CO2 Electroreduction in Water with a Heterogenized C-Substituted Nickel Cyclam Catalyst.

Molecular catalysis for selective CO2 electroreduction into CO can be achieved with a variety of metal complexes. Their immobilization on cathodes is required for their practical implementation in electrolytic cells and can benefit from the advantages of a solid material such as easy separation of products and catalysts, efficient electron transfer to the catalyst, and high stability. However, this approach remains insufficiently explored up to now. Here, using an appropriate and original modification of the cyclam ligand, we report a novel [Ni(cyclam)]2+ complex which can be immobilized on carbon nanotubes. This material, once deposited on a gas diffusion layer, provides a novel electrode which is remarkably selective for CO2 electroreduction to CO, not only in organic solvents but also, more remarkably, in water, with faradic efficiencies for CO larger than 90% and current densities of 5-10 mA cm-2 during controlled potential electrolysis in H-cells.

Functionalization of Carbon Nanotubes with Nickel Cyclam for the Electrochemical Reduction of CO2.

The exploitation of molecular catalysts for CO2 electrolysis requires their immobilization on the cathode of the electrolyzer. As an illustration of this approach, a Ni-cyclam complex with a cyclam derivative functionalized with a pyrene moiety is synthesized, found to be a selective catalyst for CO2 electroreduction to CO, and immobilized on a carbon nanotube-coated gas diffusion electrode by using a noncovalent binding strategy. The as-prepared electrode is efficient, selective, and robust for electrocatalytic reduction of CO2 to CO. Very high turnover numbers (ca. 61460) and turnover frequencies (ca. 4.27 s-1 ) are enabled by the novel electrode material in organic solvent-water mixtures saturated with CO2 . This material provides an interesting platform for further improvement.

Electroreduction of CO2 on Single-Site Copper-Nitrogen-Doped Carbon Material: Selective Formation of Ethanol and Reversible Restructuration of the Metal Sites.

It is generally believed that CO2 electroreduction to multi-carbon products such as ethanol or ethylene may be catalyzed with significant yield only on metallic copper surfaces, implying large ensembles of copper atoms. Here, we report on an inexpensive Cu-N-C material prepared via a simple pyrolytic route that exclusively feature single copper atoms with a CuN4 coordination environment, atomically dispersed in a nitrogen-doped conductive carbon matrix. This material achieves aqueous CO2 electroreduction to ethanol at a Faradaic yield of 55 % under optimized conditions (electrolyte: 0.1 m CsHCO3 , potential: -1.2 V vs. RHE and gas-phase recycling set up), as well as CO electroreduction to C2 -products (ethanol and ethylene) with a Faradaic yield of 80 %. During electrolysis the isolated sites transiently convert into metallic copper nanoparticles, as shown by operando XAS analysis, which are likely to be the catalytically active species. Remarkably, this process is reversible and the initial material is recovered intact after electrolysis.