Bromide-Mediated Photoelectrochemical Epoxidation of Alkenes Using Water as an Oxygen Source with Conversion Efficiency and Selectivity up to 100%

Abstract

In a photoelectrochemical (PEC) cell, the production of solar fuels such as hydrogen is often accompanied either by the oxidation of water or by the oxidation of organic substrates. In this study, we report bromide-mediated PEC oxidation of alkenes at a mesoporous BiVO4 photoanode and simultaneous hydrogen evolution at the cathode using water as an oxygen source. NaBr as a redox mediator was demonstrated to play a dual role in the PEC organic synthesis, which facilitates the selective oxidation of alkenes into epoxides and suppresses the photocorrosion of BiVO4 in water. This method enables a near-quantitative yield and 100% selectivity for the conversion of water-soluble alkenes into their epoxides in H2O/CH3CN solution (v/v, 4/1) under simulated sunlight without the use of noble metal-containing catalysts or toxic oxidants. The maximum solar-to-electricity efficiency of 0.58% was obtained at 0.39 V vs Ag/AgCl. The obtained epoxide products such as glycidol are important building blocks of the chemical industry. Our results provide an energy-saving and environment-benign approach for producing value-added chemicals coupled with solar fuel generation.

Photoelectrochemical Epoxidation of Cyclohexene on an α-Fe2O3 Photoanode Using Water as the Oxygen Source

“…Despite the sluggish and uphill water oxidation reaction, water and cyclohexene oxidation can simultaneously occur on the electrode surface. These results also agree with a previous study in which O 2 will be detected at the anode side in the epoxidation reactions. , …”

“…These results also agree with a previous study in which O 2 will be detected at the anode side in the epoxidation reactions. 45,61 Figure 4a shows the X-ray diffraction (XRD) analysis of α-Fe 2 O 3 , before and after the PEC epoxidation reaction. The peaks located at 35.6 and 64.0°are indexed to the (110) and (300) lattice diffractions of α-Fe 2 O 3 (JCPDS: 33-0664), respectively.…”

“…Jang et al 44 reported PEC epoxidation of propylene in an integrated photo-electro-heterogeneous catalytic system comprising three compartments performing PEC water oxidation, O 2 reduction to hydrogen peroxide, and catalytic propylene epoxidation, simultaneously. Li et al 45 studied NaBr-assisted PEC conversion of alkenes into epoxides on a BiVO 4 photoanode in a H 2 O/CH 3 CN solution. Farras et al 46 reported that a PEC system with TiO 2 as the photoanode achieves the epoxidation of styrene to yield styrene oxide and hydrogen while utilizing water as an oxygen source under 1.5 AMG (100 mW cm illumination.…”

Acceptorless Dehydrogenation of N-Heterocycles in a Photoelectrochemical Cell

“…Very recently, our group reported the bromide-mediated PEC oxidation of alkenes at a mesoporous BiVO 4 photoanode and simultaneous hydrogen evolution at the cathode using water as an oxygen source. This method enables a near-quantitative yield and 100% selectivity for the conversion of water-soluble alkenes into the epoxides . As a continuation of our endeavor to develop sustainable organic synthetic methodologies with a PEC system, herein we report acceptorless dehydrogenation of N -heterocycles coupled with hydrogen evolution in a PEC cell comprising a mesoporous BiVO 4 photoanode and Pt electrode.…”

“…This method enables a nearquantitative yield and 100% selectivity for the conversion of water-soluble alkenes into the epoxides. 29 As a continuation of our endeavor to develop sustainable organic synthetic methodologies with a PEC system, herein we report acceptorless dehydrogenation of N-heterocycles coupled with hydrogen evolution in a PEC cell comprising a mesoporous BiVO 4 photoanode and Pt electrode. Under simulated sunlight irradiation and at room temperature, a series of N-heterocyclic compounds, including the challenging cyclic amides, were effectively dehydrogenated into the corresponding products with excellent yields and Faraday efficiencies (>99%) (Scheme 1).…”