Tailoring microenvironment for enhanced electrochemical CO₂ reduction on ultrathin tin oxide derived nanosheets

Electrocatalytic CO₂ reduction powered by renewable electricity has been considered as a promising approach for sustainable energy storage and chemicals production. Herein, ultrathin few-layer SnO₂ nanosheets exposed with (001) facets were synthesized and exhibited a rather broad potential window (0.8 V) for selective CO₂ conversion to formate. Both DFT calculations and operando spectroscopic characterizations were carried out to identify key intermediate *OCHO. Systematically tailoring microenvironment in the catalyst layer of gas diffusion electrode (GDE) indicate that both flexible Nafion and solid polytetrafluoroethylene (PTFE) nanoparticles are essential to create abundant and robust triple-phase boundaries (TPB) with more active sites, where CO₂ and H₂O meet at nanosheet surface to output a high formate partial current density of 380 mA·cm^-2 with the selectivity of 88.4%. Moreover, such novel Nafion/PTFE/SnO₂ TPB porous structures above largely enhance the single-pass carbon efficiency up to 29.3% in 1 M KOH. This study implies that engineering TPB active sites is an effective approach to the design of advanced CO₂ electrolyzers.