Photoelectrochemistry of polycrystalline n-wo3

Thermomechanical and Structural Analysis of WO3 Array for Optimized Photoelectrochemical Chloride Oxidation Performance

Understanding the crystal structure of WO3 is essential for optimizing its photoelectrochemical performance. This study comprehensively analyzes the structural characteristics of WO3 during synthesis and investigates their correlation with photoelectrochemical activity. Structural analysis, incorporating annealing procedure and WO3 thickness, identifies a blend of hexagonal, monoclinic, and orthorhombic phases within WO3 array. Specifically, detailed analysis reveals a predominance of monoclinic WO3 phase alongside the orthorhombic WO3 phase, both of which are commonly characterized by their monoclinic structure. Three-dimensional thermomechanical simulations using the finite element method reveal that thermal displacement in WO3 layers increases with thickness during the thermally induced synthesis process. These results highlight a direct correlation between WO3 thickness, thermal displacement, and phase transition, with thicker layers favoring the transformation from orthorhombic to monoclinic structures due to increased thermally induced deformation. The heightened monoclinic structure, which possesses lower symmetry than the orthorhombic structure, induces more defect sites, suggesting increased donor density. Notably, the monoclinic-dominated WO3 exhibits superior performance under UV-visible irradiation in 0.5 M NaCl. Furthermore, the WO3 array demonstrates over 85% Faradaic efficiency for chloride oxidation, indicating preferential selectivity over oxygen evolution reaction in 0.5 M NaCl. This study emphasizes the pivotal role of the crystal structure of WO3 in achieving efficient photoelectrochemical seawater splitting.

HClO-Mediated Photoelectrochemical Epoxidation of Alkenes with Near 100 % Conversion Rate and Selectivity by Regulating Lattice Chlorine Cycle

Directional organic transformation via a green, sustainable catalytic reaction has attracted a lot of attention. Herein, we report a photoelectrochemical approach for highly selective epoxidation of alkenes in a salt solution using Co2 (OH)3 Cl (CoOCl) as a bridge of photo-generated charge, where the lattice Cl- of CoOCl can be oxidized to generate HClO by the photo-generated holes of BiVO4 photoanode and be spontaneously recovered by Cl- of a salt solution, which then oxidizes the alkenes into the corresponding epoxides. As a result, a series of water-soluble alkenes, including 4-vinylbenzenesulfonic acid sodium, 2-methyl-2-propene-1-sulfonic acid sodium, and 3-methyl-3-buten-1-ol can be epoxidized with near 100 % conversion rate and selectivity. Through further inserting a MoOx protection layer between BiVO4 and CoOCl, the stability of CoOCl-MoOx /BiVO4 can be maintained for at least 120 hours. This work opens an avenue for solar-driven organic epoxidation with a possibility of on-site reaction around the abundant ocean.

Photoinduced absorption spectroscopy (PIAS) study of water and chloride oxidation by a WO3 photoanode in acidic solution

The mechanisms of water and chloride oxidation by a WO3 photoanode are probed by photoinduced absorption spectroscopy (PIAS) coupled with transient photocurrent (TC) measurements. Linear sweep voltammograms (LSVs) and incident photon to current efficiencies (IPCEs) are obtained, in the water oxidation electrolyte (1 M HClO4) and chloride oxidation electrolyte (3.5 M NaCl in 1 M HClO4). Other work shows that the faradaic efficiency of water oxidation to O2 in 1 M HClO4 is ca. 1.0, and that for chloride oxidation to Cl2 in 3.5 M NaCl plus 1 M HClO4 is ca. 0.62. The PIAS/TC data reveals a 0.4 order dependency of the rate of water oxidation on the steady state concentration of photogenerated surface holes, [hs+]ss, and an approximately first order dependency of the rate of chloride oxidation on [hs+]ss. Associated mechanisms and rate determining steps for water and chloride oxidation at the photoanode surface that account for these reaction orders are proposed.

Functions of MnOx in NaCl Aqueous Solution for Artificial Photosynthesis

Photoelectrochemical water splitting has been intensively investigated as artificial photosynthesis technology to convert solar energy into chemical energy. The use of seawater and salted water has advantages for minimum environmental burden; however, the oxidation of Cl^- ion to hypochlorous acid (HClO), which has toxicity and heavy corrosiveness, should occur at the anode, along with the oxygen evolution. Here, O₂ and HClO production in aqueous solution containing Cl^- on photoanodes modified with various metal oxides was investigated. The modification of MnO_x resulted in the promotion of the O₂ evolution reaction (OER) specifically without HClO production over a wide range of conditions. The results will contribute not only to the practical application of artificial photosynthesis using salted water but also to the elucidation of substantial function of manganese as the element for OER center in natural photosynthesis.

Solar-light-driven photocatalytic production of peroxydisulfate over noble-metal loaded WO3

The high-value-added chemical reagent peroxydisulfate (S2O82-) was produced photocatalytically over noble-metal loaded WO3 powder suspensions in aqueous H2SO4 under flowing O2 and simulated solar light irradiation. Pt cocatalyst showed the highest photocatalytic activity for S2O82- formation of the studied metals (Au, Pd, Rh, and Ru). Further study indicated that continuous accumulation of S2O82- was achieved only over the Pt/WO3 photocatalyst.

Photo-electrochemical Oxidation of Organic C1 Molecules over WO3 Films in Aqueous Electrolyte: Competition Between Water Oxidation and C1 Oxidation

To better understand organic-molecule-assisted photo-electrochemical water splitting, photo-electrochemistry and on-line mass spectrometry measurements are used to investigate the photo-electrochemical oxidation of the C1 molecules methanol, formaldehyde, and formic acid over WO3 film anodes in aqueous solution and its competition with O2 evolution from water oxidation O2 (+) and CO2 (+) ion currents show that water oxidation is strongly suppressed by the organic species. Photo-electro-oxidation of formic acid is dominated by formation of CO2 , whereas incomplete oxidation of formaldehyde and methanol prevails, with the selectivity for CO2 formation increasing with increasing potential and light intensity. The mechanistic implications for the photo-electro-oxidation of the organic molecules and its competition with water oxidation, which could be derived from this novel approach, are discussed.

Photoelectrochemical Behavior of Nanostructured WO3 Thin-Film Electrodes: The Oxidation of Formic Acid

Nanostructured tungsten trioxide thin-film electrodes are prepared on conducting glass substrates by either potentiostatic electrodeposition from aqueous solutions of peroxotungstic acid or direct deposition of WO3 slurries. Once treated thermally in air at 450 degrees C, the electrodes are found to be composed of monoclinic WO3 grains with a particle size around 30-40 nm. The photoelectrochemical behavior of these electrodes in 1 M HClO4 apparently reveals a low degree of electron-hole recombination. Upon addition of formic acid, the electrode showed the current multiplication phenomenon together with a shift of the photocurrent onset potential toward less positive values. Photoelectrochemical experiments devised on the basis of a kinetic model reported recently [I. Mora-Seró, T. Lana-Villarreal, J. Bisquert, A. Pitarch, R. Gómez, P. Salvador, J. Phys. Chem. B 2005, 109, 3371] showed that an interfacial mechanism of inelastic, direct hole transfer takes place in the photooxidation of formic acid. This behavior is attributed to the tendency of formic acid molecules to be specifically adsorbed on the WO3 nanoparticles, as evidenced by attenuated total reflection infrared spectroscopy.