Hydrophobic SiO₂ Armor: Stabilizing Cu^δ+ to Enhance CO₂ Electroreduction toward C₂₊ Products in Strong Acidic...

Electroreduction of CO₂ in highly acidic environments holds promise for enhancing CO₂ utilization efficiency. Due to the HER interference and structural instability, however, challenges in improving the selectivity and stability toward multicarbon (C₂₊) products remain. In this study, we proposed an "armor protection" strategy involving the deposition of ultrathin, hydrophobic SiO₂ onto the Cu surface (Cu/SiO₂) through a simple one-step hydrolysis. Our results confirmed the effective inhibition of HER by a hydrophobic SiO₂ layer, leading to a high Faradaic efficiency (FE) of up to 76.9% for C₂₊ products at a current density of 900 mA cm^-2 under a strongly acidic condition with a pH of 1. The observed high performance surpassed the reported performance for most previously studied Cu-based catalysts in acidic CO₂RR systems. Furthermore, the ultrathin hydrophobic SiO₂ shell was demonstrated to effectively prevent the structural reconstruction of Cu and preserve the oxidation state of Cu^δ+ active sites during CO₂RR. Additionally, it hindered the accumulation of K⁺ ions on the catalyst surface and diffusion of in situ generated OH^- ions away from the electrode, thereby favoring C₂₊ product generation. In situ Raman analyses coupled with DFT simulations further elucidated that the SiO₂ shell proficiently modulated *CO adsorption behavior on the Cu/SiO₂ catalyst by reducing *CO adsorption energy, facilitating the C-C coupling. This work offers a compelling strategy for rationally designing and exploiting highly stable and active Cu-based catalysts for CO₂RR in highly acidic environments.