Metal oxides have long been used to protect carbon supports from corrosion on the anode side of a fuel cell during fuel starvation, when the metal oxides serve as a catalyst for water hydrolysis it protects the carbon supports from corrosion. Titanium dioxide (TiO2) is commonly used on the anode, and known to be effective at protecting the carbon from corrosion. However, we recently found that mechanically mixing Pt/C with some TiO2 as the anode catalyst of a PEMFC leads to a significant drop of the cell performance at a very early stage of operation. Subsequent efforts to understand the phenomenon led to the finding that the even a small amount of TiO2 seriously poison the Pt/C catalyst for the oxygen reduction reaction (ORR) by reducing the half wave potential by more than 150 mV (Figure 1), whereas the HOR rate was not significantly affected. By combing ex situ and in situ characterizations and detailed electrochemical testing, we provide solid experimental evidence for the unexpected TiOx–induced poisoning effect, which largely accounts for the activity loss. The new findings of the interactions between the Pt/C and the metal oxide help to pursue metal oxides that are better at protecting the carbon from corrosion while minimizing the poisoning effects.
Acknowledgement:
The authors gratefully acknowledge the financial support of Automotive Fuel Cell Corporation (AFCC), Canada and Ford Motor Co., Detroit, MI (under a URIP program). The authors also acknowledge instrumental support from Thermo Fisher Corp., and access to synchrotron based facility for x-ray absorption spectroscopy at National Synchrotron Light Source-II (NSLS-II) situated in Brookhaven National Laboratory (BNL), Upton, NY, under grant # DE-SC0012704