Two-step electrochemical reduction of CO₂ is investigated as an alternative to increase selectivity towards C₂ and C₃ products. In this type of proposed cascade electrocatalytic operation, CO is produced in a first step and subsequently reduced to multi-carbon products in a second step with significantly higher Faradaic efficiencies compared to a one-step process. Research efforts have been focused on the feasibility of the isolated second step with pure CO as reactant, however the interdependencies of both steps need to be considered. Accordingly, two-step electrochemical reduction of CO₂ is studied in this work as an integrated system. Taking into account that the study of this technology at high current densities is crucial for industrial applicability, gas diffusion electrodes and flow-cells were used for operation at current densities above −200 mA cm⁻² . Firstly, each step was characterized separately, the first using a silver gas diffusion electrode to generate a mixture of humidified CO, H₂, and unreacted CO₂; the second step using copper nanoparticles on a carbon-based gas diffusion structure to obtain C₂ and C₃ products. This step was studied using synthetic mixtures of CO₂ and CO with different ratios. Furthermore, experiments with isotope labeled ¹³CO₂ and ¹³CO were performed in order to obtain some insights on the (electrochemical) reaction path of gas mixtures containing CO₂ and CO. Subsequently, the two units were integrated into a system, where the full gas output of the first unit was directly fed to the second unit. The total Faradaic efficiency towards multi-carbon products of this initial system was limited to 20% at total current density of −470 mA cm⁻². These initial results together with the isotopic labeling studies indicate that the presence of significant amounts of unreacted CO₂ from the first step is detrimental for the second step. A significant improvement was achieved by introducing a CO₂ absorption column between the two units and after splitting the overall charge flow applied in each cell in accordance with the main reaction at each step. With this set-up a total Faradaic efficiency towards C₂ and C₃ products of 62% at a total current density of −300 mA cm⁻² was achieved. The results confirm the need for a gas separation technique between the two steps for a feasible two-step electrochemical reduction of CO₂.

为了增加对C ₂和C ₃产物的选择性，研究了CO ₂的两步电化学还原。在这种类型的建议的级联电催化操作中，与第一步工艺相比，第一步要生成一氧化碳，然后在第二步中将其还原成具有更高法拉第效率的多碳产物。研究工作已集中在以纯CO作为反应物的分离的第二步的可行性上，但是需要考虑这两个步骤之间的相互依赖性。因此，CO ₂的两步电化学还原在这项工作中作为一个集成系统进行了研究。考虑到在高电流密度下对该技术的研究对于工业实用性至关重要，因此气体扩散电极和流通池用于在-200 mA cm ^-2以上的电流密度下运行。首先，每个步骤分别进行特征描述，首先使用银气扩散电极产生加湿的CO，H ₂和未反应的CO ₂的混合物。第二步是在碳基气体扩散结构上使用铜纳米颗粒，以获得C ₂和C ₃产物。使用不同比例的CO ₂和CO的合成混合物研究了这一步骤。此外，用同位素标记的实验^进行13 CO ₂和¹³ CO的目的是对含CO ₂和CO的气体混合物的（电化学）反应路径有所了解。随后，将这两个单元集成到一个系统中，第一个单元的全部气体输出被直接送入第二单位。在-470 mA cm ^-2的总电流密度下，此初始系统对多碳产物的总法拉第效率限制为20％。这些初步结果以及同位素标记研究表明，第一步中存在大量未反应的CO ₂对第二步有害。通过引入CO ₂获得了显着的改善吸收塔在两个单元之间，并根据每个步骤的主要反应将施加在每个单元中的总电荷流分开后。通过这种设置，在-300 mA cm ^-2的总电流密度下，对于C ₂和C ₃产物的总法拉第效率达到62％。结果证实需要在两步之间使用气体分离技术以实现可行的两步电化学还原CO _2的方法。