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

Abstract

Conjugated microporous polymers (CMPs) with π-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 (FE_CO) (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.