NOVELTY - Liquid composition comprises a precious metal precursor compound comprising precious metal atoms, hydrogen atoms, oxygen atoms and optionally carbon atoms, and at least one acidic ionomer compound, where a liquid medium comprises pure, deionized water, and an aqueous composition comprising organic solvents, or a water-free liquid composition in a polar organic solvent.    USE - The liquid composition is useful as catalyst ink for manufacturing gas-phase active catalytic ionomer layers, catalytic combustion layers, catalyst layers, electrode layers, gas diffusion electrodes, catalyst-coated membranes, membrane-electrode assemblies for polymer electrolyte membrane fuel cells, direct-methanol fuel cells or polymer electrolyte membrane water electrolyzers and composite catalyst powders (all claimed), where the fuel cells such as power generating electrochemical devices, are useful for automotive drive train, stationary units for residential heating, embarque auxiliary power units, portable electronic equipments, and remote or portable back-up units.    ADVANTAGE - The liquid composition has mechanical strength, hydrophobicity, porosity, mass transport properties and good fuel cell performance, provides improved electrical conductivity and durability to the fuel cell, and can be manufactured with reduced cost.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a colloidal dispersion comprising nano-sized precious metal particles stabilized by the acidic ionomer compound, where the colloidal dispersion is obtained by a reduction process of the composition;    (2) preparing a colloidal, precious metal dispersion comprising precious metal particles and the acidic ionomer comprising (a) mixing the precious metal precursor compound with the acidic ionomer, and (b) reducing the precious metal precursor compound with a reducing agent to form precious metal particles stabilized by the acidic ionomer;    (3) catalyst ink, free of support material, comprising nano-sized precious metal particles, at least one acidic ionomer and electrically conductive or non-conductive support material, obtainable by the method; and    (4) use of the liquid composition for the preparation of ionomer layers, catalyst layers, electrodes or composite catalyst materials, where the reduction of the precious metal precursor takes place by hydrogen supplied to a fuel cell or produced in-situ by the water electrolyzer.