Search

Ternary and quaternary metal oxides form a rapidly emerging class of new functional materials tackling the grand challenge of efficient solar energy harvesting. Currently the main interest is devoted to the characteristics of these materials and little consideration has been given to their preparation. Solution combustion synthesis (SCS) is considered a green and sustainable alternative to the widely employed energy-and/or time-consuming synthesis methods. In this study, SCS was employed to prepare Bi2Ti2O7 and to perform bandgap engineering through foreign ion (Fe, Mn) incorporation. The synthesized materials were characterized by powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray microanalysis, diffuse reflectance UV-vis and Raman spectroscopy, and surface area determination via N-2 adsorption. We found that nanocrystalline materials were formed during the SCS synthesis. Further, the phase composition of these materials and the amount of the foreign metal ions incorporated in the parent structure, could be effectively controlled. Consequently, the SCS technique provided a simple and reliable tool for bandgap engineering. The photocatalytic activity of the materials was tested through methyl orange degradation, and the intrinsic photocatalytic activity of the various samples were compared after deconvoluting the effect of their vastly different specific surface areas., QC 20171130

Solar fuel generation through electrochemical CO2 conversion offers an attractive avenue to store the energy of sunlight in the form of chemical bonds, with the simultaneous remediation of a greenhouse gas. While impressive progress has been achieved in developing novel nanostructured catalysts and understanding the mechanistic details of this process, limited knowledge has been gathered on continuous-flow electrochemical reactors for CO2 electroreduction. This is indeed surprising considering that this might be the only way to scale-up this fledgling technology for future industrial application. In this review article, we discuss the parameters that influence the performance of flow CO2 electrolyzers. This analysis spans the overall design of the electrochemical cell (microfluidic or membrane-based), the employed materials (catalyst, support, etc.), and the operational conditions (electrolyte, pressure, temperature, etc.). We highlight R&D avenues offering particularly promising development opportunities together with the intrinsic limitations of the different approaches. By collecting the most relevant characterization methods (together with the relevant descriptive parameters), we also present an assessment framework for benchmarking CO2electrolyzers. Finally, we give a brief outlook on photoelectrochemical reactors where solar energy input is directly utilized., QC 20171211

Combination of an oxide semiconductor with a highly conductive nanocarbon framework (such as graphene or carbon nanotubes) is an attractive avenue to assemble efficient photo electrodes for solar fuel generation. To fully-exploit the possible synergies of the hybrid formation, however, precise knowledge of these systems is required to allow rational design and morphological engineering. In this paper, we present the controlled electrochemical deposition of nanocrystalline p-Cu2O on the surface of different graphene substrates. The developed synthetic protocol allowed tuning of the-morphological features of the hybrids as, deduced from electron microscopy. (Photo)electrochemical measurements (including photovoltammetry, electrochemical impedance spectroscopy, photocurrent transient analysis) demonstrated better performance for the 2D graphene containing photoelectrodes, compared to the bare Cu2O films, the enhanced performance being rooted in suppressed charge carrier recombination. To elucidate the precise role of graphene, comparative studies were performed with carbon nanotube (CNT) films and 3D graphene foams. These studies revealed, after allowing for the effect of increased surface area, that the 3D graphene substrate outperformed the other two nanocarbons. Its interconnected structure facilitated effective charge separation and transport, leading to better harvesting of the generated photoelectrons. These hybrid assemblies are shown to be potentially attractive candidates in photoelectrochemical energy conversion schemes, namely CO2 reduction., QC 20171130

Of the myriad electrode materials that have been used for electrochemical (EC) and photoelectrochemical (PEC) reduction of carbon dioxide in aqueous media, copper oxide/copper interfaces have shown a remarkable range of hydrocarbon and oxygenated products including acids, aldehydes, ketones, and alcohols. This Perspective highlights experimental evidence for the fact that both EC and PEC reduction scenarios have similar chemical and morphological underpinnings in the in situ formation of copper nano- or microcubes on the (photo)cathode surface. Recent rapid developments in our fundamental understanding of these interfaces and areas requiring further studies are discussed in light of recent studies in the authors' laboratories and elsewhere., QC 20171211

Photoelectrochemical reduction of CO2 to form useful chemicals is an increasingly studied avenue for harnessing and storing solar energy. In the quest for efficient and stable photocathode materials, nanostructured hybrid assemblies are eminently attractive candidates, because they exhibit multiple favorable properties that cannot be expected from a single material. One possible direction is to combine p-type inorganic semiconductors with highly conductive large surface area electrodes such as carbon nanotube networks. In this work, the controlled synthesis and photoelectrochemical behavior of CNT/Cu2O films was reported for the first time for CO2 reduction applications. A carefully designed, multiple-step electrodeposition protocol was developed that ensured homogeneous coating of CNTs with Cu2O nanocrystals. The hybrid materials were characterized by electron microscopy, X-ray diffraction, Raman spectroscopy, electrochemical impedance spectroscopy, and photoelectrochemical methods. The hybrid films had five-fold higher electrical conductivity compared to their pure Cu2O counterparts. This enhanced charge transport property resulted in a drastic increase in the photocurrents measured for CO2 reduction. In addition to this superior performance, long term photoelectrolysis measurements proved that the CNT/Cu2O hybrids were more stable than the oxide alone. These observations, together with the established structure/property relationships, may contribute to the rational design of nanocarbon/inorganic semiconductor hybrid photocathodes for deployment in photoelectrochemical cells., QC 20171211

Changes in the surface of an oxidized Cu(1 0 0) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600 °C. Experimental probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. The effects of oxygen adsorption on localization of positron surface state wave function and annihilation characteristics are also analyzed. Possible explanation is proposed for the observed behavior of the intensity of positron annihilation induced Cu M2,3VV and O KLL Auger peaks and probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons with changes of the annealing temperature. © 2009 Elsevier B.V. All rights reserved.

Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the positron annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300° C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600° C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. Possible explanation for the observed behavior of the intensity of positron annihilation induced Cu M2,3VV Auger peak with changes of the annealing temperature is proposed. © 2009 American Institute of Physics.

Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the positron annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300° C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600° C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. Possible explanation for the observed behavior of the intensity of positron annihilation induced Cu M2,3VV Auger peak with changes of the annealing temperature is proposed. © 2009 American Institute of Physics.

Changes in the surface of an oxidized Cu(1 0 0) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600 °C. Experimental probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. The effects of oxygen adsorption on localization of positron surface state wave function and annihilation characteristics are also analyzed. Possible explanation is proposed for the observed behavior of the intensity of positron annihilation induced Cu M2,3VV and O KLL Auger peaks and probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons with changes of the annealing temperature. © 2009 Elsevier B.V. All rights reserved.