Portable polymer electrolyte membrane fuel cells (PEMFCs) stack was assembled with sulfonated poly(fluorenyl ether ketone) (SPFEK) ionomer membranes. The portable PEMFC stack was studied by means of cell performance tests at high temperatures under low relatively humidity (RH). The experimental results showed that the output power of the stack increased from 28.74 W to 37.11 W with increasing operating temperature from 30 to 90 degrees C under 100% RH. When the operating temperature was over 100 degrees C, the output power decreased with further increasing temperature from 27.68 W (100 degrees C, 85% RH) to 19.87 W (120 degrees C, 50% RH). The output at 120 degrees C and under 50% RH was 69% output power of the stack at 30 degrees C and under 100% RH. These results demonstrated that the self-prepared SPFEK ionomer membrane was a promising PEM for the application in high-temperature PEMFC. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.