MnI-Functionalized Covalent Organic Framework as Efficient Electrocatalyst for CO2 Reduction in a Catholyte-Free Zero-Gap Electrolyzer

Covalent Organic Frameworks (COFs) have emerged as versatile platforms for the rational design of heterogeneous CO₂ electrocatalysts, offering molecular-level precision due to their well-ordered, porous structures. While COF-based hybrid electrocatalysts have demonstrated potential in lab-scale electrochemical cells with liquid electrolytes, their application in industry-relevant architectures remains largely unexplored. Here, the first successful integration of a phenanthroline-based 2D COF, modified with Mn^I single catalytic sites, into a catholyte-free membrane-electrode-assembly (MEA) cell for CO₂ electroreduction is presented. The crystalline COF catalyst achieves an outstanding turnover frequency of 617 h⁻¹ (quantified per total concentration of catalytic sites) and a CO evolution of 222 µmol cm⁻² (at a full-cell potential of 2.8 V) within 30 min. Moreover, the COF structure actively suppresses Mn⁰–Mn⁰ dimer formation and supports stable operation at high potentials with a partial current density of 23 mA cm⁻². The synergy between the crystalline nature of the COF and the MEA cell architecture, facilitating direct interactions between the modified electrode and the CO₂ gas, enhances both the catalytic activity and stability. This work paves the way for broader adoption of COF-based hybrid materials in advanced electrocatalytic CO₂ reduction technologies.