Surface-Enhanced Raman Spectroscopy for Boosting Electrochemical CO 2 Reduction on Amorphous-Surfaced Tin Oxide Supported by MXene.

Amorphous materials disrupt the intrinsic linear scalar dependence seen in their crystalline counterparts, typically exhibiting enhanced catalytic characteristics. Nevertheless, substantial obstacles remain in terms of boosting their stability, enhancing their conductivity, and elucidating distinct catalytic mechanisms. Herein, a core-shell catalyst, comprising a crystalline SnO ₂ core and an amorphous SnO _x shell supported on MXene (denoted as SnO ₂ @SnO _x /MXene), was prepared utilizing hydrothermal and solution reduction methods. The SnO ₂ @SnO _x /MXene catalyst excels in the electrocatalytic conversion of CO ₂ to formate, yielding a Faradaic efficiency (FE) as high as 93% for formate production at -1.17 V vs RHE and demonstrating exceptional durability. Both density functional theory (DFT) calculations and experimental results indicate that the SnO _x shell bolsters formate formation by fine-tuning the adsorption energy of the *OCHO intermediate. In SnO ₂ @SnO _x /MXene, MXene plays a vital role in enhancing the conductivity and stability of the amorphous shell and especially amplifying Raman signals of catalyst components. The ex/in situ surface-enhanced Raman scattering (SERS) application further confirms the formation of amorphous SnO _x and further enables the direct detection of the formation of the intermediate species. This work provides the basis for the application of amorphous materials in practical electrocatalytic reduction of CO ₂ reduction.