TY - CONF A1 - Schwarz, Irina A1 - Rieck, Arielle T1 - Valorization of carbon dioxide by electrocatalytic reduction coupled to acetogens via multiple electron carriers (Ecat-acetogens) N2 - For the realization of a sustainable energy economy, it is of great importance to develop CO2 -neutral methods producing multi-carbon organic chemicals used as feedstock as well as carbon-neutral fuels by CO2 capture and conversion. In this work, a bio-electrocatalytical system (BES) consisting of a bioreactor coupled to a CO2 electrolysis cell is established. CO2 is first electrochemically converted to CO in electrolysis cell which is then directly fed to bacteria (acetogens) to further metabolize it to valuable carbon compounds such as acetate. The objective of this study is to develop cost-efficient, biocompatible and high activity electrocatalysts that can selectively convert CO2 to CO. Porous nitrogen-doped carbons containing atomically dispersed Ni and Co (Ni or Co-N-Cs) are prepared by active-site imprinting approach. First, synthesis of Mg- or Zn-N-C was carried out through pyrolysis of precursors in a salt melt followed by exchange with Ni or Co. N2-sorption porosimetry of the materials reveal a micro-mesoporous structure with high surface areas (> 1000 m2 g-1) and a mass-transport enabling pore system. Extended X-ray absorption fine structure (EXAFS) reveal the existence of single atom sites with no formation of nanoparticles. A variety of Ni-N-Cs and Co-N-Cs were tested for CO2R activity in a rotating disc electrode (RDE) setup, showing high activity (Tafel slopes range from 77 – 130 mV/decade) and selectivity towards CO2R versus the competing HER. Before operation in the BES, first tests were performed in a single cell. Significantly increased current was detected in the CO2R test in CO2-saturated electrolyte vs. in N2 -saturated electrolyte indirectly proving formation of carbon monoxide (CO). Transfer of the electrolysis cell operation into the BES proved to be successful. For biotic operation, the BES was inoculated with Clostridium ragsdalei. Partial pressures pCO reached a maximum of 5.7 mbar and pH2 was 2.7 mbar after 30h. The reduction of partial pressures is interpreted as the consumption of the gases by C.ragsdalei. We report a specific exponential growth rate of 0.16 h-1, acetate formation rate of 1.8 mg L-1 h-1 and an acetate concetration of 0.103 g L-1 corresponding to acetate formation rate of 0.73 mmol d-1.In this work we successfully demonstrated an integrated bio-electrocatalytic system (BES) to convert CO2 into value-added chemicals. The usage of a Co- and Ni-N-Cs as the reduction catalyst within the BES allowed production of CO and H2 with relative selectivity for CO resulting in the growth of Clostridium ragsdalei and acetate production. T2 - Joint SPP Conference CY - Jena, Germany DA - 06.11.2023 KW - Bioelectrocatalytical system PY - 2023 AN - OPUS4-61995 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schwarz, Irina A1 - Rieck, Arielle T1 - Valorization of carbon dioxide by electrocatalytic reduction coupled to acetogens via multiple electron carriers (Ecat-acetogens) N2 - To alleviate CO2 emissions and their impact on climate change, converting carbon dioxide into valuable products such as multi-carbon organic chemicals is of great importance. CO2 can be converted via different pathways such as electrochemical, photo-electrochemical and biological etc. Each approach offers distinct merits but also certain challenges in terms of process efficiency, product selectivity and implementation at scale etc. Therefore, developing coupled CO2 conversion systems, for instance bioelectrochemical reactors, can potentially address some of those challenges.[1] In this work, the focus is on developing cost-efficient, biocompatible, and high activity porous M-N-C catalysts with M = Ni and Co that are atomically dispersed as NiN4 and CoN4 active sites in porous carbon matrix. Ni- and Co-N-Cs are prepared by active-site imprinting approach using Mg as an imprinter.[2][3] Pyrolysis of Mg-N-C is carried out in a salt-melt at high temperatures (≥ 800 oC) and followed by an exchange with Ni or Co at low temperatures. N2-sorption of the materials reveal a micro-mesoporous structure with high surface areas (> 1000 m2 g-1) and a mass-transport enabling pore system. Extended X-ray absorption fine structure (EXAFS) reveal the existence of atomically dispersed single atom active sites with defined active site structure. A variety of Ni-N-Cs and Co-N-Cs were tested for CO2R activity in a rotating disc electrode (RDE) setup, showing high activity and selectivity towards CO2R versus the competing HER. Subsequently, these catalysts were implemented in a home-made bio-electrocatalytical system (BES) consisting of a bioreactor coupled to a CO2 electrolysis cell. Here, CO2 is first electrochemically converted to CO in the electrolysis cell which is then directly fed to bacteria (Clostridium ragsdalei) in bioreactor who further metabolize it to valuable carbon compounds such as acetate. In the BES, partial pressures of CO reached a maximum of 5.7 mbar and that of hydrogen was 2.7 mbar after 30 h. A specific exponential bacterial growth rate of 0.16 h-1 was observed with acetate formation rate of 1.8 mg L-1 h-1 and an acetate concentration of 0.103 g L-1 corresponding to acetate formation rate of 0.73 mmol d-1. As will be discussed in greater details in this talk, we have successfully demonstrated the validity of a coupled bio-electrocatalytical system concept operating with Co- and Ni-N-C catalysts for CO2 conversion. T2 - Joint SPP Conference CY - Jena, Germany DA - 06.11.2024 KW - CO2 Reduktion KW - Bioelectrocatalytical system PY - 2024 AN - OPUS4-61993 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rieck, Arielle A1 - Schwarz, Irina T1 - Electrochemical CO2 reduction (CO2RR) coupled to gas fermentation with acetogenic bacteria N2 - For the realization of a sustainable energy economy, it is of great importance to develop CO2 -neutral methods producing multi-carbon organic chemicals used as feedstock in the chemical industry as well as carbon-neutral fuels. A promising method to alleviate the greenhouse effect and thereby forming value-added chemicals or syngas as an energy carrier, is through the electrochemical CO2 reduction reaction (CO2RR). In this work, a bioelectrotechnological approach is developed, in which the CO2RR reaction products (CO and H2) are directly fed to bacteria (acetogens), who use them as “reduction equivalents” to further metabolize CO2 to valuable carbon compounds. Therefore, a bio-electrochemical system consisting of a bioreactor coupled to a CO2 electrolysis cell will be established. Currently, scarce catalysts such as Ag and Au are used as for the CO2RR which may hamper the use of decentral CO2 conversion technology for cost reasons. The technological viability of the bacteria-assisted electrolysis depends on the usage of efficient, biocompatible, and selective electrocatalysts prepared from inexpensive precursors. Porous transition metal and nitrogen co-doped carbons (M-N-Cs) have emerged as precious-metal free electrocatalysts for the direct electrochemical reduction of CO2 into CO and are excellent candidates for scale-up and deployment in technological applications. Furthermore, Co/Ni/Zn functioning as the catalytically active sites will be used, as they are expected to depict non-bactericidal properties in contrast to Cu and Ag catalysts. The non-bactericidal property could e.g., allow for application within the hybrid device (bio-electrochemical system), without the need to separate bacteria and cathode catalyst. The MNCs with the most promising electrocatalytic activity and selectivity will be evaluated in abiotic conditions in the hybrid bio-electrochemical reactor system. T2 - DFG Summer School Workshop CY - Hamburg, Germany DA - 01.09.2022 KW - Katalysator KW - CO2 Reduktion KW - Bioelectrochemical CO2 reduction PY - 2022 AN - OPUS4-56618 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -