The very high mass activity of Pt0.25Ru0.75/pN-C makes it a promising HOR catalyst for low-PGM-loading HEMFCs. We first assembled an HEMFC using a Pt0.25Ru0.75/pN-C anode and a commercial Pt/C cathode catalyst. Using O2 as the cathodic feeding gas, the cell delivered a mass transport limited current density of 6.6 A/cm 2 and a PPD of 2.15 W/cm 2 (Fig. ). This performance is comparable to state-of-the-art HEMFCs . In addition, the cell was able to work at high current density with no decay for 5 hours (Supplementary Figure ). With air as the cathodic feeding gas, a mass transport limited current density of 4.1 A/cm 2 and a PPD of 1.05 W/cm 2 were obtained. These values are again comparable to those of state-of-the-art HEMFCs (Supplementary Table ) even though our cell has a lower loading of anode catalysts and uses zero back pressure.