Potential-Dependent Selectivity of Ethanol Complete Oxidation on Rh Electrode in Alkaline Media: A Synergistic Study of Electrochemical ATR-SEIRAS and IRAS

Rh-based catalysts might resolve the long-standing problem of poor C1 pathway efficiency toward an ethanol oxidation reaction (EOR). To facilitate the rational design and preparation of Rh-based EOR catalysts, here we fundamentally study ethanol adsorptive dissociation and oxidation on an Rh electrode surface by electrochemical infrared absorption spectroscopy. First, real-time infrared spectral results show that ethanol could be easily split on an Rh surface into COad and CHx intermediates only in alkaline media but not in acidic media. Second, the onset oxidation potential of EOR on Rh is ca. 180 mV more negative than that on Pd and Pt electrode in alkaline media. The EOR J(f)/J(b) ratio is ca. 5.73, 1.62, and 0.35 on Rh, Pt, and Pd, respectively, suggesting that COad and/or CHx intermediates could be readily oxidized into CO2 on Rh. Accordingly, the apparent selectivity efficiency of the C1 pathway (eta) is estimated to be 100% when the potential is at 0.4-0.6 V vs RHE, subsequently eta sharply decreases to zero at 0.65-0.8 V vs RHE, and then, eta gradually rebounds to ca. 15% when the potential moves positively. This work may provide some theoretical support for fabricating highly efficient EOR catalysts.