Efficient Photocatalytic Water Splitting Research Articles

Construction of ternary RuP2/Ti4P6O23@TiO2 photocatalysts for efficient photocatalytic biomass selective oxidation and water splitting

Construction of ternary RuP2/Ti4P6O23@TiO2 photocatalysts for efficient photocatalytic biomass selective oxidation and water splitting.

Janus β-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting

In this work, we have investigated the novel 2D allotropes i.e., β-Te2X (X = S, Se) using first-principles calculations and study their potential applications in light harvesting devices.

Multiple strategies of improving photocatalytic water splitting efficiency in 2D arsenic sesquichalcogenides.

Improving the solar-to-hydrogen efficiency has always been a significant topic in the field of photocatalysis. Based on first-principles calculations, herein, we propose multiple strategies to improve the photocatalytic properties of 2D arsenic sesquichalcogenides for full water splitting. The new configurations As2STe2 and As2SeTe2 monolayers, derived from the As2Te3 monolayers by surface modification, are manifested to be typical infrared-light driven photocatalysts. Notably, under the built-in electric field, As2STe2 and As2SeTe2 monolayers can fulfil overall water splitting and the predicted solar-to-hydrogen efficiencies even reach up to 36.19% and 29.36%, respectively. The Gibbs free energy calculations indicate that the OER can be successfully driven under light irradiation. In addition, the overpotentials can provide most of the energy for HER when illuminated, especially for As2STe2 with the . In addition, both As2S3 and As2Se3 monolayers are capable of satisfying the conditions for photocatalytic water splitting. Furthermore, the band gaps of As2Se3 and As2S3 can dramatically be narrowed by increasing the number of layers and doping, respectively. These findings provide a theoretical basis for As2X3 monolayers to achieve efficient photocatalytic water splitting.

Fabrication of In(OH)3–In2S3–Cu2O nanofiber for highly efficient photocatalytic hydrogen evolution under blue light LED excitation

This study synthesized the In(OH)3–In2S3 nanosheet via a simple hydrothermal method. The different amounts of In(OH)3–In2S3 nanosheet used to synthesize In(OH)3–In2S3–Cu2O composite by a wet chemical method. FESEM, FETEM, XRD, XPS, BET, UV–vis DRS, and PL spectroscopy characterized the In(OH)3–In2S3–Cu2O composite. Compared with In(OH)3–In2S3 nanosheet, In(OH)3–In2S3–Cu2O composite can exhibit the synergistic effects of higher specific surface area, higher light-harvesting capacity, and accelerating the separation and migration of photogenerated charge carriers. In addition, In(OH)3–In2S3–Cu2O nanofiber was fabricated via a facile electrospinning process at the different amounts of In(OH)3–In2S3 nanosheet. The manufacturing process offers many advantages, such as simplicity, low temperature, and without templates. The effect of operational parameters (such as the reaction conditions of photocatalysts, pH values, sacrificial reagents, and light sources) on the photocatalytic hydrogen production of In(OH)3–In2S3–Cu2O nanofiber was investigated. The results indicate that the appropriate reaction conditions of In(OH)3–In2S3–Cu2O nanofiber can reveal higher efficient photocatalytic water splitting than commercial TiO2 or ZnO nanofiber under blue light LED excitation. Furthermore, In(OH)3–In2S3–Cu2O nanofiber can provide a simple fabrication process, high photocatalytic activity, and high reusability shall be beneficial for the practical application of photocatalytic hydrogen production.

Stacking order effects on the electronic and optical properties of GaS/XMoY (X/Y = S, Se, Te) Van der Waals heterostructures: a first-principles study

Two-dimensional (2D) heterostructures formed by van der Waals (vdW) interactions have attracted considerable attention in the fields of electronics and optoelectronics. The stacking order is not only an important method for regulating interlayer interactions, but also an intrinsic property specific to 2D vdW heterostructures. Herein, the GaS/XMoY (X/Y = S, Se, Te) vdW heterostructures are proposed by first-principles calculations. The effects of stacking order (namely, GaS/SMoSe, GaS/SeMoS, GaS/SeMoTe and GaS/TeMoSe) on the electronic properties, light absorption, and photocatalysis of the heterostructures are discussed in detail. We identify stacking order as a dominant pathway for interlayer interactions, and surmise that stacking order effectively regulates dipole moment, mechanical flexibility, carrier mobility, optical absorption coefficient, and photocatalytic water-splitting of GaS/XMoY heterostructures. The in-plane biaxial strain can make the energy gap of each stacking order reach a maximum value, and their photocatalytic performance can also be improved to different degrees. This work analyzes the modulation effect of stacking order on the material properties of GaS/XMoY heterostructures, which provides theoretical clues for the design of efficient and stable optoelectronic devices and photocatalytic water-splitting.

Highly efficient photocatalytic overall water splitting in two-dimensional van der Waals MoS2/Hf2CO2 heterostructure

Two-dimensional (2D) van der Waals (vdW) heterostructures have attracted much attention due to their unique properties in photocatalysis, electronics, and energy storage. This work comprehensively analyzed the electronic properties and photocatalytic efficiency properties of 2D vdW MoS2/Hf2CO2 heterostructure by first-principles calculations and molecular dynamics simulation. An ideal band gap of 1.44 eV was found for visible light absorption. Meanwhile, a high solar-to-hydrogen efficiency of 17.14% is obtained from the calculated band-edge positions, and a high power conversion efficiency of 13.84% is also confirmed by spectroscopy limited maximum efficiency simulation. We estimate the time scale for electron–hole transfer and recombination times using a combination of non-adiabatic molecular dynamics and time-dependent density functional theory. A suitable e-h recombination time of 1.86 ns and electron (hole) transfer time of 331 (978) fs are obtained in the 2D MoS2/Hf2CO2 heterostructure, which is expected to ensure high photocatalytic efficiency. Therefore, the constructed MoS2/Hf2CO2 heterostructures provide a new example for the prediction of high-performance nano optoelectronic devices.

Two-dimensional ABC3 (A = Sc, Y; B = Al, Ga, In; C = S, Se, Te) with intrinsic electric field for photocatalytic water splitting

Hydrogen production from water photolysis is considered to be one of the main approaches to obtain clean energy in the future. Two-dimensional (2D) materials with intrinsic vertical electric field can break the band gap limitation (>1.23 eV) of photocatalysts in traditional theory, and broaden the spectrum that can be used for photocatalytic water splitting, such as infrared light. Inspired by the ferroelectric phase α-B2C3 (B = Al, Ga, In; C = S, Se, Te), we replaced one of the B atoms with IIIB elements (namely Sc and Y) of the same valency, and successfully predicted 18 kinds of ABC3 (A = Sc, Y; B = Al, Ga, In; C = S, Se, Te) monolayers with high stability. Encouragingly, 15 predicted ABC3 monolayers possess direct band gap features in contrast to that of α-B2C3, which all exhibit indirect band gap feature. Due to the large intrinsic vertical electric field, the ABC3 monolayers hold great potential for efficient photocatalytic water splitting in acidic and alkaline as well as neutral environments. The rectified solar-to-hydrogen (STH) efficiencies of 14 ABC3 MLs were larger than 20%. Excitingly, the STH efficiency limits of YGaTe3 and YInTe3 even reach 35.97% and 36.94% using the full solar spectrum, which breaks the conventional theoretical efficiency limit. In addition, considerable light absorption and large carrier mobility are confirmed in ABC3 MLs. These interesting findings render ABC3 monolayers a strong candidate for future photovoltaic and nanoelectronic applications.

2D WSe2/MoSi2N4 type-II heterojunction with improved carrier separation and recombination for photocatalytic water splitting

The use of semiconductor photocatalysis for hydrogen production is an ideal approach for achieving solar energy and conversion. In this work, we systematically examine the photocatalytic properties of WSe2/MoSi2N4 van der Waals heterojunctions using first-principles calculation and nonadiabatic molecular dynamics. The results demonstrate that the WSe2/MoSi2N4 heterojunction possesses a 1.81 eV indirect band gap and type-II band alignment, which ensures that the photoexcited electron–hole (e–h) pairs are spatially separated. The carrier lifetime of the photoexcited e–h pairs is 278 ps significantly longer than the interlayer hole transfer time of 335 fs, implying that the heterojunction has the high quantum efficiency. In addition, this heterojunction possesses superior optical absorption (105 cm−1), low overpotential for OER (0.60 V), and outstanding light absorption properties. These findings indicate that this heterojunction can achieve highly efficient and spontaneous photocatalytic water splitting.

Molten salt-assisted synthesis of nitrogen-vacancy crystalline graphitic carbon nitride with tunable band structures for efficient photocatalytic overall water splitting

The photocatalytic overall water splitting performance of graphitic carbon nitride (g-C3N4) has still been restricted by its inefficient charge separation efficiency. Herein, nitrogen-vacancy crystalline g-C3N4 nanosheets (g-C3N4-D) with tunable band structures were successfully prepared by the alkali-molten salt-assisted method for efficient photocatalytic overall water splitting. Among them, g-C3N4-D2 not only combines the advantages of the amorphous and crystalline state of two-dimensional g-C3N4 nanosheets, but also introduces nitrogen vacancy to adjust the bandgap structures of crystalline g-C3N4 by an alkali etching, thus improving the light energy utilization and charge separation efficiency. TEM and EPR spectrum prove the existence of N defects in the crystalline g-C3N4. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 with Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a significant quantum efficiency of 11.94 % at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48 %. The photocatalytic water oxidation activity of Pt/g-C3N4-D2/5%Co3O4 NRs is 42.34 μmol g−1 h−1. Additionally, the potential mechanism of photocatalytic overall water splitting was testified by in-situ XPS. This work provides a simple strategy for further advancing the potential application of g-C3N4 by molten salt-assisted alkali etching to introduce N vacancies to regulate the band gap of crystalline g-C3N4 for photocatalytic overall water splitting.

Single-atomic Co-N4-O site boosting exciton dissociation and hole extraction for improved photocatalytic hydrogen evolution in crystalline carbon nitride

Single atom co-catalyst loading has been demonstrated to be an effective strategy for achieving efficient photocatalytic water splitting. Unfortunately, the origins of the high activity of the single atom sites remain unrevealed owing to the lack of deep insight on their coordination environment. Herein, single-atom Co was loaded on crystalline g-C3N4 (CCN) nanorod in the form of five-coordination (Co-N4-O) at the heptazine cavities. Both experimental and theoretical evidences revealed that single-atomic Co-N4-O sites in CCN-Co played a key role in exciton dissociation and photogenerated charge carrier separation as well as subsequent hole extraction and transfer. Under visible light irradiation, the photogenerated holes in CCN directionally transferred to Co-N4-O sites and were rapidly extracted by hole sacrificial agent. As a result, the obtained CCN-Co sample with 0.32 wt. % Co and 1.0 wt. % Pt exhibited significantly improved photocatalytic hydrogen production rate of 32.1 mmol g−1 h−1, nearly 4 times and 38 times higher than that of CCN and bulk g-C3N4, respectively. The apparent quantum yield as high as 49.5 % was achieved at 420 nm. This work opens new insights for understanding the effect of single-atom active sites in promoting photocatalytic hydrogen production.

Noble-metal-free chalcogenide nanotwins for efficient and stable photocatalytic pure water splitting by surface phosphorization and cocatalyst modification

Chalcogenide photocatalysts are considered excellent candidates for photocatalytic water splitting because of their narrow bandgaps enabling utilization of visible light. However, severe self-oxidation of sulfide ions during water oxidation greatly restricts their application toward pure water splitting. Herein, we report the synthesis of a near-surface P-doped Cd0.5Zn0.5S (CZS) nanotwin photocatalyst, co-modified by red phosphorus (RP) and transition metal phosphides (TMPs, including FeP, Ni2P, and Co2P) by a one-step phosphorization method that enables efficient and stable pure water splitting. We demonstrate that homogenous phosphorus bridges formed from CZS to both RP and TMP because of near-surface P doping. These unique bridges enable effective charge transfer from RP to CZS and then to TMP via a two-electron Z-scheme mechanism. Significantly, the RP for photogenerated holes capture shows great corrosion–resistance during water oxidation, with simultaneous production of H2O2, while TMP promotes H2 evolution. The optimal CZS-P-Co2P shows a H2 evolution rate of 801.3 μmol/h/g for visible-light-driven pure water splitting, with an apparent quantum of 7.46% at 400 nm, which are among the highest reported values over chalcogenide photocatalysts. This work demonstrates the promising application potential of chalcogenides as photocatalysts for pure water splitting.

Piezo-Photocatalytic Synergy in BiFeO3 @COF Z-Scheme Heterostructures for High-Efficiency Overall Water Splitting.

Solar-driven overall water splitting is an ideal way to generate renewable energy while still challenging. For the first time, this work combined covalent organic frameworks (COFs) and piezoelectric material by covalent linkages to form Z-scheme core@shell heterostructure for overall water splitting. Benefiting from the synergistic effect between the polarized electric field and photo-generated charges, as well as the precise adjustment of shell thickness, the carrier separation and utilization efficiency is greatly improved. The optimal BiFeO3 @TpPa-1-COF photocatalyst revealed hydrogen (H2 ) and oxygen (O2 ) production rates of 1416.4 and 708.2 μmol h-1 g-1 under the excitation of ultrasonication coupled with light irradiation, which is the best performance among various piezo- and COF-based photocatalysts. This provides a new sight for the practical application of highly efficient photocatalytic overall water splitting.

Piezo‐Photocatalytic Synergy in BiFeO3@COF Z‐Scheme Heterostructures for High‐Efficiency Overall Water Splitting

AbstractSolar‐driven overall water splitting is an ideal way to generate renewable energy while still challenging. For the first time, this work combined covalent organic frameworks (COFs) and piezoelectric material by covalent linkages to form Z‐scheme core@shell heterostructure for overall water splitting. Benefiting from the synergistic effect between the polarized electric field and photo‐generated charges, as well as the precise adjustment of shell thickness, the carrier separation and utilization efficiency is greatly improved. The optimal BiFeO3@TpPa‐1‐COF photocatalyst revealed hydrogen (H2) and oxygen (O2) production rates of 1416.4 and 708.2 μmol h−1 g−1 under the excitation of ultrasonication coupled with light irradiation, which is the best performance among various piezo‐ and COF‐based photocatalysts. This provides a new sight for the practical application of highly efficient photocatalytic overall water splitting.

Fabrication of 0D/1D/2D ZnS–CuS nanodots/GNRs/g-C3N4 heterojunction photocatalyst for efficient photocatalytic overall water splitting

Photocatalytic water splitting has become a significant challenge in modern chemistry. In this process, the rate-determining step is the hydrogen evolution reaction (HER). In the present work, a surface modification approach for graphitic carbon nitride (g-C3N4) was applied to improve its photocatalytic HER. 0D ZnS–CuS nanodots were synthesized with the hydrothermal method as a co-catalyst to enhance the capability and stability of water splitting in the presence of visible light irradiation. Also, graphene nanoribbons were synthesized from CNTs unzipping to reduce the energy barrier of HER, improve the HE kinetic, and enhance the catalytic performance of the g-C3N4. By using ZnS–CuS/GNRs(2)/g-C3N4 photocatalyst, a low onset potential of 130 mV, slight Tafel slope of 41 mV dec−1, as well as excellent stability of 2000 s was obtained in acidic media. This efficient performance is attributed to the increased visible light absorption level in the proposed photocatalyst and the high stability in electron-hole pairs.

Conduction band tuning by strengthening s-p hybridization of novel layered oxyhalide Bi4SbO8Cl for efficient visible-light photocatalytic water splitting

Bismuth-based Sillen–Aurivillius oxyhalide Bi4MO8Cl are promising visible-light photocatalysts. The element M of [MO4]3- perovskite layer in the Bi4MO8Cl is always a transition element. Due to d orbitals in transition element weakening the Bi 6s and O 2p orbitals hybridization, the bandgap energy would be decreased and the CBM would be lowered. Thus, Bi4MO8Cl always shows feeble reducibility for photocatalytic hydrogen generation. In this paper, we choose the main group element Sb substitute for transition element M in the Sillen–Aurivillius Bi4MO8Cl. Due to the s-p-d hybridization in Bi4NbO8Cl being replaced by only s-p hybridization in Bi4SbO8Cl, the strengthened Bi 6s and O 2p orbitals hybridization would eventually lead to the enlarged energy bandgap and elevated CBM. The bandgap of Bi4SbO8Cl was about 2.53 eV with the CBM estimated about −0.33 eV. Because of the high carrier mobility and strong reducibility brought by the dispersed Bi 6s states in the whole unoccupied states and the raised position of Bi 6p states in the CBM and linearity Sb–O–Sb, Bi4SbO8Cl shows enhanced photocatalytic H2 generation compared to Bi4NbO8Cl under the visible-light irradiation.

ZnInGaS4 heterojunction with sulfide vacancies for efficient solar-light photocatalytic water splitting and Cr(VI) reduction

ZnInGaS4 heterojunction with S vacancies was prepared via the microwave hydrothermal route to boost the solar-light photocatalytic activity for water splitting and Cr (VI) reduction. The tight interface between ZnIn2S4 and ZnGa2S4 favors the rapid separation and transfer of photo-induced electron-hole pairs, and the narrowed band gap is suitable for visible-light harvesting. In addition, S vacancies serve as the adsorption sites and photons capture, leading to the efficient solar utilization. Compared with ZnIn2S4 (0.94 mmol g-1h−1) and ZnGa2S4 (0.33 mmol g-1h−1), the optimal ZnInGaS4 with a In/Ga molar ratio of 1:1 exhibits the better H2 evolution rate (4.47 mmol g-1h−1) and the apparent quantum yield of 20.16 % at wavelength of 400 nm. The removal efficiency of ZnInGaS4 for solar-light driven Cr (VI) reduction is 99.46 % within 140 min, which is higher than ZnIn2S4 (93.14 %) and ZnGa2S4 (89.31 %). The photo-corrosion induces to the deactivation of ZnGa2S4 for solar-light driven H2 evolution and Cr (VI) reduction after five cycles.

Constructing 0D/1D/2D Z-scheme heterojunctions of Ag nanodots/SiC nanofibers/g-C3N4 nanosheets for efficient photocatalytic water splitting

Efficiently constructing nanostructured Z-scheme heterojunctions with good interface contact is a desired route to optimize the photocatalytic property of the materials. In this work, novel 0D/1D/2D Z-scheme silver/silicon carbide/graphitic carbon nitride (Ag/SiC/CN) photocatalysts were prepared from Ag nanodots loaded on SiC nanofibers/CN nanosheets (SiC/CN) composite, using the calcination and chemical reduction routes. The Ag/SiC/CN composite with an optimal 3% Ag loading dose performs the best H2 evolution rate of 2971 μmol g−1 h−1, which is approximately 8.8, 1.5 and 4.5 times compared to CN, SiC/CN and 3% Ag/CN, respectively. Besides the Ag/SiC/CN composite presents a high apparent quantum efficiency (7.3%) and outstanding photo-corrosion resistance stability. The Ag nanodots are served as efficient carriers transfer center and cocatalyst to construct Z-scheme heterojunction interface, which can help to generate more photo-generated carries, shorten the electron transmission distance and increase the electron transfer rate, certifying that 0D/1D/2D Z-scheme photocatalytic system is high-efficiency and has great advantages in photocatalytic applications.

Ferroelectric polarization enabled spatially selective adsorption of redox mediators to promote Z-scheme photocatalytic overall water splitting

<h2>Summary</h2> Although the artificial Z-scheme system, mimicking natural photosynthesis, has shown promising applications in photocatalytic water splitting, it often suffers from the side reaction of redox mediator, which considerably undermines the efficacy of photocarrier utilizations. Herein, we propose to suppress the side reaction by using ferroelectric polarization, which not only provides a strong driving force to spatially separate photocarriers to the oppositely poled surface but also induces spatially selective adsorption of redox ions. Single-domain ferroelectric PbTiO₃ nanoplates have been adopted as a model ferroelectric to construct the Z-scheme system with BiVO₄ particles and a cationic redox mediator. In contrast to the inactive multi-domain ferroelectric PbTiO₃-based system, the so-formed Z-scheme system delivers stable high activity for photocatalytic overall water splitting under both visible light and simulated solar insolation. This work offers a proof of concept to realize efficient solar photocatalytic water splitting based on single-domain ferroelectric Z-scheme system.

TiO2/SiO2 dopant-free nanophotocatalysts for highly efficient photocatalytic water splitting: Challenging traditional TiO2-based systems

Three preparation methods of mesoporous silica nanosupports were investigated for H2 production: molecular imprinting, surface functionalization, and hybrid framework. The effect of the surface nature of SiO2 on the growth and distribution of TiO2 actives sites, as well as on photocatalytic reactions, was also explored. TiO2 and TiCl4 were used as precursors for the catalytic centers, and the results were compared to each other. The molecular imprinting created on the SiO2 support improved the exposure of catalytic species and changed the electronic properties, resulting in a narrow energy bandgap (Eg, 2.85-2.94 eV). A deep discussion of the textural, morphological, optical, spectral, electronic, surface fractal, and crystal structure characteristics of the TiO2/SiO2 metal-free nanocatalyst performance for water splitting is presented. The dopant-free nanocatalysts stand out for the small amount of TiO2 (0.0778–0.1747% wt. Ti/SiO2) used in their preparation and for their high catalytic activity for H2 photoproduction. A surprising performance was achieved by the SiTi1200 sample, 140.22 mmol H2.g−1, mainly due to the specific surface area, the surface fractal structure, and the band gap energy. This performance was much higher than that of commercial P25 and other TiO2 materials, which are more complex catalytic systems reported in the literature. The study shows that easily synthesized TiO2/SiO2 nanosystems with tunable main characteristics may overcome the existing limitations for water splitting by TiO2-based photocatalysts, allowing new opportunities for other catalytic applications.

In situ synthesis of Cu‐doped ZIF‐8 for efficient photocatalytic water splitting

Metal–organic frameworks (MOFs) reached a new level of research in photocatalysis by their virtue of tunable structure, modifiable pores, and a large surface area. Herein, we employed a simple metal ion exchange method to change ZIF‐8 from UV light to visible light absorption photocatalyst. In this work, Cu2+ ions are integrated within the ZIF‐8 framework to synthesize Cu‐doped ZIF‐8 photocatalysts and well characterized by using both the spectroscopic and electrochemical studies. The Cu@ZIF‐8 (CDZ‐20) photocatalyst shows enhanced light‐harvesting ability and remarkable hydrogen generation rate of 13.9 mmolg−1 h−1 with an apparent quantum efficiency (AQE) of 9.08%, which is 17 times higher than that of pristine ZIF‐8 photocatalyst. The higher photocurrent density of 34 μA/cm2 in CDZ‐20 further reinforced the superiority over the ZIF‐8 (1 μA/cm2). This work paves the way to engineer robust copper doped ZIFs photocatalyst under mild synthesis approach for efficient H2 evolution.