Selective and High Current CO₂ Electro-Reduction to Multicarbon Products in Near-Neutral KCl Electrolytes

Abstract

Reducing CO₂ to value-added multicarbon (C₂₊) fuels and chemicals using renewable energy is a viable way to circumvent CO₂ buildup in the atmosphere and facilitate closing the carbon cycle. To date it remains a challenge to achieve high product selectivity and long-term stability of electrocatalytic carbon dioxide reduction reaction (CO₂RR) especially at practically relevant high current levels >100 mA cm^-2. Here, we report a simple electrodeposited Cu electrocatalyst on a hydrophobic porous gas-diffusion layer (GDL) electrode affording stable and selective CO₂RR to C₂₊ products in near-neutral KCl electrolytes. By directing the CO₂ stream to fully submerged hydrophobic GDLs in a H-cell, high C₂₊ partial current densities near 100 mA cm^-2 were achieved. In a flow-cell setup, the Cu/GDL cathode in 2 M KCl afforded stable CO₂RR superior to that in widely used KOH electrolytes. We found that Cu etching/corrosion associated with trace oxygen played a role in the catalyst instability in alkaline media under cathodic CO₂RR conditions, a problem largely suppressed in near-neutral electrolyte. A two-electrode CO₂ electrolyzer was constructed with a Cu/GDL cathode in KCl catholyte and an anode comprised of nickel-iron hydroxide on nickel foam (NiFe/NF) in a KOH anolyte separated by Nafion membrane. By periodically adding HCl to the KCl catholyte to compensate the increasing pH and remove accumulated (bi)carbonates, we observed little decay over ∼30 h in flow-cell CO₂RR activity and selectivity at 150 mA cm^-2 with a high Faradaic efficiency (FE) of ∼75% and energy efficiency of 40% for C₂₊ products.