One of the strategies for reducing CO₂ emissions from industrial sources involves electrochemical conversion and utilization of CO₂ to create valuable products. This method is considered efficient and promising as it allows the storage of excess energy from renewable sources in CO₂-reduced products such as formic acid, formate, methanol, or ethylene. The process occurs in an electrochemical reactor where CO₂ is supplied to the cathode. When an external voltage is applied, the CO₂ molecules undergo transformation over a catalyst surface, while an oxidation reaction occurs at the counter-electrode. Typically, an ion exchange membrane separates both compartments, facilitating the separation of reaction products and increasing the overall system efficiency.[1].

This work aims to develop a prototype of a CO₂ electrolyzer for industrial use, as the first phase in the full-scale implementation of CO₂ electroreduction to formate. The design and testing of the prototype have been a collaborative effort involving the DePRO research group, which has been actively engaged in advancing CO₂ conversion technology in recent years [1-3], and APRIA Systems, a technology supplier company responsible for constructing the CO₂ electrolyzer.

The electrolyzer comprises various components, i) outer closure plates made of stainless steel, ii) the external reactor structure constructed from polypropylene, iii) internal spacers composed of Viton, and iv) titanium current collectors. In the anode compartment, an iridium mixed oxide plate acts as the counter electrode for the water oxidation reaction. As the cathode, a Gas Diffusion Electrode (GDE) is employed, with an active geometric area of 100 cm². This electrode is fabricated by automated spray pyrolysis, a process that has been previously optimized [2]. The catalytic ink consists of the catalyst (commercial Bi₂O₃) and Vulcan, with a mass ratio of 50:50, suspended in ethanol as a solvent and Nafion D-521 as a binder. This ink is applied over a Teflon-coated (50 %) carbon paper. Finally, a Nafion cation exchange membrane (CEM) separates the cathode and anode compartments.

The electrochemical reactor operates in an L-G configuration, a humified CO₂ pure stream is fed to the cathode compartment with a flow rate of 20 mL min^-1 cm^-2, while in the anode an alkaline 1 M KOH anolyte is pumped at 0.57 mL min^-1 cm^-2. Preliminary tests were carried out in the L-G configuration, supplying a current density in a range of 30 to 300 mA cm^-2 to the system.

After construction, the prototype underwent testing to evaluate its performance. In this regard, the system operated continuously for 2 hours with a single pass of CO₂ and electrolyte through the system. The applied current density was varied in a range from 30 to 300 mA cm^-2 in different experiments.  The results of these preliminary tests are shown in Figure 1. The most promising performance is reached working at 200 mA cm^-2, with a formate concentration of 760 g L^-1, an FE of 67 %, and an Energy consumption of 510 kWh kmol^-1. These outcomes improve the performance in prior lab-scale experiences within the research group [3], therefore, the system is demonstrated to be scalable. Nevertheless, ongoing efforts are necessary to improve the system's stability and efficiency, optimizing the electrochemical cell's operational variables, such as the humidity in the cathode feed, the anolyte composition and flowrate, or the CO₂ feed flowrate.

The efforts invested in designing and constructing an industrial demonstrator of a CO₂ electrolyzer have yielded a functional prototype with promising results in preliminary tests, showcasing the scalability of CO₂ electroreduction technology. Future work should be dedicated to maximizing the stability and efficiency of the system in long-term operations.