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

Abstract

Conjugated microporous polymers (CMPs) with π-conjugated framework, inherent porosity and tunable structure have been considered as the promising platforms as electrocatalysts for carbon dioxide reduction reaction (CO2RR). Promoting the proton transfer dynamic to modulate microenvironment of active sites in CMPs plays an important role on 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 by the Buchwald–Hartwig coupling polymerization approach. Owing to the three-dimensional geometry of these polymeric skeleton, microenvironment of catalytic CoN4 site could be readily regulated by incorporation of nitrogen-doped diamino aromatic, leading to the enhancement of electrocatalytic activity for the carbon monoxide (CO) production. Notably, pyrazine-containing CMPANI (CMPANI-3) shows the 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 the efficient proton absorption and transfer. Moreover, in-situ Fourier transform infrared spectra demonstrate that the protonated pyrazinyl-N would promote the generation and stabilization of *COOH intermediate via the coordination interaction around CoN4 site, thus favoring the electroreduction of CO2-to-CO conversion. This work provides a new sight in the design of polymeric electrocatalyst system with superior electron and proton transport for boosting CO2RR applications.