Newly developed electrosynthesis of Layered Double Hydroxides: application to sensing, energy storage and conversion

Layered Double hydroxides (LDHs) have been widely studied for their plethora of fascinating features and applications. The potentiostatic electrodeposition of LDHs has been extensively applied in the literature as a fast and direct method to substitute classical chemical routes. However, it does not usually allow for a fine control of the M(II)/M(III) ratio in the synthesized material and it is not suitable for large anions intercalation. Therefore, in this work a novel protocol has been proposed with the aim to overcome all these constraints using a method based on potentiodynamic synthesis. LDHs of controlled composition were prepared using different molar ratios of the trivalent to bivalent cations in the electrolytic solution ranging from 1:1 to 1:4. Moreover, we were able to produce electrochemically LDHs intercalated with carbon nanomaterials for the first time. A one-step procedure which contemporaneously allows for the Ni/Al-LDH synthesis, the reduction of graphene oxide (GO) and its intercalation inside the structure has been developed. The synthesised materials have been applied in several fields of interest. First of all, LDHs with a ratio 3:1 were exploited, and displayed good performances as catalysts for 5-(hydroxymethyl)furfural electro-oxidation, thus suggesting to carry out further investigation for applications in the field of industrial catalysis. The same materials, but with different metals ratios, were tested as catalysts for Oxygen Evolution Reaction, obtaining results comparable to LDHs synthesised by the classical co-precipitation method and also a better activity with respect to LDHs obtained by the potentiostatic approach. The composite material based on LDH and reduced graphene oxide was employed to fabricate a cathode of a hybrid supercapacitor coupled with an activated carbon anode. We can thus conclude that, to date, the potentiodynamic method has the greatest potential for the rapid synthesis of reproducible films of Co and Ni-based LDHs with controlled composition.

Polyaniline-based materials and nanocomposites: from energy storage to sensing applications

The research work described in this thesis concerns materials for both energy storage and sensoristics applications. Firstly, the synthesis and characterization of magnetite (Fe3O4) functionalyzed with [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS) capable to reduce the gold precursor chloroauric acid (HAuCl4) without the need of additional reducing or stabilising agents is described. These nanoparticles were tested to improve performances of symmetric capacitors based on polyaniline and graphite foil. Energy storage applications were investigated also during six months stay at EPFL University of Lausanne where an investigation about different tailored catalysts for Oxygen Evolution Reaction in a particular Redox Flow Battery was carried out. For what concerns sensing applications, new materials based on cellulose modified with polyaniline and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA) were synthesized, characterized and applied to monitor pressure, humidity, heart rate and lastly, bread fermentation in collaboration with the University of Fribourg and Zurich. The characterizations of all the materials investigated compriseed numerous techniques such as infrared attenuated total reflectance spectroscopy (IR-ATR), thermogravimetric analysis (TGA), scanning and transmission electron microscopy (SEM and TEM), alongside linear and cyclic voltammetry (LSV and CV), electrochemical impedance spectroscopy (EIS) and chronoamperometric analyses.

Chemical looping reforming from methane to syngas: investigation on CeO2 oxygen carrier lifetime and optimal process times

Emissions of CO2 are constantly growing since the beginning of industrial era. Interruption of the production of major emitters sectors (energy and agriculture) is not a viable way and reducing all the emission through carbon capture and storage (CCS) is not economically viable and little publicly accepted, therefore, it becomes fundamentals to take actions like retrofitting already developed infrastructure employing cleanest resources, modify the actual processes limiting the emissions, and reduce the emissions already present through direct air capture. The present thesis will deeply discuss the aspects mentioned in regard to syngas and hydrogen production since they have a central role in the market of energy and chemicals. Among the strategies discussed, greater emphasis is given to the application of looping technologies and to direct air capture processes, as they have been the main point of this work. Particularly, chemical looping methane reforming to syngas was studied with Aspen Plus thermodynamic simulations, thermogravimetric analysis characterization (TGA) and testing in a fixed bed reactor. The process was studied cyclically exploiting the redox properties of a Ce-based oxide oxygen carrier synthetized with a simple forming procedure. The two steps of the looping cycles were studied isothermally at 900 °C and 950° C with a mixture of 10 %CH4 in N2 and of 3% O2 in N2, for carrier reduction and oxidation, respectively. During the stay abroad, in collaboration with the EHT of Zurich, a CO2 capture process in presence of amine solid sorbents was investigated, studying the difference in the performance achievable with the use of contactors of different geometry. The process was studied at two concentrations (382 ppm CO2 in N2 and 5.62% CO2 in N2) and at different flow rates, to understand the dynamics of the adsorption process and to define the mass transfer limiting step.