Water splitting via a photocatalysis-electrolysis hybrid system has been investigated as a potentially scalable and economically feasible means of producing renewable H. However, there are no reports demonstrating a scalable system for stoichiometric water splitting using an efficient and stable photocatalyst, and the key operating conditions for efficiently driving the entire system have not been established. Herein, we address the issues required to efficiently drive the entire system of a Cs, Fe, and H ion-modified WO (denoted as H-Fe-Cs-WO) photocatalyst fixed reactor combined with a polymer electrolyte membrane (PEM)-type electrolyzer.
View Article and Find Full Text PDFSunlight-driven photocatalytic water splitting shows promise for green H production. In an attempt to achieve seawater splitting, we constructed a new stoichiometric brine splitting system that produces H along with Cl instead of O. Cl-a more potent high-value-added oxidant than O-was obtained with 100% selectivity over 10 h by adjusting the solution pH to acidic using a UV-light-driven Pt-loaded TiO photocatalyst.
View Article and Find Full Text PDFWhile dye-sensitized metal oxides are good candidates as H evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remain low because of uncontrolled charge recombination reactions. Here, we show that modification of Ru dye-sensitized, Pt-intercalated HCaNbO nanosheets (/Pt/HCaNbO) with both amorphous AlO and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO-based O evolution photocatalyst and an I/I redox mediator, relative to an analogous system that uses unmodified /Pt/HCaNbO. By using the optimized photocatalyst, PSS//AlO/Pt/HCaNbO, a maximum STH of 0.
View Article and Find Full Text PDFEfficient HO production both on a carbon cathode modified with various metal salts and on an oxide photoanode was investigated. The cathodic current density and faradaic efficiency for HO production (FE(HO)) on a carbon cathode in KHCO aqueous solution were significantly improved by the loading of an insoluble nickel carbonate basic hydrate catalyst. This electrode was prepared by a precipitation method of nickel nitrate and KHCO aqueous solution at ambient temperature.
View Article and Find Full Text PDFIn the quest for efficient use of solar energy to produce high-value-added chemicals, we first achieved the photoelectrochemical (PEC) diketonization of naphthalene, using a BiVO/WO photoanode, to obtain naphthoquinone, an important pharmaceutical raw material with excellent efficiency by solar energy conversion. In the electrochemical (EC) reaction using F-doped SnO (FTO) substrates and a 0.5 M HSO HO-acetone (60 vol %) mixed solution containing 5 mM naphthalene, we produced a small amount of naphthoquinone evolution in the dark.
View Article and Find Full Text PDFWe have revealed for the first time that BiVO photoanodes can be used even in strong acid media by mixing organic solvents into the electrolyte and depositing multilayers with a WO bottom layer. In general, the BiVO photoanodes are photocorrosive, especially in acid solutions. However, this shortcoming has been overcome using a combination of the two aforementioned modifications.
View Article and Find Full Text PDFPhotoelectrochemical 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, O and HClO production in aqueous solution containing Cl on photoanodes modified with various metal oxides was investigated.
View Article and Find Full Text PDFSensitization of a wide-gap oxide semiconductor with a visible-light-absorbing dye has been studied for decades as a means of producing H from water. However, efficient overall water splitting using a dye-sensitized oxide photocatalyst has remained an unmet challenge. Here we demonstrate visible-light-driven overall water splitting into H and O using HCaNbO nanosheets sensitized by a Ru(II) tris-diimine type photosensitizer, in combination with a WO-based water oxidation photocatalyst and a triiodide/iodide redox couple.
View Article and Find Full Text PDFThe selective photo-electrochemical oxidation of cyclohexene to 2-cyclohexene-1-one was successfully performed with excellent Faraday efficiency (>99%) via indirect oxidation with a PINO/NHPI mediator and O on a BiVO/WO photoanode under low applied bias.
View Article and Find Full Text PDFChem Commun (Camb)
March 2019
Angew Chem Int Ed Engl
August 2018
The photo-electrochemical C-H bond activation of cyclohexane to produce cyclohexanol and cyclohexanone (KA oil) with high partial oxidation selectivity (99 %) and high current utilization ratio (76 %) was achieved in air at room temperature at atmospheric pressure. The production rate of KA oil was accelerated by applying a bias. The incident photon to current efficiencies at 365 and 420 nm were 57 % and 24 %, respectively.
View Article and Find Full Text PDFThe photoelectrochemical production and degradation properties of hydrogen peroxide (H O ) were investigated on a WO /BiVO photoanode in an aqueous electrolyte of hydrogen carbonate (HCO ). High concentrations of HCO species rather than CO species inhibited the oxidative degradation of H O on the WO /BiVO photoanode, resulting in effective oxidative H O generation and accumulation from water (H O). Moreover, the Au cathode facilitated two-electron reduction of oxygen (O ), resulting in reductive H O production with high current efficiency.
View Article and Find Full Text PDFWe applied an automated semiconductor synthesis and screen system to discover overcoating film materials and optimize coating conditions on the BiVO4/WO3 composite photoelectrode to enhance stability and photocurrent. Thirteen metallic elements for overcoating oxides were examined with various coating amounts. The stability of the BiVO4/WO3 photoelectrode in a highly concentrated carbonate electrolyte aqueous solution was significantly improved by overcoating with Ta2O5 film, which was amorphous and porous when calcined at 550 °C.
View Article and Find Full Text PDFAg cocatalyst-loaded ALa(4)Ti(4)O(15) (A = Ca, Sr, and Ba) photocatalysts with 3.79-3.85 eV of band gaps and layered perovskite structures showed activities for CO(2) reduction to form CO and HCOOH by bubbling CO(2) gas into the aqueous suspension of the photocatalyst powder without any sacrificial reagents.
View Article and Find Full Text PDFPhotophysical properties and photocatalytic activities for water splitting over KM(2)Nb(5)O(15) (M = Sr and Ba) and K(2)LnNb(5)O(15) (Ln = La, Pr, Nd, and Sm) with tungsten bronze-type structure were investigated. Single phases of KM(2)Nb(5)O(15) and K(2)LnNb(5)O(15) were successfully prepared by solid-state reaction (SSR) method and polymerizable complex (PC) method. The band gaps of these niobates were estimated to be 3.
View Article and Find Full Text PDFA combinatorial approach has been carried out to systematically investigate visible-light responsiveness of Fe-Ti-M (M: various metal elements) oxides for photoelectrochemical water splitting. Among the 25 elements tested, strontium was the most effective. A ternary metal oxide with the composition Fe(86.
View Article and Find Full Text PDFThis critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent. Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade. The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials.
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