In this study, an attempt was made to reduce CO2 to formic acid in an acidic environment with appropriate electrolysers. At first, the operability of Sn and Bi-based catalysts was investigated using a cell with a geometric surface area of 1 cm2. However, the central part of this work was the study conducted on an scale up electrolyser with a geometric surface area of 25 cm2. For the latter, experiments were conducted on design parameters such as different electrode-membrane distances and different membranes. Subsequently various operation conditions were studied, such as: current density, as well as temperature, concentration and flow rate of the catholyte. Finally, it was investigated the possibility to operate in continuous mode with the single passage of catholyte in the cell, but no relevant results could be achieved. From this study it was possible to identify the importance of the distances between the anode-membrane and GDE-membrane to ensure adequate Faraday efficiency towards formic acid. Additionally, an improved performance was reported using a catholyte with higher concentrations of K2SO4 and heated to a temperature of 35°C. However, the cell still has many limitations including the difficulty of operating with current densities more negative than -100 mA/cm2 as well as generally presenting high cell potentials. Because of that, further investigations are necessary.
In questo studio è stato indagato il processo di riduzione della CO2 in acido formico in ambiente acido mediante l’utilizzo di appositi elettrolizzatori. In primo luogo si è approfondita l’operabilità dei catalizzatori a base di Sn e Bi con l’utilizzo di una cella avente un area geometrica superficiale di 1 cm2. Parte centrale di questo lavoro è però lo studio condotto su una scala maggiorata avente un’ area geometrica superficiale di 25 cm2. Per quest’ultimo, sono state condotte delle analisi sui parametri strutturali quali diverse distanze elettrodo membrana e diverse membrane. Successivamente sono state studiate diverse condizioni di operazione quali: la densità di corrente, così come la temperatura, la concentrazione ed il flow rate del catolita. Infine, è stata indagata la possibilità di operare in modalità continua con il passaggio singolo di catolita nella cella senza ottenere però risultati rilevanti. Da questo studio è stato possibile individuare l’importanza delle distanze che intercorrono tra anodo-membrana e GDE-membrana allo scopo di garantire una adeguata efficienza faradica nei confronti dell’acido formico. Inoltre, sono state riportate delle prestazioni migliori utilizzando un catolita con concentrazioni maggiori di K2SO4 e riscaldato ad una temperature di 35°C. Tuttavia la cella maggiorata presenta ancora molte limitazioni tra cui la difficoltà ad operare con densità di corrente più negative di -100 mA/cm2. Inoltre, sono richiesti dei potenziali di cella ancora troppo elevati che rendono necessarie ulteriori indagini.
Investigating a scaled-up electrolyser for acidic electrochemical CO2 reduction to formic acid
CARLETTO, ALBERTO
2022/2023
Abstract
In this study, an attempt was made to reduce CO2 to formic acid in an acidic environment with appropriate electrolysers. At first, the operability of Sn and Bi-based catalysts was investigated using a cell with a geometric surface area of 1 cm2. However, the central part of this work was the study conducted on an scale up electrolyser with a geometric surface area of 25 cm2. For the latter, experiments were conducted on design parameters such as different electrode-membrane distances and different membranes. Subsequently various operation conditions were studied, such as: current density, as well as temperature, concentration and flow rate of the catholyte. Finally, it was investigated the possibility to operate in continuous mode with the single passage of catholyte in the cell, but no relevant results could be achieved. From this study it was possible to identify the importance of the distances between the anode-membrane and GDE-membrane to ensure adequate Faraday efficiency towards formic acid. Additionally, an improved performance was reported using a catholyte with higher concentrations of K2SO4 and heated to a temperature of 35°C. However, the cell still has many limitations including the difficulty of operating with current densities more negative than -100 mA/cm2 as well as generally presenting high cell potentials. Because of that, further investigations are necessary.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/43803