Water-based catalyst inks and their use for manufacture of catalyst-coated substrates

The present invention relates to water-based catalyst inks and their use for manufacture of catalyst-coated substrates. The catalyst layer is applied to the hydrophobic surface of a substrate by using a water-based catalyst ink comprising an electrocatalyst, an ionomer and water. The catalyst ink further comprises a highly volatile surfactant having a vapour pressure at ambient temperature in the range of 1 to 600 Pa. The use of this surfactant allows applying the water-based ink to the hydrophobic surface of a variety of substrates, such as gas diffusion layers, advanced ionomer membranes or polymer substrates. The required coating deposit can be applied in only one coating pass and the resulting catalyst layer exhibits improved performance due to the absence of residual surfactant in the catalyst layer.