Li/air batteries: new nanostructured materials for oxygen electrodes
The main aim of the work consists in the development of efficient cathode for lithium-air batteries to be used for future generation electric vehicles (EVs). In this sense, the great advantages in adopting lithium-air batteries is their impressive energy and power density and specific energy bound to a high operative voltage (more than 2V).
The chemical phenomena at the basis of lithium-air batteries technology is still far to be completely understood. This in turn means that the principles on which the research of materials constituting all cell main components are still not completely known.
This leads to two main issues: on one side, there is an urgent need of understanding the phenomena occurring at the electrode surface and, on the other, finding suitable materials for optimizing the reaction kinetics and the cell durability while keeping the costs low.
Lithium-air batteries represent nowadays one of the main challenges in electrochemistry. This is mainly due to the intrinsic complexity of the system and to the difficulty in performing both in situ and ex-situ analysis on the cell components needed to highlight the reaction intermediates/products. In this context the main purpose of this research was aimed to characterize transition metal oxide as potential electrocatalysts. In particular, electrolytic MnO2 was chosen as the reference system and starting from this material we synthesized MnO2 via sol-gel route, that allows for a fine control of particle morphology and chemical surface speciation. The nominal composition of the electrocatalysts and the typical operative parameters of the sol-gel method have been modulated. In particular, different precursors, i.e. inorganic or organic (metal alkoxides) compounds, have been used and different synthetic conditions, by varying e.g. water/alkoxide and water/solvent ratios, hydrolysis temperature and time, solvent removal procedure, calcination temperature, have been adopted. This allows to prepare nanopowders showing, on one side, identical nominal composition, but on the other side largely different physical features between one another; the characterization of these materials will provide the scientific basis for designing more efficient electrocatalysts. We decided also to dope the MnO2 nanoparticles in order to increase the electronic conductivity, using Ag and Sn. The scope is to prepare a composite cathode with the possibility to limit the material pore choking at the positive pole by lithium oxides, with the aim to increase the specific capacity of the battery, which decreases with the charging/discharging cycles due to the isolation of the electrode surface from the electron transfer process.
Multiphase matrices based on nanostructured metal oxides for oxygen reduction electrodes in direct alcohol fuel cells (DAFC)
The research is centred on the synthesis, characterization and development of multiphase nanostructured systems for the preparation of electrodes (cathodes) for oxygen reduction, to be used in direct alcohol fuel cells, with specific reference to the “alkaline” type, i.e. those adopting a polymeric anion exchanger electrolyte. The recent improvement of anion membranes, that allow for alkaline operating conditions with predictable advantages in terms of energy yield, makes the development of alkaline DAFCs competitive with the acid ones. The research deals with the characterization of metal (Ag/C) synthetized by the wet method and metal oxides synthetized by the sol-gel technique (IrO2-SnO2), as possible cathode materials in alkaline DAFCs. The investigation is carried out using potentiodynamic techniques and the Rotating Ring Disk Electrode (RRDE) as support. The use of RRDE allow to obtain important information about the reaction mechanism since it is possible quantify inter alia the amount of hydrogen peroxide produced in a broad range of potentials. A comparison study of different electrode materials in term of kinetic current, amount of hydrogen peroxide produced and the potential of the beginning the ORR was also carried out during this year.
Energy conversion and storage; environmental recovery and waste water treatments
This topic is focused on to the development of nanostructured multifunctional materials. These particular materials are, in fact, the core of modern electrochemical systems; their electrocatalytic and functional properties can be modulated through the appropriate design, synthesis and application to the wide areas of green chemistry and energy conversion. In this context, the research interest has been devoted to the electro-synthesis of silver nanoparticles (Ag-NP) for preparation of nanostructured multifunctional materials. These compounds can be used in applications for the rational use of energy (e.g. for the optimization of new energy device as Li-Air battery) and in environmentally oriented processes (e.g. depollution processes). In particular Ag-NP were supported on a carbon matrix and used for the electrochemical dehalogenation of chlorinated organic compounds. The research interest was also focused on the preparation methodologies of the electrode material to improve the catalyst performance and to reduce the silver content at the cathode electrode; there is evidence that nano-structured particles exhibit better behaviour than massive silver while allowing a substantial reduction of Ag loading. The characterization of all materials has been conducted both in aqueous media, using a Cavity MicroElectrode (CME) with chloroform as model molecule, and in organic media using acetonitrile (ACN) as solvent with benzylchloride (BzCl)as molecule test. The particular attention for BzCl reduction is due to the recent new proposal for the reaction pathway that implies the formation sequence of silver-substrate/product adducts, starting from a weakly adsorbed benzyl chloride-Ag specie, followed by the strongly adsorbed benzyl radical-Ag and benzyl anion-Ag species. The last ultimately desorbing to give the final reaction products. In this context, has been studied the effect on voltammetric signal of the presence of small water amounts in ACN. The source of proton from water may affect the normal reaction pathway and change the electrode activity of the silver. This provokes significant variations in electrode currents and potentials even at very low water content, thus providing an internal diagnostic signal for the quality of the solvent and a study for a correct understanding of the effective catalytic power of silver-based materials. In summary, the electrocatalytic activity of Ag-NP, with a low silver loading (20 wt%), was confirmed by the CVs results of the CHCl3 and BzCl reduction. To date experimental data confirm the better performance of the silver nanoparticles, synthesized with different methodologies, in comparison with commercial silver catalysts.