Selective electrocatalysis imparted by metal–insulator transition for durability enhancement of automotive fuel cells

Repetitive start-up and shut-down events in polymer electrolyte membrane fuel cells for automotive applications lead to serious corrosion of the cathode due to an instantaneous potential jump that results from unintended air leakage into the anodic flow field followed by a parasitic oxygen reduction reaction (ORR) on the anode. Here we report a solution to the cathode corrosion issue during the start-up/shut-down events whereby intelligent catalyst design is used to selectively promote the hydrogen oxidation reaction (HOR) while concomitantly suppressing the ORR on the anode. Platinum thin layers supported on hydrogen tungsten bronze (Pt/HxWO3) suppressed the ORR by converting themselves into an insulator following exposure to oxygen, while selectively promoting the HOR by regaining metallic conductivity following subsequent exposure to hydrogen. The HOR-selective electrocatalysis imparted by a metal–insulator transition in Pt/HxWO3 demonstrated a remarkably enhanced durability of membrane electrode assemblies compared to those with commercial Pt/C catalysts. The stability of polymer electrolyte membrane fuel cells is limited by the degradation of the cathode catalyst during repetitive start-up/shut-down events — a parasitic oxygen reduction reaction on the anode causes an instantaneous potential jump at the cathode. The issue is now addressed by selectively suppressing the oxygen reduction reaction on the anode by exploiting the metal–insulator transition behaviour of Pt/HxWO3 catalysts.