Prototype Validation of a Large-Scale CO₂-to-Formate Zero-Gap Electrolyzer

The scale-up of gas-phase CO₂ electroreduction to formate is crucial for its industrial application but remains largely unexplored. This work presents the design and validation of a 100 cm² electrolyzer prototype featuring a zero-gap configuration and a serpentine flow field to ensure uniform CO₂ distribution. Scaling up a CO₂ electrolyzer requires optimized flow field design, in this case, a serpentine geometry enhances CO₂ transport and minimizes mass transfer limitations, thereby improving overall performance. Experimental prototype testing is conducted to evaluate the effects of current density and water content in the CO₂ feed. Optimal performance is achieved at 200 mA cm^{- 2} and a water content of 15 g h^{- 1}, yielding a formate concentration of 760 g L^{- 1}, a Faradaic efficiency of 67%, a production rate of 7 mmol m^{- 2} s^{- 1}, and an energy consumption of 507 kWh kmol^{- 1}. Comparisons with a 10 cm² lab-scale reactor reveal improved CO₂ conversion and production rate, validating the benefits of optimized flow field design and scale-up approach. While energy efficiency is somewhat reduced to increased Ohmic losses, the overall results support the technical feasibility of scaling gas-phase CO₂-to-formate electrolysis. Further improvements in design and energy management are still needed to advance toward industrial implementation.