Block Copolymer Particle‐Templated Cavitated Carbons Achieve Local Alkalinity for Enhancing Acidic Electrochemical CO ₂ Reduction

ABSTRACT Electrochemical CO ₂ reduction reaction (CO ₂ RR) in neutral or alkaline environment suffers from carbonate formation, leading to low CO ₂ utilization. Acidic operation can mitigate this issue, but is hampered by the dominant hydrogen evolution reaction (HER). Here, we report a cavitated carbon particle (CCP)–supported Au catalyst featuring abundant inner cavities that sustain elevated local alkalinity. These cavities could be formed by inducing interfacial instability in block copolymer particles. A solid carbon particle (SCP)‐supported Au catalyst, which does not possess any cavities, was also synthesized, and the effect of the cavity for the CO ₂ RR was evaluated in 5 wt.% Au/CCP and Au/SCP catalysts at pH 2. Flow cell data and multi‐physics simulation results confirm that a confined cavity geometry (diameter ∼130 nm) could increase local alkalinity significantly, suppressing HER and enhancing CO ₂ reduction. The microenvironment was further modulated by changing the binder type, cation identity, and cation concentration. These findings establish cavity confinement as a powerful strategy to modulate the local reaction environment and enable selective CO ₂ RR under highly acidic conditions, providing a viable pathway for efficient CO ₂ electrolysis.