(307e) Insights from the Systems Scale to Design Practical CO2 Electrolyzers

Electrochemical CO₂ reduction (CO₂R) can convert captured CO₂ into chemical feedstocks and fuels using renewable electricity and water, but scaleup has been limited. To guide academic research towards the most important problems facing industrial-scale CO₂R, I will discuss process and reactor co-design in this talk. We use a physics-informed technoeconomic assessment to address the sensitivity of overall process cost towards improvements at the electrolyzer scale, identifying the most impactful research directions for the field to pursue. The assessment confirms the importance of better materials (membranes, catalysts), which has been the focus of the field, and of cheaper electricity. However, we find a critical and overlooked need for improved reactor design to make CO₂R economically viable.

Our work has shown the tradeoff between single-pass conversion and selectivity for CO₂ electrolyzers, a limitation that arises directly from current reactor design. Selectivity hugely impacts costs because low selectivity wastes electrolyzer energy on making hydrogen. Due to selectivity loss, we show that increasing single-pass conversion beyond ~10% increases process cost. The relationship between selectivity and single-pass conversion arises directly from the plug-flow channel design. Therefore, we call on the field to investigate reactor designs that modify this crucial handle on CO₂R cost. Mitigating carbonate crossover, an effort within the field, leads to relatively small improvements in cost. Moreover, current density >1 A/cm² has been repeatedly proposed as a target. However, we show that a tradeoff arises between capex and utility cost. At current electricity prices, the optimal total current density is <300 mA/cm². High operating currents will worsen process costs, unless accompanied by much lower electricity costs.