Direct oxidation fuel cells with improved cathode gas diffusion media for low air stoichiometry operation

Abstract

A cathode for use in a direct oxidation fuel cell (DOFC) comprises a gas diffusion medium (GDM) including a backing layer and a microporous layer comprising a fluoropolymer and an electrically conductive material, wherein loading of the fluoropolymer in the microporous layer is in the range from about 10 to about 60 wt. %. In use, a concentrated solution of a liquid fuel is supplied to an anode and an oxidant to the cathode of the fuel cell, and the fuel cell may be operated at a low oxidant stoichiometry ξ c not greater than about 2.5.

1 - 19 . (canceled) 
     
     
         20 . A cathode electrode for use in a direct oxidation fuel cell (DOFC), the cathode comprising: a catalyst layer and a gas diffusion medium (GDM);
 wherein the GDM comprises a microporous layer (MPL) and a backing layer;   wherein the MPL has a thickness of about 10 μm to about 50 μm, an average pore size between 10 nm and 500 nm, and comprises a fluoropolymer and an electrically conductive material, wherein the electrically conductive material comprises carbon particles or carbon nanofibers, wherein loading of the fluoropolymer is in the range of about 30 wt. % to 40 wt. %, and loading of the carbon particles or carbon nanofibers is about 0.5 mg/cm 2  to about 5 mg/cm 2 ;   wherein the backing layer has a porosity greater than about 70%, and comprises carbon paper, woven paper, or non-woven cloth, and includes loading of a fluoropolymer from about 5 wt. % to about 30 wt. %; and   wherein the catalyst layer, the MPL, and the backing layer are arranged in direct overlying sequence in the recited order.   
     
     
         21 . The cathode as in  claim 20 , wherein the fluoropolymer in the MPL comprises poly(tetrafluoroethylene) (PTFE). 
     
     
         22 . The cathode as in  claim 20 , wherein said electrically conductive material comprises carbon particles. 
     
     
         23 . The cathode as in  claim 20 , further comprising: a hydrophobic microporous layer between said MPL and said GDM. 
     
     
         24 . A direct oxidation fuel cell comprising the cathode of  claim 20 .