Activity Enhancement of PtIr Catalysts for Complete Ethanol Oxidation Reaction by Tuning C–O Coupling Abilities

Abstract

Designing efficient catalysts for the complete ethanol oxidation reaction (EOR) remains challenging because of its complex reaction network, which involves more than 70 reactions of C2 species, many reactions of C1 species, water dissociation, as well as reactions leading to by-products. Recently, the promising EOR performance of the one-atom-thick Ir-rich skin of a bimetallic PtIr electrocatalyst was illustrated and its further improvement requires a thorough understanding of the complete EOR mechanism that is still largely lacking. Therefore, we studied 58 critical elementary reactions of complete EOR including all three stages of catalysis of ethanol oxidation, i.e., dehydrogenation, C–C bond cleavage, and CO2 formation, as well as including water dissociation, on three (100)-exposed layered bimetallic Pt–Ir catalysts using density functional theory (DFT) calculations. Based on the activation and reaction energies, we mapped out the mechanisms of complete EOR on these layered PtIr catalysts. The DFT results demonstrated that the different C–O coupling abilities of the catalyst plays a leading role in the complete EOR performance of Pt–Ir catalysts. We further performed DFT studies on the reactions on a Ir@Pt(100) surface with about 6% Pt atoms on the Ir layer. The surface Pt atoms exhibit excellent C–O coupling of C1 species (e.g., CO + O → CO2), while the Ir atoms prevent the C–OH coupling to form CH3COOH (CH3CO + OH → CH3COOH). Both DFT and kinetics studies indicate that the Ir@Pt(100) surface with Pt-doped active sites is the best for complete EOR and is responsible for the experimentally observed high catalytic performance. This work indicates effective EOR catalysis need to go beyond single metal catalysts and the core–shell structures of multimetallic catalysts.