Synthesis of Fe-filled Carbon Nanotubes for electrocatalytic reduction of CO2

Recently the carbon dioxide scenario is significantly changed evolving towards a new approach which considers the CO2 as a new valued resource and a business opportunity rather than a waste with a cost of disposal. In this frame CO2 electrocatalytic reduction back to liquid fuels represents a highly challenging process to i) close the CO2 cycle, ii) greatly increase carbon recycling and iii) reduce fossil fuel consumption. We report here a new approach to recycle CO2 to fuels in a gas-phase electrocatalytic cell by using a nanostructured carbon-based material with Fe as electrocatalyst. The investigated materials have a different degree of graphitization depending on the thermal post-treatment that commercial Carbon Nanotubes (CNTs) have undergone before to be filled with the metal. Selective filling of metal nanoparticles on CNTs is possible by using a simple incipient wetness impregnation technique followed by a selective washing on the basis of the difference in the surface tension between aqueous or organic impregnating solvents and CNTs surface. We demonstrate here that by reducing CO2 at 60°C and atmospheric pressure, it is possible to obtain high productivity also by using iron nanoparticles instead of noble metals. We observed, in fact, the formation of liquid fuels in particular of oxygenated C3 products that are easy recovered by condensation from the reactor outlet stream. The higher catalytic activity may be attributed to the existence of a nanoconfinement effect, related to the use of nanocavities, which significantly alters the reactant partial pressure inside the tube thus increasing the local concentration of CO2 and coordinating the consecutive formation of C-C bond. The results obtained from these experiments with nanostructured C-based electrocathodes (based on the concept of nanoconfinement) are very promising in the final attempt to develop a novel solar photoelectrocatalytic (PEC) reactor which integrates the photoanode (for water dissociation) to the electrocatalyst (for CO2 reduction) resembling the PEM fuel cells technology. This full process therefore represents a highly challenging approach to mimic photosynthesis for the production of solar fuels via chemical recycling of CO2.