Titanium dioxide (TiO2) and zinc oxide (ZnO) nanostructures have been widely used as photo-catalysts due to their low-cost, high surface area, robustness, abundance and non-toxicity. In this work, four TiO2 and ZnO-based nanostructures, i.e. TiO2 nanoparticles (TiO2 NPs), TiO2 nanotubes (TiO2 NTs), ZnO nanowires (ZnO NWs) and ZnO@TiO2 core-shell structures, specifically prepared with a fixed thickness of about 1.5 μm, are compared for the solar-driven water splitting reaction, under AM1.5G simulated sunlight. Complete characterization of these photo-electrodes in their structural and photo-electrochemical properties was carried out. Both TiO2 NPs and NTs showed photo-current saturation reaching 0.02 and 0.12 mA cm(-2), respectively, for potential values of about 0.3 and 0.6 V vs. RHE. In contrast, the ZnO NWs and the ZnO@TiO2 core-shell samples evidence a linear increase of the photocurrent with the applied potential, reaching 0.45 and 0.63 mA cm(-2) at 1.7 V vs. RHE, respectively. However, under concentrated light conditions, the TiO2 NTs demonstrate a higher increase of the performance with respect to the ZnO@TiO2 core-shells. Such material-dependent behaviours are discussed in relation with the different charge transport mechanisms and interfacial reaction kinetics, which were investigated through electrochemical impedance spectroscopy. The role of key parameters such as electronic properties, specific surface area and photo-catalytic activity in the performance of these materials is discussed. Moreover, proper optimization strategies are analysed in view of increasing the efficiency of the best performing TiO2 and ZnO-based nanostructures, toward their practical application in a solar water splitting device.

A fast and low-cost sol-gel synthesis used to deposit a shell of TiO2 anatase onto an array of vertically aligned ZnO nanowires (NWs) is reported in this paper. The influence of the annealing atmosphere (air or N2) and of the NWs preannealing process, before TiO2 deposition, on both the physicochemical characteristics and photoelectrochemical (PEC) performance of the resulting heterostructure, was studied. The efficient application of the ZnO@TiO2 core-shells for the PEC water-splitting reaction, under simulated solar light illumination (AM 1.5G) solar light illumination in basic media, is here reported for the first time. This application has had a dual function: to enhance the photoactivity of pristine ZnO NWs and to increase the photodegradation stability, because of the protective role of the TiO2 shell. It was found that an air treatment induces a better charge separation and a lower carrier recombination, which in turn are responsible for an improvement in the PEC performance with respect to N2-treated core-shell materials. Finally, a photocurrent of 0.40 mA/cm(2) at 1.23 V versus RHE (2.2 times with respect to the pristine ZnO NWs) was obtained. This achievement can be regarded as a valuable result, considering similar nanostructured electrodes reported in the literature for this application.

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oxidation methods. In particular, a zinc nanobranched structure is deposited by radio-frequency magnetron sputtering on conductive substrates. Then impregnation of the samples in an antimony acetate solution is performed at different times (2 and 4 h) at room temperature. It has to be noted that longer times produce however an appreciable and even complete dissolution of the zinc material in the Sb acetate solution (at 8 and 16 h, respectively), whereas very short impregnation times (30 min) did not result in a signifi cant doping. Therefore, it resulted that a reasonable impregnation time for inducing a satisfying doping level, without altering the morphological properties of the investigated materials, lies in the range of 2-4 h. The impregnation is then followed by a thermal oxidation at 380 °C, having the dual function to oxidize Zn to ZnO and successfully promote the insertion of Sb in the wurtzite structure, leading to doped ZnO at different ratios depending on the impregnation time. This doping results in a p-type conductive structure and we show that ZnO:Sb nanobranched fi lms can be successfully used as piezoelectric nanogenerators, while the presence of ferro electricity, together with a nonzero spontaneous polarization, is found to give rise to the ferroelectric-photovoltaic effect, [ 11 ] which is here reported for the fi rst time for a ZnObased nanomaterial.The highly nanoporous morphology of the starting Zn layer is shown in Figure S1 (Supporting Information). We take advantage of such a high porous volume and exposed surface area to succeed in the optimal impregnation of the Zn materials with the Sb-precursor solution. Figure 1 a shows the surface morphology of pristine ZnO sample, after calcination of Zn grown on a fl uorine-doped tin oxide (FTO)/glass substrate, and considered the reference sample of this work. The surface is mainly formed by elongated and branched nanostructures, giving rise to a nanoporous network (surface area 14 m 2 g −1 , pore volume 0.095 cm 3 g −1 ). [ 7b ] The presence of a similar highly porous and nanobranched morphology (with a pore volume variation of about ±5% with respect to pristine ZnO fi lm) is also visible in the ZnO:Sb fi lms (Figure 1 b,c) and it is found to be independent from the impregnation time and not signifi cantly altered by doping and thermal processes. Further insight into the morphology of the nanoporous fi lms is given by high-resolution transmission electron microscopy (HRTEM) images (from Figure 1 d-f), showing that the nanobranches are actually constituted by grains smaller than 50 nm for both the pristine and the impregnated samples. Moreover, it can be inferred from HRTEM and fast Fourier transform (FFT) image processing that the grains are single crystals with hexagonal Wurtzite ZnO nanomaterials are widely investigated thanks to the copresence of several unique physical properties like their semiconducting and piezoelectric behaviors. Among all the different morphologies, high-surface area nanostructures are of great interest, such as ZnO n...

Sn-decorated Cu (Cu-Sn) electrodes were proposed as an alternative to Ag-and Au-based electrocatalysts for the selective reduction of CO 2 to CO. Here we demonstrate that selectivity does not only depend on catalyst surface composition, but is strongly affected by the electrode morphology. At current densities above 10 mA•cm -2 , we find that morphology can control the CO 2 reduction pathways to CO and other products, including the competing H 2 evolution, on the Cu-Sn surface. An electrode design with dendritic morphological features yields the highest CO partial current density of 11.5 mA•cm -2 at -1.1 V vs. RHE, avoiding the significant loss of CO selectivity observed for an electrode with less sharp, rounder morphological features. Efficient CO 2 mass transport to the catalyst surface and a high local CO 2 concentration, promoted by the dendritic structure, stabilize the Cu-SnO overlayer, suppress the competing H 2 evolution reaction, and maintain CO selectivity above 85% over a wide potential range.

Herein, we present the production of dualatom (B and N)-codoped carbon nano-onions (BN-CNOs) by a standard annealing method. The proposed codoping approach is efficient to introduce both heteroatoms in the graphitic skeleton, as revealed by several characterization techniques, and suitable for a low-cost mass production of Cbased catalysts. The activity of the CNO-based electrocatalysts toward oxygen reduction reaction has been investigated in alkaline media, showing comparable catalytic performance, higher long-term stability (retaining 98.7% of the initial current over 3 h of testing), and excellent immunity toward methanol crossover compared to the standard Pt/Cbased catalysts. Our findings confirm that B/N-codoped CNOs are promising candidates to efficiently catalyze the oxygen reduction in energy devices.