Block Copolymer Particle-Templated Cavitated Carbons Achieve Local Alkalinity for Enhancing Acidic Electrochemical CO2 Reduction.

Electrochemical CO2 reduction reaction (CO2RR) in neutral or alkaline environment suffers from carbonate formation, leading to low CO2 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 CO2RR 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 CO2 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 CO2RR under highly acidic conditions, providing a viable pathway for efficient CO2 electrolysis.