Porous transport layer

A porous transport layer for an electrolyser or for a fuel cell, comprising

• a first nonwoven layer of metal fibers provided for contacting a proton exchange membrane, wherein the first nonwoven layer of metal fibers comprises metal fibers of a first equivalent diameter,
• wherein the first nonwoven layer of metal fibers has a first surface roughness and a first porosity,
• a second nonwoven layer of metal fibers, wherein the second nonwoven layer of metal fibers comprises metal fibers of a second equivalent diameter, wherein the second nonwoven layer of metal fibers has a second surface roughness and a second porosity,
• wherein the first surface has a material ratio of less than 5% of material at a height of 5 μm, and more than 70% of material at a depth of −5 μm,
• the first equivalent diameter is smaller than the second equivalent diameter, the first surface roughness is smaller than the second surface roughness for at least 20%, e.g., in a range of 20% to 120%,
• the first porosity is smaller than the second porosity for at least 10%, e.g., in a range of 10% to 50%, and
• wherein the first nonwoven layer is metallurgically bonded to the second nonwoven layer.