Layered structure for a fuel cell and method for producing a layered structure of this type

1. A layered structure for a fuel cell, comprising:

a carbon-based catalyst-free gas diffusion layer substrate; and

a carbon-based microporous layer joined to the gas diffusion layer substrate,

wherein the carbon-based microporous layer includes a plurality of carbon carriers or carbon fibers embedded into an ion-conducting polymer binder mixture, and

wherein the polymer binder mixture includes a sulfur-free binding polymer and a sulfonated polymer, and a fraction of the binding polymer at or near a surface of the microporous layer that faces away from the gas diffusion layer substrate is less than or equal to a fraction of the sulfonated polymer,

wherein the fraction of the binding polymer in the microporous layer increases in the direction of the gas diffusion layer substrate, and the fraction of the sulfonated polymer decreases in the direction of the gas diffusion layer substrate, and

wherein the fraction of the binding polymer increases continuously in the direction of the gas diffusion layer.

2. The layered structure according to claim 1 , wherein the carbon carriers of the microporous layer comprise first carbon particles at a volume region facing away from the gas diffusion layer substrate, and second carbon particles at a second volume region facing the gas diffusion layer substrate, and the first and/or second carbon particles are provided with a coating for functionalization.

3. The layered structure according to claim 1 , wherein a catalyst coating is applied, or introduced into the microporous layer, from the side of the microporous layer which faces away from the gas diffusion layer substrate.

4. A method for producing a layered structure for a fuel cell, comprising:

providing a carbon-based catalyst-free gas diffusion layer substrate;

embedding a plurality of carbon carriers or carbon fibers into an ion-conducting polymer binder mixture comprising a sulfur-free binding polymer and a sulfonated polymer;

forming a microporous layer, in which a fraction of the binding polymer at or close to a surface of the microporous layer facing away from the gas diffusion layer substrate is less than or equal to a fraction of the sulfonated polymer; and

applying a catalyst metal or a catalyst metal alloy onto the surface facing away from the gas diffusion layer substrate or from the side of the microporous layer facing away from the gas diffusion layer substrate,

wherein the fraction of the binding polymer in the microporous layer increases in the direction of the gas diffusion layer substrate, and the fraction of the sulfonated polymer decreases in the direction of the gas diffusion layer substrate, and

wherein the fraction of the binding polymer increases continuously in the direction of the gas diffusion layer.

5. The method according to claim 4 , wherein the application of the catalyst metal is carried out using one cycle or using a plurality of cycles encompassing:

applying an amount of atoms, or of molecular compounds, corresponding to a sub-monolayer, comprising the catalyst metal, onto the microporous layer forming a substrate;

applying a precursor, or a passivation gas, onto the microporous layer for the passivation of the atoms, or of the molecular compounds, of the catalyst metal; and

applying a further amount of atoms, or molecular compounds, corresponding to a sub-monolayer, comprising the catalyst metal.

6. The method according to claim 4 , wherein the carbon carriers are designed as carbon particles, which are functionalized chronologically before the catalyst metal is applied, and/or one or more of the polymers of the polymer binder mixtures are functionalized chronologically before the catalyst metal is applied.

7. The method according to claim 4 , wherein the gas diffusion layer and the microporous layer comprising the catalyst metal are hot-pressed, together with a membrane, to form an assembly comprising a gas diffusion electrode and a membrane.