Joule-heating synthesis of Sn-In bimetallic freestanding electrode for efficient electrocatalytic CO2 reduction to formic acid

The development of efficient, stable, and rapidly fabricated catalytic electrodes is crucial for the practical application of electrochemical CO 2 reduction (CO 2 RR). Herein, a Sn-In bimetallic freestanding electrode was synthesized on carbon fiber substrate via Joule heating within only ~800 ms. The preferred Sn-In 50% /C electrode exhibited a formate Faradaic efficiency of 92.28% at −1.4 V vs. RHE in an H-cell and a pure formic acid selectivity of 90.2% at −200 mA·cm −2 in a solid-state electrolyte cell. Combining the X-ray photoelectron spectroscopy with density functional theory (DFT) calculations, we found the In doping triggers directional electron transfer from In to Sn, thermodynamically driven by the higher electronegativity of Sn (1.96) relative to In (1.78), thus create electron-rich Sn sites for CO 2 activation while simultaneously shifting the interface from hydrogen-philic to hydrogen-phobic. This electronic modulation optimizes the binding strength of the key *OCHO intermediate by lowering the energy barrier from + 0.53 eV on pure Sn to + 0.20 eV on the Sn-In composite. This work not only provides a rapid synthesis strategy for high-performance CO 2 RR electrodes but also offers atomic-level insights into the synergistic catalytic mechanism at bimetallic interfaces.