In another aspect of the present invention, provided is a method of manufacturing a membrane-electrode assembly for fuel cells including preparing a composition for forming a catalyst layer including a catalyst and a binder resin, coating one surface of a porous support with the composition for forming the catalyst layer, to form the catalyst layer, and disposing the catalyst layer such that the other surface of the porous support on which the catalyst layer is not disposed faces the polymer electrolyte membrane.

The composition for forming the catalyst layer may further include permeating the composition for forming the catalyst layer while filling inner pores of the porous support.

In the composition for forming the catalyst layer, the binder resin may permeate to the entire depth of the porous support and the catalyst may permeate only to a partial depth of the porous support.

In yet another aspect of the present invention, provided is a fuel cell system comprising a fuel supply for supplying a fuel mixture of fuel and water, a modifier for modifying the fuel mixture to generate a modification gas including hydrogen gas, a stack including the membrane-electrode assembly and generating electric energy by electrochemical reaction between the modification gas including hydrogen gas supplied from the modifier with an oxidant, and an oxidant supply for supplying the oxidant to the modifier and the stack.