Polyaniline anchoring environment facilitates highly efficient CO2 electroreduction of cobalt phthalocyanine over a wide potential window

Abstract

Metallophthalocyanines (MPcs) with the especially active metal-N4 catalytic sites have the great potential for the electrocatalytic CO2-to-CO conversion. However, the masking of metal-N4 catalytic sites attributed to the strong π-π interaction and the difficulty in capturing CO2 severely limits their catalytic efficiency. Herein, we designed a self-supported electrode that tetra-β-carboxy phthalocyanine cobalt(II) (TcPcCo) was anchored into polyaniline (PANI) chain in isolation using the carbon paper (CP) as a support. The PANI with unique porous structure provides large surface area, rapid electron transfer, and unimpeded pathways for CO2 diffusion. More importantly, sufficient CO2 captured by PANI can continuously spill over to metal-N4 active sites and be reduced into CO. The synthesized electrode for CO2 reduction reaction (CO2RR) could maintain a high CO Faraday efficiency of over 95% (maximum 99.3%) at an extraordinary wide potential range of 450 mV (from -0.50 V to -0.95 V vs. RHE), ranking foremost among the previously reported phthalocyanine-based electrocatalysts. Furthermore, relative to TcPcCo, the CO turnover frequency (TOF) of PANI-TcPcCo/CP significantly improves, especially at the more negative operating potential (about 7 ∼ 68 times). Theoretical calculations further reveal that the introduce of PANI optimizes the free energy barrier of CO2RR intermediate at Co-N4 site, thus accommodating the*COOH formation, and also suppresses the competition of hydrogen evolution reaction. This work presents a new perspective on advancing the catalytic CO2RR capability of molecular materials by regulating the chemical environment surrounding a catalytically active site.