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Abstract Intrinsic structural and oxidic defects activate graphitic carbon electrodes towards electrochemical reactions underpinning energy conversion and storage technologies. Yet, these defects can also disrupt the long‐range and periodic arrangement of carbon atoms, thus, the characterization of graphitic carbon electrodes necessitatesin‐situatomistic differentiation of graphitic regions from mesoscopic bulk disorder. Here, we leverage the combined techniques ofin‐situattenuated total reflectance infrared spectroscopy and first‐principles calculations to reveal that graphitic carbon electrodes exhibit electric‐field dependent infrared activity that is sensitive to the bulk mesoscopic intrinsic disorder. With this platform, we identify graphitic regions from amorphous domains by discovering that they demonstrate opposing electric‐field‐dependent infrared activity under electrochemical conditions. Our work provides a roadmap for identifying mesoscopic disorder in bulk carbon materials under potential bias. 

Iron–sulfur clusters play essential roles in biological systems, and thus synthetic [Fe4S4] clusters have been an area of active research. Recent studies have demonstrated that soluble [Fe4S4] clusters can serve as net H atom transfer mediators, improving the activity and selectivity of a homogeneous Mn CO2 reduction catalyst. Here, we demonstrate that incorporating these [Fe4S4] clusters into a coordination polymer enables heterogeneous H atom transfer from an electrode surface to a Mn complex dissolved in solution. A previously reported solution-processable Fe4S4-based coordination polymer was successfully deposited on the surfaces of different electrodes. The coated electrodes serve as H atom transfer mediators to a soluble Mn CO2 reduction catalyst displaying good product selectivity for formic acid. Furthermore, these electrodes are recyclable with a minimal decrease in activity after multiple catalytic cycles. The heterogenization of the mediator also enables the characterization of solution-phase and electrode surface species separately. Surface enhanced infrared absorption spectroscopy (SEIRAS) reveals spectroscopic signatures for an in situ generated active Mn–H species, providing a more complete mechanistic picture for this system. The active species, reaction mechanism, and the protonation sites on the [Fe4S4] clusters were further confirmed by density functional theory calculations. The observed H atom transfer reactivity of these coordination polymer-coated electrodes motivates additional applications of this composite material in reductive H atom transfer electrocatalysis.