Electrochemical CO2 reduction is a selectivity problem: the same cell can yield CO, formate, syngas, ethylene or methane depending on catalyst, potential and transport. A flow electrolyzer makes those variables controllable, and then product analysis has to keep up with the data rate.
CO2 electrolysis is mass-transport limited at practically interesting currents: the reactant is a dissolved gas with modest solubility. Flow cells with gas diffusion electrodes feed CO2 directly to the catalyst layer, bypassing the solubility ceiling. Hydrodynamics, electrolyte flow and CO2 delivery, become designed parameters instead of stirring artifacts.
Fix the electrolyte composition and flow; control cell temperature; and hold potentials long enough for selectivity to settle, product distributions drift during the first minutes at a new potential. Report partial current densities per product, total current times faradaic share, which separates activity from selectivity cleanly.
Gas products (CO, CH4, C2H4, H2) to online GC or detectors on a continuous basis; liquid products (formate, alcohols) from electrolyte aliquots by NMR, IC or chromatography. The analysis must close the carbon balance, when current flows but carbon is missing, the measurement, not the catalyst, is failing.
Faradaic efficiency per product, energy efficiency including cell voltage, single-pass conversion, and stability at industrially relevant current densities. A catalyst that is selective only at low current solves a laboratory problem, not the world's.
Perfectlight's electrolysis reactors and online analysis support CO2RR campaigns; see electrocatalysis solutions.
