The electrochemical CO₂ reduction reaction (CO₂RR) is a key enabling technology for transitioning from fossil-derived feedstocks toward sustainable manufacturing using CO₂. Among the most relevant application areas is the textile industry, where polyester production remains almost entirely dependent on petrochemical intermediates despite its significant environmental footprint. Achieving industrial production of polyester precursors from CO₂ requires efficient and scalable electrolysis of CO₂ to CO, placing electrolyzer and system-level scale-up at the core of technological development.

In this work, we investigate the scale-up of CO₂ electrolysis systems from laboratory scale to a TRL 6 pilot-scale platform, with a focus on electrolyzer design, long-term operation, and system integration. To address the issue of large hydraulic pressure, we developed robust in-house cathodes capable of withstanding flooding while maintaining electrochemical performance. Furthermore, the differential pressure was studied, to maintain electrolysis in flow-by operation window. High CO₂ flow rates improve throughput but lead to product dilution and increased downstream separation costs. In addition, ion crossover across the membrane was identified as a major driver of electrolyte imbalance and long-term performance degradation, highlighting critical constraints for durable operation at scale. Through optimization of operating conditions and cell design, stable operation for over 60 h was demonstrated at 150 mA/cm² in a flow-by electrolyzer configuration, maintaining CO selectivity above 90%. We further established preliminary operational recovery protocols following cell failure, enabling robust restart.

These findings were translated into pilot-scale system engineering through comprehensive process flow diagrams (PFDs) and piping and instrumentation diagrams (P&IDs). The balance-of-plant was designed for fully automated operation enabling real-time monitoring, and process control. A modular electrolyzer platform with a 0.36 m² unit cell area was designed and scaled to stacks of up to 80 cells. Parallel development of scalable cathode manufacturing, including ink formulation and batch processing, enabled translation to large-area electrodes. This work demonstrates a complete scale-up pathway for CO₂ electrolysis, towards high CO production.