Electrochemical CO₂ reduction is a promising carbon capture and utilisation technology. Herein, a continuous flow gas diffusion electrode (GDE)-cell configuration has been studied to convert CO₂ via electrochemical reduction under atmospheric conditions. To this purpose, Cu-based electrocatalysts immobilised on a porous and conductive GDE have been tested. Many system variables have been evaluated to find the most promising conditions able to lead to increased production of CO₂ reduction liquid products, specifically: applied potentials, catalyst loading, Nafion content, KHCO₃ electrolyte concentration, and the presence of metal oxides, like ZnO or/and Al₂O₃. In particular, the CO productivity increased at the lowest Nafion content of 15%, leading to syngas with an H₂/CO ratio of ~1. Meanwhile, at the highest Nafion content (45%), C₂₊ products formation has been increased, and the CO selectivity has been decreased by 80%. The reported results revealed that the liquid crossover through the GDE highly impacts CO₂ diffusion to the catalyst active sites, thus reducing the CO₂ conversion efficiency. Through mathematical modelling, it has been confirmed that the increase of the local pH, coupled to the electrode-wetting, promotes the formation of bicarbonate species that deactivate the catalysts surface, hindering the mechanisms for the C₂₊ liquid products generation. These results want to shine the spotlight on kinetics and transport limitations, shifting the focus from catalytic activity of materials to other involved factors.

The electrochemical reduction of CO ₂ into valuable products is a promising strategy for mitigating atmospheric CO ₂ emissions, particularly coupled with solar energy. Among the possible products, CO is currently most attractive, both because it can combine with hydrogen to produce syngas, and because CO is a key reactant in the chemical industry. Copper‐based electrocatalysts are extensively investigated for CO ₂ reduction; however, their morphological and chemical evolution under operating conditions still needs to be clarified, to understand the relationship between morphology, structure, and catalytic activity. This paper discusses a Cu ₂ O–SnO ₂ based‐catalyst, designed to enhance CO selectivity, and studies its evolution under reaction conditions by operando electrochemical liquid‐phase transmission electron microscopy (EC‐LPTEM). First, the morphology and composition of the as‐prepared catalyst is characterized. Then, operando EC‐LPTEM is discussed and compared to the post mortem catalyst characterization, together with electrochemical behavior evaluated in the lab‐scale device. Different experimental conditions were studied to provide insights on how the catalyst modifies during the electrochemical activity. This characterization contributes to a better understanding of the possible mechanisms involved in the CO ₂ reduction, and of the factors influencing the catalyst stability and selectivity, supporting the development of improved catalysts for CO ₂ to syngas conversion.

Nowadays, it has become clear that the ever-increasing concentration of carbon dioxide (CO₂) in the atmosphere is a threat to global security¹. Therefore, the adverse climate events remind us that a transition towards a carbon neutral economy is more necessary than ever. Several approaches have been proposed to convert CO₂ to valuable products and, among these, the electrochemical reduction of CO₂ (ECR-CO₂) represents one of the most promising alternatives. Herein, the ECR-CO₂ has been carried out for the first-time employing silver based-gas diffusion electrodes (GDEs) within a continuous flow cell and in the presence of ionic liquids (ILs)-based solutions, which have been known to boost CO₂-derived products². As reported in the literature, the instability of GDEs is initiated by the high overpotentials needed during the CO₂ reduction reactions and usually culminates in flooding³. This eventually has a negative impact on the product selectivity as well as limits the perspectives of scalability. In particular, in this work, different stability issues have been faced and visualized, for example, in the blackening of typical carbon-based gas diffusion layers (GDLs) and in the degradation/colour changes of ILs-electrolyte. Interestingly, by switching to non-carbon based GDLs it has been possible to reach and maintain a steady-state production of carbon monoxide (CO) both at -10 mA cm^-2 and at -20 mA cm^-2 for at least 40 minutes, with a H₂/CO ratio slightly above 2 in the former case. Field Emission Scanning Electron Microscopy (FESEM) and Electrochemical Impedance Spectroscopy (EIS) techniques have been employed to carry out the physicochemical characterization of the electrodes and to assess the electrochemical interfaces within the system, respectively. The observed findings definitely encourage us to proceeding with our study on GDL-supported catalyst for the continuous ECR-CO₂ in the presence of ILs solutions and offers openings for a large-scale deployment. Acknowledgments The financial support of the SUNCOCHEM project (Grant Agreement No 862192) of the European Union’s Horizon 2020 Research and Innovation Action programme is acknowledged. References IEA. Global Energy Review: CO₂ Emissions in 2021. (2021). Kunene, T., Atifi, A. & Rosenthal, J. Selective CO₂ Reduction over Rose’s Metal in the Presence of an Imidazolium Ionic Liquid Electrolyte. ACS Appl. Energy Mater. 3, 4193–4200 (2020). Yang, K., Kas, R., Smith, W. A. & Burdyny, T. Role of the Carbon-Based Gas Diffusion Layer on Flooding in a Gas Diffusion Electrode Cell for Electrochemical CO₂ Reduction. ACS Energy Lett. 6, 33–40 (2021).

The most challenging deal we face today is the need to lower greenhouse gas (GHG) emissions and tackle climate change. Though calls to reduce them are growing louder yearly, emissions remain unsustainably high. CO₂ is the key contributor to global climate change in the atmosphere. Electrochemical CO₂ reduction (EC CO₂R) into chemicals or fuels holds great research interest as a promising approach to mitigate CO₂ emissions and reach a carbon-neutral future.¹ In this regard, an extraordinary effort has been made to discover new efficient and sustainable catalysts at the laboratory level over recent years. High-performance electrocatalysts in aqueous electrolytes often rely on noble metals, which may hinder their industrial applications. Herein, we successfully synthesized core-shell Cu₂O/SnO₂ nanoparticles^2–4 functionalized with a silane group, using a simple and versatile methodology based on a three-step scalable synthesis method involving wet precipitation followed by salinization and, finally, a rhenium-based complex has been assembled by electro-polymerization.⁵ The carbon paper-supported Cu₂O/SnO₂-Re electrocatalyst was characterized at 10 cm² scale achieving a CO:H₂ ratio from 3 to 9, and demonstrating an stable syngas production up to 24 hours at -20 mA·cm^-2. To translate those developments from the laboratory level to a higher TRL towards the practical application of CO₂ capture and utilization⁶, an additional chamber was added to the system for the continuous CO₂ capture and electrochemical conversion, increasing the electrode area from 10 cm² to 100 cm². Captured CO₂ co-electrolysis to syngas (H₂:CO ratio of 5) in one step was demonstrated with a high CO₂ conversion at a current up to -2 A, indicating the scale-up potential of this intensified system. The technology is currently under validation in a TRL4 reactor composed of an array of 5 modules (i.e., 4 x 5 cells x 100 cm²) with a total active area of or 0.2m² for direct CO₂ conversion from simulated anthropogenic sources. The design integrates low-cost photovoltaic (PV) cells to provide any required additional bias to drive the reaction, thus, Perovskite PV panels with a cost of up to 5 times lower (10 €/m²) than Si PV cells were used. The TRL5 demonstration of the developed technology will be done with real flue gas emissions the first semester of 2024. Acknowledgements The financial support of the SUNCOCHEM project (Grant Agreement No 862192) of the European Union’s Horizon 2020 Research and Innovation Action programme is acknowledged. References Guzmán, H., Russo, N. & Hernández, S. CO₂ valorisation towards alcohols by Cu-based electrocatalysts: challenges and perspectives. Green Chemistry vol. 23 1896–1920 Preprint at https://doi.org/10.1039/d0gc03334k (2021). Cuatto, G. et al. Standardization of Cu2O nanocubes synthesis: Role of precipitation process parameters on physico-chemical and photo-electrocatalytic properties. Chemical Engineering Research and Design 199, 384–398 (2023). Zoli, M., Guzmán, H., Sacco, A., Russo, N. & Hernández, S. Cu2O/SnO2 Heterostructures: Role of the Synthesis Procedure on PEC CO2 Conversion. Materials 16, (2023). Zoli, M. et al. Facile and scalable synthesis of Cu2O-SnO2 catalyst for the photoelectrochemical CO2 conversion. Catal Today 413–415, 113985 (2023). Miró, R. et al. Solar-driven CO2 reduction catalysed by hybrid supramolecular photocathodes and enhanced by ionic liquids. Catal Sci Technol 13, 1708–1717 (2023). Sullivan, I. et al. Coupling electrochemical CO₂ conversion with CO₂ capture. Nat Catal 4, 952–958 (2021). Figure 1