Synthesis of free-standing ternary Rh–Pt–SnO2-carbon nanotube nanostructures as a highly active and robust catalyst for ethanol oxidation

Abstract

The rational design of durable materials is an important issue for improving the performance of electrocatalysts towards the ethanol oxidation reaction (EOR). In this work, binderless thin nanostructured layers of SnO₂, Pt, Rh, bilayers of Pt/SnO₂, Rh/Pt and tri-layers of Rh (ca. 10 nm thickness)/PtSnO₂ are directly grown by pulsed laser deposition onto carbon nanotubes (CNTs). SEM analysis shows that CNTs are perfectly coated with the catalysts. The onset potentials of the CO stripping and EOR indicate that Rh/Pt/SnO₂ is the most active for the CO and the EOR. The incorporation of the CNTs in the catalyst layer is outstandingly beneficial to both the catalytic current activity and the durability. Indeed Rh/Pt/SnO₂/CNT delivers mass activity as high as 213.42 mA mg⁻¹_Pt. Moreover, Rh/Pt/SnO₂/CNT demonstrates not only the lowest poisoning rate (by intermediate species, such as adsorbed CO) but also the highest durability current of 132.17 mA mg⁻¹_Pt far superior to CNT-free Rh/Pt/SnO₂/CP (58.33 mA mg⁻¹_Pt). XPS shows that SnO₂, Pt and Rh are all present at the surface of Rh/Pt/SnO₂/CNT, the presence of two oxophilic materials like SnO₂ and Rh, implies an earlier source of OH_ads-species, which facilitates the oxidation of CO and assuming a second contribution from Rh is to enhance the cleavage of the C–C bond for the complete oxidation of ethanol. The 3D porous and binderless structure, the low amount of the noble catalyst, the excellent electroactivity and durability of the Rh₅/PtSnO₂/CNT/CP composite represents an important step in advancing its use as an anode in commercial applications in DEFC.