Modulating Active Center Microenvironment in Phthalocyanine-Based Covalent Organic Frameworks for Enhanced Electrocatalytic CO₂ to CH₃OH.

Abstract

Developing catalysts for electrocatalytic CO₂ to CH₃OH still faces great challenge due to the involvement of multiple proton-coupled electron transfer (PCET) processes. Molecular phthalocyanine electrocatalysts on carbon nanotubes have achieved production of methanol as the sole liquid-phase product but with the activity and stability far from meeting industrial demands. Herein, phthalocyaninato cobalt is fabricated into covalent organic frameworks PE-COF via polymerization with ellagic acid. Subsequent hydrolyzation of the ester groups in this framework affords COOH/OH-containing PEH-COF, resulting in the successful modulation over the local microenvironment of Co as electrochemical active center and in turn rendering the production of CH₃OH with high yield and durability. Experimental and theoretical investigations reveal that construction of the COOH group and H₂O participated catalytic cages in PEH-COF can effectively fix hydrated potassium ions, which efficiently enhances the PCET kinetics and lowers the energy barriers for the conversion of CO₂ to CH₃OH. The partial current density (j) and Faraday efficiency of methanol for PEH-COF could reach 100.9 mA cm^-2 and 38.5%, respectively. Moreover, the <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msub><mi>j</mi> <mrow> <msub><mrow><mi>C</mi> <mi>H</mi></mrow> <mn>3</mn></msub> <mi>O</mi> <mi>H</mi></mrow> </msub> <annotation>$\mathrm{j}_{{CH}_3OH}$</annotation></semantics> </math> of PEH-COF can be maintained at 100.4 mA cm^-2 after 9 h of electrocatalysis, superior to the thus far reported catalysts.