Breaking the water barrier: synergistic regulation of the reaction route in plasma-catalytic CO₂–H₂O conversion to acetic acid using biochar and a hydrophobic catalyst

While serving as a safe, abundant hydrogen source, H₂O plays a dual role in plasma-enabled CO₂–H₂O conversion into hydrocarbons, presenting seemingly inevitable challenges for high conversion rate and selectivity by promoting recombination, water–gas shift and steam reforming reactions. To address these challenges, we demonstrate a novel pathway of plasma-catalytic CO₂–H₂O conversion into acetic acid (AA) by introducing biochar to mitigate the recombination reaction and designing a hydrophobic core–shell catalyst to suppress H₂O-induced side reactions. The synergism of plasma-driven radical generation, biochar-mediated radical regulation and hydrophobic shell-protected catalysis enables efficient delivery of intermediates to Fe–Zn sites, facilitating the conversion of CO₂ into AA through the Eley–Rideal mechanism, confirmed by in situ Fourier transform infrared characterization and density functional theory calculations. When implemented in a scale-up conversion (2000 sccm) at current densities up to 7000 mA cm⁻², the integrated system achieves record-high metrics: 99% liquid-phase selectivity, 38 mmol h⁻¹ production rate and stable operation for 50 h, marking a significant step toward industrial feasibility in CO₂–H₂O conversion.