Our results reveal that the anodic oxygen evolution reaction (OER) accounts for the largest overpotential—approximately 40% of the total cell voltage. By tailoring anode catalyst composition and interface chemistry, we achieve a 0.8 V reduction, significantly improving system efficiency. DRT enables precise assignment of physical and electrochemical processes: water transport (<1 Hz), gas diffusion (1–10 Hz), and charge transfer (5–20 kHz) for CO2 reduction, HER, and OER. Importantly, we report the first observation of water dissociation (WD) in BPMs at >20 kHz, with frequency and resistance signatures varying across membrane chemistries.
These insights also uncover cathodic mass transport limitations, guiding ionomer and catalyst layer optimization to suppress HER and enhance CO selectivity at high current densities. This work demonstrates how frequency-resolved diagnostics can enable rational MEA design and accelerate the development of energy-efficient BPM-CO2 electrolysis systems.