Direct ethanol fuel cells (DEFCs) are well-known as emerging power converters that have attracted enormous attention due to their high theoretical energy density, low operating temperature and low toxicity. Electrooxidation of ethanol on noble metals, such as platinum is of particular interest due to its potential application in low-temperature DEFCs. The slow, incomplete oxidation of ethanol as well as the high price of platinum has impeded the wide application of DEFCs. In response to these challenges, several core-shell electrocatalysts were designed with better electrochemical performance and lower cost than pure Pt/C.

Five groups of Au nanoparticles (NPs) were successfully synthesized with narrow size distributions: 1.9 ±0.3 nm, 2.8 ± 0.4 nm, 3.6 ±0.3 nm, 4.8 ±0.4 nm and 5.6...[ Read more ]

Direct ethanol fuel cells (DEFCs) are well-known as emerging power converters that have attracted enormous attention due to their high theoretical energy density, low operating temperature and low toxicity. Electrooxidation of ethanol on noble metals, such as platinum is of particular interest due to its potential application in low-temperature DEFCs. The slow, incomplete oxidation of ethanol as well as the high price of platinum has impeded the wide application of DEFCs. In response to these challenges, several core-shell electrocatalysts were designed with better electrochemical performance and lower cost than pure Pt/C.

Five groups of Au nanoparticles (NPs) were successfully synthesized with narrow size distributions: 1.9 ±0.3 nm, 2.8 ± 0.4 nm, 3.6 ±0.3 nm, 4.8 ±0.4 nm and 5.6 ± 1.1 nm. These samples are nearly spherical in shape and well dispersed on high-surface area carbon. Then, Au@Pt core-shell electrocatalysts were prepared by the two-step process, in which a Cu monolayer was underpotentially deposited (UPD) on surfaces of Au NPs followed by the replacement of Cu with Pt. The much higher activity toward ethanol oxidation reaction (EOR) on the core-shell structure (Au@Pt) than Pt/C was demonstrated by higher current density and negative shift of onset potential. The activity enhancement was caused by the ligand and strain effects from the Au core. The particle size and Pt shell thickness effects have been systematically studied. The current densities decreased in the order of Au@Pt (2.8 nm) ＞ Au@Pt (3.6 nm) ＞ Au@Pt (4.8 nm) ＞ Au@Pt (5.8 nm) ＞ Au@Pt (1.9 nm). The Au@Pt (2.8 nm) was at least seven times more active than commercial Pt/C in terms of peak current density. The EOR activity decreased with a thicker Pt shell due to a weaker effect from the Au core. SnO₂ nanoparticles were also loaded on carbon surface to introduce the bi-functional mechanism to further improve the activity by 170%.

In a further study, the Au@Pt surface was modified with Ru, Rh and SnO₂. Compared to Au@Pt/C, the peak current densities of Au@Pt-Ru-SnO₂/C and Au@Pt-Ru/C were enhanced by 250% and 220%, respectively, while the Au@PtRh did not change the activity significantly. Due to the bifunctional effect, the Ru could produce OH^- at lower potential with respect to Pt. Therefore, the catalytic system with Ru has a lower onset potential for the CO oxidation. Based on the surface modification results, the Pt-Ru mixed shell was optimized to further combine the bifunctional and ligand effects of Ru.