A Scalable, Biopolymer-Based Microenvironment for Electrochemical CO2 Conversion to Multicarbon Products with Current Densities Over 2 A/cm2

The electrochemical CO₂ reduction reaction (CO₂RR) offers a sustainable approach for converting CO₂ into valuable fuels and chemicals. CO₂RR relies on copper (Cu) catalysts to produce desirable multicarbon (C₂₊) products, but C₂₊ yields rely heavily on the surrounding microenvironment. Moreover, controlling the microenvironment to achieve high C₂₊ yields at industrially-relevant current densities remains a persistent challenge. To address this challenge, we show that biopolymer coatings on the Cu electrodes can tune the microenvironment, enabling a new strategy to achieve high yields of C₂₊ products at ultra-high current densities. This approach achieves remarkable C₂₊ Faradaic efficiencies (FE_C2+) of 90±1.7% at 1.6 A cm^-2 and FE_C2+=83±3.2% at 2.2 A cm^-2 with a formation rate of 5925.9 μmol h⁻¹ cm⁻². Furthermore, these biopolymers can even fully substitute traditional ionomers and binders, such as Nafion, within the cathode. Our findings challenge previous assumptions about the non-viability of hydrophilic materials for CO₂RR and provide critical new insights into microenvironment design to enhance C-C coupling. Several complementary investigations reveal that biopolymer coatings increase local CO₂/CO concentration, lower local water activity, and provide suitable ion conductivity and local pH. We anticipate that these molecular-level insights represent a paradigm shift in catalyst design to unlock new approaches to optimize the microenvironment for CO₂RR to enable high rates of C-C coupling without the typical unwanted increase in hydrogen evolution. These abundant biopolymer coatings are environmentally benign, solution-processable, and highly accessible, which is expected to provide researchers with a facile route towards high-performance CO₂RR at both laboratory and industrial scales.