Enhanced mass transfer and proton conduction of cathode catalyst layer for proton exchange membrane fuel cell through filling polyhedral oligomeric silsesquioxane

Mass transfer and charge conduction are vital to proton exchange membrane fuel cell (PEMFC). A series of novel cathode catalyst layer (CCL) with various contents of hydrophobic and cage-structured polyhedral oligomeric silsesquioxane (POSS) is prepared. Compared with the common CCL, additional 15% POSS in CCL can increase 30.3% power density and achieve the maximum value of 965.2 mW cm(-2) at 80% relative humidity (RH). Correspondingly, the Warburg admittance representing mass transfer increases by 2 times, and proton transfer resistance reduces 32.2%. Besides, the voltage drop of the optimized CCL with POSS at 1800 mA cm(-2) is voided, though the voltage of pure CCL drops by 21 mV, as RH increases from 50% to 80%. We propose that the hydrophobic branches of POSS facilitate water to leave secondary pores. Moreover, the hydrophilic inner core of POSS can trap water and induce sulfonic acid group aggregation by hydrogen-bonding, which contributes to proton transfer through proton hopping mechanism. POSS-modified CCL exceedingly improves the reliability and performance to operate at a wide range of current density and RH conditions. We provide an available strategy to address the trade-off between proton conduction and mass transfer.

Automated summary

The addition of 15% POSS in the cathode catalyst layer significantly improves the efficiency and performance of PEMFC, especially in high humidity conditions. POSS improves the arrangement of water molecules and promotes proton transfer through a hopping mechanism.