Simulated Solar Illumination Research Articles

Hydrothermal preparation of carbon modified KNb3O8 nanosheets for efficient photocatalytic H2 evolution

The carbon loaded KNb3O8 nanosheets composite has been synthesized for the first time by hydrothermal method, displaying an outstanding performance in photocatalytic H2 evolution. The optimal C/KNb3O8 sample exhibits a H2-generation rate of 1148 μmol g−1 h−1 under simulated solar illumination, which is 1.8 times that of pristine KNb3O8. Various characterizations including N2 adsorption, XRD, XPS, Raman, DRS, transient photocurrent, EIS, LSV have been applied to investigate the behind mechanism. It is found that the introduction of carbon shows a slight effect on the specific surface area, but obviously improves the optical property and charge separation efficiency. The introduced carbon mainly acts as electron trapper to accept the photoexcited electrons from the conduction band of KNb3O8, and hence enhances the efficiency in separating electron-hole pairs, which plays a key role in improving the photocatalytic reaction. The cycling test further demonstrates that the C/KNb3O8 has high photocatalytic stability, indicating its good potential for practical photocatalytic H2 evolution.

Near-infrared absorbing 2D/3D ZnIn2S4/N-doped graphene photocatalyst for highly efficient CO2 capture and photocatalytic reduction

Hierarchical heterostructure photocatalysts with broad spectrum solar light utilization, particularly in the near-infrared (NIR) region, are emerging classes of advanced photocatalytic materials for solar-driven CO2 conversion into value-added chemical feedstocks. Herein, a novel two-demensional/three-demensional (2D/3D) hierarchical composite is hydrothermally synthesized by assembling vertically-aligned ZnIn2S4 (ZIS) nanowall arrays on nitrogen-doped graphene foams (NGF). The prepared ZIS/NGF composite shows enhancement in photothermal conversion ability and selective CO2 capture as well as solar-driven CO2 photoreduction. At 273 K and 1 atm , the ZIS/NGF composite with 1.0 wt% NGF achieves a comparably high CO2-to-N2 selectivity of 30.1, with an isosteric heat of CO2 adsorption of 48.2 kJ mol−1 . And in the absence of cocatalysts and sacrificial agents, the ZIS/NGF composite with cyclability converts CO2 into CH4, CO and CH3OH under simulated solar light illumination, with the respective evolution rates about 9.1, 3.5, and 5.9 times higher than that of the pristine ZIS. In-depth analysis using in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) in conjunction with Kelvin probe measurements reveals the underlying charge transfer pathway and process from ZIS to NGF.

Decoupled Photoelectrochemical Water Splitting System for Centralized Hydrogen Production

Photoelectrochemical (PEC) water splitting offers an elegant approach for solar energy conversion into hydrogen fuel. Large-scale hydrogen production requires stable and efficient photoelectrodes and scalable PEC cells that are fitted for safe and cost-effective operation. One of the greatest challenges is the collection of hydrogen gas from millions of PEC cells distributed in the solar field. In this work, a separate-cell PEC system with decoupled hydrogen and oxygen cells was designed for centralized hydrogen production, using 100 cm2 hematite (a-Fe2O3) photoanodes and nickel hydroxide (Ni(OH)2) / oxyhydroxide (NiOOH) electrodes as redox mediators. The operating conditions of the system components and their configuration were optimized for daily cycles, and ten 8.3 h cycles were carried out under solar simulated illumination without additional bias at an average short-circuit current of 55.2 mA. These results demonstrate successful operation of a decoupled PEC water splitting system with separate hydrogen and oxygen cells.

Porphyrin functionalized bismuth ferrite for enhanced solar light photocatalysis.

In this work, multiferroic bismuth ferrite (BFO) was functionalized with meso-tetraphenylporphine-4,4',4'',4'''-tetracarboxylic acid (TCPP). This new hybrid organic-inorganic material shows an enhanced photocatalytic activity for the degradation of organic dyes as it combines the properties of BFO which is an efficient visible light photocatalyst with peculiar porphyrin absorption in visible light. The anchoring of TCPP to the OH-terminations of the BFO surface through its carboxylic tethering groups was demonstrated using X-ray photoelectron spectroscopy and FT-IR spectroscopy. The photocatalytic activity of the material was also demonstrated through the photocatalytic degradation of Methylene Blue (MB) and Rhodamine-B (Rhd-B) in water under simulated solar light illumination. The TCPP molecules anchored to BFO slightly decrease (∼0.06 eV) the bandgap energy of the system and act as new catalytic centres, thus improving its photocatalytic activity. A photodegradation mechanism was also proposed. This new material is reusable and stable, as it maintains an unmodified photo-activity after several MB discoloration runs.

High performance and toxicity assessment of Ta3N5 nanotubes for photoelectrochemical water splitting

In this work, Co-based cocatalysts are electrodeposited on mesoporous Ta3N5 nanotubes. The electrodeposition time is varied and the optimized photoelectrode reaches a photocurrent density of 6.3 mA/cm2 at 1.23 V vs. SHE, under simulated solar illumination of 1 Sun, in 1 M NaOH. The best performing electrode, apart from the high photocurrent density, shows improved stability under intense photoelectrochemical water splitting conditions. The dual function of the cocatalyst to improve not only the photoelectrochemical performance, but also the stability, is highlighted. Moreover, we adopted a simple protocol to assess the toxicity of Co and Ta contained nanostructured materials (representing used photoelectrodes) employing the human cell line HeLa S3 as target cells.

Photoelectrocatalyzed degradation of organophosphorus pesticide fenamiphos using WO3 nanorods as photoanode.

In this study, WO3 nanostructures were synthesized by the electrochemical anodization technique to use them on the degradation of persistent organic compounds such as the pesticide fenamiphos. The acids electrolyte used during the anodization were two different: 1.5M H2SO4 - 0.05M H2O2 and 1.5M CH4O3S - 0.05M H2O2. Once the samples have been manufactured, they have been subjected to different tests to analyze the properties of the nanostructures. With Field Emission Scanning Electron Microscopy (FE-SEM) the samples have been examined morphologically, their composition and crystallinity has been studied through Raman Spectroscopy and their photoelectrochemical behaviour by Photoelectrochemical Impedance Spectroscopy (PEIS). Finally, degradation tests have been carried out using the technique known as photoelectrocatalysis (PEC). The conditions that were applied in this technique were a potential of 1 VAg/AgCl and simulated solar illumination. The degradation process was monitored by UV-Visible and High-Performance liquid Chromatography (HPLC) to control the course of the experiment. The nanostructures obtained with 1.5M CH4O3S - 0.05M H2O2 electrolyte showed a better photoelectrochemical behaviour than nanostructures synthesized with 1.5M H2SO4 - 0.05M H2O2. The fenamiphos degradation was achieved at 2h of experiment and the intermediate formation was noticed at 1h of PEC experiment.

Ternary Metal Chalcogenide Heterostructure (AgInS2-TiO2) Nanocomposites for Visible Light Photocatalytic Applications.

Hybrid nanoarchitectures of AgInS2 and TiO2 photocatalysts were prepared by using a modified sol–gel method. The experimental results reveal that these nanocomposites display enhanced visible light absorption and effective charge carrier separation compared to their pristine parent samples (AgInS2 or TiO2). 0.5 wt % AgInS2 loading was found to be the optimum concentration for photocatalytic applications. More than 95% of doxycycline degradation was achieved within 180 min of solar light illumination. Similarly, the dopant concentrations at lower values (<2 wt %) exhibited 300 times higher H2 generation rate under visible light irradiation compared to AgInS2 and TiO2. The microbial strains (Escherichia coli and Staphylococcus aureus) exhibited a 99.999% reduction within half an hour of simulated solar light illumination. The computational investigation was employed to understand the structural, electronic, and the dielectric properties of AgInS2 and TiO2 composites. The improved photocatalytic results are explained as a result of the decreased rate of exciton recombination. The current investigation opens up new insights into the use of novel ternary heterostructure nanocomposites for improved visible light activity.

A Ni2P nanocrystal cocatalyst enhanced TiO2 photoanode towards highly efficient photoelectrochemical water splitting

Developing low-cost oxygen evolution reaction (OER) cocatalysts with high conductivity and excellent catalytic activity is highly desirable for mitigating interfacial charge recombination and accelerating the OER reaction kinetics of the semiconductor photoanode for photoelectrochemical (PEC) water splitting. Herein, a hybrid photoanode integrating a high-quality light absorber, a bilayer TiO2 nanorod-inverse opal (NR-IO) semiconductor and an efficient OER cocatalyst consisting of colloidal Ni2P nanocrystals is constructed via a spin-coating process. The resulting TiO2/Ni2P NR-IO photoanode yields an impressive photocurrent density of 1.93 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE) under simulated solar illumination (AM 1.5G, 100 mW cm−2), corresponding to a more than 2-fold increase compared to the pristine TiO2 NR-IO. The photoelectrochemical electrochemical impedance spectroscopy (PEIS) and photoluminescence (PL) results reveal that the Ni2P cocatalyst not only accelerates the interfacial charge transfer from TiO2 NR-IO to Ni2P but also efficiently transmits the holes to participate in aqueous OER. Moreover, the Ni2P cocatalyst effectively prevents the substantial dark current observed with fully covered transition-metal-phosphide shell modification. This work is expected to spur more insights into integrating semiconductors with proper OER cocatalysts for highly efficient and stable solar water spitting.

PEG assisted P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst with enhanced elimination of emerging organic pollutants in salinity condition under solar light illumination

In this study, the effect of salinity on degradation of model environmental pollutants (organic dyes and E. coli) was investigated using polyethylene glycol (PEG) assisted P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst. The photocatalyst was firstly synthesized with structure modifier PEG to determine the optimum molecular weight by sol-gel method, and was characterized by XRD, UV–Vis, PL, SEM, TEM, EDS, and photocurrent experiment. The PEG300 modified P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst was found to be the optimal molecular weight which exhibited small crystalline size, narrow band gap, better absorption ability, smaller particles size, large photocurrent density, low recombination rate and higher photocatalytic activity among other PEG modified photocatalyst. The PEG300-P/Ag/Ag2O/Ag3PO4/TiO2 photocatalytic degradation of emerging organic pollutants such as rhodamine B, methyl orange, and methylene blue was significantly higher at aqueous NaCl (2.6 and 3.2 wt%) and artificial salinity (25 and 35‰) compared to freshwater under simulated solar light illumination. Furthermore, the elimination of organic dyes under different environmental factors such as initial pH, light intensity, reaction temperature showed substantial degradation in real environmental conditions at salinity. Moreover, PEG300-P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst demonstrated high practicability on complete inactivation of E. coli, simultaneous degradation of organic dyes, and high stability in seawater. Superoxide anion (O2−) radicals was found to be the dominant reactive species, and subsequent formation of Cl and free chlorine oxidative agents further improved the photocatalytic purification process. The PEG300-P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst showed great potential in treating environmental organic pollutants at salinity condition under solar light illumination.

Visible/near-infrared driven highly efficient photocatalyst based on upconversion nanoparticles/g-C3N4 nanocomposite

Graphitic carbon nitride (g-C3N4) is widely considered as a promising visible-driven photocatalyst. It is a type of inexpensive, air-stable, and non-toxic material that has been proven to exhibit high performance in photocatalysis. For more efficient use of solar energy, it is necessary to enhance the light absorption of g-C3N4. To take advantage of the near-infrared (NIR) region of the solar energy, g-C3N4 was combined with upconversion nanoparticles (UCNPs), in this study. The UCNPs can convert NIR photons into ultraviolet (UV) and visible light, which can then activate the g-C3N4 photocatalyst. The use of visible and NIR light sources improves the photocatalytic activity of the UCNPs/g-C3N4 nanocomposite. In order to optimize the photocatalytic efficiency of the nanocomposite, the absorption and emission wavelengths of the UCNPs were tuned by controlling the lanthanide dopant composition where the core UCNPs were coated with an inner active shell and an outer inert shell. It is shown in this study that the nanocomposite can exhibit excellent photocatalytic activities under simulated solar light illumination.

Nanoscale Mn3O4 Thin Film Photoelectrodes Fabricated by a Vapor-Phase Route

α-Mn3O4 (hausmannite) nanostructured films were fabricated by chemical vapor deposition (CVD) on indium tin oxide (ITO)-coated glass substrates from a β-diketonate–diamine Mn(II) precursor. Materials were grown in a N2 + O2 atmosphere in the presence of water vapor, investigating the influence of growth temperature and total pressure on the system structural, compositional, morphological, and optical properties through a multitechnique characterization approach. The obtained α-Mn3O4 nanodeposits were ultimately tested as catalysts in the photoelectrochemical (PEC) splitting of water under simulated solar illumination, with particular focus on the interplay relationships between the adopted preparative conditions and the resulting functional performances. The amphoteric semiconducting behavior along with the PEC properties markedly dependent on the deposit nanoscale organization opens interesting avenues to an eventual implementation of the target materials in view of sustainable applications.

Hexagonal CdS photoanode modified with Pt and cobalt phosphate cocatalyst for efficient photoelectrochemical performance

The recombination of electron-hole pairs and the slow surface catalytic reactions have been deemed as the core problem affecting the efficiency of photoelectrochemical (PEC) performance. Here we synthesized hexagonal CdS photoanode on FTO substrate by hydrothermal method. Cobalt-phosphate (Co-Pi) and Pt cocatalysts were simultaneously decorated on the inner and outer surfaces of CdS (denoted as Pt/CdS/Co-Pi), which showed efficient charge separation/transfer performance on account of trapping the electrons with Pt and transferring holes with Co-Pi. As a result, the Pt/CdS/7.5Co-Pi photoanode showed a maximum photo-current of 5.05 mA/cm−2 at 0.28 V vs RHE under solar simulated illumination, which was 8.3 times higher than that of pure CdS photoanode. This work presents a promising guideline to design and fabricate an eco-friendly and sunlight-driven photoanode for the PEC water-splitting system.

Synergistic cocatalytic effect of ultra-thin metal-organic framework and Mo-dopant for efficient photoelectrochemical water oxidation on BiVO4 photoanode

Bismuth vanadate (BiVO4) has been regarded as a promising photoanode material for photoelectrochemical water oxidation, but its performance is greatly limited by the poor electron-hole separation and utilization efficiency. Here, a highly-efficient Mo:BiVO4 photoanode cocatalyzed with an ultrathin metal-organic frameworks layer was fabricated through hydrothermal method to meet the meet the limitations of BiVO4. The optimized MIL-101(Fe)/Mo:BiVO4 photoanode showed remarkable stable photocurrent density of 4.01 mA cm−2 at 1.23 V versus a reversible hydrogen electrode in Na2SO4 electrolyte under AM 1.5G simulated solar light illumination. The ηinjection and ηseparation of 76.4% and 69.5%, which were greatly higher than that of 58.5 and 25.4% for pristine BiVO4 photoanode at 1.23 V vs. RHE. Moreover, the MIL-101(Fe)/Mo:BiVO4 photoanode showed excellent stability for fast light off-on cycles. The photocurrent enhancement is attributed to the improved conductivity, facilitated charge separation efficiency, extended visible-response ability, and more accessible active sites for water oxidation.

Photoinduced K+ Intercalation into MoO3/FTO Photoanode\u2014the Impact on the Photoelectrochemical Performance

In this work, thin layers of MoO3 were tested as potential photoanodes for water splitting. The influence of photointercalation of alkali metal cation (K+) into the MoO3 structure on the photoelectrochemical properties of the molybdenum trioxide films was investigated for the first time. MoO3 thin films were synthesized via thermal annealing of thin, metallic Mo films deposited onto the FTO substrate using a magnetron sputtering system. The Tauc and Mott–Schottky plots analysis were performed in order to determine the energy bands position of the investigated material. The photointercalation effect of K+ on photoelectrochemical properties of FTO/MoO3 photoanodes was studied using electrochemical techniques performed under simulated solar light illumination. It was proven that pristine MoO3 layers cannot act as effective photoanodes for water splitting due to the utilization of the photoexcited electrons in the intercalation process. The photochromic phenomenon related to Mo6+ centers reduction, and K+ intercalation occurs at a potential range in which the photoanode exhibits photoelectrochemical activity towards water photooxidation.Graphical Schematic presentation of the photointercalation phenomenon influence on the photocurrent generation

Spectral response measurements of each subcell in monolithic triple-junction GaAs photovoltaic devices

Multijunction photovoltaic devices have gained attention for both solar cells and wireless power transmission. Herein, we present the spectral response of each subcell in a monolithic triple-junction photovoltaic device composed of only GaAs subcells with different thicknesses, which clarifies current matching among the GaAs subcells under simulated solar illumination conditions. In addition, the spectral response curves of each subcell show that the power-dependent spectral responses under laser illumination with wavelengths of 405, 660, and 785 nm are explained by the top GaAs subcell, which has a slightly lower shunt resistance and experiences the effects of luminescent coupling.

Investigation of the structural, optical, and photoelectrochemical properties of α-Fe2O3 nanorods synthesized via a facile chemical bath deposition

In this study, a simple and cost-effective chemical bath deposition was employed to deposit nan-sized hematite (α-Fe2O3) directly on fluorine-doped tin oxide (FTO) substrates. The structure, morphology, and optical properties of α-Fe2O3 were manipulated by adjusting the experimental parameters, particularly the deposition temperature and precursor concentration. With increase in Fe precursor concentration from 0.1 M to 0.3 M, the surface morphology was changed from granular-shape condensed particles to vertically aligned rod-like structures. XRD spectra indicated signals from FTO substrate and pure α-Fe2O3 phase which corresponds to the rhombohedral system. The XPS analysis revealed the presence of α-Fe2O3 in the film and no tin (Sn) impurities from the FTO substrate. By changing the deposition temperature from 60 ℃ to 90 ℃, the size of particles increased; whereas, the surface morphology was not altered. The resultant films were examined as photoanode for photoelectrochemical (PEC) water splitting. The optimized electrode exhibited maximum water splitting photocurrent density of 700 μA.cm−2 at 1.6 V versus reversible hydrogen electrode (RHE) under simulated solar illumination (AM 1.5, 100 mW.cm−2) in 1 M NaOH. This could be attributed to the large electrode electrolyte interfacial area and low charge transfer resistance offered by nanorods of α-Fe2O3 of high surface-to-volume ratio.

A ternary nanostructured α-Fe2O3/Au/TiO2 photoanode with reconstructed interfaces for efficient photoelectrocatalytic water splitting

In this study, a ternary nanostructured α-Fe2O3/Au/TiO2 film with integrating a crystalline α-Fe2O3 core, metallic Au nanoparticles (NPs), and an amorphous TiO2 overlayer is fabricated and examined as a photoanode for photoelectrocatalytic water splitting. Under simulated solar illumination, the as-prepared photoanode exhibits a four-fold increase (1.05 mA cm−2) in photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) relative to bare α-Fe2O3. Based on systematic investigations, it is proposed that Au NPs extract photoholes from the bulk of α-Fe2O3 core and then shuttle them to the outer TiO2 overlayer, and meanwhile, TiO2 overlayer efficiently captures and stores the photoholes and facilitates the hole injection into electrolyte. Thus, the remarkably improved photoelectrocatalytic water splitting performance of α-Fe2O3/Au/TiO2 photoanode is attributed to the significantly suppressed bulk and surface charge recombination due to the relayed pumping of the photogenerated charge carriers through the photoanode/electrolyte interfaces reconstructed by Au NPs and TiO2 overlayer.

Direct Z-scheme Bi2O2CO3/porous g-C3N4 heterojunction for improved photocatalytic degradation performance

Abstract In this study, a series of direct Z-scheme bismuth subcarbonate (Bi2O2CO3)/porous graphitic carbon nitride (g-C3N4) composites was prepared by using a simple two-stage template free process. The structure, morphology, textural and optical properties were characterized by X-ray diffraction, N2-physisorption, transmission electron microscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, UV–vis analysis and photoluminescence spectroscopy. The catalytic properties of Bi2O2CO3/porous g-C3N4 composites were assessed using tetracycline hydrochloride under simulated solar light illumination. When the loading amount of Bi2O2CO3 was 2 wt%, the composite showed the highest catalytic activity, which was 5.1 times that of porous g-C3N4 nanosheets (PCNS). The enhanced photocatalytic properties of Bi2O2CO3/porous g-C3N4 may be attributed to the formation of heterojunction between Bi2O2CO3 and PCNS, resulting in the effective separation of photogenerated carriers and enhanced absorption of visible light. Furthermore, the novel photocatalyst had an excellent catalytic stability and could be recycled for five times without distinct loss of catalytic activity.

Interplay between Light Flux, Quantum Efficiency, and Turnover Frequency in Molecular-Modified Photoelectrosynthetic Assemblies.

We report on the interplay between light absorption, charge transfer, and catalytic activity at molecular-catalyst-modified semiconductor liquid junctions. Factors limiting the overall photoelectrosynthetic transformations are presented in terms of distinct regions of experimental polarization curves, where each region is related to the fraction of surface-immobilized catalysts present in their activated form under varying intensities of simulated solar illumination. The kinetics associated with these regions are described using steady-state or pre-equilibrium approximations yielding rate laws similar in form to those applied in studies involving classic enzymatic reactions and Michaelis-Menten-type kinetic analysis. However, in the case of photoelectrosynthetic constructs, both photons and electrons serve as reagents for producing activated catalysts. This work forges a link between kinetic models describing biological assemblies and emerging molecular-based technologies for solar energy conversion, providing a conceptual framework for extracting kinetic benchmarking parameters currently not possible to establish.

Synergistic effects of dual-electrocatalyst FeOOH/NiOOH thin films as effective surface photogenerated hole extractors on a novel hierarchical heterojunction photoanode structure for solar-driven photoelectrochemical water splitting

Herein, we report the rational design of a novel hierarchical V2O5/BiVO4 heterojunction photoanode structure with rGO interlayer that functionalises as photogenerated electron collector, and dual electrocatalyst thin films of FeOOH and NiOOH as photogenerated hole extractors for solar-driven PEC water splitting. Results showed that the novel hierarchical FTO/V2O5/rGO/BiVO4/FeOOH/NiOOH photoanode exhibited an unprecedented and stable photocurrent density of 3.06 mA/cm2 at 1.5 V vs Ag/AgCl, and an apparent cathodic onset potential shift down to 0.2 V under AM 1.5 G simulated solar light illumination. The significant enhancement in PEC performance is ascribed to band potentials matching between V2O5 and BiVO4 in forming a Type II staggered heterojunction alignment, and further coupling with rGO interlayer and dual-electrocatalyst thin films as photogenerated electron collector and photogenerated hole extractors, respectively. Three different configurations of the novel hierarchical FTO/V2O5/rGO/BiVO4 photoanodes without electrocatalyst, with mono- and dual-electrocatalyst thin films were systematically examined. It was proven though EIS and IMPS measurements that the dual-electrocatalyst configuration photoanode exhibited the shortest transit time (τ) of 31.8 ms for the diffusion of photogenerated electrons to the counter electrode, and the lowest charge transfer resistance across the interface of electrode/electrolyte as estimated using the Randles-Ershel model. We believe that the proof-of-principle work described here not only provides an in-depth understanding on the roles of electrocatalyst thin films but also provides a design guide over the incorporation of electrocatalyst materials for further improving the photogenerated charge carrier dynamics in photoanodes used in solar-driven PEC water splitting.