Visible light driven photoanodes for water oxidation based on novel r-GO/\u3b2-Cu2V2O7/TiO2 nanorods composites

This paper describes the preparation and the photoelectrochemical performances of visible light driven photoanodes based on novel r-GO/-Cu2V2O7/TiO2 nanorods/composites. -Cu2V2O7 was deposited on both fluorine doped tin oxide (FTO) and TiO2 nanorods (NRs)/FTO by a fast and convenient Aerosol Assisted Spray Pyrolysis (AASP) procedure. Ethylenediamine (EN), ammonia and citric acid (CA) were tested as ligands for Cu2+ ions in the aerosol precursors solution. The best-performing deposits, in terms of photocurrent density, were obtained when NH3 was used as ligand. When -Cu2V2O7 was deposited on the TiO2 NRs a good improvement in the durability of the photoanode was obtained, compared with pure -Cu2V2O7 on FTO. A further remarkable improvement in durability and photocurrent density was obtained upon addition, by electrophoretic deposition, of reduced graphene oxide (r-GO) flakes on the -Cu2V2O7/TiO2 composite material. The samples were characterized by X-ray Photoelectron Spectroscopy (XPS), Raman, High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM), Wide Angle X-ray Diffraction (WAXD) and UV\u2013Vis spectroscopies. The photoelectrochemical (PEC) performances of -Cu2V2O7 on FTO, -Cu2V2O7/TiO2 and r-GO/-Cu2V2O7/TiO2 were tested in visible light by linear voltammetry and Electrochemical Impedance Spectroscopy (EIS) measurements

Ag-Vanadates/GO Nanocomposites by Aerosol-Assisted Spray Pyrolysis: Preparation and Structural and Electrochemical Characterization of a Versatile Material

In this article, we describe the deposition by aerosol-assisted spray pyrolysis of different types of silver vanadate nanocomposites with and without graphene oxide (GO) on different substrates (carbon paper (CP) and fluorine-doped tin oxide (FTO)). When deposited on CP, different amounts of GO were added to the Ag and V precursor solution to study the effect of GO on the physicochemical properties of the resulting Ag-vanadate. It is shown that the addition of GO leads mainly to the formation of nanoparticles of the Ag2V4O11 phase, whereas Ag2V4O11 and Ag3VO4 are obtained without the addition of GO. The morphology and chemical properties of the composites were determined by scanning and transmission electron microscopies, X-ray diffraction, X-ray photoemission spectroscopy, and UV\u2013visible and Raman spectroscopies. In addition, the photoelectrochemical (PEC) properties of such composites were studied by CV, linear sweep voltammetry, and electrochemical impedance spectroscopy. The ideal AgxVOy and GO ratio was optimized for obtaining higher photocurrent values and a good stability. The results showed that the presence of GO improves the electrical conductivity of the catalyst layer as well as the electron injection from the oxide to the electrode surface. The deposition of pure Ag2V4O11 on FTO does not lead to samples with stable PEC performances. Samples grown on CP supports showed an efficient electrochemical detection of small amounts of ethylenediamine in water solution

Multimodal hybrid 2D networks via the thiol-epoxide reaction on 1T/2H MoS2 polytypes

The study adds a fundamental tile to the still incomplete puzzle of covalent functionalization tools of 2D inorganic networks and describes a protocol where organic moieties are covalently grafted at both phases (1T and 2H) of a CE-MoS2 sample

Indium selenide: An insight into electronic band structure and surface excitations

We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at similar to 1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed

Oxygen reduction reaction at La_xCa_1-xMnO₃ nanostructures: interplay between A-site segregation and B-site valency

The mean activity of surface Mn sites at LaxCa1-xMnO3 nanostructures towards the oxygen reduction reaction (ORR) in alkaline solution is assessed as a function of the oxide composition. Highly active oxide nano-particles were synthesised by an ionic liquid-based route, yielding phase-pure nanoparticles, across the entire range of compositions, with sizes between 20 and 35 nm. The bulk vs. surface composition and structure are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). These techniques allow quantification of not only changes in the mean oxidation state of Mn as a function of x, but also the extent of A-site surface segregation. Both trends manifest themselves in the electrochemical responses associated with surface Mn sites in 0.1 M KOH solution. The characteristic redox signatures of Mn sites are used to estimate their effective surface number density. This parameter allows comparing, for the first time, the mean electrocatalytic activity of surface Mn sites as a function of the LaxCa1-xMnO3 composition. The ensemble of experimental data provides a consistent picture in which increasing electron density at the Mn sites leads to an increase in the ORR activity. We also demonstrate that normalisation of electrochemical activity by mass or specific surface area may result in inaccurate structure–activity correlations

Copper single-atoms embedded in 2D graphitic carbon nitride for the CO2 reduction

AbstractWe report the study of two-dimensional graphitic carbon nitride (GCN) functionalized with copper single atoms as a catalyst for the reduction of CO2 (CO2RR). The correct GCN structure, as well as the adsorption sites and the coordination of the Cu atoms, was carefully determined by combining experimental techniques, such as X-ray diffraction, transmission electron microscopy, X-ray absorption, and X-ray photoemission spectroscopy, with DFT theoretical calculations. The CO2RR products in KHCO3 and phosphate buffer solutions were determined by rotating ring disk electrode measurements and confirmed by 1H-NMR and gas chromatography. Formate was the only liquid product obtained in bicarbonate solution, whereas only hydrogen was obtained in phosphate solution. Finally, we demonstrated that GCN is a promising substrate able to stabilize metal atoms, since the characterization of the Cu-GCN system after the electrochemical work did not show the aggregation of the copper atoms

Chitosan-derived nitrogen-doped carbon electrocatalyst for a sustainable upgrade of oxygen reduction to hydrogen peroxide in UV-assisted electro-Fenton water treatment

The urgency to move from critical raw materials to highly available and renewable feedstock is currently driving the scientific and technical developments. Within this context, the abundance of natural resources like chitosan paves the way to synthesize biomass-derived nitrogen-doped carbons. This work describes the synthesis of chitosan-derived N-doped mesoporous carbon in the absence (MC-C) and presence (N-MC-C) of 1,10-phenanthroline, which acted as both a porogen agent and a second nitrogen source. The as-prepared MC-C and N-MC-C were thoroughly characterized and further employed as catalytic materials in gas-diffusion electrodes (GDEs), aiming to develop a sustainable alternative to conventional GDEs for H2O2 electrogeneration and photoelectro-Fenton (PEF) treatment of a drug pollutant. N-MC-C presented a higher content of key surface N-functionalities like the pyrrole group, as well as an increased graphitization degree and surface area (63 vs 6 m2/g), comparable to commercial carbon black. These properties entailed a superior activity of N-MC-C for the oxygen reduction reaction, as confirmed from its voltammetric behavior at a rotating ring-disk electrode. The GDE prepared with the N-MC-C catalyst showed greater H2O2 accumulation, attaining values close to those obtained with a commercial GDE. N-MC-C- and MC-C-derived GDEs were employed to treat drug solutions at pH 3.0 by the PEF process, which outperformed electro-oxidation. The fastest drug removal was achieved using N-MC-C, requiring only 16 min at 30 mA/cm2 instead of 20 min required with MC-C. The replacement of the dimensionally stable anode by a boron-doped diamond accelerated the degradation process, reaching an almost complete mineralization in 360 min. The main degradation products were identified, revealing the formation of six different aromatic intermediates, alongside five aliphatic compounds that comprised three nitrogenated structures. The initial N was preferentially converted into ammonium