(309b) In-Situ Activation of Pre-Catalyst Improves CO2 Conversion to Ethanol in Pulsed Electrolysis

Electrochemical conversion of dissolved CO₂ in bicarbonate electrolytes, i.e., bicarbonate electrolysis, offers distinct advantages over gas diffusion electrode systems by allowing direct utilization of CO₂ capture solution as electrolyte while bypassing the energy-intensive CO₂ release and by eliminating the need for CO₂ separation and purification. However, bicarbonate electrolysis is prone to CO₂ mass transfer limitations and local pH-driven CO₂ depletion. Pulsed electrolysis with resting time > 10 sec has increased CO₂ concentration, but the required cathodic potentials remained very high (e.g., -1.6 V vs RHE for 300 mA/cm²). The higher potential often causes catalyst surface reorganization, gradually losing active sites and variations in selectivity to CO₂ reduction reaction (CO₂RR). Here, we report directed pre-catalyst evolution via an in-situ activation method that allows pre-catalysts to equilibrate under dynamic (pulsed) electrolysis conditions before employing it for CO₂RR. We demonstrate in-situ activation of Cu₂O/Cu mesh, which under short-width (t = 4s) pulsed electrolysis provides stable mixed oxidation states of Cu, favoring ethanol-rich crude mixture formation. The pulse electrolysis waveform consisting of six distinct segments is tuned to form Cu¹⁺ oxides, followed by its reduction to generate local alkaline conditions favoring C-C coupling. This synergistic effect results in FEs of 72% for C₂₊ products, 52% for total liquid products, and 39% for ethanol at an applied current density of 150 mA/cm² and a cathodic potential of -1.1V vs. RHE. The in-situ cyclic voltammetry confirms the formation of Cu²⁺/Cu¹⁺, whereas ex-situ elemental and structural analysis show a near-stable state of post-electrolysis samples. The 1D electrochemical model explains the role of pulsed CO₂RR in dynamic local pH and enhanced CO₂ concentration gradients near the catalyst/electrolyte interface, which helps steer selectivity towards C₂₊ products. Overall, this study provides new insights into the synergistic effect of in-situ activation of pre-catalyst and pulsed electrolysis for higher selectivity towards C₂₊ products.