CO2 conversion to synthetic fuels using flow cell reactor over Cu and Ag based cathodes

Materials for Renewable and Sustainable Energy https://doi.org/10.1007/s40243-024-00263-w ORIGINAL PAPER CO2 conversion to synthetic fuels using flow cell reactor over Cu and Ag based cathodes Sabrina C. Zignani1 · Antonino S. Aricò1 Received: 28 February 2024 / Accepted: 22 April 2024 © The Author(s) 2024 Abstract As a result of electrochemical conversion of carbon dioxide (CO2), value-added chemicals like as synthetic fuels and chemical feedstocks can be produced. In the current state of the art, copper-based materials are most widely used being the most effective catalysts for this reaction. It is still necessary to improve the reaction rate and product selectivity of CuOx for electrochemical CO2 reduction reaction (CO2RR). The main objective of this work was synthesized and evaluate the copper oxide electrocatalyst combined with silver (CuO 70% Ag 30%) for the conversion of carbon dioxide into synthetic fuels. The catalysts have been prepared by the oxalate method and assessed in a flow cell system. The results of electrochemical experiments were carried out at room temperature and at different potentials (-1.05 V–0.75 V vs. RHE in presence of 0.1 M KHCO3) and gas and liquid chromatographic analysis are summarized. The CuOx-based electrodes demonstrated the selective of ~ 25% at -0.55 V for formic acid (HCOOH) and over CuO -Ag and selective of ethylene at ~ 20% over CuOx at -1.05 V. Other products were formed as ethylene, ethanol, and propanol (C2H4, EtOH, PrOH) at more positive potentials. On the other hand, carbon monoxide, acetate, ethylene glycol, propinaldehyde, glycoaldehyde and glyoxal (CO, CH3COO, C2H6O2, C3H6O, C2H4O2, C2H2O2) have been formed and detected. Based on the results of these studies, it appears that the formation of synthetic fuels from CO2 at room temperature in alkaline environment can be very promising. Keywords CO2 conversion · Flow electrochemical cell · Synthetic fuels · Copper oxide · No critical raw catalyst Introduction There is an urgent need for technological solutions to remove carbon dioxide (CO2) from the atmosphere to combat global warming, which is caused by an increase in the amount of carbon dioxide that is being emitted into the atmosphere. Innovative solutions are essential to achieving global energy and climate change goals [1]. It is essential that both existing technologies and those not yet on the market are deployed as soon as possible. During this decade, major efforts must be made in the area of innovation as well as deployment of these new technologies in order to bring them to market in time. By next twenty years it is expected that most of the CO2 emissions from the world’s Sabrina C. Zignani 1 Institute of Advanced Energy Technologies (ITAE) of the Italian National Research Council (CNR), Rome, Italy energy sector will be reduced using new technologies that are readily available today [2–8]. To reduce CO2 emissions, and to store renewable energy, it is necessary to use renewable energy to convert carbon dioxide and water into synthetic fuels and chemical feedstocks [9, 10]. An abundance of evidence suggests that carbon dioxide can be converted into organic compounds using electrochemical cells with active electrocatalysts at the cathode of the cells [11–13]. . However, the carbonaceous synthetic fuels can be applied in several energy technologies like combined heat and power systems [14, 15]. There has been considerable interest in the development of novel, structured materials from nonnoble and non-critical raw materials in recent years [16–18]. There are a wide variety of electrocatalysts that can be used for the CO2RR, and reduction products are highly dependent on the electrocatalyst used [19, 20]. In electrochemical CO2RR, three steps are involved, which begin with the adsorption of carbon dioxide on catalyst surfaces. A second step in carbon dioxide reduction involves activating and reducing CO2 molecules. Generally, electron transfer is the 13 Materials for Renewable and Sustainable Energy rate-determining step in creating CO2 intermediates, since it imposes a high energy barrier. Finally, the catalyst surface is recovered for further reactions after desorption of products. As an important intermediate in carbon dioxide reaction reduction, CO2 plays a significant role in determining how final products are distributed [21, 22]. It should be noted that copper-based catalysts perform differently depending on the state of oxidation of the catalyst. There is a direct relationship between the catalytic performance of an electrocatalyst and its structure and active site. Other study by Zheng et al. [23], examined the connection between the fundamentals of the reaction and the effectiveness of electrocatalysts in their critical assessment of CO2 reduction to C2 products by focusing on the fundamentals of the reaction. During a comprehensive discussion of the mechanistic aspects of the C2 reactions under electrocatalytic conditions, copper-based catalysts are discussed in terms of both mechanics and practical aspects under electrocatalytic conditions. The authors also visualized the roadmap for generating C2 products by demonstrating the advantages of integrating theoretical calculations, surface characterization, and electrochemical measurements into one process. Concerning Gao et al. [24]. , have been demonstrated that selected geometries and compositions of catalysts in combination with a carefully selected electrolyte are responsible for the enhanced selectivity of C2+ in the reaction. As it is known, copper-based catalysts exhibit different performance for carbon dioxide reduction depending on their oxidation state. Hori et al., investigated in aqueous inorganic electrolytes the acid-base equilibrium between bicarbonate and CO2 reactant involving H+ (CO2 (g) + H2O (l) + H2CO3 (aq) + H+ (aq)), whereas reduction entails protonation. As a result, H+ concentration on the surface of catalysts plays an important role in deterring their product selectivity. The C2H4 is favored when the electrolyte concentration is low (0.1 M) whereas CH4 and H2 are favored when the electrolyte concentration is high [25]. However, there is a limitation on the carbon dioxide conversion rate of electrocatalysts due to their structure and oxidation state, but it is possible to optimize their electrocatalytic performance. In general, surface vacancies are also important factors that influence electrochemical performance. Copper catalysts are one of the most commonly used electrocatalysts in electrochemical CO2 reduction [26–29] by multiple electron transfer reactions. To achieve high efficiency in CO2 reduction, however, it is necessary to have a sufficient number of active sites. It can electrochemically convert CO2 into different products, such as hydrocarbons and alcohols, due to its electrochemical properties [11, 30–32]. Selectivity of the products is directly related to the active copper species and the morphology, howev (...truncated)