Multilayer GDEs for long-term stable acidic CO2 reduction to formic acid

Abstract

Employing green electricity and shifting from fossil to renewable feedstock to reduce anthropogenic CO2 emissions is a sustainable method contributing to cracking down the challenges for achieving greenhouse gas neutrality. Recently, electrochemical reduction methods using gas diffusion electrodes (GDEs) have become a viable approach for converting CO2 from sources like waste incineration, cement industry, or biogenic sources to valuable platform chemicals like CO, ethylene and formic acid. Previous research from our group has demonstrated the feasibility of bismuth (Bi) based GDEs in acidic CO2 electrolysis to produce formic acid which comes with the advantage of a significantly simplified upstream processing and reduced carbonate precipitation within the electrode. However, the process still faces severe challenges associated with long-term stability and the accumulation of product which is essential for reaching a commercially competitive process. The reason for the negative impact of increasing formic acid concentration in acidic environment is still not fully understood [1]. Recent studies have shown that systematic GDE engineering and applying a protective layer (PL) for the catalyst can improve stability by regulating the ion transport and shield the catalyst from harsh conditions. Meanwhile, the hydrophobic gas diffusion layer prevents electrode flooding, ensuring continuous CO2 diffusion to the catalyst layer during operation [2]. The presented work aims at the fabrication and optimization of such multilayer substrates for GDEs for formic acid production starting from the already established single layer architecture which reaches current densities of several 100 mA/cm² but lacks sufficient long-term stability. Based on this, the beneficial effect of electrodeposited Bismuth catalyst to produce a very thin and well-defined catalyst layer is demonstrated. Through optimization the electrode properties, we try to get a better understanding of how the electrode needs to be tailored in order to reach the required performance metrics for industrial operation with high durability. To this end, physical characterizations and advanced microstructural studies to understand the complex electrode framework before and after electrolysis complement the electrochemical characterization and give insights into electrode degradation.