Silver and Copper Nitride Cooperate for CO Electroreduction to Propanol.

The need of carbon sources for the chemical industry, alternative to fossil sources, has pointed to CO2 as a possible feedstock. While CO2 electroreduction (CO2 R) allows production of interesting organic compounds, it suffers from large carbon losses, mainly due to carbonate formation. This is why, quite recently, tandem CO2 R, a two-step process, with first CO2 R to CO using a solid oxide electrolysis cell followed by CO electroreduction (COR), has been considered, since no carbon is lost as carbonate in either step. Here we report a novel copper-based catalyst, silver-doped copper nitride, with record selectivity for formation of propanol (Faradaic efficiency: 45 %), an industrially relevant compound, from CO electroreduction in gas-fed flow cells. Selective propanol formation occurs at metallic copper atoms derived from copper nitride and is promoted by silver doping as shown experimentally and computationally. In addition, the selectivity for C2+ liquid products (Faradaic efficiency: 80 %) is among the highest reported so far. These findings open new perspectives regarding the design of catalysts for production of C3 compounds from CO2 .

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.

Molecular Inhibition for Selective CO2 Conversion.

Electrochemical CO2 reduction presents a sustainable route to the production of chemicals and fuels. Achieving a narrow product distribution with heterogeneous Cu catalysts is challenging and conventional material modifications offer limited control over selectivity. Here, we show that surface-immobilised molecular species can act as inhibitors for specific carbon products to provide rational control over product distributions. Combined experimental and computational results showed that anchoring of a thiol-functionalised pyridine on Cu destabilises a surface-bound reaction intermediate to energetically block a CO-producing pathway, thereby favouring formate production. The nitrogen atom was shown to be essential to the inhibition mechanism. The ability of molecules to control selectivity through inhibition of specific reaction pathways offers a unique approach to rationally modify heterogeneous catalysts.

Electrochemical CO2 reduction on Cu single atom catalyst and Cu nanoclusters: an ab initio approach.

The electrochemical CO2 reduction presents a sustainable route to the production of chemicals such as ethylene or ethanol, however the design of selective catalysts is still challenging. The use of single site copper nitrogen doped carbon materials with porphyrin-like Cu graphene structures have shown a significant improvement towards the production of multi carbon products, particularly ethanol. Nonetheless, during reaction the porphyrin like Cu sites transiently convert into metallic copper nanoclusters in a reversible process, making difficult to understand the actual role of each phase. Here, we present a computational study, where adequate structural models to describe the experimentally determined phases of the single atom catalyst (Cu-N-C material) have been constructed. Moreover, the electrochemical reduction of CO2 to ethanol and ethylene has been addressed via periodic DFT calculations on each of the systems. On the basis of the computed free energies of reaction, it was found that the Cu nanoclusters exhibit a superior performance for the CO reduction in comparison with the single site. Moreover, they possess a high activity towards the production of ethanol, suggesting them as the active phase responsible for the catalytic performance of the studied material.