Spatially Engineered Cu(II)-Containing Polyphosphazene-Based Catalysts Enable Electrochemical CO2 Reduction to Ethanol.

Abstract

Electrochemical CO2 reduction to value-added multi-carbon products is attractive, whereas the low-efficiency C─C coupling hinders the electrocatalytic selectivity and activity. Herein, we synthesize a polyphosphazene network with a precise supramolecular configuration of the neighboring dual catalytic centers by introducing dendritic molecules. The reasonable ratio of 5,10,15,20-tetrakis-(4-aminophenyl)-porphyrin-Cu-(II) and hexachlorocyclotriphosphazene results in an ultrathin polymer sheath around carbon nanotubes, exhibiting π-π stacking between the adjacent porphyrin molecules and the optimized spatial distance (3.8 Å) between the neighboring Cu active sites, featuring dual-atom catalytic centers bound to carbon nanotubes. Given the controlled geometric structure, the catalysts can boost C─C coupling reactions during CO2 electrocatalysis, thereby improving the selectivity of the multi-carbon product (EtOH) with a high Faradic efficiency (FEmax of 61.1% at -1.0 V) in broad potential windows. The strategy of achieving precise control over the spatial distance between adjacent metal catalytic centers by incorporating dendritic molecules into a polyphosphazene network provides a viable approach for designing polymer-based single-atom electrocatalysts.