Residence Time Distribution of Solid Particles in a High-Aspect Ratio Multiple-Impeller Stirred Vessel

Despite its importance, experimental information on the Residence Time Distribution (RTD) of solid particles in continuous-flow stirred vessels is still scant. In this work, experimental data on particle RTD in a high-aspect-ratio vessel stirred by three equally-spaced Rushton turbines, was obtained by means of a special technique named Twin System Approach (TSA). Quite surprisingly, results indicate that, among the various possibilities that could have been devised (e.g. 6, or 3, or 1 ideal tanks in series), the flow model closest to reality for the particle phase, at least in the experimental range here investigated, is that of a single perfectly stirred vessel

Inkjet printed doped polyaniline: navigating through physics and chemistry for the next generation devices

Innovative benzidine-free PANI-based inks for electrically conducive inkjet printed devices were developed and tested and the results compared with those obtained by traditional PANI. NMR investigations evidenced the presence of quinones and phenolic groups on the backbone of the innovative PANIs that are thought being responsible for the higher solubility in DMSO. A mechanism of reaction was proposed. The numerous characterizations (NMR, UV-Vis, FTIR, XPS and electrical investigations) allowed to compare protonation level, doping level, valence band maximum for both the type of PANI. The correlation among structural properties, printability, conductivity and solubility was discussed

Li+ Insertion in Nanostructured TiO2 for Energy Storage

Nanostructured materials possess unique physical-chemical characteristics and have attracted much attention, among others, in the field of energy conversion and storage devices, for the possibility to exploit both their bulk and surface properties, enabling enhanced electron and ion transport, fast diffusion of electrolytes, and consequently high efficiency in the electrochemical processes. In particular, titanium dioxide received great attention, both in the form of amorphous or crystalline material for these applications, due to the large variety of nanostructures in which it can be obtained. In this paper, a comparison of the performance of titanium dioxide prepared through the oxidation of Ti foils in hydrogen peroxide is reported. In particular, two thermal treatments have been compared. One, at 150 °C in Ar, which serves to remove the residual hydrogen peroxide, and the second, at 450 °C in air. The material, after the treatment at 150 °C, results to be not stoichiometric and amorphous, while the treatment at 450 °C provide TiO2 in the anatase form. It turns out that not-stoichiometric TiO2 results to be a highly stable material, being a promising candidate for applications as high power Li-ion batteries, while the anatase TiO2 shows lower cyclability, but it is still promising for energy-storage devices

Exploring nature-behaviour relationship of carbon black materials for potassium-ion battery electrodes

An essential component of a working electrode is the conductive additive: whether it is used in very low amounts or constitutes the conductive matrix, its electrochemical response is not negligible. Commercially diffused carbon black species (i.e., Super P, Super C65, and Super C45) still lack an in-depth electrochemical characterisation in the emerging field of potassium-ion battery systems, which are on the way towards large-scale stationary storage application. Thus, this work aims to provide strong tools to discriminate their active role in such secondary cells. First, the effect of their pseudo-amorphous structure on the storage mechanism of potassium ions, which tend mainly to adsorb on their surface rather than intercalate within graphene layers, leading to a pseudocapacitive response, is discussed. Then, Dunn’s and Trasatti’s methods are considered to identify the potential ranges in which surface-dominated reactions occur, quantifying their weight at the same time. This observation is surely linked with surface properties and exposed functional groups; thus, X-ray photoelectron spectroscopy is exploited to correlate electrochemical features with both pristine and cycled surfaces of the carbon black species

Standardization of Cu2O nanocubes synthesis: Role of precipitation process parameters on physico-chemical and photo-electrocatalytic properties

A facile, reproducible, and scalable wet precipitation method was optimized to synthetise Cu2O nanocubes with tuneable morphology and photocatalytic properties. The synthesis process was standardized by controlling the flow rate of addition of the reducing agent. This allowed to control the Cu2O crystallites size, which decreased from 60 nm to 30 nm by increasing the L-ascorbic acid flow rate, while maintaining a high yield (ranging from 87% to 97%) and reproducibility, as confirmed by X-Ray diffraction, scanning electron microscopy, and X-Ray photoelectron spectroscopy analyses. Moreover, the role of the synthesis conditions on the Cu2O nanocubes specific surface area and electrochemical surface area (ECSA) were investigated and correlated to their photo-electrocatalytic activity for the reduction of water and CO2 under ambient conditions, on electrodes made by air brushing. Decreasing of the Cu2O crystallites size enhanced the photo-electrocatalytic activity most probably due to a superior surface area, ECSA and an optimum valence and conduction band positions, which improves the charge transfer properties of the photocatalyst. The here proposed methodology and outcomes are very promising for the scale-up of the precipitation synthesis, not only of Cu2O but also of other nanostructured metal oxides to be exploited as photo-catalysts for environmental and energy applications

CuZnAl-oxide nanopyramidal mesoporous materials for the electrocatalytic CO2 reduction to syngas: Tuning of H2/CO ratio

Inspired by the knowledge of the thermocatalytic CO2 reduction process, novel nanocrystalline CuZnAl-oxide based catalysts with pyramidal mesoporous structures are here proposed for the CO2 electrochemical reduction under ambient conditions. The XPS analyses revealed that the co-presence of ZnO and Al2O3 into the Cu-based catalyst stabilize the CuO crystalline structure and introduce basic sites on the ternary as-synthesized catalyst. In contrast, the as-prepared CuZn-and Cu-based materials contain a higher amount of superficial Cu0 and Cu1+ species. The CuZnAl-catalyst exhibited enhanced catalytic performance for the CO and H2 production, reaching a Faradaic efficiency (FE) towards syngas of almost 95% at −0.89 V vs. RHE and a remarkable current density of up to 90 mA cm−2 for the CO2 reduction at −2.4 V vs. RHE. The physico-chemical characterizations confirmed that the pyramidal mesoporous structure of this material, which is constituted by a high pore volume and small CuO crystals, plays a fundamental role in its low diffusional mass-transfer resistance. The CO-productivity on the CuZnAl-catalyst increased at more negative applied potentials, leading to the production of syngas with a tunable H2/CO ratio (from 2 to 7), depending on the applied potential. These results pave the way to substitute state-of-the-art noble metals (e.g., Ag, Au) with this abundant and cost-effective catalyst to produce syngas. Moreover, the post-reaction analyses demonstrated the stabilization of Cu2O species, avoiding its complete reduction to Cu0 under the CO2 electroreduction conditions