A bioinspired electrocatalyst for CO2 electroreduction to ethanol via secondary-sphere synergy in Fe porphyrinic-based metal–organic frameworks

Abstract

The carbon dioxide electroreduction reaction (CO₂RR) to ethanol (C₂H₅OH) represents a sustainable route toward carbon neutrality. Herein, we present the design of enzyme-inspired zirconium–Fe porphyrinic-based metal–organic framework (MOF) nanosheets functionalized with 5-benzimidazolecarboxylic acid (FeTCPP-NSs-BAA) for the CO₂RR. Electrochemical performances in a H-cell reveal that FeTCPP-NSs-BAA shows C₂H₅OH faradaic efficiencies (FEs) of 79.8% under neutral and 89.2% under acidic conditions, with C₂H₅OH FEs exceeding 60% over wide potential windows of −0.3 to −0.6 V and −0.3 to −0.8 V, respectively. In flow cell tests under acidic conditions, FeTCPP-NSs-BAA delivers the highest C₂H₅OH partial current density of 8.1 mA cm⁻² with pure CO₂, and a C₂H₅OH partial current density of 5.6 mA cm⁻² when using 30% low-concentration CO₂. In situ spectroscopic characterization and theoretical calculations reveal that the superior C₂H₅OH performance of FeTCPP-NSs-BAA arises from the enzyme-like non-covalent synergistic effects between FeTCPP and the secondary-sphere functionalities of BAA and Zr₆ clusters. Specifically, BAA enhances CO₂ enrichment and facilitates the tilted *CO adsorption at Fe centers on FeTCPP, which significantly reduces energy barriers for *CO–CO coupling compared to linearly adsorbed *CO. Meanwhile, the subsequent hydrogenation of *CO–CO to C₂H₅OH can be further accelerated by proton shuttling mediated through hydrogen-bonding networks introduced by Zr₆ clusters.