<i>Operando</i> Infrared Spectroscopy Insights into Methane C–H Bond Activation and Conversion on Platinum

Elucidating the mechanistic pathways of methane (CH₄) electrooxidation is crucial for advancing sustainable C₁ chemical synthesis. Herein, we report a comprehensive mechanistic picture of CH₄ activation and conversion on Pt/C membrane electrode assemblies (MEAs), through highly sensitive <i>operando</i> infrared spectroscopy and density functional theory (DFT) calculations. A characteristic vibrational band at ∼2916 cm^-1, assigned to a key intermediate of *CH species formed via CH₄ dehydrogenation, was detected across a wide potential window from -0.4 to 0.3 V vs RHE. This activation step is thermodynamically favorable and nearly potential independent. In contrast, the subsequent oxidation of *CH to *CO, *COOH, and ultimately, CO₂ is strongly governed by applied potentials and competitive *OH adsorption. DFT calculations validate the energetics and site-specific interactions of these intermediates, highlighting the critical role of surface coverage and adsorbate migration in controlling reaction selectivity. These findings provide direct spectroscopic evidence for CH₄ activation on Pt surfaces and suggest that stabilizing and selectively oxidizing *CH intermediates represent key challenges for catalyst design. This study establishes a mechanistic foundation for the rational design of catalysts capable of selective CH₄ electrooxidation.