Dynamics at polarized carbon dioxide-iron oxyhydroxide interfaces unveil the origin of multicarbon product formation

Surface-sensitive ambient pressure X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy combined with an electrocatalytic reactivity study, multilength-scale electron microscopy, and theoretical modeling provide insights into the gas-phase selective reduction of carbon dioxide to isopropanol on a nitrogen-doped carbon-supported iron oxyhydroxide electrocatalyst. Dissolved atomic carbon forms at relevant potentials for carbon dioxide reduction from the reduction of carbon monoxide chemisorbed on the surface of the ferrihydrite-like phase. Theoretical modeling reveals that the ferrihydrite structure allows vicinal chemisorbed carbon monoxide in the appropriate geometrical arrangement for coupling. Based on our observations, we suggest a mechanism of three-carbon-atom product formation, which involves the intermediate formation of atomic carbon that undergoes hydrogenation in the presence of hydrogen cations upon cathodic polarization. This mechanism is effective only in the case of thin ferrihydrite-like nanostructures coordinated at the edge planes of the graphitic support, where nitrogen edge sites stabilize these species and lower the overpotential for the reaction. Larger ferrihydrite-like nanoparticles are ineffective for electron transport

Interfacial chemistry in the electrocatalytic hydrogenation of CO2 over C‑supported Cu-based systems

Operando soft and hard X-ray spectroscopic techniques were used in combination with plane-wave density functional theory (DFT) simulations to rationalize the enhanced activities of Zn-containing Cu nanostructured electrocatalysts in the electrocatalytic CO2 hydrogenation reaction. We show that at a potential for CO2 hydrogenation, Zn is alloyed with Cu in the bulk of the nanoparticles with no metallic Zn segregated; at the interface, low reducible Cu­(I)–O species are consumed. Additional spectroscopic features are observed, which are identified as various surface Cu­(I) ligated species; these respond to the potential, revealing characteristic interfacial dynamics. Similar behavior was observed for the Fe–Cu system in its active state, confirming the general validity of this mechanism; however, the performance of this system deteriorates after successive applied cathodic potentials, as the hydrogen evolution reaction then becomes the main reaction pathway. In contrast to an active system, Cu­(I)–O is now consumed at cathodic potentials and not reversibly reformed when the voltage is allowed to equilibrate at the open-circuit voltage; rather, only the oxidation to Cu­(II) is observed. We show that the Cu–Zn system represents the optimal active ensembles with stabilized Cu­(I)–O; DFT simulations rationalize this observation by indicating that Cu–Zn–O neighboring atoms are able to activate CO2, whereas Cu–Cu sites provide the supply of H atoms for the hydrogenation reaction. Our results demonstrate an electronic effect exerted by the heterometal, which depends on its intimate distribution within the Cu phase and confirms the general validity of these mechanistic insights for future electrocatalyst design strategies

Microstrip Copper Nanowires Antenna Array for Connected Microwave Liquid Sensors

In this contribution, a 25 GHz planar antenna, designed and realized in microstrip technology, is exploited as a lightweight and compact liquid sensor. The high working frequency allows minimization of the sensor dimension. Moreover, particular attention was paid to keeping the design cost low. Indeed, the frequency of 25 GHz is widely exploited for many applications, e.g., up to the last decade concerning radars and, recently, 5G technology. Available commercial antennas allowed minimization of the effort that is usually required to design the microstrip sensor. The antenna was in-house realized, and the microstrip Cu conductor was modified through controlled anodic oxidation in order to enhance the sensing features. The sensor capability of detecting the presence and concentration of ethanol in water was experimentally demonstrated. In detail, a sensitivity of 0.21 kHz/(mg/L) and an average quality factor of 117 were achieved in a very compact size, i.e., 18 mm × 19 mm, and in a cost-effective way. As a matter of fact, the availability of devices able to collect data and then to send the related information wirelessly to a remote receiver represents a key feature for the next generation of connected smart sensors

Photo-Electrochemical Sensing of Dopamine by a Novel Porous TiO2 Array-Modified Screen-Printed Ti Electrode

In this paper, the development of a nanoporous TiO2 array-modified Ti electrode for photo-electrochemical (PEC) sensing of dopamine (DA) is reported. A porous TiO2 array-modified electrode was fabricated from the controlled anodic oxidation of a Ti working electrode of commercial screen-printed electrodes (SPE). The anodization process and the related morphological and microstructural transformation of the bare Ti electrode into a TiO2/Ti electrode was followed by scanning electron microscopy (SEM) and UV-visible reflectance spectroscopy (DR-UV-Vis). The modified electrode was irradiated with a low-power (120 mW) UV-Vis LED lamp (λ = 400 nm) and showed good performance for the detection of DA with a large linear response range, a sensitivity of 462 nA mM−1 cm−2, and a limit of detection of 20 µM. Moreover, it showed higher photocurrents in the presence of DA in comparison to some foreign species such as ascorbic acid, uric acid, glucose, K+, Na+, and Cl−. Thus, this proposed low-cost photo-electrochemical sensor, with the advantage of very simple fabrication, demonstrates potential applications for the determination of dopamine in real samples

Room-Temperature Electrocatalytic Synthesis of NH3 from H2O and N-2 in a Gas-Liquid-Solid Three-Phase Reactor

Fe2O3-CNT samples are studied for the room temperature electrocatalytic synthesis of NH3 from H2O and N-2 in a gas-liquid-solid three-phase reactor. A 30 wt % iron-oxide loading was found to be optimal. The performances greatly depend on the cell design, where the possibility of ammonia crossover through the membrane has to be inhibited. The reaction conditions also play a significant role. The effect of electrolyte (type, pH, concentration) was investigated in terms of current density, rate of ammonia formation, and Faradaic efficiency in continuous tests up to 24 h of time on stream. A complex effect of the applied voltage was observed. An excellent stability was found for an applied voltage of -1.0 V vs Ag/AgCl. At higher negative applied voltages, the ammonia formation rate and Faradaic selectivity are higher, but with a change of the catalytic performances, although the current densities remain constant for at least 24 h. This effect is interpreted in terms of reduction of the iron-oxide species above a negative voltage threshold, which enhances the side reaction of H+/e(-) recombination to generate H-2 rather than their use to reduce activated N-2 species, possibly located at the interface between iron-oxide and functionalized CNTs

Photoactive materials based on semiconducting nanocarbons - A challenge opening new possibilities for photocatalysis

This perspective paper introduces the concept that nanocarbons and related materials such as carbon dots are an interesting intrinsic photocatalytic semiconducting material, and not only a modifier of the existing (semiconducting) materials to prepare hybrid materials. The semiconducting properties of the nanocarbons, and the possibility to have the band gap within the visible-light region through defect band engineering, introduction of light heteroatoms and control/manipulation of the curvature or surface functionalization are discussed. These materials are conceptually different from the "classical" semiconducting photocatalysts, because semiconductor domains with tuneable characteristics are embedded in a conductive carbon matrix, with the presence of various functional groups (as C=0 groups) enhancing charge separation by trapping electrons. These nanocarbons open a range of new possibilities for photocatalysis both for energetic and environmental applications. The use of nanocarbons as quantum dots and photo luminescent materials was also analysed. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

Photoactive materials based on semiconducting nanocarbons-A challenge opening new possibilities for photocatalysis

This perspective paper introduces the concept that nanocarbons and related materials such as carbon dots are an interesting intrinsic photocatalytic semiconducting material, and not only a modifier of the existing (semiconducting) materials to prepare hybrid materials. The semiconducting properties of the nanocarbons, and the possibility to have the band gap within the visible-light region through defect band engineering, introduction of light heteroatoms and control O groups) enhancing charge separation by trapping electrons. These nanocarbons open a range of new possibilities for photocatalysis both for energetic and environmental applications. The use of nanocarbons as quantum dots and photoluminescent materials was also analysed

Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon-Nanotube-Based Electrocatalyst

Ammonia is synthesized directly from water and N-2 at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half-cell for the NH3 synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half-cell. A rate of ammonia formation of 2.2 X 10 (-3) g(NH3) m (-2) h (- 1) was obtained at room temperature and atmospheric pressure in a flow of N-2, with stable behavior for at least 60h of reaction, under an applied potential of - 2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1% was obtained. Data also indicate that the active sites in NH3 electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N-2, making it more reactive towards hydrogenation

Photoactive materials based on semiconducting nanocarbons-A challenge opening new possibilities for photocatalysis

This perspective paper introduces the concept that nanocarbons and related materials such as carbon dots are an interesting intrinsic photocatalytic semiconducting material, and not only a modifier of the existing (semiconducting) materials to prepare hybrid materials. The semiconducting properties of the nanocarbons, and the possibility to have the band gap within the visible-light region through defect band engineering, introduction of light heteroatoms and control O groups) enhancing charge separation by trapping electrons. These nanocarbons open a range of new possibilities for photocatalysis both for energetic and environmental applications. The use of nanocarbons as quantum dots and photoluminescent materials was also analysed

Cover Feature: Direct Synthesis of Ammonia from N2 and H2O on Different Iron Species Supported on Carbon Nanotubes using a Gas-Phase Electrocatalytic Flow Reactor (ChemElectroChem 14/2020)

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