In Situ Phase Transformation-Enabled Metal–Organic Frameworks for Efficient CO2 Electroreduction to Multicarbon Products in Strong Acidic Media

The electrochemical CO₂ reduction reaction (CO₂RR) has been acknowledged as a promising strategy to relieve carbon emissions by converting CO₂ to essential chemicals. Despite significant progresses that have been made in neutral and alkaline media, the implementation of CO₂RR in acidic conditions remains challenging due to the harsh conditions, especially in producing high-value multicarbon products. Here, we report that Cu-btca (btca = benzotriazole-5-carboxylic acid) metal–organic framework (MOF) nanostructures can act as a stable catalyst for the CO₂RR in an acidic environment. The Cu-btca MOF undergoes phase transformation and morphology evolution during electrolysis, forming a stable porous Cu-btca MOF network. The resultant MOF network exhibits excellent selectivity toward ethylene and multicarbon products with Faradaic efficiencies of 51.2% and 81.9%, respectively, in a strong acidic electrolyte with a flow cell at 300 mA/cm². Mechanism studies uncover that the Cu-btca MOF network can limit the proton reduction to suppress hydrogen evolution and maintain high local *CO concentration to promote CO₂RR. Theoretical calculations suggest that two adjacent Cu sites in the Cu-btca MOF provide a favorable microenvironment for carbon–carbon coupling, facilitating the multicarbon production. This work reveals that rational structure control of MOFs can enable highly selective and efficient CO₂ electroreduction to multicarbon products in strong acidic conditions toward practical applications.