Synthesis of highly water-absorbing chromium oxyhydroxide as a dopant in a hybrid proton-conducting membrane

Proton-conductive membranes restrict the energy conversion efficiency and operating performance of the proton exchange membrane fuel cells. In this work, we develop a simple and easy scale-up method to synthesise a new proton-conductive material, amorphous chromium oxyhydroxide (CrO(OH)center dot xH(2)O). The CrO(OH)center dot xH(2)O shows a high water-adsorption value of 450 mg g(-1), contributing to the construction of continuous and ordered hydrogen-bonding network within the materials. An ultra-high proton conductivity of 0.31 S cm(-1) is obtained in CrO(OH)center dot xH(2)O at 90 degrees C and 98% relative humidity, with an activation energy of 0.39 eV, which indicates a proton hopping mechanism. To further study the application potential of CrO(OH)center dot xH(2)O in proton exchange membranes, CrO(OH)center dot xH(2)O is added to sulfonated poly(ether ether ketone) (SPEEK) as a dopant, forming a SPEEK-CrO(OH) proton exchange membrane. The composite membrane exhibits a proton conductivity comparable to Nafion, 0.17 S cm(-1) at 80 degrees C in water without decreasing in 36 hours. This research enlightens us the development of metal oxyhydroxide via a simple and feasible strategy as efficient proton conductors.