Mechanism Of Photocatalytic Hydrogen Production Research Articles

Study on the performance and mechanism of photocatalytic hydrogen production by NiO/ZnO-graphene composite materials under low irradiation conditions

Using different mass ratios of NiO, ZnO, and corn stover-based graphene (GR), NiO/ZnO-graphene (NZGR) composite photocatalytic materials, which demonstrated photocatalytic water splitting for hydrogen production under low irradiation, were prepared by an in-situ deposition method. The microstructure and optoelectronic properties of the NZGR materials were characterized. The heterostructure formed by NiO and ZnO in the photocatalytic NZGR material was coupled with the graphene-like structure of GR, resulting in the rapid transfer of electrons to the graphene surface, causing electron accumulation and ensuring the ability of the material to produce hydrogen by the photocatalytic decomposition of water under low irradiation. Under the optimal mixing ratio of the components of the NZGR photocatalyst with a graphene mass fraction of 30 %, hydrogen production exhibited the highest rate and was 350 times faster than the photocatalytic hydrogen production of NiO/ZnO under the same conditions. This study provides a new approach to producing hydrogen by the photocatalytic decomposition of water under low irradiation conditions.

CdS Deposited In Situ on g-C3N4 via a Modified Chemical Bath Deposition Method to Improve Photocatalytic Hydrogen Production

Ultra-thin two-dimensional materials are attracting widespread interest due to their excellent properties, and they are becoming ideal candidates for a variety of energy and environmental photocatalytic applications. Herein, CdS nanorods are successfully grown in situ between a monolayer of g-C3N4 using a chemical water bath method. Continuous ultrasound is introduced during the preparation process, which effectively prevents the accumulation of a g-C3N4 layer. The g-C3N4@CdS nanocomposite exhibits significantly enhanced photocatalytic activity for hydrogen production under visible-light irradiation, which is attributed to a well-matched band structure and an intimate van der Waals heterojunction interface. The mechanism of photocatalytic hydrogen production is discussed in detail. Moreover, our work can serve as a basis for the construction of other highly catalytically active two-dimensional heterostructures.

Pt loaded porphyrin-functionalized polysulfone membrane for visible-light driven H2 evolution

Photocatalytic hydrogen production has been described as a promising way to obtain green hydrogen energy. Effective proton reduction sites were added to the photocatalyst's surface in order to significantly increase the photocatalytic performance. Herein, Pt atoms were anchored onto porphyrin grafted polysulfone (THPP-g-PSf) membrane by the impregnation-photoreduction method, which was marked as Pt@THPP-g-PSf. Fourier transform infrared (FT-IR), ultraviolet-visible (UV–vis), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and fluorescence spectroscopy were used to systematically characterize the successful preparation of Pt@THPP-g-PSf. The results show that Pt atoms have been successfully loaded into the center of porphyrin on the membrane surface. Furthermore, the performance of the Pt@THPP-g-PSf membrane for the visible light-induced splitting of water to hydrogen was studied. It is found that the hydrogen production rate of Pt@THPP-g-PSf can reach 5.7 mmol·m−2·h−1, which is two times of that of the THPP-g-PSf membrane. In addition, the electron transfer mechanism of photocatalytic hydrogen production was further investigated by time-resolved specify. The results showed that the anchored Pt atoms can facilitate the electron-hole pair (e−/h+) separation, thus improving the photocatalytic activity. This work provides a facile method to construct Pt supported porphyrin functionalized PSf membrane for visible-light induced hydrogen production.

Carbon nitride quantum dots-modified cobalt phosphate for enhanced photocatalytic H2 evolution.

In the present work, carbon nitride quantum dots (CNQDs)-modified cobalt phosphate (CoPi) composites CNQDs/CoPi-x (x = 1, 2, 3) were prepared at room temperature and characterized by FTIR, XRD, UV-Vis DRS, EIS, SEM, TEM/HR-TEM, XPS, and N2 gas adsorption. The morphologies and surface areas of CNQDs/CoPi-x have no remarkable change after modification of CNQDs, compared with pure CoPi. The obtained CNQDs/CoPi-x shows enhanced activity and stability of photocatalytic H2 evolution compared to pure CoPi using Eosin Y (EY) as a sensitizer and triethanolamine as an electron donor. The CNQDs/CoPi-2 possesses the highest hydrogen evolution rate, 234.5 μmol h-1 g-1 , upon visible light, which outshines that of CoPi by 2.4 times. It was believed that the enhanced photocatalytic performances of the CNQDs/CoPi-2 could result from the boosted electron transfer from radical EY·- to CNQDs/CoPi-2 by the employment of CNQDs; in addition, the visible-light activity of CNQDs contributes to hydrogen evolution. The mechanism of photocatalytic hydrogen production was discussed. This study may contribute toward the development of production of "green hydrogen" using solar.

Short stick-shaped MnS/Mn0·5Cd0·5S grown in situ on CuSe nanosheets for efficient photocatalytic hydrogen evolution

The development of efficient and stable photocatalysts is very important for photocatalytic hydrogen evolution. In this work, a series of CuSe/MnS/Mn0·5Cd0·5S composites with high hydrogen evolution performance were synthesized by a simple hydrothermal method. The synthesized products were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Mapping, X-ray photoelectron spectroscopy, UV–Vis diffuse reflection spectroscopy, Mott–Schottky, Transient photocurrent response, Electrochemical impedance spectroscopy, and Photoluminescence spectroscopy. The obtained products showed efficient photocatalytic hydrogen evolution efficiency in Na2S–Na2SO3 solution under 300 W Xe lamp (λ ＞ 420 nm), with the highest photocatalytic hydrogen evolution efficiency reaching 24.7 mmol g−1 h−1, which was 4.1 times higher than pure MnS/Mn0·5C0·5S (5.99 mmol h−1 g−1) and 6.3 times higher than pure CdS (3.59 mmol h−1 g−1). A possible mechanism of photocatalytic hydrogen production was proposed. The addition of CuSe effectively enhances the photogenerated electron-hole separation efficiency and reduces the electron-hole pair complexation rate of CuSe/MnS/Mn0·5C0·5S composites. This work provides an effective way to improve the photocatalytic activity of Mn0·5Cd0·5S using transition metal selenide cocatalysts.

Photocatalytic Hydrogen Production from Formic Acid Solution with Titanium Dioxide with the Aid of Simultaneous Rh Deposition

Photocatalytic hydrogen production was studied with a formic acid solution with titanium dioxide (TiO2) with the aid of simultaneous Rh deposition. The optimum conditions were as follows: Rh loading, 0.1 wt%; formic acid concentration, 1.0%; solution, pH 2.2; temperature, 50 °C. Under the optimum conditions, the photocatalytic hydrogen production with TiO2 by the simultaneous deposition of Rh was 5.0 mmol g−1, 12.2 mmol g−1 and 16.0 mmol g−1 after 1 h, 3 h and 5 h of irradiation time for black light, respectively. Rh/TiO2 photocatalysts were characterized by XRD, SEM, photoluminescence spectra, diffuse reflectance spectra and the BET surface area. The reaction mechanism of photocatalytic hydrogen production from formic acid by Rh/TiO2 was also proposed.

An efficient photocatalytic system under visible light: In-situ growth cocatalyst Ni2P on the surface of CdS

Cocatalyst contributes to promote the separation and transfer of charge in photocatalytic system, which is an important factor to improve photocatalytic decomposition of water to produce hydrogen. Here, a simple and effective method to combine the main catalyst and the cocatalyst by a modified impregnation method is provided. A novel Ni2P/CdS is prepared by in-situ growth of Ni2P cocatalyst on the CdS surface using the modified impregnation method. The research shows that Ni2P, as an electron carrier, can promote the separation of electrons and holes, and significantly improve the photocatalytic activity of Ni2P/CdS. When Ni2P was 3% in Ni2P/CdS, the photocatalytic activity of hydrogen production was the highest, and the hydrogen production rate reached an astonishing 16.02 mmol h−1g−1 under visible light, which was 57 times that of CdS. Moreover, Ni2P/CdS photocatalyst has outstanding stability for hydrogen production. The mechanism of photocatalytic hydrogen production by Ni2P/CdS is proposed.

Reaction Mechanism of Photocatalytic Hydrogen Production at Water/Tin Halide Perovskite Interfaces

While instability in aqueous environment has long impeded employment of metal halide perovskites for heterogeneous photocatalysis, recent reports have shown that some particular tin halide perovskites (THPs) can be water-stable and active in photocatalytic hydrogen production. To unravel the mechanistic details underlying the photocatalytic activity of THPs, we compare the reactivity of the water-stable and active DMASnBr3 (DMA = dimethylammonium) perovskite against prototypical MASnI3 and MASnBr3 compounds (MA = methylammonium), employing advanced electronic–structure calculations. We find that the binding energy of electron polarons at the surface of THPs, driven by the conduction band energetics, is cardinal for photocatalytic hydrogen reduction. In this framework, the interplay between the A-site cation and halogen is found to play a key role in defining the photoreactivity of the material by tuning the perovskite electronic energy levels. Our study, by elucidating the key steps of the reaction, may assist in development of more stable and efficient materials for photocatalytic hydrogen reduction.

Strategies for Optimizing the Photocatalytic Water‐Splitting Performance of Metal–Organic Framework‐Based Materials

Semiconductor photocatalytic hydrogen production technology is a pollution‐free and low‐cost technology, which is principal to alleviate the energy crisis. The metal–organic frameworks (MOFs)‐based materials have been widely used in this field because of their regular and controllable pore structure and high specific surface area. Accordingly, the recent progress of MOFs‐based materials in the production of hydrogen through water splitting is reviewed. First, the mechanism of photocatalytic hydrogen production and the existing problems are proposed and then their advantages in photocatalytic hydrogen production and various photocatalytic hydrogen production catalysts based on MOFs are summarized. Subsequently, several methods to improve their photocatalytic hydrogen production property are summarized. Finally, some views on the prospects and challenges of the use of MOFs‐based catalysts for photocatalytic hydrolysis are expounded. Although some reviews associated with MOFs for solar‐driven H2 production have been published, most of them focus on the classification of MOFs photocatalysts. This is the first comprehensive review concentrating on the strategies for optimizing the photocatalytic activity of MOFs‐based materials for H2 production. It is believed that the suggestions provided here can help to study MOFs‐based photocatalytic reactions and to further promote the development of this research direction in the future.

A New Allotrope of Carbon—Graphdiyne (g‐CnH2n−2) Boosting with Mn0.2Cd0.8S form S‐Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution

AbstractAs a new 2D carbon hybrid material, graphdiyne has attracted much attention due to its good conductivity, adjustable electronic structure, and special electron transfer enhancement properties. It has great potential in the field of hydrogen evolution by photocatalytic water splitting due to its special properties. In this paper, layered graphdiyne is prepared by crosscoupling method, using CuI instead of typical copper film as catalyst. Graphdiyne/CuI is used to modify Mn0.2Cd0.8S (MCS) solid solution for the first time, which greatly improves the optical properties and hydrogen production performance of the photocatalyst. The S‐scheme heterojunction constructed between graphdiyne and MCS greatly improves the transfer rate of photoinduced electrons. In addition, the results of fluorescence spectra and photoelectrochemical tests show that the nanocomposites have longer carrier lifetime, lower recombination rate, faster carrier migration rate, and lower hydrogen evolution overpotential. Therefore, the hydrogen evolution rate of the MnCdS/graphdiyne/CuI with the best performance can reach 9.904 mmol g−1 h−1, which is 4.02 times of that of pure MCS. This work not only proposes the possible mechanism of photocatalytic hydrogen production but also provides an important strategy for the application of graphdiyne in the field of photocatalytic hydrogen production.

Efficient photocatalytic hydrogen production from formic acid on inexpensive and stable phosphide/Zn3In2S6 composite photocatalysts under mild conditions

Developing an efficient, stable and low-cost photocatalytic hydrogen production from formic acid is a daunting challenge and has attracted the intense interest of many of researchers. In this paper, we report the synthesis of novel composite photocatalysts (Ni2P/Zn3In2S6 (ZIS6) and MoP/ZIS6) and their catalytic performance for H2 production reaction from formic acid under visible light irradiation, in which Ni2P and MoP were used as cocatalysts to enhance hydrogen generation activity of ZIS6. The photocatalytic hydrogen production rates of the optimized 1.5 wt% Ni2P/ZIS6 (45.73 μmol·h−1) and 0.25 wt% MoP/ZIS6 (92.69 μmol·h−1) were 3.5 times and 7.2 times higher than that of the pure ZIS6 (12.88 μmol·h−1), respectively. The apparent quantum efficiency at wavelength λ = 400 ± 10 nm for the two photocatalysts was about 1.8% and 6.4%, respectively. Significantly, it was found that the remarkable improvement of hydrogen production performance is attributed to the introduction of the phosphide cocatalysts, which can serve as a charge separation center and an active site for photocatalytic hydrogen production from the decomposition of formic acid. The reaction mechanism of photocatalytic hydrogen production from formic acid was also proposed.

Orderly designed functional phosphide nanoparticles modified g-C3N4 for efficient photocatalytic hydrogen evolution

The synthesis of highly efficient and stable photocatalysts has always been one of the key research objects in the field of photocatalysis. Increasing the efficiency of charge separation is an important aspect of improving photocatalytic activity. In this work, the Co-W-P cocatalysts were loaded on g-C3N4, synthesized for the first time and the electron transport routes were appropriately adjusted, which extremely improved efficiency of photocatalytic decomposition of water for hydrogen evolution. A composite photocatalyst with high-efficiency photocatalytic H2 production performance under visible light was obtained by loading the Co-W-P composites on a g-C3N4 nanosheet. It was ascribed to the efficient interfacial electron transfer routes. This has contributed to the synthesis of high-priority and stable photocatalysts. Besides, the composite catalysts were characterized by SEM, TEM, XRD, XPS, UV-vis, BET, transient photocurrent, and FT-IR etc. And a mechanism of photocatalytic hydrogen production was hypothesized.

An orderly assembled g-C3N4, rGO and Ni2P photocatalyst for efficient hydrogen evolution

On account of on the dominant performance of Ni2P, rGO and g-C3N4 itself, with a view to conquer the disadvantages of Ni2P, rGO and g-C3N4 its own, the g-C3N4/rGO/Ni2P is successfully designed and prepared by a simple hydrothermal reaction, which is used in dye-sensitized system for high-efficient photocatalytic H2 evolution. The rGO is adhered to the outside appearance of the g-C3N4 nanosheets and fish-scale shape Ni2P is anchored on the surface of rGO and g-C3N4. The above three forms a synergistic effect. The maximum amount of H2 evolution reaches about 266 μmol for 5 h over the g-C3N4/rGO/Ni2P photocatalyst when the content of rGO is 8%, which is 10.6 times higher than g-C3N4. Synergy between the above three materials is certified by some characterizations and the results of which are consistent with each other. In addition, the possible mechanism of photocatalytic hydrogen production is proposed.

Orderly-designed Ni2P nanoparticles on g-C3N4 and UiO-66 for efficient solar water splitting

Stable and efficient photocatalyst is the key important research goals up to now. On account of the dominant performance of Ni2P, g-C3N4 (graphitized carbonitride) and UiO-66 (Universitetet i Oslo) themselves, an orderly-designed assemble of g-C3N4/UiO-66/Ni2P is successfully designed and assembled with capability of high-efficient dye-sensitized photocatalytic H2 evolution. The electron transport routes are successfully adjusted and the hydrogen evolution is greatly improved. It exhibits synergistic effect on highly efficient photocatalytic hydrogen production. The maximum amount of hydrogen evolution reaches about 200 μmol for 5 h over the g-C3N4/UiO-66/Ni2P photocatalyst under the 5 W LED white light at 420 nm. The H2 evolution rate is 12 times high than over g-C3N4. Such synergistically increased effect in photocatalytic properties is certified by related characterization results such as TEM, SEM, XPS, XRD, UV–vis DRS, Transient photocurrent and FT-IR etc. The above studies show that the Ni2P nanoparticles modified on the g-C3N4/UiO-66 provides the more active sites and improves the efficiency of photo-generated charge separation. In addition, the possible mechanism of photocatalytic hydrogen production is proposed.

Two-dimensional germanium monochalcogenides for photocatalytic water splitting with high carrier mobility

Highly efficient utilization of solar energy to split water into hydrogen and oxygen is regarding as a promising strategy to deal with the future energy crisis and environmental problems. To explore highly efficient and low-cost photocatalysts is highly desired. Herein, phosphorene-like germanium monochalcogenides (GeS and GeSe monolayers) are proposed here as efficient photocatalysts for water splitting. After confirming their stabilities, we observe that GeS exhibits an indirect band gap of 2.29eV while GeSe reveals a direct band gap of 1.59eV by HSE hybrid functional. Remarkably, high and directionally anisotropic carrier mobilities (2430.50cm2V−1s−1 for GeS and 4032.64cm2V−1s−1 for GeSe) are quantitatively investigated by using deformation potential theory. In addition, GeS and GeSe monolayers exhibit a good separation of electrons and holes, which effectively reduces the photocatalytic activity with high efficiency. Upon the application of strain, the band structure can be modulated from semiconductor to metal and a direct-indirect bandgap transition is observed. Most intriguingly, the band gaps and band edge alignments at certain pH value can be effectively tuned to meet the requirement of the redox potential in water splitting. Finally, the adsorption and decomposition of water molecules on the surface of 2D GeS and the subsequent formation of hydrogen were explored, which unravels the mechanism of photocatalytic hydrogen production on 2D GeS. Our findings will be valuable for facilitating the exploration and application of GeS and GeSe for photocatalytic water splitting.

Mechanism of photocatalytic hydrogen generation by a polypyridyl-based cobalt catalyst in aqueous solution.

The mechanism of photocatalytic hydrogen production was studied with a three-component system consisting of fac-[Re(py)(CO)3bipy](+) (py = pyridine, bipy = 2,2'-bipyridine) as photosensitizer, [Co(TPY-OH)(OH2)](2+) (TPY-OH = 2-bis(2-pyridyl)(hydroxy)methyl-6-pyridylpyridine), a polypyridyl-based cobalt complex, as water reduction catalyst (WRC), and triethanolamine (TEOA) as sacrificial electron donor in aqueous solution. A detailed mechanistic picture is provided, which covers all processes from excited state quenching on the time scale of a few nanoseconds to hydrogen release taking place between seconds and minutes at moderately basic reaction conditions. Altogether these processes span 9 orders of magnitude in time. The following reaction sequence was found to be the dominant pathway for hydrogen generation: After reductive quenching by TEOA, the reduced photosensitizer (PS) transfers an electron to the Co(II)-WRC. Protonation of Co(I) yields Co(III)H which is reduced in the presence of excess Co(I). Co(II)H releases hydrogen after a second protonation step, which is detected time-resolved by a clark-type hydrogen electrode. Aside from these productive steps, the role of side and back reactions involving TEOA-derived species is assessed, which is particularly relevant in laser flash photolysis measurements with significantly larger transient concentrations of reactive species as compared to continuous photolysis experiments. Most notable is an equilibrium reaction involving Co(I), which is explained by a nucleophilic addition of Co(I) to the oxidation product of TEOA, an electrophilic iminium ion. Quantum chemical calculations indicate that the reaction is energetically feasible. The calculated spectra of the adduct are consistent with the spectroscopic observations.

The mechanism of photocatalytic hydrogen production from gaseous methanol and water: IR spectroscopic approach

IR spectroscopic and volumetric study under reaction conditions of the mechanism of photocatalytic hydrogen production from gaseous methanol and water revealed that CO 2 and H 2 were produced by reaction between adsorbed CH 3O(ad) and H 2O. Another reaction path for H 2 production, CH 3 OH(ad) → H 2 + HCHO, was suggested which is dominant in the absence of water.