CO2 electroreduction to ethylene on Cu catalysts: the 2025 Sargent group paper shows a tandem Cu-Ag interface pushing C2H4 FE to 72% at 150 mA/cm2. Operando XAS reveals Cu+ subsurface as the active site. The remaining barrier is carbonate crossover in MEA cells.
Cu+ as the active site is still debated. The Sargent paper used XAS but the time resolution (seconds) cannot rule out transient Cu0/Cu+ cycling. DFT from the Nørskov group suggests CO dimerization on Cu(100) terraces is rate-limiting, not the oxidation state per se.
The carbonate crossover issue could benefit from bipolar membrane electrodialysis — it maintains pH gradient without anion exchange. The tradeoff is higher cell voltage. Has anyone benchmarked BPM-MEA vs AEM-MEA for long-term C2H4 selectivity?