Abstract: Carbon capture, utilization, and storage (CCUS) strategies are increasingly recognized as effective means to achieve carbon neutrality, while simultaneously enabling the conversion of CO2 into value-added products. Among these approaches, electrochemical CO2 reduction (CO2RR) stands out due to its operation under mild temperature and pressure conditions and its potential to store intermittent renewable energy-such as solar or wind-in the form of chemical products like formic acid and formate. The Development of Chemical Processes and Pollution Control (DePRO) research group at the University of Cantabria (Spain) has been actively involved in advancing continuous CO2 electroreduction to formate. Over the past years, the group has systematically investigated a wide range of cathodic and anodic electrocatalysts, as well as various electrode configurations, to optimize the performance and stability of the system. This communication presents recent advances and persistent challenges in the development of efficient continuous-flow CO2 electroreduction systems, with a particular focus on the influence of the cathodic electrocatalytic area, an aspect that has been scarcely explored to date. All experiments were conducted under a standardized setup and operating conditions, while varying key parameters such as cathodic electrocatalysts-including Sn-, Bi-, and Sb-based materials and electrode architectures, such as planar electrodes, particulate electrodes (PE), gas diffusion electrodes (GDEs), catalyst-coated membrane electrodes (CCMEs), and membrane electrode assemblies (MEAs), operating in the gaseous-phase, using a geometric area of 10 cm2. On the anodic side, different materials have been explored, including DSA/O2 and Ni-based electrodes, with electrolysis typically coupled to the oxygen evolution reaction (OER). Both cation exchange membranes (CEM, e.g., Nafion) and anion exchange membranes (AEM, e.g., Sustainion) were tested, allowing for comparative performance analysis and identification of optimal cell configurations. The promising results obtained by the research group have enabled the scale-up of the CO2 electroreduction technology from a lab-scale reactor (10 cm²) to semi-industrial pilot plant configurations (100 and 1000 cm²) within the framework of various projects aimed at constructing and testing a CO? electrolyzer under real industrial conditions, including textile and cement plants. During the initial scale-up to a geometric area of 100 cm2, optimal performance was achieved at a current density of 200 mA·cm-² and a water feed rate of 15 g·h?¹, resulting in a formate concentration of 760 g·L-¹, a Faradaic efficiency of 67%, a production rate of 7 mmol·m-²·s¹, and an energy consumption of 507 kWh·kmol-¹. When compared with the 10 cm² lab-scale reactor, the scaled-up system demonstrated enhanced CO2 conversion and higher product formation rates, thereby validating the advantages of optimized flow field design and the overall scale-up strategy. Although a moderate decrease in energy efficiency was observed-mainly due to increased ohmic losses-these findings support the technical viability of gas-phase CO2 electrolysis for formate production at larger scales. Further improvements in cell design, materials selection, and energy management are necessary to move closer to industrial implementation. Nonetheless, these developments represent a significant step forward in the advancement and potential application of CO2 electroreduction technologies.

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