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Publisher: Weinheim : Wiley-VCH × Subject: electrocatalysis × WGL Institute: LIKAT ×

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Now showing 1 - 4 of 4
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    Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex
    (Weinheim : Wiley-VCH, 2020) De, Ratnadip; Gonglach, Sabrina; Paul, Shounik; Haas, Michael; Sreejith, S.S.; Gerschel, Philipp; Apfel, Ulf-Peter; Vuong, Thanh Huyen; Rabeah, Jabor; Roy, Soumyajit; Schöfberger, Wolfgang
    The controlled electrochemical reduction of carbon dioxide to value added chemicals is an important strategy in terms of renewable energy technologies. Therefore, the development of efficient and stable catalysts in an aqueous environment is of great importance. In this context, we focused on synthesizing and studying a molecular MnIII-corrole complex, which is modified on the three meso-positions with polyethylene glycol moieties for direct and selective production of acetic acid from CO2. Electrochemical reduction of MnIII leads to an electroactive MnII species, which binds CO2 and stabilizes the reduced intermediates. This catalyst allows to electrochemically reduce CO2 to acetic acid in a moderate acidic aqueous medium (pH 6) with a selectivity of 63 % and a turn over frequency (TOF) of 8.25 h−1, when immobilized on a carbon paper (CP) electrode. In terms of high selectivity towards acetate, we propose the formation and reduction of an oxalate type intermediate, stabilized at the MnIII-corrole center. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Avoiding Pitfalls in Comparison of Activity and Selectivity of Solid Catalysts for Electrochemical HMF Oxidation
    (Weinheim : Wiley-VCH, 2021) Wöllner, Sebastian; Nowak, Timothy; Zhang, Gui-Rong; Rockstroh, Nils; Ghanem, Hanadi; Rosiwal, Stefan; Brückner, Angelika; Etzold, Bastian J. M.
    Electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) offers a renewable approach to produce the value-added platform chemical 2,5-furandicarboxylic acid (FDCA). The key for the economic viability of this approach is to develop active and selective electrocatalysts. Nevertheless, a reliable catalyst evaluation protocol is still missing, leading to elusive conclusions on criteria for a high-performing catalyst. Herein, we demonstrate that besides the catalyst identity, secondary parameters such as materials of conductive substrates for the working electrode, concentration of the supporting electrolyte, and electrolyzer configurations have profound impact on the catalyst performance and thus need to be optimized before assessing the true activity of a catalyst. Moreover, we highlight the importance of those secondary parameters in suppressing side reactions, which has long been overlooked. The protocol is validated by evaluating the performance of free-standing Cu-foam, and CuCoO modified with NaPO2H2 and Ni, which were immobilized on boron-doped diamond (BDD) electrodes. Recommended practices and figure of merits in carefully evaluating the catalyst performance are proposed. © 2021 The Authors. Published by The Chemical Society of Japan & Wiley-VCH GmbH
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    TEMPO‐Modified Polymethacrylates as Mediators in Electrosynthesis – Redox Behavior and Electrocatalytic Activity toward Alcohol Substrates
    (Weinheim : Wiley-VCH, 2021) Mohebbati, Nayereh; Prudlik, Adrian; Scherkus, Anton; Gudkova, Aija; Francke, Robert
    Homogeneous catalysts (“mediators”) are useful for tuning selectivity in organic electrosynthesis. However, they can have a negative impact on the overall mass and energy balance if used only once or recycled inefficiently. In a previous work, we introduced the polymediator concept, in which soluble redox-active polymers catalyze the electrochemical reaction, allowing for recovery by dialysis or pressure-driven membrane filtration. Using anodic alcohol oxidation as a test case, it was shown that TEMPO-modified polymethacrylates (TPMA) can serve as efficient and reusable mediators. In the present study, the properties of a TPMA sample with well-defined molecular weight distribution were studied using cyclic voltammetry and compared to low-molecular TEMPO species. The non-catalytic profiles of TPMA are shaped by diffusive and adsorptive processes, whereby the latter only become pronounced at low mediator concentrations and high scan rates. Electrocatalytic studies suggest that under the applied conditions, TPMA-catalyzed alcohol oxidation is a predominantly homogeneous process. The homogeneous kinetics are determined rather by the mediator potential than by steric influences of the polymer backbone. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
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    TEMPO-Modified Polymethacrylates as Mediators in Electrosynthesis: Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity
    (Weinheim : Wiley-VCH, 2023) Prudlik, Adrian; Mohebbati, Nayereh; Hildebrandt, Laura; Heck, Alina; Nuhn, Lutz; Francke, Robert
    Homogeneous catalysts (“mediators”) are frequently employed in organic electrosynthesis to control selectivity. Despite their advantages, they can have a negative influence on the overall energy and mass balance if used only once or recycled inefficiently. Polymediators are soluble redox-active polymers applicable as electrocatalysts, enabling recovery by dialysis or membrane filtration. Using anodic alcohol oxidation as an example, we have demonstrated that TEMPO-modified polymethacrylates (TPMA) can act as efficient and recyclable catalysts. In the present work, the influence of the molecular size on the redox properties and the catalytic activity was carefully elaborated using a series of TPMAs with well-defined molecular weight distributions. Cyclic voltammetry studies show that the polymer chain length has a pronounced impact on the key-properties. Together with preparative-scale electrolysis experiments, an optimum size range was identified for polymediator-guided sustainable reaction control.