In some embodiments, the depth of the manifold and/or the cross sectional area of the manifold and/or the outlet tube needs to be optimized to be deep enough to provide a large cross sectional area of the manifold in order to avoid slug and plug flow of the two phase system; but also to provide enough space between the wall of the manifold and the electrode placed on top of the pan for the gas and liquid to have an unimpeded flow and for the membrane to stay wetted.