Stability and Performance of Sn–Zn/C versus Sn–Cu/C Bimetallic Catalysts for Electrochemical Formic Acid Production Under Realistic Diluted Feed Conditions

Electrochemical CO 2 reduction to formic acid enables sustainable carbon utilization, yet industrial deployment demands catalysts stable under realistic diluted feeds (10%–20% CO 2 ) rather than laboratory‐standard pure CO 2 . We systematically compare electrodeposited Sn–Zn/C and Sn–Cu/C bimetallic cathodes in Proton Exchange Membrane electrolyzers under pure (100%) and diluted (50%) CO 2 feeds, bridging the lab‐to‐industry gap. Under pure CO 2 , Sn–Zn/C achieves 40.81% Faradaic efficiency (FE) for formic acid versus 29.17% for Sn–Cu/C. Critically, under diluted CO 2 , Sn–Zn/C retains 42.7% activity (17.44% FE), while Sn–Cu/C completely deactivates (0% FE). Multimodal characterization (scanning electron microscopy‐energy‐dispersive X‐ray spectroscopy, X‐ray diffractometer, Brunauer‐Emmett‐Teller (BET), Fourier transform infrared, electrochemical impedance spectroscopy) reveals that Sn–Zn/C's superior performance stems from thermodynamically compatible SnO 2 /ZnO phases, which exhibit beneficial textural evolution (+61% surface area) and compositional stability (ΔSn = −0.95%, ΔZn = −2.62%). Conversely, Sn–Cu/C suffers phase instability (complete CuO loss), textural collapse (‐66% surface area), and severe compositional drift (ΔCu = −7.85%). This work demonstrates that pure CO 2 testing alone cannot predict industrial viability and establishes design principles for practical CO 2 ‐to‐formic acid catalysts: prioritize oxide phase compatibility, stable heterointerfaces, and robust textural properties. The findings expose the “purity bias” masking deactivation mechanisms and establish diluted‐feed testing as indispensable for bridging laboratory performance with real‐world electrochemical CO 2 utilization.