fast separation of photogenerated electrons and holes. Thus, a superior photocatalytic performance was obtained over this novel Cu-ZTO photocatalyst system.

Cobalt ferrite supported platinum nanoparticles: Superb catalytic activity and outstanding reusability in hydrogen generation from the hydrolysis of ammonia borane

In this work, platinum(0) nanoparticles are deposited on the surface of magnetic cobalt ferrite forming magnetically separable Pt0/CoFe2O4 nanoparticles, which are efficient catalysts in H2 generation from the hydrolysis of ammonia borane. Catalytic activity of Pt0/CoFe2O4 nanoparticles decreases with the increasing platinum loading, parallel to the average particle size. Pt0/CoFe2O4 (0.23% wt. Pt) nanoparticles have an average diameter of 2.30 ± 0.47 nm and show an extraordinary turnover frequency of 3628 min−1 in releasing 3.0 equivalent H2 per mole of ammonia borane from the hydrolysis at 25.0 °C. Moreover, the magnetically separable Pt0/CoFe2O4 nanoparticles possess high reusability retaining 100% of their initial catalytic activity even after ten runs of hydrolysis. The superb catalytic activity and outstanding reusability make the Pt0/CoFe2O4 nanoparticles very attractive catalysts for the hydrogen generation systems in portable and stationary fuel cell applications.

In Situ Synthesis of Mo2C Nanoparticles on Graphene Nanosheets for Enhanced Photocatalytic H2-Production Activity of TiO2

Molybdenum carbide (Mo₂C) has been proven to be the most promising candidate for the H₂-evolution cocatalyst due to the similar H⁺-adsorption ability to Pt. However, owing to its limited electrical conductivity, the Mo₂C-modified photocatalysts usually exhibit a low H₂-evolution performance. Considering the perfect electron mobility of graphene nanosheets, in this article, Mo₂C nanoparticles (ca. 5 nm) were in-situ and evenly grown on the reduced graphene oxide (rGO) to prepare the graphene-modified Mo₂C (rGO-Mo₂C) nanoparticles to improve the photocatalytic hydrogen-generation rate of TiO₂. Herein, the rGO-Mo₂C is obtained by the direct calcination of graphene oxide (GO) as the carbon source and (NH₄)₆Mo₇O₂₄ at 800 °C, which is further coupled with the TiO₂ to synthesize the efficient TiO₂/rGO-Mo₂C photocatalyst. The greatest hydrogen-generation activity of TiO₂/rGO-Mo₂C achieved 880 μmol h–¹ g–¹ (AQE = 2.64%), which was 5.5 and 88 times higher than that of TiO₂/rGO and TiO₂, respectively. The boosted performance of TiO₂/rGO-Mo₂C can be attributed to the synergetic action that the rGO nanosheets can act as electron media to promote the photoelectron transfer, and the Mo₂C nanoparticles can serve as active centers to improve the interfacial hydrogen-generation reaction. This work can provide a new synthesis strategy for the design of efficient cocatalysts for potential applications.

Rational design of isostructural 2D porphyrin-based covalent organic frameworks for tunable photocatalytic hydrogen evolution

Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H2, Co, Ni, Zn) and their photocatalytic activity in hydrogen generation. Our results clearly show that all four covalent organic frameworks adopt AA stacking structures, with high crystallinity and large surface area. Interestingly, the incorporation of different transition metals into the porphyrin rings can rationally tune the photocatalytic hydrogen evolution rate of corresponding covalent organic frameworks, with the order of CoPor-DETH-COF < H2Por-DETH-COF < NiPor-DETH-COF < ZnPor-DETH-COF. Based on the detailed experiments and calculations, this tunable performance can be mainly explained by their tailored charge-carrier dynamics via molecular engineering. This study not only represents a simple and effective way for efficient tuning of the photocatalytic hydrogen evolution activities of covalent organic frameworks at molecular level, but also provides valuable insight on the structure design of covalent organic frameworks for better photocatalysis.

Engineering Ru atomic structures toward enhanced kinetics of hydrogen generation

Herein, we demonstrate a strategy of engineering Ru atomic structures by fine-tuning Cl and Co coordination to synergize the quantity and quality of Ru active sites for boosting hydrogen generation from ammonia borane hydrolysis, via engineering the Cl-free/Cl-containing monometallic Ru catalysts and Co-leaching/Co-containing bimetallic Ru-Co catalysts. Under similar Ru particle sizes, the correlation between Ru binding energy and hydrogen generation activity affords a quantitative discrimination of Ru electronic and geometric contributions, where the site blockage and steric hindrance of Ru by Cl are more detrimental to hydrogen generation compared with the electronic modification by charge donation from Co to Ru. Reversely, the acid-leaching of Co from bimetallic catalysts creates abundant edge-like Ru active sites with much lower H2O activation barrier, as indicated by the kinetics switch from a Cl coverage-limited regime to a reactant activation regime, thus yielding a significant 4.1-fold increase in hydrogen generation activity.

Black titania an emerging photocatalyst: review highlighting the synthesis techniques and photocatalytic activity for hydrogen generation.

The TiO2 semiconductor photocatalyst is in the limelight of sustainable energy research in recent years because of its beneficial properties. However, its wide band-gap and rapid exciton recombination rate makes it a lame horse, and reduces its photocatalytic efficiency. Recently, researchers have developed facile methods for lowering the band-gap, so that it captures a wide range of solar spectrum, but the efficiency is still way behind the target value. After the discovery of black titania (B-TiO2), the associated drawbacks of white TiO2 and its modified forms were addressed to a large extent because it not only absorbs photons in a broad spectral range (UV to IR region), but also modifies the structural and morphological features, along with the electronic properties of the material, significantly boosting the catalytic performance. Hence, B-TiO2 effectively converts solar energy into renewable chemical energy i.e. green fuel H2 that can ultimately satisfy the energy crisis and environmental pollution. However, the synthesis techniques involved are quite tedious and challenging. Hence, this review summarizes various preparation methods of B-TiO2 and the involved characterization techniques. It also discusses the different modification strategies adopted to improve the H2 evolution activity, and hopes that this review acts as a guiding tool for researchers working in this field.

Highly crystalline anatase TiO2 nanocuboids as an efficient photocatalyst for hydrogen generation.

Highly crystalline anatase titanium dioxide (TiO2) nanocuboids were synthesized via a hydrothermal method using ethylenediamine tetraacetic acid as a capping agent. The structural study revealed the nanocrystalline nature of anatase TiO2 nanocuboids. Morphological study indicates the formation of cuboid shaped particles with thickness of ∼5 nm and size in the range of 10–40 nm. The UV-visible absorbance spectra of TiO2 nanocuboids showed a broad absorption with a tail in the visible-light region which is attributed to the incorporation of nitrogen atoms into the interstitial positions of the TiO2 lattice as well as the formation of carbonaceous and carbonate species on the surface of TiO2 nanocuboids. The specific surface areas of prepared TiO2 nanocuboids were found to be in the range of 85.7–122.9 m2 g−1. The formation mechanism of the TiO2 nanocuboids has also been investigated. Furthermore, the photocatalytic activities of the as-prepared TiO2 nanocuboids were evaluated for H2 generation via water splitting under UV-vis light irradiation and compared with the commercial anatase TiO2. TiO2 nanocuboids obtained at 200 °C after 48 h exhibited higher photocatalytic activity (3866.44 μmol h−1 g−1) than that of commercial anatase TiO2 (831.30 μmol h−1 g−1). The enhanced photoactivity of TiO2 nanocuboids may be due to the high specific surface area, good crystallinity, extended light absorption in the visible region and efficient charge separation.

Nanoporous carbon doped ceria bismuth oxide solid solution for photocatalytic water splitting

Carbon-doped ceria bismuth oxide solid solution can break pure water into H2 and O2 under natural sunlight as well as under artificial light. Hydrogen generation activity proportionate to the degree of porosity of the solid solutions.

Synthesis of ternary nanoparticles using the complexation-reduction method and their catalytic activities for hydrogen generation from formic acid

A complex-reduction method was used for the synthesis of glycine-capped copper nanoparticles (Gly-CuNPs). Glycine-Cu2+ was prepared at room temperature, and the resulting complex was treated with NaBH4. Gly-Cu/Ag and Gly-Cu/Ag/MnO2 were prepared by using the stepwise metal displacement plating method. Gly-Cu, Gly-Cu/Ag and Gly-Cu/Ag/MnO2 were employed as catalysts for hydrogen generation from the decomposition of formic acid. The alkaline barium hydroxide solution was employed to trap CO2 formation, and pseudo-first-order rate constants were calculated by using the kobs = 2.303/t log(Aα-A0/Aα-At) relation. Hydrogen generation followed fractional order kinetics with formic acid, and various kinetic parameters were calculated for various concentrations of promoter (sodium format), catalyst and temperature. The catalytic activity was found to increase with an increasing number of incorporated metals, and the order of reactivity was as follows: Gly-Cu/Ag/MnO2 > Gly-Cu/Ag > Gly-Cu. For Gly-Cu/Ag/MnO2, the values of activation parameters (Ea = 56 kJ/mol, ∆H# = 53 kJ/mol, ∆S# = − 68 J/K/mol) were determined with the Arrhenius and Eyring equations, which show higher catalytic efficiency than that of Gly-Cu/Ag (Ea = 69 kJ/mol, ∆H# = 66 kJ/mol, ∆S# = − 25 J/K/mol) due to the synergistic effect and strong interactions between the three metals. The catalytic stability and recyclability were excellent for five consecutive cycles, but the stability and recyclability decreased due to the higher reactivity of MnO2 NPs.

Enhancing the hydrogen evolution performance of CdS by synergistic effect of Ni doping and SnO2 coupling: Improved efficiency of charge transfer and H2O disassociation

Photocatalytic hydrogen production via conversion of solar energy shows great potential in addressing both environmental contamination and energy shortage. In the present study, a new CdS–NiS/SnO2 photocatalyst was designed based on the strategies of enhancing the efficiency of water dissociation and electron transfer/separation. A prominent H2 generation rate of 35,176 μmol g−1 h−1 (λ ≥ 420 nm) was obtained for the optimal sample, which was 12.8 and 6 times as that of CdS and CdS/SnO2, respectively. The significantly high performance of CdS–NiS-10%/SnO2 could primarily be attributed to the synergistic effect of the improved efficiency of charge transfer, H2O adsorption and dissociation. Fourier transform infrared (FT-IR) demonstrated that NiS can increase the adsorption of H2O molecules. Further, pursuant to linear sweep voltammetry (LSV), Tafel and photoluminescence (PL) results, a faster kinetics process of water dissociation could be obtained through the addition of SnO2. Meanwhile, electrochemical impedance spectroscopy (EIS), photocurrent characterizations revealed that CdS–NiS-10%/SnO2 exhibited faster charge transfer efficiency. This work is hoped to offer a new approach/concept in researching CdS-based photocatalysts with enhanced hydrogen generation activity under the irradiation of visible light.

Immobilized molybdic acid on porous silica-alumina hollow sphere particles for acid-promoted hydrolytic hydrogen evolution from ammonia borane

This work presented influence of preparation conditions on immobilized molybdic acid on porous silica-alumina hollow sphere particles for acid-promoted hydrolytic hydrogen generation from ammonia borane. The main component of the immobilized molybdic acid was heptamolybdic acid with molybdic tetraoxide as the minor component. Their dispersion of the active heptamolybdic acid species depends on the amount of aqueous l-aspartic acid solutions adding during the immobilization of the active species on the hollow sphere particles, and treatment of the hollow sphere particles in aqueous ammonia solution. The immobilized active molybdic acid with high dispersion tended to exhibit high activity for acid-promoted hydrolytic hydrogen generation from ammonia borane.

Pt21(C4O4SH5)21 clusters: atomically precise synthesis and enhanced electrocatalytic activity for hydrogen generation

How to effectively enhance the catalytic performance and simultaneously reduce the usage of Pt-based catalysts is always the goal of catalyst design for electrochemical energy devices. Platinum nanoclusters (Pt NCs) have aroused massive concerns in recent years because of the excellent activity of Pt-based materials themselves and the unique physical and chemical properties of nanoclusters. However, the studies on the synthesis, properties and applications of Pt NCs have been rarely reported. Here, we report a simple avenue to synthesize Pt nanoclusters through using K2PtCl4 as precursor and mercaptosuccinic acid (MSA) as not only ligand but also the reducing agent at the room temperature. Based on the matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), the obtained Pt NCs have the composition of Pt21(C4O4SH5)21. By loading the Pt NCs on reduced graphene oxide nanosheets (rGO) and the following removal of MSA ligands upon annealing treatment, the obtained surface-clean Pt NCs/rGO exhibits excellent hydrogen evolution reaction (HER) catalytic performance and superior stability with Pt loading as low as 0.8 wt%. Especially, the HER mass catalytic activity of the Pt NCs/rGO is much higher than that of the 20.0 wt% commercial Pt/C catalyst. Meanwhile, this kind of cluster catalyst also shows large exchange current density (574 µA•cm−2) and high turn-over frequency (1.19 s−1). The experimental result in this work clearly indicates that Pt catalyst on cluster scale can obviously improve the catalytic performance. Therefore, this study provides an effective avenue to enhance the utilization of noble metals and to develop high-performance and cost-effective catalysts.

Cu oxide quantum dots loaded TiO2 nanosheet photocatalyst for highly efficient and robust hydrogen generation

To simultaneously enhance both the hydrogen generation activity and long term stability of a TiO2 based photocatalyst using Cu species as co-catalyst is a great challenge. In this work, highly reactive TiO2 nanosheets with {001} facets were prepared by a hydrothermal method, and then Cu oxides quantum dot was loaded on the nanosheets by an impregnation method. Comprehensive analysis demonstrates that the Cu species change from CuO to Cu2O and partially to Cu during photocatalysis, and this process is reversed during oxidation. The exposed TiO2 (001) planes provide a platform for a strong interaction between the Cu oxide and TiO2 nanosheets, enabling the firmly anchor and charge transfer between the Cu oxide and TiO2. The optimized composite photocatalyst shows a high efficiency and robust, long term stability for H2 evolution. With simple O2 regeneration, the H2 generation rate maintains to 98% after irradiation for 30 h. It is expected that Cu2O is sandwiched between TiO2 and CuO, and the composite configuration changes to TiO2/Cu2O/Cu after long term irradiation. The energy band alignment of the double heterojunction provides the effective charge separation and maintains the structural stability during the photocatalysis.

Facile synthesis of agglomerated Ag–Pd bimetallic dendrites with performance for hydrogen generation from formic acid

We report a simple method for the fabrication of agglomerated Ag–Pd bimetallic dendrites by the addition of NaCOOH. The agglomerated Ag–Pd bimetallic dendrites are characterized SEM, TEM, XRD and XPS measurements. The prepared Ag–Pd bimetallic dendrites exhibited catalytic activity in hydrogen generation from decomposition of formic acid at room temperature (~25 °C). Herein, the present Ag–Pd bimetallic dendrites possess the new type of agglomerated structure against to dispersion, which make them easily separated from the reaction system. It is convenient for operator to cease catalytic reaction at any moment. Moreover, the resulting Ag–Pd bimetallic dendrites can be easily reactivated simply by drying after water cleaning for reuse, which saved the cost of catalysts. Among them, Ag1Pd1 sample showed nice performance of recycle test and long lifetime for the decomposition of formic acid at room temperature.

Self-assembled supramolecular nanostructure photosensitizers for photocatalytic hydrogen evolution

Supramolecular self-assembly as a breakthrough methodology in the nanoscience and nanotechnology fields has attracted increasing attention. Highly ordered self-assembled supramolecular nanostructures aim to emulate natural light-harvesting and energy transfer and electron transfer processes, which have been an active and rapidly developing field for visible-light-driven photocatalytic applications. This Research Update aims to present the recent progress of the self-assembly of π-conjugated molecules, including perylene diimides (PDIs), porphyrin, and co-assembly of peptide–porphyrin as well as the shape-defined functional hierarchical structures. First, the basic principles of π-conjugated molecular structure design are described. The two nitrogen positions and the bay positions of PDIs can effectively regulate their electronic properties and geometric skeleton, and the functional groups and the good solvents of porphyrin effectively determine the choice of self-assembly methods. Then, the key morphology dependent optoelectronic properties and charge-transport and energy-transport functionalities are also discussed. These self-assembled supramolecular nanostructures’ inherent optoelectronic properties correlated with applications in photocatalytic water splitting into hydrogen evolution are overviewed. By now, the self-assembled In(III) meso-tetraphenylporphine (InTPP) porphyrin nanostructures exhibited the highest photocatalytic hydrogen generation activity among the reported supramolecular nanostructures owing to the central metal of porphyrin and small size of the InTPP nanostructure. Finally, perspectives on the crucial issues and potential future research directions are addressed. This Research Update will provide a new reference for building high performance, stable, and durable photosensitizers based on the supramolecular assembly.

Infrared response in photocatalytic polymeric carbon nitride for water splitting via an upconversion mechanism

Broad-spectrum light activation in photocatalytic materials is considered vital for effective solar-to-hydrogen energy conversion. Here, we propose an upconversion process in oxygen-doped polymeric carbon nitride (C3N4) nanosheets, resulting in high photocatalytic activity for hydrogen generation from water splitting under infrared light irradiation. Due to the upconversion, the photoexcited electrons are transferred to the conduction band, and a σ* carbon-oxygen orbital localized on the triazine matrix ring resulting from oxygen doping extends the lifetime of photogenerated electrons, which increases the photocatalytic activity under both infrared and visible light. Our material exhibits high apparent quantum efficiency of 0.014% and 23% at 850 nm and 420 nm, respectively. Under infrared light (λ ≥ 800 nm, 24 mW cm−2), the hydrogen production rate of our material is 22.84 μmol h−1 g−1, which can reach a yield similar to that of pristine C3N4 under visible light.