Tailoring N-decorated Carbon Nanotubes as Highly Efficient Electrocatalysts for the Selective CO2 Reduction to CO

The electrocatalytic reduction of CO2 into chemicals and/or energy vectors of added value is a highly challenging approach to cope with the growing global energy demand while limiting the impact of atmospheric CO2 levels on climate changes and related global warming issues. To date, large efforts in this area have been focused on the development of metal-containing catalysts and in particular precious and noble metals (i.e. Pd, Au, Ag, and Cu) that however suffer of poor sustainability both from an economical and an environmental viewpoint. Relatively few examples of metal-free catalysts for CO2 electroreduction have been developed up to now, most of them raising from the class of light-heterodoped carbon nanomaterials. In particular, a series of N-doped carbon-based systems have been investigated but the nature of active sites responsible for CO2 electroreduction still remains highly controversial. Recent findings from some of us have demonstrated how a fine tuning of the surface properties of carbon nanomaterials can be conveniently achieved by chemical functionalization of their outer surface with tailored N-containing heterocycles. The chemical approach allows a precise control of N-dopants in terms of N-configuration and electronic charge distribution, offering a unique tool to the comprehension of the role played by specific N-functionalities in the activation of small molecules. In this contribution we report the chemical decoration of MWCNTs with NH-aziridine groups (MW@NAz) and their application as highly efficient and selective metal-free electrocatalysts for CO2 reduction to CO. With a Faradaic efficiency (FE) close to 90 % at -1.2 V (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. At the same time, a privileged view-point on the structure-reactivity relationship of light-heterodoped CNMs in the process is provided.