Dynamics of Volatile Products in the Electro-oxidation of Ethanol on Pt/C and PtSn/C Catalysts

Ethanol electro-oxidation reaction (EEOR) is a strategically important reaction for the development of fuel cells and low-temperature electrolysis technologies, although its application is hindered by slow kinetics and poor selectivity toward the C1 pathway (CO₂ formation) on platinum-based catalysts. In this study, the dynamic formation of volatile products (acetaldehyde, acetic acid, and CO₂) was investigated during the EEOR on Pt/C and PtSn/C electrodes in acidic media, with particular emphasis on oscillatory conditions using online electrochemical mass spectrometry (OLEMS). PtSn/C catalysts were synthesized via chemical reduction and characterized by XRD, TEM, and XPS, revealing smaller particle sizes, a higher proportion of oxidized Pt species, and the presence of Sn⁴⁺ as SnO₂. OLEMS experiments showed earlier onset for acetaldehyde, CO₂, and acetic acid products for PtSn/C. Despite the low volatility of acetic acid, its production was confirmed and quantified by high-performance liquid chromatography (HPLC), reaching up to 965.2 ppm at 0.5 V, which is 97 times higher than that of Pt/C. Multivariate linear regression (MLR) analysis revealed a greater contribution of acetic acid and CO₂ to the faradaic current for PtSn/C, indicating a substantial shift in the reaction pathway. Under oscillatory conditions, PtSn/C exhibited greater robustness, lower potential amplitude, and reduced susceptibility to surface poisoning. These results highlight the role of Sn in enhancing surface regeneration and promoting deeper oxidation pathways, demonstrating the importance of catalyst design in tuning the selectivity and efficiency of the EEOR.