Rosalba Passalacqua

Synthesis of solar fuels by a novel photoelectrocatalytic approach

The characteristics of nanostructured (a) TiO2 thin films (based on an ordered array of titania nanotubes) and their performances as photoanode in H2 production by water splitting or photoreforming of ethanol (in liquid or gas phase) and (b) carbon-nanotube based electrodes for the gas-phase reduction of CO2 to liquid fuels (mainly isopropanol) are discussed together with their application for the design of a novel photoelectrocatalytic approach for the synthesis of solar fuels.

Recent advances in luminescent polymetallic dendrimers containing the 2,3-bis(2′-pyridyl)pyrazine bridging ligand

Abstract Some new developments in the area of metal-based light-harvesting dendrimers based on the 2,3-bis(2′-pyridyl)pyrazine bridging ligand are presented, with particular regard to unidirectional energy transfer, enhanced light absorption, coupling dendritic structures with electron donors, and measurement of some of the ultra-fast processes occurring in this class of compounds.

H2 production by selective photo-dehydrogenation of ethanol in gas and liquid phase on CuOx/TiO2 nanocomposites

CuOx/TiO2 nanocomposites prepared by copper photodeposition (1.0 and 2.5 wt% copper loading) on TiO2 (synthesized by three different routes) are studied in the ethanol photo-dehydrogenation in gas- and liquid-phase operations, and characterized in terms of surface area, phase composition by XRD, morphology and copper-oxide nanoparticle size distribution, and copper species by UV-visible diffuse reflectance spectroscopy. Cu2+ ions partially enter into the titania structure leading to the creation of oxygen vacancies responsible for the shift in the band gap, but also the creation of traps for photogenerated holes and electrons. While the band gap shifts to lower energies with the copper content, a maximum photocatalytic activity is shown for the intermediate copper loading. Gas-phase operations allow a higher H2 productivity with respect to liquid-phase operations, and especially a higher selectivity (about 92–93%) to acetaldehyde. It is remarked that the route of photo-dehydrogenation of ethanol to H2 and acetaldehyde has an economic value about 3.0–3.5 times higher than the alternative route of photoreforming to produce H2. Gas-phase operations would be preferable for the photo-dehydrogenation of ethanol.

Oxide thin films based on ordered arrays of 1D nanostructure. A possible approach toward bridging material gap in catalysis.

TiO(2) thin films based on ordered arrays of 1D nanostructures (nanorods, nanotubes) are proposed as suitable model materials in studies for bridging material and complexity gap in catalysis. The samples were prepared by anodic oxidation of Ti foils. By changing the preparation conditions (pH, procedure of application of the potential), different types of 1D nanostructure and different characteristics of the ordered array of these 1D nanostructures could be obtained. This allows studying the effect of nanodimension and 3D nanoarchitecture on the characteristics and reactivity of these catalysts. It is also shown that TiO(2) thin films characterized by a well-ordered array of titania nanorod behave as photonic materials, thus showing unique properties of light harvesting efficiency.

The use of a solar photoelectrochemical reactor for sustainable production of energy

The conversion of solar energy into H2 via water splitting process is one of the most attractive ways to obtain clean and renewable energy. Unfortunately, the fast back reaction of recombination and high band gap needed to activate the photo-catalytic materials, strongly limit the performances in conventional slurry photo-reactors. In this context we present a new photoelectrochemical approach with a double-chamber reactor configuration for H2 production by water photo-electrolysis. The core of the photo-system is a membrane electrode assembly consisting of different layers which hold distinct two areas of the reactor where the generation of O2 and H2 occurs separately. Particular attention is given to the development, on a nano-scale level, of the materials to be used as photoanode and electrocathode: nanostructured TiO2 arrays and carbon nanotubes are used respectively in the form of thin films separated by a proton conductive membrane. Results showed 3.2 mmol h−1 g−1 of H2 evolution that is about one order of magnitude higher with respect to the activity obtained with conventional slurry photoreactors. Moreover, we present the opportunity to recycle CO2 back to liquid fuels by using the same photoelectrochemical approach.

Nanoscale Engineering in the Development of Photoelectrocatalytic Cells for Producing Solar Fuels

Engineering at the nanoscale level is a key aspect for the design of novel devices for sustainable energy to address the changeover from fossil fuels to renewable energy sources. This perspective paper, after introducing this topic, analyses the design and development of photoelectrocatalytic cells for producing solar fuels. To overcome limitations in the design of photoelectrocatalytic cells, a different one is proposed which eliminates the need of having a liquid electrolyte, where the electrodes are immersed. This cell design requires specific characteristics in the related electrodes/materials, which in combination with the different operation conditions, determine the need to investigate new fundamental aspects in the area. Some of the aspects analyzed regard (i) the role of nanostructure for visible light absorption of the semiconductor used, (ii) the need to use catalytic concepts (photoelectro-catalysis rather than photoelectro-chemistry), (iii) the mobility of charge carriers and relation with electrode characteristics, and (iv) space charge and Helmholtz layer.

Electrochemical behaviour of naked sub-nanometre sized copper clusters and effect of CO2

The study of the electrochemical behavior (in the presence of N2 or CO2) of size-controlled naked Cu5 and Cu20 nanoclusters, prepared using a combination of gas-phase cluster ion sources, mass spectrometry, and soft-landing techniques, evidences some relevant results regarding the redox behavior of these sub-nanometre sized copper particles and the effect of CO2 on them. Cu20 nanoclusters show anodic redox processes occurring at much lower potential with respect to Cu5 nanoclusters, which behave relatively similar to much larger Cu particles. However, Cu5 nanoclusters coordinate effectively CO2 (hydrogen carbonate) in solution, different from Cu20 nanoclusters and larger Cu particles. This effect, rather than the redox behavior, is apparently connected to the ability of Cu5 nanoclusters to reduce CO2 under cathodic conditions at low overpotential. Although preliminary, these results provide rather exciting indications on the possibility of realizing low overpotential electrocatalytic conversion of CO2.

Hydrogen Sensing Capability of Nanostructured Titania Films

The expected wide diffusion of hydrogen in the near future as clean fuel for PEM fuel cells and the potential danger of explosion consequent to the mixing of hydrogen with air, demands the introduction of reliable, robust and low cost hydrogen sensors. Titanium dioxide is a well known sensitive material for hydrogen sensors and the use of suitable titania nanostructures could be an efficient ways to promote the performances of these devices. Aim of this work is then aimed to synthesize and characterize different TiO2 nanostructures and investigate their capability in hydrogen sensing. Preliminary sensing tests here reported give helpful information for the development of MOS hydrogen sensors based on TiO2 nanostructures.