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Engineering a hydrogen-bonding microenvironment to boost CO₂ electroreduction

Catalytic conversion of waste CO₂ into value-added fuels and chemicals offers unprecedented opportunities for both environmental protection and economic development. Electrocatalytic CO₂ reduction reaction (CO₂RR) has garnered significant attention for its ability to efficiently convert CO₂ into clean chemical energy under mild conditions. However, the relatively high energy barrier for *COOH intermediate formation often becomes the determining step in CO₂RR, significantly limiting reaction efficiency.

Inspired by enzyme catalysis, a team led by Prof. Jiang Hai-Long and Prof. Jiao Long from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) developed a novel strategy to stabilize *COOH intermediate and enhance electrochemical CO₂ reduction by constructing and modulating the hydrogen-bonding microenvironment around catalytic sites. Their work is in the Proceedings of the National Academy of Sciences.

In this work, the team co-grafted catalytically active Co(salen) units and proximal pyridyl-substituted alkyl carboxylic acids (X-PyC_n) onto Hf-based MOF nanosheets (MOFNs) via a post decoration route, affording Co&X-PyC_n/MOFNs (X = o, m or p representing the ortho-, meta-, or para- position of pyridine N relative to alkyl chain; n = 1 or 3 representing the carbon atom number of alkyl chains) materials.

The Co&X-PyC_n/MOFNs achieve precise control over the spatial positioning of the N atoms in pyridine groups relative to the Co(salen), which provides a novel and facile approach to microenvironment modulation around catalytic sites at atomic scale.

Among the catalysts, the optimized Co&p-PyC₃/MOFNs exhibits significantly enhanced catalytic activity and selectivity in electrochemical CO₂ reduction, superior to Co/MOFNs without pyridine unit and other Co&X-PyC_n/MOFNs counterparts.

Furthermore, the in situ reduction of pyridine to pyridinyl radical (PyrH•) is observed during electrochemical CO₂ reduction and the in situ formed PyrH• species are confirmed to be the real microenvironment around Co(salen) for enhanced performance.

Mechanism investigations reveal that PyrH• can collaborate with trifluoroethanol (TFE) molecules in electrolyte to stabilize the *COOH intermediate by generating *COOH···TFE···PyrH• triad intermediate via hydrogen-bonding interaction, greatly minimizing reaction energy barrier. This provides a clear picture on the working mode of microenvironment for performance optimization during the catalysis.

This work unambiguously demonstrates the significance of microenvironment modulation around catalytic sites for enhancing catalysis, paving a new way for understanding the mechanism in future catalysis studies.