As global efforts to achieve carbon neutrality intensify, electrochemical CO₂ reduction (CO₂RR) has emerged as a promising pathway for converting waste CO₂ into value-added chemicals and fuels. However, the competing hydrogen evolution reaction (HER) severely limits the selectivity and efficiency of CO₂-to-C₂+ conversion. Now, a collaborative team led by Professor Chanyeon Kim (DGIST), Professor Chang Hyuck Choi (POSTECH), and Professor Seoin Back (Korea University) has presented a breakthrough strategy that redefines interfacial water management for selective CO₂-to-ethanol electrolysis.

Why This Microenvironment Matters

Traditional approaches to suppress HER have focused on tuning catalyst hydrophobicity or modifying bulk electrolyte pH—yet these methods either impede CO₂ mass transport or fail to inhibit water dissociation under neutral/alkaline conditions. The novel hetero-solvent microenvironment overcomes these limitations by confining diglyme (DiG) near the Cu catalyst via a Nafion protective layer, fundamentally restructuring interfacial water hydrogen-bonding networks without altering the catalyst itself.

Innovative Design and Mechanism

The Naf/DiG/Cu electrode architecture strategically localizes DiG within the catalytic microenvironment rather than the bulk electrolyte. In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and ab initio molecular dynamics (AIMD) simulations reveal that DiG strengthens the hydrogen-bonding network of interfacial water, substantially reducing free-water populations prone to dissociation. This modulation simultaneously suppresses the Volmer step of HER and redirects hydrogenation pathways: the solvent-mediated Eley-Rideal (ER) mechanism favoring ethylene formation is kinetically hindered (1.468 eV barrier), while the Langmuir-Hinshelwood (LH) pathway promoting ethanol becomes dominant (0.951 eV barrier).

Outstanding Performance

The Naf/DiG/Cu electrode achieves unprecedented CO₂-to-ethanol metrics under neutral conditions. The ethanol partial current density reaches 89.5 mA cm^-2 at 3.6 V cell voltage—2.6-fold higher than Naf/Cu and 5.3-fold higher than bare Cu. Notably, the ethanol-to-ethylene selectivity ratio is fundamentally inverted: while conventional Cu intrinsically favors C₂H₄, the hetero-solvent microenvironment steers selectivity toward C₂H₅OH across all tested potentials. HER is suppressed by 2.4-fold compared to bare Cu, with overall CO₂RR activity reaching 219.6 mA cm^-2.

Scalability and Record-Breaking Results

Because this strategy engineers the microenvironment rather than the catalyst, it readily extends to other systems. When applied to Cu-Ag bimetallic catalysts, the Naf/DiG/Cu-Ag electrode delivers a record-breaking ethanol partial current density of 184.2 mA cm^-2 at 3.6 V—the highest reported for MEA-based CO₂RR under neutral conditions—while maintaining an exceptional ethanol-to-ethylene ratio of 2.6. Long-term stability tests demonstrate 100 hours of continuous operation at 150 mA cm^-2 with minimal degradation, confirming that DiG remains stably confined within the microenvironment.

Applications and Future Outlook

This work establishes interfacial water control via hetero-solvent microenvironments as a universal design principle for aqueous electrocatalysis. Beyond CO₂RR, the strategy opens promising avenues for ammonia synthesis, water electrolysis, and organic electrosynthesis where interfacial water management is critical. By decoupling microenvironment engineering from catalyst design, this approach offers a scalable, cost-effective pathway toward industrial-scale electrochemical manufacturing.
Stay tuned for more groundbreaking research from this collaborative team at DGIST, POSTECH, Korea University, and KIST!