Bioinspired Electrocatalyst for CO2 Electroreduction to Ethanol via Secondary-Sphere Synergy in Fe Porphyrinic-Based Metal-Organic Frameworks

Abstract

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 CO2RR. Electrochemical performances in H-cell reveal that FeTCPP-NSs-BAA achieves 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 a 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. Operando spectroscopic characterizations 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 formation of 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.