The electrochemical CO₂ reduction reaction (CO₂RR) into carbon-based fuels provides a promising strategy to mitigate the CO₂ emission and promotes the utilization of renewable energy.

The Cn (n≥2) liquid products are desirable because of their high energy densities and ease of storage. However, manipulation of C-C coupling pathway remains a challenge due to the limited mechanistic understanding.

Recently, a research group led by Profs. ZHANG Tao and HUANG Yanqiang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has developed a Sn-based tandem electrocatalyst (SnS₂@Sn₁-O3G), which could reproducibly yield ethanol with a Faradaic efficiency of up to 82.5% at -0.9 V_RHE and a geometric current density of 17.8 mA/cm².

The study was published in Nature Energy on Oct. 30.

The researchers fabricated the SnS₂@Sn₁-O3G through solvothermal reaction of SnBr₂ and thiourea on a three-dimensional carbon foam. The electrocatalyst comprised SnS₂ nanosheets and atomically dispersed Sn atoms (Sn₁-O3G).

Mechanistic study showed that this Sn₁-O3G could respectively adsorb *CHO and *CO(OH) intermediates, therefore promoting C-C bond formation through an unprecedented formyl-bicarbonate coupling pathway.

Moreover, by using isotopically labelled reactants, the researchers traced the pathway of the C atoms in the final C2 product formed over the catalyst of Sn₁-O3G. This analysis suggested that the methyl C in the product comes from formic acid whereas the methylene C was from CO₂.

"Our study provides an alternative platform for C–C bond formation for ethanol synthesis and offers a strategy for manipulating CO₂ reduction pathways towards desired products," said Prof. HUANG.

This work was supported by the National Natural Science Foundation of China and CAS Project for Young Scientists in Basic Research.