Breaking the C–C coupling barrier in pressurized CO2RR: local alkalinity control against buffering of CO2 species at industrial current densities

Abstract

Elevating the operating pressure could significantly enhance CO₂ accessibility on the catalyst in electrochemical CO₂ reduction (CO₂RR); however, achieving selective production of multi-carbon (C₂₊) products under pressurized conditions remains a critical challenge because elevated pressure could shift the selectivity towards C₁ products. This work systemically investigated the variation of product selectivity induced by pressure and electrolyte composition, and demonstrates that a local pH drop induced by increased pressure is the key reason for hindered C–C coupling, as confirmed by in situ Raman and multi-physics simulation. The elevated pressure results in an increase of the electrolyte's buffering capacity, which neutralizes the alkaline microenvironment near the catalyst, thereby impeding the C–C coupling. Decreasing the buffering ability (using non-buffered KCl electrolyte) or increasing the current density (from 0.4 A cm⁻² to 1.0 A cm⁻²) could maintain a high interfacial alkalinity under elevated pressure, promoting C–C coupling. By mapping pressure–current density operational windows, the optimal conditions were identified, achieving 70% C₂ faradaic efficiency (50% for C₂H₄) at 5 bar and 1 A cm⁻², demonstrating superior C₂ product selectivity. This work establishes electrolyte engineering principles for industrial CO₂RR, enabling carbon-neutral chemical production under practical pressurized conditions through microenvironmental regulation.