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.