Ink for producing catalyst layers
The invention relates to an ink for producing catalyst layers for electrochemical devices. The ink comprises catalyst materials, ionomer material, water and at least one organic solvent. The organic solvent belongs to the class of tertiary alcohols and/or the class of aliphatic diketones and bears functional groups which are stable to oxidative degradation in the ink. This prevents formation of decomposition products in the ink. The ink of the invention displays a high storage stability and is used for producing catalyst-coated substrates for electrochemical devices, in particular fuel cells (PEMFCs, DMFCs).
1. Ink for producing catalyst layers for electrochemical devices which comprises catalyst material, ionomer material, water and a mixture of the organic solvents tert-butanol and 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol).
2. Ink according to claim 1 , wherein the mixture of organic solvents is present in an amount of 5 to 80% by weight, based on the total weight of the ink.
3. Ink according to claim 1 , wherein the mixture of organic solvents is present in an amount of 10 to 50% by weight, based on the total weight of the ink.
4. Ink according to claim 1 , wherein the water content is in the range of 1 to 50% by weight, based on the total weight of the ink.
5. Ink according to claim 1 , wherein the water content is in the range of 5 to 25% by weight, based on the total weight of the ink.
6. Ink according to claim 1 , wherein the ionomer material comprises a tetrafluoroethylene-fluorovinyl ether copolymer bearing acid functions, in particular sulphonic acid groups.
7. Ink according to claim 1 , wherein the ionomer material is used in an aqueous solution having an ionomer content of 5 to 30% by weight (based on the total weight of the solution).
8. Ink according to claim 1 , wherein the ionomer material is used in an aqueous dispersion having an ionomer content of from 5 to 30% by weight (based on the total weight of the dispersion).
9. Ink according to claim 1 , wherein supported catalysts comprising finely divided, electrically conductive carbon black and, as catalytically active components, elements of the platinum group of the Periodic Table (i.e. Pt, Pd, Ag, Au, Ru, Rh, Os, Ir) or mixtures or alloys thereof are used as catalyst material.
10. Ink according to claim 1 , wherein finely divided blacks or powders of the elements of the platinum group of the Periodic Table (i.e. Pt, Pd, Ag, Au, Ru, Rh, Os, Ir) or mixtures or alloys thereof are used as catalyst material.
11. Ink according to claim 1 , further comprising additives such as wetting agents, antifoaming agents, surfactants, anti-settling agents, preservatives, pore formers, levelling agents, stabilizers, pH modifiers, sodium hydroxide (NaOH) or potassium hydroxide (KOH).
12. A catalyst-coated substrate comprising the ink according to claim 1 .