CO2Enrich - Carbon dioxide conversion into energy-rich molecules with tailored catalysts

Abstract:

The use of fossil fuels, contributing to the large majority of all CO2 emissions, is the main cause of the greenhouse effect and dramatic climate changes. The ambitious target of zeroing CO2 emissions by 2050 will not be sufficient to slow down the global warming. In order to reverse this trend, it is now imperative not only to reduce our fossil fuels consumption, but also to develop sustainable technologies to remove CO2 from the atmosphere (negative emissions). In nature, CO2 is converted into carbohydrates and O2 by green plants utilizing the abundant energy from the sun through photosynthesis, with an efficiency lower than 1%. We urgently need to develop artificial approaches to reduce carbon dioxide, mimicking the natural photosynthesis process, with a much higher conversion efficiency and employing renewable energy. Indeed, carbon dioxide, though being an extremely stable molecule, can be re-used as feedstock source or as a fuel source. Instead of being a potential origin of damage for our planet, it can be envisaged as a cheap, ubiquitous and abundant carbon feedstock of valuable compounds that can also replace fossil fuels. By this way the carbon cycle would be closed and the equilibrium between energy rich organic and inorganic carbon would be restored.

The ideal artificial photosynthesis process would involve the use of sunlight to directly convert carbon dioxide into energy rich molecules, a process which is rather difficult because CO2 reduction can efficiently occur only through a multi-electron transfer process, whereas light absorption is a one-photon process that results in one electron charge separation. Much more appealing is the electrochemical reduction of CO₂, which allows to transform CO₂ from concentrated sources (industrial plants) into value-added chemicals (CO, formic acid, methane, methanol, ethanol, ethylene), especially if coupled with now mature technologies exploiting renewable energy sources to produce electricity at relatively low cost, such as photovoltaics and wind energy. Intermittent renewable energy can be stored by this way under the form of chemical bonds with high volumetric and gravimetric energy density, at the same time offering a solution towards building a sustainable carbon-neutral economy.

In the present project we propose to reutilize CO₂ from the atmosphere electrocatalytically, through the carbon dioxide reduction reaction (CO2RR), employing electricity from renewable sources. The main focus is on the development of catalytic materials able to selectively produce liquid, easily transportable energy-rich chemicals, trying to avoid any expensive separation of CO2 reduction products. Innovative metal-based composite materials will thus be synthesized, fully characterized according to complementary techniques, and tested both in a lab scale reactor and in a photovoltaics-powered electrochemical cell. Computational studies on these novel electrocatalytic materials are foreseen to guide the tuning of their composition and unveil the reaction paths and the involved intermediate species, in order to gain a better understanding of the optimal materials design in relation to the expected or targeted product selectivity. The structural, morphological and electrochemical characterization of the materials will be employed to establish relationships between the catalyst composition and structure, and the electrochemical activity, indispensable, together with the results of modeling the reaction mechanism, to develop innovative electrocatalytic materials with properties tailored for high selectivity toward a specific carbon dioxide reduction product (e.g. ethanol). The newly produced composite materials will be tested in a modern flow cell system that will allow to obtain products at high rates and with high stability.

The project will be carried out by three University groups, the University of Milano (UniMi) Leading unit, the University of Milano-Bicocca (UniMiB) and the University of Ferrara (UniFe), with well-defined tasks. The synthesis, characterization and preliminary testing of the electrocatalytic materials will be carried out mainly by the UniMi group, in collaboration with the UniFe group, while reaction modeling and structure design will be performed by UniMiB. Besides in the preparation of specific electrocatalysts, UniFe will be mainly involved in the flow cell design, optimization and prototype validation, and in the testing of the optimized electrocatalytic materials. Thus, the project will cover various aspects of selective CO2RR, from the fundamental understanding, through first principles calculations of the electronic structure of the electrocatalytic materials, to their synthesis and thorough structural characterization, to electrocatalytic tests at the lab scale, up to the design and realization of a working sun-powered prototype cell for carbon dioxide conversion into valuable chemicals.