Metal-Dependent Regulation of CO2-to-Syngas Electroreduction in Cation-Exchanged SU-102.

Electrochemical CO2-to-syngas conversion requires simultaneous control over CO2 reduction and hydrogen evolution within stable electrocatalysts. Here, we show that post-synthetic cation exchange in the robust anionic Zr-based MOF SU-102 enables tunable syngas electrosynthesis while preserving framework crystallinity. Exchange of the charge-balancing DMA+ cations with Zn2+ or Ag species generates distinct catalytic behaviors during CO2 electroreduction. SU-102-Zn exhibits balanced and relatively potential-independent syngas production, whereas SU-102-Ag promotes CO-rich syngas generation with strongly potential-dependent selectivity, reaching a CO Faradaic efficiency of 93% at −1.4 V versus RHE. Structural characterization reveals that Zn remains incorporated as exchanged cationic species, while Ag undergoes partial reduction to form metallic Ag domains stabilized by the MOF scaffold. Density functional theory calculations indicate that Zn2+ and Ag regulate syngas formation through distinct catalytic mechanisms, where Zn2+ sites within the MOF framework promote balanced syngas production, while metallic Ag domains drive potential-dependent CO selectivity. This work demonstrates that post-synthetic cation exchange in stable anionic MOFs provides an effective strategy for regulating syngas composition through modulation of local catalytic environments.