Production of H2 and Glucaric Acid Using Electrocatalyst Glucose Oxidation by the Ta NiFe LDH Electrode.

The slow anodic oxygen evolution reaction (OER) significantly limits electrocatalytic water splitting for hydrogen production. We proposed the electrocatalyst for glucose oxidation by Ta-doping NiFe LDH nanosheets to simultaneously obtain glucaric acid (GRA) and hydrogen gas as a useful byproduct. Superior glucose oxidation reaction (GOR) activity is demonstrated by the optimized Ta-NiFe LDH, which has a low overpotential of 192 mV, allowing for a small Tafel slope of 70 mV dec-1 and a current density of 50 mA cm-2. The Ta NiFe LDH-oxidized glucose to GRA with a 72.94% yield and 64.3% Faradaic efficiency at 1.45 VRHE. Herein, we report the Ta NiFe LDH/NF electrode for the GOR&hydrogen evolution reaction (HER), which exhibits a cell voltage of 1.62 V to reach a current density of 10 mA cm-2, which is 250 mV lower compared to OER&HER (1.87 V). This study reveals that GOR is an energy-efficient and cost-effective method for producing H2 and valorizing biomass.

Electrocatalytic Reactions for Converting CO2 to Value-Added Products: Recent Progress and Emerging Trends.

Carbon dioxide (CO2) emissions are an important environmental issue that causes greenhouse and climate change effects on the earth. Nowadays, CO2 has various conversion methods to be a potential carbon resource, such as photocatalytic, electrocatalytic, and photo-electrocatalytic. CO2 conversion into value-added products has many advantages, including facile control of the reaction rate by adjusting the applied voltage and minimal environmental pollution. The development of efficient electrocatalysts and improving their viability with appropriate reactor designs is essential for the commercialization of this environmentally friendly method. In addition, microbial electrosynthesis which utilizes an electroactive bio-film electrode as a catalyst can be considered as another option to reduce CO2. This review highlights the methods which can contribute to the increase in efficiency of carbon dioxide reduction (CO2R) processes through electrode structure with the introduction of various electrolytes such as ionic liquid, sulfate, and bicarbonate electrolytes, with the control of pH and with the control of the operating pressure and temperature of the electrolyzer. It also presents the research status, a fundamental understanding of carbon dioxide reduction reaction (CO2RR) mechanisms, the development of electrochemical CO2R technologies, and challenges and opportunities for future research.

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

This study developed a safe and sustainable route for the epoxidation of cyclohexene using water as the source of oxygen at room temperature and ambient pressure. Here, we optimized the cyclohexene concentration, volume of solvent/water (CH3CN, H2O), time, and potential on the photoelectrochemical (PEC) cyclohexene oxidation reaction of the α-Fe2O3 photoanode. The α-Fe2O3 photoanode epoxidized cyclohexene to cyclohexene oxide with a 72.4 ± 3.6% yield and a 35.2 ± 1.6% Faradaic efficiency of 0.37 V vs Fc/Fc+ (0.8 VAg/AgCl) under 100 mW cm-2. Furthermore, the irradiation of light (PEC) decreased the applied voltage of the electrochemical cell oxidation process by 0.47 V. This work supplies an energy-saving and environment-benign approach for producing value-added chemicals coupled with solar fuel generation. Epoxidation with green solvents via PEC methods has a high potential for different oxidation reactions of value-added and fine chemicals.

Simultaneous Enhancement of Charge Separation and Hole Transportation in a W:α-Fe2O3/MoS2 Photoanode: A Collaborative Approach of MoS2 as a Heterojunction and W as a Metal Dopant.

In this study, a facile approach has been successfully applied to synthesize a W-doped Fe2O3/MoS2 core-shell electrode with unique nanostructure modifications for photoelectrochemical performance. A two-dimensional (2D) structure of molybdenum disulfide (MoS2) and tungsten (W)-doped hematite (W:α-Fe2O3) overcomes the drawbacks of the α-Fe2O3 and MoS2 semiconductor through simple and facile processes to improve the photoelectrochemical (PEC) performance. The highest photocurrent density of the 0.5W:α-Fe2O3/MoS2 photoanode is 1.83 mA·cm-2 at 1.23 V vs reversible hydrogen electrode (RHE) under 100 mW·cm2 illumination, which is higher than those of 0.5W:α-Fe2O3 and pure α-Fe2O3 electrodes. The overall water splitting was evaluated by measuring the H2 and O2 evolution, which after 2 h of irradiation for 0.5W:α-Fe2O3/MoS2 was determined to be 49 and 23.8 µmol.cm-2, respectively. The optimized combination of the heterojunction and metal doping on pure α-Fe2O3 (0.5W:α-Fe2O3/MoS2 photoanode) showed an incident photon-to-electron conversion efficiency (IPCE) of 37% and an applied bias photon-to-current efficiency (ABPE) of 26%, which are around 5.2 and 13 times higher than those of 0.5W:α-Fe2O3, respectively. Moreover, the facile fabrication strategy can be easily extended to design other oxide/carbon-sulfide/oxide core-shell materials for extensive applications.

Ultrasonically prepared photocatalyst of W/WO3 nanoplates with WS2 nanosheets as 2D material for improving photoelectrochemical water splitting.

A sonochemical treatment has been an emerged technique as an interesting method for fabricating different photocatalysts with unique photoelectrochemical (PEC) properties. This study investigated the PEC performance of WO3 with WS2 nanosheets as a 2D material before calcination (WO3/WS2-90) and after calcination (WO3/WS2-450) prepared with sonochemical treatment. The WS2 nanosheets were prepared from a liquid exfoliation phase with few-layer nanosheets, approximately 6.5 nm in thickness. The nanosheets were confirmed by UV-Vis spectroscopy and atomic force microscopy. Further, XPS, RAMAN, and SEM-EDAX analyses indicated that, following calcination of the WO3/WS2 electrode, the WS2 nanosheets initially transformed to 2D-WO3. After depositing the WS2 nanosheets on the WO3, the photocurrent density increased substantially. The WO3/WS2-450 films after calcination showed a photocurrent density of 5.6 mA.cm-2 at 1.23 V vs. Ag/AgCl, which was 3.1 and 7.2 times higher, respectively than those of the WO3/WS2-90 before calcination and pure WO3. Mott-Schottky and electrochemical impedance spectroscopy analyses confirmed the fabrication of the WO3/WS2 photoanode after calcination. The deposition of WS2 nanosheets onto pure WO3 increased the donor concentration (24-fold), reduced the space charge layer (4.6-fold), and decreased the flat band potential (1.6-fold), which could all help improve the photoelectrochemical efficiency. Moreover, the incorporation of WO3 with WS2 nanosheets as a 2D material (WO3/WS2-450) enhanced the incident photon current efficiency (IPCE) by 55%. In addition, the applied-bias photon-to-current conversion efficiency of the WO3/WS2-450 films was approximately 2.26% at 0.75 V (vs. Ag/AgCl), which is 5.6 and 9 times higher, respectively than those of WO3/WS2-90 and pure WO3.

Ultrasonication-assisted liquid-phase exfoliation enhances photoelectrochemical performance in α-Fe2O3/MoS2 photoanode.

This study successfully manufactured a p-n heterojunction hematite (α-Fe2O3) structure with molybdenum disulfide (MoS2) to address the electron-hole transfer problems of conventional hematite to enhance photoelectrochemical (PEC) performance. The two-dimensional MoS2 nanosheets were prepared through ultrasonication-assisted liquid-phase exfoliation, after which the concentration, number of layers, and thickness parameters of the MoS2 nanosheets were respectively estimated by UV-vis, HRTEM and AFM analysis to be 0.37 mg/ml, 10-12 layers and around 6 nm. The effect of heterojunction α-Fe2O3/MoS2 and the role of the ultrasonication process were investigated by the optimized concentration of MoS2 in the forms of bulk and nanosheet on the surface of the α-Fe2O3 electrode while measuring the PEC performance. The best photocurrent density of the α-Fe2O3/MoS2 photoanode was obtained at 1.52 and 0.86 mA.cm-2 with good stability at 0.6 V vs. Ag/AgCl under 100 mW/cm2 (AM 1.5) illumination from the back- and front-sides of α-Fe2O3/MoS2; these values are 13.82 and 7.85-times higher than those of pure α-Fe2O3, respectively. The results of electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis showed increased donor concentration (2.6-fold) and decreased flat band potential (by 20%). Moreover, the results of IPCE, ABPE, and OCP analyses also supported the enhanced PEC performance of α-Fe2O3/MoS2 through the formation of a p-n heterojunction, leading to a facile electron-hole transfer.

Effect of graphene oxide nanosheets on visible light-assisted antibacterial activity of vertically-aligned copper oxide nanowire arrays.

In the present work, the effect of graphene oxide (GO) nanosheets on the antibacterial activity of CuO nanowire arrays under visible light irradiation is shown. A combined thermal oxidation/electrophoretic deposition technique was employed to prepare three-dimensional networks of graphene oxide nanosheets hybridized with vertically aligned CuO nanowires. With the help of standard antibacterial assays and X-ray photoelectron spectroscopy, it is shown that the light-activated antibacterial response of the hybrid material against gram-negative Escherichia coli is significantly improved as the oxide functional groups of the GO nanosheets are reduced. In order to explore the physicochemical mechanism behind this behavior, ab-initio simulations based on density functional theory were performed and the effect of surface functional groups and hybridization were elucidated. Supported by the experiments, a three-step photo-antibacterial based mechanism is suggested: (i) injection of an electron from CuO into rGO, (ii) localization of the excess electron on rGO functional groups, and (iii) release of reactive oxygen species lethal to bacteria. Activation of new photoactive and physical mechanisms in the hybrid system makes rGO-modified CuO nanowire coatings as promising nanostructure devices for antimicrobial applications in particular for dry environments.