Electronic Modulation of Bismuth Active Sites in Bimetallic Zeolitic Imidazolate Frameworks Enables Selective CO2 Electroreduction in a Bipolar Membrane Flow Cell

Abstract Here, we report the rational design of two bimetallic zeolitic imidazole frameworks (M-Bi@ZIF-8; M = Cu, Ag) that function as electronically coupled molecular assemblies for selective CO2 reduction to formate. We demonstrate that the secondary Cu/Ag ZIF-8 nodes act as electronic promoters, influencing the Bi p-band center through electron density induction through the aromatic framework. To improve the stability of the metal organic framework (MOF), a custom 3D-printed laminar gas flow cell and a zero-gap cell were employed with a bipolar membrane (BPM). It was found that both catalysts exhibited great stability and selectivity toward formate in the flow cell architecture. At –100 mA/cm2, both catalysts reported a Faradaic efficiency (FE) of ∼90% toward formate. At a maximum current density of –250 mA/cm2, both catalysts demonstrated a FE of ∼20% toward methane, indicating a potential shift from O-coordinated to C-coordinated adsorption pathways. Long-term stability showed 100 h of continuous operation in the zero-gap cell at –100 mA/cm2. Time-evolved inline 1H NMR spectroscopy showed rapid reduction of CO2 to formate after 5 min. Further in situ surface enhanced Raman spectroscopy (SERS) was done to confirm that the reaction mechanism to formate proceeds via the *OCHO pathway with minimal surface reconstruction. This work demonstrates a pathway for the convergence of atomic-level catalyst tuning and cell design engineering for scalable CO2 valorization.