Not noble metals/CNF as electrocatalysts for CO2 gaseous stream conversion to liquid fuels

The issues related to greenhouse gas emissions and depletion of fossil fuels are becoming the critical factors to be solved for the future of society. One of the most attractive solutions is to diminish the level of CO2 in the environment by converting it back to liquid fuels and other chemicals thus closing the CO2 cycle. In that point of view the carbon dioxide may be considered as a resource and a business opportunity rather than a waste with a cost of disposal. Therefore there is the need to develop advanced low-cost materials to be used efficiently in CO2 reduction processes for the production of long-carbon chain hydrocarbons (C>2). In this contribution we synthesized novel nano-carbon electrocatalysts doped with not noble metals and investigated their behaviour in gas phase operations. Our approach is quite different from the conventional reactors based on liquid phase operations: the photocatalytic side (anode) consists of a nanostructured TiO2-based thin film, where water is splitted using solar light to produce O2, protons and electrons. On the electrocatalytic side (cathode), based on C-based substrates, CO2 in the gas phase is converted using the protons and electrons coming from the photocatalytic side and passing through a selective protonic membrane (Nafion®) and a wire, respectively. Even though carbon black materials (i.e. Ketjen and Vulcan) allow to obtain good performances, a proper design of the cathodic electrode at a nanoscale level may overcome the typical critical issues related to the reaction kinetics, mass transport and electron mobility. We started from commercial carbon nanofibers (CNF) and doped their surface with Fe. A co-metal (Co, Cu) was also deposited in alloy or in bimetallic phase with respect to Fe, with the aim to control the process yield and selectivity. An important aspect to evaluate is the size distribution and dispersion of the metal particles on the surface of CNF, as well as their localization in the inner or outer walls of the CNF. The testing experiments were carried out in a homemade reactor and for simplicity the photo-generated current was simulated by applying a small bias between the electrodes (10 mA as resulting current). In this configuration the photo-anode was replaced by a compartment filled with an aqueous electrolyte solution which was used as source of protons.