Aziridine functionalized carbon nanotubes as highly efficient electrocatalysts for the selective CO2 reduction to CO

The steady state increase of CO2 levels in the atmosphere as a result of main anthropic activities is directly linked to climate change, leading to, for example, erratic weather patterns and rising ocean temperatures. Multiple approaches need to be implemented to curb with these phenomena, including carbon sequestration, electrification of the transportation sector and switching from the use of fossil fuels to renewable energy. One interesting method to mitigate CO2 impact while providing a means of mass energy storage, is the electrochemical reduction of CO2 into chemicals and fuels, which can be stored and used on demand. However, electrocatalysts for the CO2 conversion into products, such as CO, formic acid, methanol, and small hydrocarbons, still suffer of moderate productivity and/or poor selectivity. To date, Ag and Au-based electrocatalysts exhibit the best performance for the conversion of CO2 to CO although, from a sustainable viewpoint, metal-free systems have recently emerged as highly attractive candidates to replace metal-based systems in the process. Relatively few examples of metal-free catalysts for CO2 reduction exist, most of them raising from the class of light-heterodoped carbon nanomaterials (CNMs). In particular, a series N-doped systems (N-CNMs) have been investigated, although the role of nitrogen doping and its configuration as "catalytically active species" in the process still remain controversial. Recent findings from our group have demonstrated how a tight control of the surface properties of carbon-based nanomaterials can be conveniently achieved by chemical functionalization of their outer surface with tailored Ncontaining heterocycles. The chemical approach allows for a fine control of N-dopants in terms of N-configuration and electronic charge distribution at the heterocycles, and it offers a unique tool for the in-depth comprehension of the role of specific N-functionalities in the activation of small molecules and their subsequent (electrochemical) conversion. In this contribution we discuss the chemical decoration of MWCNTs with NH-aziridine functionalities (MW@NAz) and their application as highly efficient and selective metal-free electrocatalysts for CO2 reduction into CO.