Spatial confinement enables CO2 activation via a molecular redox mediator for multicarbon electrosynthesis

Post-synthetic strategy modularly integrates CO 2 -to-CO and CO-to-C 2+ sites. • Redox mediator and confinement synergize to regulate cascade reactions. • Confined TEMPOL acts as PCET mediator, lowering CO 2 -to-*COOH barrier. • Inactive MOF is transformed into an efficient CO 2 -to-C 2+ electrocatalyst. Efficient electrochemical conversion of CO 2 to multi-carbon (C 2+ ) products requires the integration of two sequential functionalities: CO 2 activation to *CO and subsequent CO-initiated C-C coupling. Conventional strategies typically rely on the rigid, pre-designed incorporation of these two functional units during catalyst synthesis. In contrast, we propose a post-synthetic modification strategy that introduces a molecular CO 2 activation unit into a pre-formed catalyst scaffold, thereby enabling its spatially proximal coupling with intrinsic CO reduction sites. This concept is demonstrated by encapsulating 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) into the pores of a tetrapyrazolylporphyrin copper-based metal–organic framework (FICN-8). Owing to the well-matched molecular dimensions, the confined TEMPOL and adjacent Cu nodes cooperatively define a cavity that spatially accommodates a CO 2 molecule. Reduced TEMPOL acts as a proton-coupled electron transfer (PCET) mediator, while spatial confinement regulates the local reaction environment, jointly lowering the free energy barrier for *COOH formation. The confined *COOH intermediate is subsequently converted to CO and further undergoes C–C coupling. As a result, FICN-8—originally inactive for CO 2 -to-C 2+ conversion (Faradaic Efficiency, FE< 0.6%)—is transformed into an efficient electrocatalyst, delivering a C 2+ Faradaic efficiency of 42.6% with a two-orders-of-magnitude enhancement in C 2 H 4 formation rate. Download: Download high-res image (123KB) Download: Download full-size image