Nanocapillarity and Nanoconfinement Effects of Pipet-like Bismuth@Carbon Nanotubes for Highly Efficient Electrocatalytic CO₂ Reduction

Electrocatalytic CO₂ reduction reaction is regarded as an intriguing route for producing renewable chemicals and fuels, but its development is limited by the lack of highly efficient and stable electrocatalysts. Herein, we propose the pipet-like bismuth (Bi) nanorods semifilled in nitrogen-doped carbon nanotubes (Bi-NRs@NCNTs) for highly selective electrocatalytic CO₂ reduction. Benefited from the prominent capillary and confinement effects, the Bi-NRs@NCNTs act as nanoscale conveyors that can significantly facilitate the mass transport, adsorption,and concentration of reactants onto the active sites, realizing rapid reaction kinetics and low cathodic polarization. The spatial encapsulation and separation by the NCNT shells prevents the self-aggregation and surface oxidation of Bi-NRs, increasing the dispersity and stability of the electrocatalyst. As a result, the Bi-NRs@NCNTs exhibit high activity and durable catalytic stability for CO₂-to-formate conversion over a wide potential range. The Faradaic efficiency for formate production reaches 90.9% at a moderate applied potential of −0.9 V vs reversible hydrogen electrode (RHE).