Substituent tuning of Cu coordination polymers enables carbon-efficient CO2 electroreduction to multi-carbon products.

CO₂ electroreduction is a potential pathway to achieve net-zero emissions in the chemical industry. Yet, CO₂ loss, resulting from (bi)carbonate formation, renders the process energy-intensive. Acidic environments can address the issue but at the expense of compromised product Faradaic efficiencies (FEs), particularly for multi-carbon (C₂₊) products, as rapid diffusion and migration of protons (H⁺) favors competing H₂ and CO production. Here, we present a strategy of tuning the 2-position substituent length on benzimidazole (BIM)-based copper (Cu) coordination polymer (CuCP) precatalyst – to enhance CO₂ reduction to C₂₊ products in acidic environments. Lengthening the substituent from H to nonyl enhances H⁺ diffusion retardation and decreases Cu-Cu coordination numbers (CNs), favoring further reduction of CO. This leads to a nearly 24× enhancement of selectivity towards CO hydrogenation and C-C coupling at 60 mA cm⁻². We report the highest C₂₊ product FE of more than 70% at 260 mA cm⁻² on pentyl-CuCP and demonstrate a CO₂-to-C₂₊ single-pass conversion (SPC) of ~54% at 180 mA cm⁻² using pentyl-CuCP in zero-gap electrolyzers. Acidic CO₂ electroreduction suffers poor selectivity for multi-carbon products. Here, the authors report that lengthening the 2-position substituents of benzimidazole-based copper coordination polymer precatalysts retards H⁺ diffusion, reduces Cu-Cu coordination numbers, and promotes C-C coupling. [ABSTRACT FROM AUTHOR]