Promoting CO2 electroreduction activity of porphyrinic conjugated microporous polyanilines via accelerating proton transfer dynamics

Conjugated microporous polymers (CMPs) with pi-conjugated frameworks, inherent porosity and tunable structures have been considered promising platforms as electrocatalysts for the carbon dioxide reduction reaction (CO2RR). Promoting proton transfer dynamics to modulate the microenvironment of active sites in CMPs plays an important role in the improvement of their electrocatalytic activity. Herein, we developed a series of novel porphyrinic conjugated microporous polyanilines (CMPANI-n) constructed from tetrabromo-cobalt(ii) porphyrin and diamino aromatics using the Buchwald-Hartwig coupling polymerization approach. Owing to the three-dimensional geometry of these polymeric skeletons, the microenvironment of catalytic CoN4 sites could be readily regulated by the incorporation of nitrogen-doped diamino aromatics, leading to the enhancement of electrocatalytic activity for carbon monoxide (CO) production. Notably, pyrazine-containing CMPANI (CMPANI-3) shows high CO faradaic efficiency (FECO) (97 % at -0.7 V vs. RHE), excellent turnover frequency (TOF) (2264 h(-1) at -0.7 V vs. RHE) and large current density (>200 mA cm(-2)). The kinetic isotope effect results indicate that the pyrazinyl-N in CMPANI-3 facilitates efficient proton absorption and transfer. Moreover, in situ Fourier transform infrared spectra demonstrate that the protonated pyrazinyl-N promotes the generation and stabilization of the *COOH intermediate via coordination interactions around the CoN4 site, thus favoring the electroreduction of CO2 to CO. This work provides a new insight into the design of polymeric electrocatalyst systems with superior electron and proton transport for boosting CO2RR applications.