(A) study on highly durable Pt-Ir catalysts for polymer electrolyte membrane fuel cells

Abstract

Polymer electrolyte membrane fuel cell (PEMFC) is a promising energy conversion device which could replace conventional power generation system using fossil fuels. The critical issue to overcome for commercialization of fuel cell electric vehicle (FCEV) is stability of Pt/C catalyst at high potential. The corrosion of carbon support at high potential leads detachment platinum nanoparticles from carbon supports and the cell performance decreases. To prevent carbon corrosion, we report highly durable PtIr alloy catalysts for cathode in PEMFC. The PtIr/C catalyst oxidizes water in PEMFC into oxygen, so carbon corrosion is not corroded. We synthesized $Pt_xIr_y/C$ catalysts with various ration of Pt and Ir, and measured oxygen reduction reaction (ORR) activity and oxygen evolution reaction (OER) activity to find the optimal composition of Pt and Ir. We also conducted the accelerated degradation test (ADT) from 1.0 V to 1.5 V to verify the carbon corrosion resistance of catalysts. The ORR activity of the commercial Pt/C decreased from 0.12 $A/mg_{Pt}$ to 0.017 $A/mg_{Pt}$ which is about 86 % of decrease. However, the ORR activity of synthesized $Pt_{85}Ir_{15}/C$ catalyst increased from 0.029 $A/mg_{PGM}$ to 0.071 $A/mg_{PGM}$ which is about 145 % increase after 5,000 durability cycles. In addition, a membrane electrode assembly (MEA) was fabricated to demonstrate the feasibility of commercializing PtIr/C catalyst in practical applications. The $Pt_{85}Ir_{15}/C$ catalyst also showed higher stability than the commercial Pt/C in single-cell system. This results showed that PtIr/C catalysts could be utilized as a catalyst for highly durable FCEVs.