In Situ Phase Transformation-Enabled\nMetal–Organic\nFrameworks for Efficient CO<sub>2</sub> Electroreduction to Multicarbon\nProducts in Strong Acidic Media

The\nelectrochemical CO<sub>2</sub> reduction reaction\n(CO<sub>2</sub>RR) has been acknowledged as a promising strategy to\nrelieve carbon\nemissions by converting CO<sub>2</sub> to essential chemicals. Despite\nsignificant progresses that have been made in neutral and alkaline\nmedia, the implementation of CO<sub>2</sub>RR in acidic conditions\nremains challenging due to the harsh conditions, especially in producing\nhigh-value multicarbon products. Here, we report that Cu-btca (btca\n= benzotriazole-5-carboxylic acid) metal–organic framework\n(MOF) nanostructures can act as a stable catalyst for the CO<sub>2</sub>RR in an acidic environment. The Cu-btca MOF undergoes phase transformation\nand morphology evolution during electrolysis, forming a stable porous\nCu-btca MOF network. The resultant MOF network exhibits excellent\nselectivity toward ethylene and multicarbon products with Faradaic\nefficiencies of 51.2% and 81.9%, respectively, in a strong acidic\nelectrolyte with a flow cell at 300 mA/cm<sup>2</sup>. Mechanism studies\nuncover that the Cu-btca MOF network can limit the proton reduction\nto suppress hydrogen evolution and maintain high local *CO concentration\nto promote CO<sub>2</sub>RR. Theoretical calculations suggest that\ntwo adjacent Cu sites in the Cu-btca MOF provide a favorable microenvironment\nfor carbon–carbon coupling, facilitating the multicarbon production.\nThis work reveals that rational structure control of MOFs can enable\nhighly selective and efficient CO<sub>2</sub> electroreduction to\nmulticarbon products in strong acidic conditions toward practical\napplications.