Scientists at EPFL, ICIQ and TUM have built new hybrid materials based on molecular Fe porphyrins and Cu nanocubes that act in tandem for the electrocatalytic reduction of CO₂ to ethylene. The modular nature of this hybrid materials opens up facile and versatile routes towards the preparation of this type of hybrid materials that can further enhance the CO₂ reduction efficiency and selectivity.

The EU-funded LICROX project aims to develop a new type of photoelectrochemical cell (PEC) to transform sunlight, water and CO₂ into carbon-based molecules capable of storing chemical energy. The LICROX design for the PEC combines different research layers to achieve the conversion of sunlight, water and CO₂ into carbon-based molecules. Scientists at EPFL, TUM and ICIQ came together to develop a tandem catalytic system composed of a molecular catalyst, able to transform CO₂ into CO, and copper nanocubes that allow carbon-carbon (C-C) coupling.

The electrochemical CO₂ reduction reaction (CO₂RR) offers the opportunity to convert CO₂ into fuels and chemical feedstocks while mitigating anthropogenic CO₂ emissions and storing renewable energy. Multi-carbon (C₂₊) compounds (e.g., ethylene, ethanol, propanol) are among the most attractive CO₂RR products owing to their commercial value and high energy densities. However, optimizing the activity of CO₂RR electrocatalysts towards one particular product remains a crucial challenge that is not trivial to address because multiple intermediates are involved in the CO₂ to C₂₊ conversion pathway.

“Molecular Fe Porphyrins complexes constitute a tunable class of robust and extremely active CO₂ reduction catalysts for the formation of CO, in a highly selective manner” says Prof. Antoni Llobet, ICIQ Group Leader, LICROX Coordinator

Copper-based materials have been widely employed as CO₂RR catalysts due to their unique ability to facilitate the electroreduction of CO₂ beyond two electron reduction products. In particular, copper nanocubes are particularly selective for C₂₊ .

In this recent publication, Buonsanti, Sharp and Llobet teams have worked together coupling the molecular Fe porphyrins and the copper nanocubes to further enhance the intrinsic selectivity of the copper towards multi-carbon products at lower overpotentials. This work demonstrates that the CO generated by the molecular catalyst is transferred to the copper when it is further converted in a so-called tandem scheme. A 22-times increase in ethylene selectivity and 100 millivolts positive shift of the onset potential was observed compared to the nanocubes alone.

Schematic representation of the proposed mechanism for ethylene (C₂H₄) promotion in Cu_cub/Fe-Por tandem catalysts.

 

This article is part of the 2022 Chemical Science HOT Article Collection.

“These results encourage further studies on the design of hybrid materials including molecules and well-defined nanoparticles as a promising strategy to create more active and selective catalysts for the electrochemical CO₂ reduction reaction” says Prof. Raffaella Buonsanti, Associate Professor at EPFL, LICROX partner.

Reference article:

Min Wang, Vasilis Nikolaou, Anna Louidice, Ian D. Sharp, Antoni Llobet, Raffaella Buonsanti. Tandem electrocatalytic CO₂ reduction with Fe-porphyrins and Cu nanocubes enhances ethylene production. Chem. Sci, 2022, 13, 12673.

https://doi.org/10.1039/D2SC04794B

This project has received funding from the European Union’s Horizon 2020 research and innovation Programme under the grant agreement No. 951843.