Engineering Cu2O Nanowire Surfaces for Photoelectrochemical Hydrogen Evolution Reaction

Cu2O is a narrow band gap material serving as an important candidate for photoelectrochemical hydrogen evolution reaction. However, the main challenge that hinders its practical exploitation is its poor photostability, due to its oxidation into CuO by photoexcited holes. Here, we thoroughly minimize the photo-oxidation of Cu2O nanowires by growing a thin layer of the TiO2 protective layer and an amorphous layer of the VOx cocatalyst using magnetron sputtering and atomic layer deposition, respectively. After optimization of the protective and the cocatalyst layers, the photoelectrode exhibits a current density of -2.46 mA/cm2 under simulated sunlight (100 mW/cm2) at 0.3 V versus reversible hydrogen electrode, and its performance is stable for an extended illumination time. The chemical stability and the good performance of the engineered photoelectrode demonstrate the potential of using earth-abundant materials as a light-harvesting device for solar hydrogen production

Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed

Silica-zirconia mixed oxide samples from silica-based hybrid materials: influence of preparation procedure and composition on the active sites

In this work, the interaction of amorphous silica\u2013zirconia mixed oxide samples obtained from inorganic\u2013 organic silica-based hybrid materials with pyridine and CO2 was studied to investigate their acid/base character. Several silica\u2013zirconia mixed oxide powders characterized by different [Zr/Si] atomic ratios were prepared and treated at increasing temperatures both in a conventional muffle and with microwave technology. The powder samples were characterized with Diffuse Reflectance Infrared Fourier Transform (DRIFT) and X-ray Photoelectron (XP) spectroscopies. The surface acidic and basic active sites were investigated (with DRIFT spectroscopy) by chemisorbing probe molecules (pyridine, carbon dioxide). The obtained results revealed the presence of both Lewis and Br\uf8nsted acidic sites on the amorphous silica\u2013 zirconia mixed oxide powder surfaces. Several acidic sites characterized by different strength were observed; the acidic sites distribution is markedly influenced by the sample composition and by the heat treatment: more numerous acidic sites form on the surface of the samples treated with microwaves with respect to the muffle treated ones; the increment of the temperature and the decrease of the zirconium content cause a significant decrement of the acidic sites. No basic sites were revealed

Cu/CGO cermet based electrodes for Symmetric and Reversible Solid Oxide Fuel Cells

Cu-based cermets suitable for electrodes in Symmetric and Reversible Solid Oxide Fuel Cells (SR-SOFCs) based on the Cerium Gadolinum Oxide (CGO) electrolyte were developed and successfully tested in the intermediate temperature range (600-800 degrees C). The Cu/CGO cermets were prepared by means of a self-combustion based citrate procedure and the effects of synthesis conditions were studied. Characterization of the Cu/CGO nanocomposites by XPS, XRD, SEM, TPR suggested that this procedure allows obtaining highly dispersed CuO on the cerium gadolinium oxide. Conversion higher than 80% was observed above 600 degrees C in methane total oxidation. Synthesis parameters affected both properties and catalytic performance. The behaviour under redox conditions was studied by operando high-energy XRD under oscillating H-2/O-2 feed. Reducing conditions converted CuO into Cu(0) passing through an intermediate Cu2O phase while increasing the conductivity and the reactivity. This structural modification was completely reversible. The high stability, reversibility, catalytic activity and electrochemical performance make these electrodes promising for SR-SOFCs. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Hybrid thermal-field emission of ZnO nanowires

The electron emission properties of an array of ZnO nanowires were studied in the temperature range of 300-473 K. An almost doubling of the current density at 473 K under an electric field of 8 V/lm (j(T¼473 K) ¼ 190 lA/cm2, j(T¼300 K)¼114 lA/cm2) was observed together with a reduction of the turn-on field from 552 V/lm to 482 V/lm. Theoretical model that combines the thermal-field emission for high electric field and the Schottky emission for the low field can satisfactorily account for temperature dependence of current at low as well as at high applied bias. The obtained effect is particularly appealing for the application in micro-gun for THz vacuum tubes

Sequential physical vapor deposition and chemical vapor deposition for the growth of In2O3-SnO2 radial and longitudinal heterojunctions

Heterostructures of In2O3 and SnO2 were produced by sequential application of the physical- and chemical-vapor deposition techniques usually adopted for nanowire fabrication. In2O3 nanowires exhibit a single crystal body-centered cubic structure oriented along the [1 0 0] direction and grow epitaxially on alpha-sapphire substrate by means of a transport and condensation method assisted by Au nanoparticles. Nucleation and growth occurred via direct vapor solid (VS) mechanism competing with catalyst-mediated vapor-liquid-solid (VLS). SnO2 nanowires were obtained in a single crystal tetragonal (cassiterite) structure and oriented along the [1 0 1] direction, the growth being promoted by the gold particle at the apex of the In2O3 nanowires. The size of the catalyst thereby determines the main morphological features of SnO2 wires. CVD deposition allows precise control of the geometrical features of the heterojunction, also limiting detrimental nucleation of SnO2 on the lateral sides of In2O3 nanowires due to lower longitudinal growth rate. These results can help in improving the ability of finely tuning the morphological and structural properties of heterostructured oxide nanocrystals. (C) 2014 Elsevier B.V. All rights reserved

Electronic properties of chelating dicarbene palladium complexes: A combined electrochemical, NMR and XPS investigation

A series of N-heterocyclic dicarbene palladium(II) complexes has been characterised combining different techniques (cyclic voltammetry, XPS and 13CNMR spectroscopy), in order to evaluate the in\ufb02uence of the dicarbene ligand on the electronic properties of the metal centre. The data obtained with the three techniques give relevant information, cyclic voltammetry appearing the most useful approach. In addition,the observed variations of the physico-chemical properties of the complexes con\ufb01rm the possibility of \ufb01nely tuning the electronic properties of the palladium(II)centre by changing the characteristics of the dicarbene ligand (wingtip substituents, bridging group between the carbene units, type of heterocyclic ring)

Graphene below the percolation threshold in TiO2 for dye-sensitized solar cells

We demonstrate a fast and large area-scalable methodology for the fabrication of efficient dye sensitized solar cells (DSSCs) by simple addition of graphene micro-platelets to TiO2 nanoparticulate paste (graphene concentration in the range of 0 to 1.5 wt%). Two dimensional (2D) Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm the presence of graphene after 500 degrees C annealing for 30 minutes. Graphene addition increases the photocurrent density from 12.4 mA cm(-2) in bare TiO2 to 17.1 mA cm(-2) in an optimized photoanode (0.01 wt% graphene, much lower than those reported in previous studies), boosting the photoconversion efficiency (PCE) from 6.3 up to 8.8%. The investigation of the 2D graphene distribution showed that an optimized concentration is far below the percolation threshold, indicating that the increased PCE does not rely on the formation of an interconnected network, as inferred by prior investigations, but rather, on increased charge injection from TiO2 to the front electrode. These results give insights into the role of graphene in improving the functional properties of DSSCs and identifying a straightforward methodology for the synthesis of new photoanodes