Aziridine Functionalized Carbon Nanotubes as Highly Efficient Electrocatalysts for the Selective CO2 Reduction to CO

The constant increase of CO2 levels in the atmosphere as a result of anthropic activities is directly linked to climate changes and global warming issues.[1] Multiple approaches need to be implemented to curb with these phenomena, including carbon sequestration, electrification of the transportation sector and switching from fossil fuels to renewable energy. One of the most promising methods to mitigate CO2 impact while providing a means of mass energy storage, is the electrochemical reduction of CO2 (CO2RR) into chemicals and fuels of added value.[2] However, electrocatalysts for 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, but they irremediably suffer of poor sustainability. On this ground, metal-free systems have recently emerged as highly attractive candidates to replace metal-based systems in the process. To date, relatively few examples of metal-free catalysts for CO2RR exist, most of them raising from the class of light-heterodoped carbon nanomaterials (CNMs). In particular, a series of N-doped systems have been investigated but the nature of active sites responsible for CO2RR remains highly controversial.[3] Recent findings from some of us have demonstrated how a fine tuning of the surface properties of CNMs can be conveniently achieved by chemical functionalization of their outer surface with tailored N-containing heterocycles.[4] The chemical approach allows a precise control of N-dopants in terms of N-configuration and electronic charge distribution, offering a unique tool for the comprehension of the role of specific N-functionalities in the activation of small molecules. In this contribution we report 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. With a Faradaic efficiency (FE) close to 90% at -1.2V (vs. Ag/AgCl/KClsat.) and productivity as high as 48 NLCOh-1gN-1, MW@NAz ranks among the metal-free systems with the highest performance reported so far providing, at the same time, a privileged view-point on the structure-reactivity relationship of light-heterodoped CNMs and a powerful tool to the unambiguous comprehension of the underlying CO2RR mechanism.[5]