Cationic carbon nanotube modulates surface fields for general acidic CO2 reduction with aqueous organic cations

The (bi)carbonate formation in neutral or alkaline media severely limits the carbon and energy efficiency of electrochemical CO2 reduction reaction (CO2RR). Alkali metal cations and polymer coatings employed to inhibit hydrogen evolution reaction (HER) during acidic CO2RR often exacerbate salt precipitation or increase cell resistivity. Here we report cationic carbon nanotubes (CCNTs) as universal additives enabling efficient CO2RR in strong acids. Using bismuth, silver, and copper oxide catalysts, we attain Faradaic efficiency (FE) of 95%, 100%, and 67% for HCOOH, CO, and C2H4 in pH≤1 electrolyte. Notably, while organic cations typically suffer from poor proton shielding and inferior selectivity, CCNT additives enable their use as electrolytes for selective acidic CO2RR. Their higher solubility permits elevated concentrations, improving stability and energy efficiency. Quantum Mechanics reveals that CCNTs physically mixed with metal catalysts alter the distribution of electric field at the electrolyte/electrode interfaces, impeding HER by suppressing hydronium ions migration while promoting CO2RR. These findings highlight CCNTs as versatile and effective additives for advancing acidic CO2RR with improved selectivity, carbon efficiency, energy efficiency, and stability. Carbonate formation limits the efficiency of CO2 electroreduction in neutral or alkaline media. Here, the authors report that cationic carbon nanotubes as universal additives enable efficient acidic CO2 reduction by suppressing H2 evolution with improved carbon efficiency and product selectivity.