Mechanistic insight into methanol electro-oxidation catalyzed by PtCu alloy

Abstract

In this work, we have performed density functional theory (DFT) calculations to investigate the methanol electro-oxidation reaction (MOR) catalyzed by the Pt, PtCu alloy and Cu. The complex reaction networks, including the intermediate dehydrogenation, water dissociation and anti-poison reaction steps, are systematically investigated to explore the mechanisms. At the standard condition of pH = 0 and zero potential, for Cu, most dehydrogenation steps along the favorable pathway are endergonic, making it less active in MOR. For the Pt and PtCu alloy, their dehydrogenation steps are mainly exergonic, but the formed CO intermediate binds too tightly on Pt, that can accumulate on active sites to poison the electro-catalyst. The CO can be consumed by the thermodynamic reaction with OH*, which comes from water dissociation. DFT calculation shows alloying the Pt with Cu could not only reduce the free energy barrier for binding between CO* and OH*, but also assist the water dissociation to produce more OH* for that anti-poison reaction. That makes the PtCu alloy more active than the pure Pt electrode in experiment. The results reveal the importance of anti-poison reaction and water dissociation in MOR, which could be applied to the rational design of more active alloy electro-catalysts in future. In methanol electro-oxidation reaction, theoretical calculation shows alloying the Pt with Cu could promote the anti-poison reaction of binding between CO* and OH*, which makes it more active than the pure Pt electrode.