Evaluating the Stability of Oxide-Derived Cu─Sn Catalysts for CO₂ Reduction in Zero-Gap Electrolyzers

Bimetallic electrocatalysts hold substantial potential for scaling up CO₂ electroreduction, yet their practical deployment is hindered by a persistent gap between conventional three-electrode testing and industrially relevant electrolyzer conditions. In this study, we employed an oxide-derived Cu─Sn catalyst with a high CO Faradaic efficiency (FE) of 92.4% as a model catalyst to evaluate the electrochemical stability under realistic zero-gap CO₂ electrolyzers. During extended operation, the FE of CO gradually decreased before stabilizing after approximately 48 h, reaching a CO-to-formate ratio close to 1:1. In-situ and quasi-in-situ spectroscopic analyses revealed that this shift in selectivity correlates with the partial transformation of the catalyst into a Cu₆Sn₅ alloy. To remediate this performance loss and regenerate the active state, an in-situ cyclic voltammetry (CV) protocol was applied to re-oxidize the metallic components, effectively reversing the alloying process and restoring the high CO selectivity. This work correlates the oxidation state of Cu─Sn with its catalytic behavior in zero-gap electrolyzers, and demonstrates a practical recovery protocol to enhance operational stability, highlighting the potential of dynamic catalyst management for industrial CO₂ electrolysis.