Photooxidation Of Water Research Articles

Band structure and optical properties of MoS2/SnO2 hetero-bilayer from hybrid functional calculations

The electronic structure and optical properties of MoS2/SnO2 hetero-bilayer have been systematically investigated with hybrid functional calculations. The band dispersion character of monolayer MoS2 at the VBM and that of monolayer SnO2 at CBM are well preserved in the MoS2/SnO2 hetero-bilayer, and thus the effective separation of electrons and holes is expected. Besides, the band gap narrowing in the MoS2/SnO2 hetero-bilayer can accordingly enhance the effective utilization of the solar spectrum, especially in the visible light region. Additionally, the MoS2/SnO2 hetero-bilayer that is active for both the photo-oxidation and photo-reduction of water possesses superior photocatalytic activity than that of monolayer MoS2 and SnO2.

A general strategy for the preparation of semiconductor-oxide-nanowire photoanodes

Semiconductor photoelectrodes for photoelectrochemical water splitting are at the heart of the area of renewable energy. Among various semiconductors as photoelectrode materials, metal oxide nanowires have attracted exceptional attention due to their favorable band-edge positions, wide distribution of bandgaps, low cost, and outstanding stability. In this study, we develop a general strategy for the preparation of semiconductor-oxide-nanowire photoanodes. Various metal oxide nanowires are grown directly from and on the metal or alloy substrates by thermal oxidation at ultra-low pressure using the corresponding metal or alloy foil as substrates. These metal oxide nanowires and their underlying conductive substrates are used directly as integrated photoanodes, which effectively avoids the detachment of the active light-harvesting materials from the substrates during the photoelectrochemical test. For example, a water photo-oxidation current density of the iron oxide photoanode reaches 0.71 mA/cm2 over a period of 20 h under 100 mW cm−2 illumination at the potential of 1.23 V versus the reversible hydrogen electrode. The successful preparation of these semiconductor-oxide-nanowire photoanodes have important implications for further development of photoelectrodes and highly efficient solar water-splitting devices.

Productivity and Community Composition of Low Biomass/High Silica Precipitation Hot Springs: A Possible Window to Earth's Early Biosphere?

Terrestrial hot springs have provided a niche space for microbial communities throughout much of Earth’s history, and evidence for hydrothermal deposits on the Martian surface suggest this could have also been the case for the red planet. Prior to the evolution of photosynthesis, life in hot springs on early Earth would have been supported though chemoautotrophy. Today, hot spring geochemical and physical parameters can preclude the occurrence of oxygenic phototrophs, providing an opportunity to characterize the geochemical and microbial components. In the absence of the photo-oxidation of water, chemoautotrophy in these hot springs (and throughout Earth’s history) relies on the delivery of exogenous electron acceptors and donors such as H2, H2S, and Fe2+. Thus, systems fueled by chemoautotrophy are likely energy substrate-limited and support low biomass communities compared to those where oxygenic phototrophs are prevalent. Low biomass silica-precipitating systems have implications for preservation, especially over geologic time. Here, we examine and compare the productivity and composition of low biomass chemoautotrophic versus photoautotrophic communities in silica-saturated hot springs. Our results indicate low biomass chemoautotrophic microbial communities in Yellowstone National Park are supported primarily by sulfur redox reactions and, while similar in total biomass, show higher diversity in anoxygenic phototrophic communities compared to chemoautotrophs. Our data suggest productivity in Archean terrestrial hot springs may be directly linked to redox substrate availability, and there may be high potential for geochemical and physical biosignature preservation from these communities.

A Self-Assembled Organic/Metal Junction for Water Photo-Oxidation.

We report the in situ self-assembly of TTF, TTF•+, and BF4- or PF6- into p-type semiconductors on the surface of Pt microparticles dispersed in water/acetonitrile mixtures. The visible light photoactivation of these self-assemblies leads to water oxidation forming O2 and H+, with an efficiency of 100% with respect to the initial concentration of TTF•+. TTF•+ is then completely reduced to TTF upon photoreduction with water. The Pt microparticles act as floating microelectrodes whose Fermi level is imposed by the different redox species in solution; here predominantly TTF, TTF•+, and HTTF+, which furthermore showed no signs of decomposition in solution.

Enhanced photocatalytic activity of single-layered Hittorf’s violet phosphorene by isoelectronic doping and mechanical strain: A first-principles research

A systematic theoretically study is performed for violet phosphorus monolayer nanosheet with the objective of improving its photocatalytic activity in water splitting under visible light by isoelectronic elements (N, As, Sb, and Bi) doping and strain engineering. The results show that compared with N-, As-, and Sb-doping, the introduced Bi impurity can effectively enhance visible light absorption efficiency. By applying an in-layer strain for Bi-doping violet phosphorene, the modulation of band edges further narrows the band gap. In particular, for compressive strain, the absorption extends into the overall visible region, greatly increasing the visible light absorption efficiency, which could be attributed to the significant reduced band gap and highly dispersive electronic states around the topmost valence band. Moreover, the band alignments for Bi-doped violet phosphorus monolayer are well positioned for the feasibility of both photo-oxidation and photo-reduction of water within the range of 0 to −3% biaxial strains and 0 to −7% uniaxial strains. Hence, compressive strained Bi-doped violet phosphorus monolayer can be a promising metal-free photocatalyst for water splitting owing to its improved visible light activity as well as the high carrier mobility.

Dual Photocatalytic Roles of Light: Charge Separation at the Band Gap and Heat via Localized Surface Plasmon Resonance To Convert CO2 into CO over Silver-Zirconium Oxide.

Confirmation of 13CO2 photoconversion into a 13C-product is crucial to produce solar fuel. However, the total reactant and charge flow during the reaction is complex; therefore, the role of light during this reaction needs clarification. Here, we chose Ag-ZrO2 photocatalysts because beginning from adventitious C, negligible products are formed using them. The reactants, products, and intermediates at the surface were monitored via gas chromatography-mass spectrometry and FTIR, whereas the temperature of Ag was monitored via Debye-Waller factor obtained by in situ extended X-ray absorption fine structure. With exposure to 13CO2, H2, and UV-visible light, 13CO selectively formed, while 8.6% of the 12CO mixed in the product due to the formation of 12C-bicarbonate species from air that exchanged with the 13CO2 gas-phase during a 2 h reaction. By choosing the light activation wavelength, the CO2 photoconversion contribution ratio was charge separated at the ZrO2 band gap (λ < 248 nm): 70%, localized at the Ag surface plasmon resonance (LSPR) (330 < λ < 580 nm): 28%, and characterized by a thermal energy of 295 K: 2%. LSPR at the Ag surface was converted to heat at temperatures of up to 392 K, which provided an efficient supply of activated H species to the bicarbonate species, combined with separated electrons and holes above the ZrO2, which generated CO at a rate of 0.66 μmol h-1 gcat-1 with approximately zero order kinetics. Photoconversion of 13CO2 using moisture was also possible. Water photo-oxidation step above ZrO2 was rate-limited, and the side reactions that formed H2 above the Ag were successfully suppressed instead to produce CO via the Mg2+ addition to trap CO2 at the surface.

Pyrochlore-structured Y2Ti2O7–2TiO2 composite thin films for photovoltaic applications

A titanium-based heterobimetallic single-source precursor [Y2Ti4(μ3-O)4(μ2-O)3(H2O)(TFA)8(THF)5].3(THF) (1) (where TFA = trifluoroacetato and THF = tetrahydrofuran) was successfully used to fabricate pyrochlore-structured Y2Ti2O7–2TiO2 composite thin films on fluorine-doped tin oxide (FTO) substrates using the aerosol-assisted chemical vapor deposition technique (AACVD). The precursor complex (1), isolated in crystalline form by reacting yttrium (III) acetate monohydrate with titanium (IV) isopropoxide and trifluroacetic acid in THF solution, was characterized by physicochemical methods such as melting point, microanalysis, FT-IR, 1H-NMR, thermogravimetric analyses (TGA/DTG), and single-crystal X-ray diffraction. Thin films prepared at 550 °C were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission gun-scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX) which demonstrated the development of mesoporous structured microballs of Y2Ti2O7–2TiO2 with precise stoichiometry. The optical analysis showed that Y2Ti2O7–2TiO2 has a direct optical band gap of 1.8 eV. Photo-oxidation of water via Y2Ti2O7–2TiO2 thin films was carried out under simulated solar irradiation of AM 1.5 G (100 mW cm−2) using three-electrode photoelectrochemical cell in of in three separate 0.5 M electrolyte solutions of NaOH (pH = 13.5), Na2SO4 (pH = 7.2), and citrate buffer (pH = 4). A best photocurrent density of ~ 60 μA cm−2 at + 0.8 V vs. SCE was observed at pH of 13.5. These observations were further validated by electrochemical impedance spectroscopy (EIS) studies in terms of charge transportation and its recombination time.

Optimization of conditions for improved solar energy harvesting application by hydrothermally grown TiO2 nanorods

In this study, using the optimum annealing temperature and time for hydrothermally grown TiO2 nanorods, photooxidation of water at different pH values of the electrolyte solution is investigated. The composition, crystallinity and topographic studies of films, sintered at different temperatures of 200–500 °C for 2 h and annealed for 1–4 h at 400 °C, were evaluated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and field emission scanning electron microscopy. The sintering at high temperature and for longer time demonstrates an increase in crystallinity, but at the same time agglomeration of nanorods for prolonged heating and at high temperature leads to cracking at the surface of the films. Further, UV–Vis spectroscopic studies revealed prolonged heating and high-temperature sintering resulted in a red shift in light absorption edge of the films. The chronoamperometric measurement results under regular interrupted chopping revealed that the sample annealed at 400 °C for 2 h gives the best photoelectrochemical response with photocurrent density of 522 µA cm− 2 using 0.5M NaOH. The chronoamperometric response under different pH values of 13.7, 7.2 and 2.5 proved that TiO2 gives the best response under a basic pH of 13.7 and the least under acidic media. The electrochemical impedance studies provided an insight into the charge transfer mechanism under dark and illumination with Rct value of 1188.8 Ω under dark and 164.5 Ω under light conditions for the film annealed at 400 °C for 2 h.

One-Step Solvothermal Formation of Pt Nanoparticles Decorated Pt2+-Doped α-Fe2O3 Nanoplates with Enhanced Photocatalytic O2 Evolution

The photooxidation of water into O2 has been identified as the barrier of water-splitting, and light-driven water oxidation catalysts have been intensively explored to develop highly active water splitting materials. Despite the fascinating advantages for photocatalytic water oxidation, such as abundance in nature, inexpensiveness, low toxicity, thermo/photostability, and suitable electronic band structures, hematite α-Fe2O3 is a poor photocatalyst for water oxidation due to its short exciton lifetime and hole diffusion length, weak carrier mobility, and shallow sunlight penetration depth. In this work, we have synthesized Pt nanoparticles decorated Pt2+-doped α-Fe2O3 nanoplates (Pt/Pt-Fe2O3 NPs) by a one-step solvothermal route which exhibit the enhanced photoactivity and photostability for water oxidation. The introduction of the Pt into the α-Fe2O3 by the means of elemental doping and nanoparticle decoration accounts for the enhanced performance. The doping of Pt2+ into α-Fe2O3 improves the isolation e...

A comparison of water photo-oxidation and photo-reduction using photoelectrodes surface-modified by deposition of co-catalysts: Insights from photo-electrochemical impedance spectroscopy

The purpose of this research paper is to highlight the similarities in the kinetic treatment between water photo-oxidation into molecular oxygen and water photo-reduction into molecular hydrogen, using photoelectrodes surface modified by deposition of co-catalysts. Photo-anodes made of TiO2 nanorods surface-covered by crystals of cobalt Zeolitic Imidazolate Framework (ZIF-67), and photo-cathodes made of Rh:SrTiO3 particles surface-modified by adsorption of molecules of trisdioximate hexa-chlorine cobalt (II) clathrochelate (Co(Cl2Gm)3(BCH3)2), have been prepared and used for water photo-oxidation and photo-reduction experiments, respectively. Both photoelectrodes have been characterized by SEM and cyclic voltammetry under illumination conditions. Charge transfer mechanisms have been investigated by photo-electrochemical impedance spectroscopy (PEIS). It is shown that for both systems, the presence of a co-catalyst increases the charge transfer kinetics, and that the trapping resistance is larger than the charge transfer resistance, at any operating potential.

Two-site H2O2 photo-oxidation on haematite photoanodes

H2O2 is a sacrificial reductant that is often used as a hole scavenger to gain insight into photoanode properties. Here we show a distinct mechanism of H2O2 photo-oxidation on haematite (α-Fe2O3) photoanodes. We found that the photocurrent voltammograms display non-monotonous behaviour upon varying the H2O2 concentration, which is not in accord with a linear surface reaction mechanism that involves a single reaction site as in Eley–Rideal reactions. We postulate a nonlinear kinetic mechanism that involves concerted interaction between adions induced by H2O2 deprotonation in the alkaline solution with adjacent intermediate species of the water photo-oxidation reaction, thereby involving two reaction sites as in Langmuir–Hinshelwood reactions. The devised kinetic model reproduces our main observations and predicts coexistence of two surface reaction paths (bi-stability) in a certain range of potentials and H2O2 concentrations. This prediction is confirmed experimentally by observing a hysteresis loop in the photocurrent voltammogram measured in the predicted coexistence range.

Development of bovine serum albumin–capsaicin nanoparticles for biotechnological applications

The main use of capsaicin is as a condiment in food industry. Pharmaceutical and biotechnological applications of capsaicin have been restricted by photooxidation, chemical decomposition and low solubility in water. Protein-based particles represent an alternative for encapsulation. The aim of this work was to develop bovine serum albumin (BSA)-capsaicin nanoparticles and analyse the effect of the capsaicin concentration on the properties of nanoparticles. We prepared nanoparticles at 0, 625, 1250, 1875 and 2500 µg/mL of capsaicin with BSA. The concentration of capsaicin was positively correlated with BSA (R = 0.9910) and encapsulated capsaicin (R = 0.9977). We found that at 1250 µg/mL of capsaicin the nanoparticles showed the highest encapsulated efficiency (82.3%), the smallest size (131 nm) and the lowest ζ-potential (-54.82 mV), while the aspect ratio (Ar = 1.08) and shape factor (Sf = 0.65) showed a circular shape with one single capsaicin core. In contrast, at 1875 and 2500 µg/mL of capsaicin, coalescence between particles increased, resulting in a larger size of nanoparticles with elliptical shape (Ar = 1.29; Sf = 0.59, and Ar = 1.55; Sf = 0.54, respectively).

Comparative study of photo-excited charge carrier dynamics of atomic layer deposited and solution-derived hematite films: Dependence of charge carrier kinetics on surface orientations

Charge carrier kinetics of hematite films prepared via atomic layer deposition and solution-derived methods were investigated using heterodyne transient grating technique in aqueous solution, depending on bias voltage, to reveal the effects of surface orientation differences on the charge carrier dynamics. We found that the electron/hole recombination in atomic layer deposited hematite was slower than that in solution-derived hematite, indicating the generated charge carriers in atomic layer deposited hematite can survive longer than that in solution-derived hematite, which is usually beneficial for water oxidation. On the other hand, the trapping dynamics of the long-lived holes to the surface state for water photo-oxidation in the solution-derived hematite was observed at faster time region than that in atomic layer deposited hematite, implying that the diffusion of the holes in atomic layer deposited hematite was slower than that in solution-derived hematite due to the different barrier height and width of the space charge layer which strongly depends on the surface orientations. It means that the low charge carrier mobility rather than the retardation of the charge recombination in the atomic layer deposited hematite is a dominant factor in its low photoelectrochemical performance.

Photo-assisted acid-base machine: Battery ensemble to perform work from neutralization reactions

This study proposes a power source that operates between acidic and basic reservoirs under sunlight to treat acidic wastewater sustainably. We present a strategy that harvests energy from an ionic gradient associated with acidic solution neutralization and water photo-oxidation under UV light. In contrast to neutralization batteries, these photo-assisted acid-base machines operate with an interconnected battery ensemble comprising (A) a photo-assisted acid battery composed of photo-anode (TiO2) for water photo-oxidation and a selective self-assembled cathode consisting of poly(3,4-ethylenedioxythiophene) and phosphomolybdic acid for proton insertion; (B) a proton-alkali ion battery composed of the self-assembled electrode for proton deinsertion and a cathode made of copper hexacyanoferrate for potassium ion electro-insertion, which can be used as portable or stationary power source; (C) an alkali ion-air battery composed of the polycyanometalate for potassium ion deinsertion and a platinum cathode for the oxygen reduction reaction (ORR). This ensemble avoids reverse water splitting reactions and dismisses the need for external electrical power sources, which increases machine efficiency. Experiments demonstrate that acidic solution neutralization from pH = 1.3 to pH = 6.0 can harvest 102.6 kJ per mol of electro-inserted proton: this process converts energy from sunlight and from ionic gradient into electrical work. Therefore, the strategy presented here may contribute to environmental preservation and sustainable growth.

Graphdiyne-Promoted Highly Efficient Photocatalytic Activity of Graphdiyne/Silver Phosphate Pickering Emulsion Under Visible-Light Irradiation.

As a new kind of two-dimensional carbon allotrope, graphdiyne (GDY) consists of sp- and sp2-hybridized carbon atoms and has recently been used for developing highly efficient photocatalytic systems because of its unique properties. In this study, we find that GDY can form a Pickering emulsion with silver phosphate (Ag3PO4) nanoparticles that exhibits largely enhanced photocatalytic activity in the visible-light region. In this system, Ag3PO4 acts as a photocatalytically active semiconductor with GDY as the hydrophobic nanostructure. Photocatalytic activity of the Ag3PO4/GDY-based Pickering emulsion toward the photodegradation of methylene blue (MB) and photooxidation of water is investigated under visible-light irradiation. Compared to previous Ag3PO4/CNT- or Ag3PO4/graphene-based Pickering emulsions, the Ag3PO4/GDY-based emulsion efficiently catalyzes MB degradation with a higher apparent rate constant k being ∼0.477 min-1, while for water oxidation its photocatalytic activity is also improved by 1.89 and 1.75 times, respectively. Such an enhancement in the photocatalytic activity is mainly ascribed to the capability of GDY in acting as an acceptor of the photogenerated electrons from Ag3PO4 nanoparticles and in facilitating the hole transportation as well as in reducing Ag+ to Ag0. This study demonstrates that GDY is a new candidate with a promising future in developing photocatalytic systems with high efficiency for real applications.

(Invited) Influence of Nanoscale Surface Structure of TiO2 Single Crystal Electrode on Water Photooxidation Reaction Process

The oxygen photoevolution reaction on TiO2 and related metal oxides has attracted strong attention from the point of view of solar water splitting. In our previous study, we have proposed a new reaction model in which generated holes are consumed not only by the O2 evolution reaction but also by three competitive paths possibly occur at different surface sites; photoluminescence, surface roughening (i.e. photocorrosion), and nonradiative recombination [1,2]. Actually, we found that the branch ratio for these paths on TiO2 (110) changed by the density and the direction of steps (i.e. atomic leveled surface structure) [3]. On the other hand, it is expected that the nano-sized structure of the TiO2 surface also affect the branch ratio of 4 competitive photooxidation reactions. Thus, in this study, we investigated oxygen photoevolution efficiency on a nanostructured TiO2 electrode that exposes different facets. A Pt wire and an Ag/AgCl/sat.KCl electrode were used as a counter and a reference electrode, respectively. An n-type TiO2 (110) doped with 0.05wt% Nb was used as a working electrode. The j−U curves were measured in 0.1 M HClO4 (pH 1.1) under UV irradiation. Nanostructured TiO2(110) surfaces were prepared by photoetching in 0.05 M H2SO4 [4]. We obtained the nanostructured surfaces on which shallow grooves are regularly arranged. We should note that formed surface of the nanostructure is composed by (100) facet faces [4]. Photocurrent generated along with the O2 evolution from H2O on the nanostructured TiO2 (110) was apparently different from that on the flat TiO2 (100). The onset potential of nanostructured TiO2 electrode was shifted toward negative voltage, indicating that the activation energy of oxygen evolution reaction was smaller than that on the flat surface. In addition, the consumption ratio of the photogenerated holes by above mentioned 4 competitive reactions was largely different from that on the atomically flat (100) surface. Considering the fact that the photoetched TiO2(110) surface is composed by (100) microfacets[4], this result can be attributed to the nanostructuring effect. We also carried out the same experiment using the some other TiO2 electrode those have different nanostructure on their surfaces, and found that the nanostructuring effect (1. Branch ratio of 4 competitive photooxidation reactions, 2. Activation energy of O2 evolution reaction) depends on the nano-sized surface morphology of the TiO2 electrode. [1] A. Imanishi, T. Okamura, N. Ohashi, R. Nakamura, Y. Nakato, J. Am. Chem. Soc., 129 (2007) 11569. [2] A. Imanishi, K. Fukui, J. Phys. Chem. Lett., 5 (2014) 2108. [3] M. Kadono, Master’s thesis, Osaka Univ. (2013). [4] A. Imanishi, H. Suzuki, K. Murakoshi, Y. Nakato, J. Phys. Chem. B, 110 (2006) 21050.

Porous titania photoelectrodes built on a Ti-web of microfibers for polymeric electrolyte membrane photoelectrochemical (PEM-PEC) cell applications

Conventional photoelectrochemical (PEC) cells are based on planar photoelectrodes supported on glass substrates and liquid electrolytes. Only few recent studies have examined an alternative PEC design which is robust and scalable, where the key elements are polymeric electrolyte membranes and porous photoelectrodes. This work aims to give further insights on the operation of such cells utilizing titania photoelectrodes and proton and hydroxide ion conducting membranes. Two families of photoelectrodes were developed on Ti porous substrate; TiO2 nanotubes grown by anodization and subsequent oxygen annealing, and TiO2 layers developed under oxygen annealing. Initial screening of the photoanodes for water splitting and (poly)alcohol photo-oxidation took place in conventional PEC cells. We found that the annealing temperature affects the performance of the photoanodes, evidenced by a monotonic increase in the activity for water photo-oxidation with increasing annealing temperature. Moreover it was demonstrated that anatase phase is predominantly active for the (poly)alcohol electro-oxidation, while there is a synergy between rutile and anatase which is beneficial for water splitting. In addition, the most promising photoanodes for water splitting were evaluated in our polymeric electrolyte membrane photoelectrochemical(PEM-PEC) cell during gas phase operation. It was found that PEM-PEC operation is more efficient when OH- conducting membranes are used, while the nature of the carrier gas does not significantly influence the activity. Overall, PEM-PEC operation is more promising than conventional PEC in both acidic and alkaline media, since comparable (or even at some cases higher) photocurrents were obtained while liquid pumping systems are not required for PEM-PEC devices.

Facial-hydroxylated pure-phase BiFeO3 with controllable micro-morphology: performance as a highly efficient visible light photocatalyst

The pure-phase BiFeO3 crystals with distinguished micro-morphologies were successfully prepared by a novel coprecipitation-hydrothermal collaborative synthesis method. Hydroxylation technique was innovatively employed to hydroxylate BiFeO3 samples. XPS and PL spectra proved that hydroxylation treatment indeed introduced more ·OH radicals on the surfaces of the BiFeO3 samples. Sample E (hydroxylated BiFeO3 ultra-thin slices) showed the highest photocatalytic activity. Hydroxylated BiFeO3 prepared in this work also showed high activities in water photo-oxidation reactions for producing oxygen gas. All hydroxylated samples showed notably enhanced photocatalytic activities due to the large specific surface areas, strong visible light responses, diminished recombination rates of the photo-excited carriers and excess ·OH radicals introduced by surface hydroxylation. All BiFeO3 samples showed good photochemical stabilities for reusage. This work provides valuable contributions in the future preparations and applications for BiFeO3 photocatalysts.

Building of peculiar heterostructure of Ag/two-dimensional fullerene shell-WO3-x for enhanced photoelectrochemical performance

Photoelectrochemical (PEC) water splitting has been a promising approach for solar energy conversion to meet the clean energy demand. Design and fabrication of high-quality photoelectrode for water splitting with enhanced light absorption, as well as efficient charge separation and transport are challenging. Herein, two-dimensional (2D) WO3-x nanosheets with unique fullerene shell-like nanostructure are prepared with assistance of supercritical CO2 (SC CO2). Then a novel plasmonic photoanode heterostructure composed of plasmonic Ag and fullerene shell-WO3-x is synthesized for PEC water splitting and photooxidation degradation. The unique co-existence of amorphous and crystalline structure of WO3-x leads to uniformly distribution of Ag nanoparticles, simultaneously increasing the active site density and improving the electron transport. Femtosecond time-resolved IR absorption spectrum analysis indicates the surface plasmonic resonance (SPR) effect of Ag nanoparticles can mediate efficient electron transfer to fullerene shell-WO3-x nanosheets. The photoresponse of the plasmonic Ag/fullerene shell-WO3-x heterostructure is 2.5 times higher than that of fullerene shell-WO3-x. By combining the synergistic effects of the special microstructures of plasmonic Ag and fullerene shell-WO3-x, we are able to design a low-cost photoelectronic catalyst for efficient PEC water splitting and photooxidation degradation. The strategy developed here provides a fascinating way to synthesize high efficient photoelectronic catalysts for solar energy conversion.

Improvement of sol-gel prepared tungsten trioxide photoanodes upon doping with ytterbium

The development of efficient and stable photoelectrodes keeps on being critical in the implementation of practical water splitting devices. Sol-gel synthesized tungsten trioxide thin film electrodes modified with ytterbium have been prepared on conducting glass substrates. All the obtained electrodes were found to be composed of monoclinic WO3, which is the photoactive crystal phase of WO3 for water oxidation. The photoelectrochemical behavior of both WO3 and WO3:Yb nanostructured electrodes in 0.1 M HClO4 is apparently characterized by a low degree of recombination. Ytterbium addition to tungsten trioxide improves its photoelectrochemical response as larger photocurrents are obtained without a significant change of the onset potential. This behavior is attributed primarily to a surface effect rather than to bulk doping. The addition of H2O2 to the aqueous electrolyte gives rise to both an increment in photocurrent and a shift of the photocurrent onset potential toward less positive values, which can be linked to the fact that hydrogen peroxide acts as an efficient hole scavenger. The implications of these findings in the mechanism of water photooxidation on WO3 are discussed.