An efficient strategy to promote novel products on Cu-based catalysts

The electrochemical CO₂ reduction reaction (CO₂RR) to high-value-added products with two or more carbons (C₂₊ products) provides a viable strategy to close the anthropogenic carbon cycle and increase economic efficiency. Cu is generally considered to be the most effective active metal that exhibits notable catalytic performances for CO₂RR-to-C₂₊.

The rationally designed Cu-based electrocatalysts for CO₂RR have been extensively developed. However, direct conversion of CO₂ to C₂₊ products with high selectivity and efficiency is still a formidable challenge because of complex reaction networks. In particular, precise control of the products to a specific C₂₊ product with high selectivity has not been achieved.

So far, it still lacks the systematic guiding laws of catalysts surface regulation to improve C₂₊ productivity. This is needed to deeply get insight into the reaction mechanism of CO₂RR-to-C₂₊ on surface and/or interfaces. Thus, a comprehensive review covering achievements on surface state modification, which could influence the catalytic performances, for high-efficiency CO₂RR-to-C₂₊ is high desired.

Recently, a research team led by Prof. Qun Xu from Zhengzhou University, China, summarized the recent advances in surface engineering of Cu-based catalysts from four crucial steps in CO₂RR-to-C₂₊:

1. Inhibition of HER. Modification with organic molecules on Cu-based electrodes surface enhances the hydrophobicity for inhibiting HER. Another way for this goal is designing specific morphology of nanoneedle shape and hydrophobic porous structure for reducing the surface wettability.
2. CO₂ adsorption and activation. Cu-based catalysts supported by CO₂-capture materials can potentially form a local microenvironment with high CO₂ concentration. While, introducing halide ions can donate lone-electron pairs to the unoccupied orbital of CO₂ to facilitate its activation through the formation of the CO₂^•– radical. In addition, synergistic effect between Cu^δ+ and Cu⁰ in Cu surfaces is also efficient to activate CO₂.
3. CO formation and adsorption. The effective methods include addition of foreign component served as CO-generation sites and construction of specific structures with enhanced local electric-thermal fields. They can efficiently modulate the CO coverage, adsorption capacity and adsorption configurations for C−C coupling.
4. C−C coupling. This step can be promoted through constructing confinement structures, adding oxidation states, building defects, designing single-atom catalysts, and constructing heterojunction structures. Cu-based electrode with confinement structure can prolong retention times of intermediates.

Introduction of positive valence Cu sites, defects and heterojunction interfaces mainly modulate the adsorption behaviors of C₁ intermediates and lower the energy barrier of C–C coupling. The ligand groups in single-atom catalysts affect the C–C coupling path between different C₁ intermediates through modulating the coordination micro-environment of Cu sites.

In addition, this work gives insight into the reaction mechanism of CO₂RR by deeply understanding the relationship between surface properties of Cu-based catalysts and improved performances. Meanwhile, the current challenges and potential strategies of CO₂RR-to-C₂₊ are envisioned. The work was published in Chinese Journal of Catalysis.