The present invention relates to an electrode assembly and an electrolyser using said assemblies/structures, wherein the electrode assembly comprises an anode structure and a cathode structure, each of said anode structure and cathode structure comprising an outlet header for evolved gas and spent liquid, wherein each of said anode structure and cathode structure comprising an outlet header for evolved gas and spent liquid, wherein the outlet header on the anode structure has a total internal volume of VA cm3 and the outlet header on the cathode structure has a total volume of VC cm3 wherein VA is less than VC, and/or i) the outlet header on the anode structure has an internal volume, VA cm3, an internal cross sectional area at the exit end of the header of ΑA cm2 and an internal length LA cm, and ii) the outlet header on the cathode structure has an internal volume, VC cm3, an internal cross sectional area at the exit end of the header of AC cm2 and an internal length LC cm, and one or both of the ratios VA
