Temperature dependent performance and catalyst layer properties of PtRu supported on modified few-walled carbon nanotubes for the alkaline direct ethanol fuel cell

Abstract

The performance of PtRu on three differently modified few-walled carbon nanotube (FWCNT) supports for ethanol electro-oxidation is evaluated in alkaline media both with rotating disc electrode (RDE) and direct ethanol fuel cell (DEFC) measurements at various temperatures (0–60°C). FWCNT are modified with oxidative treatment (O-FWCNT), aniline coating (A-FWCNT) and N-doped carbon layer (N-FWCNT). RDE testing shows that A-FWCNT/PtRu outperforms both O-FWCNT/PtRu and N-FWCNT/PtRu especially at high temperatures giving 1.5 times higher current at 60°C. The poisoning resistance of N-FWCNT/PtRu is high over the temperature range, while O-FWCNT/PtRu and A-FWCNT/PtRu become increasingly poisoned with increasing temperature. Alkaline DEFC testing at 30°C and 50°C indicates similar dependence to temperature as in RDE tests. However, only N-FWCNT/PtRu can sustain currents for longer than 20–30h during constant voltage measurement. SEM images of the catalyst layers reveal that both O-FWCNT/PtRu and A-FWCNT/PtRu form a dense structure with little pores for reactant and product transport explaining the quick performance loss, while large pores are formed with N-FWCNT/PtRu facilitating the transport. These results underline that the interactions between the catalyst support and the ionomer in the fuel cell catalyst layer are important in forming a suitable pore structure for efficient mass transfer.