Impact of a protic dimeric ionic liquid on PEM fuel cell performance and durability

Protic dimeric ionic liquid (IL) 9′9'-(butane-1, 4-diyl)bis (3,4,6,7,8,9-hexahydro-2H-pyrimido [1,2-a]pyrimidin-1-ium) 1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulfonate (D-HTBD) has been developed as a surface modifier to a PtCo/C oxygen reduction reaction (ORR) catalyst for polymer electrolyte membrane fuel cells (PEMFCs). Thermal properties, intrinsic conductivity, and viscosity were studied to understand the ionic liquid's protonation effect. The protic IL was incorporated into the PtCo/C catalyst and its effect on MEA performance at various humidities were evaluated and compared with pristine PtCo/C catalyst. Electrochemically active surface area, AC impedance and gas diffusion resistance of the MEAs with IL were compared with the PtCo/C catalyst without modification by IL. Besides promoting the oxygen reduction reaction activity of the PtCo/C catalyst, the protic dimeric IL enhances dry condition MEA performance significantly, attributed to the hydrogen bonds between the Brønsted acids and Brønsted bases. A durability study of the PtCo/C catalyst with and without IL shows the reduction of catalyst degradation after incorporating IL. This work suggests that the protic dimeric IL could be a promising modifier to enhance ORR catalyst activity, fuel cell performance and durability.