The simple design of this module allowed the upscaling of the membrane element. However, the circular disk design of the above module limits the ability to achieve the practical cross-flow configuration. Therefore, larger decimeter-scale modules were designed by including cross-flow permeation channels (Figure ). The membrane stacking order and Cu etching strategy were identical (Figure ). The module consisted of a symmetrical body frame and two identical cover plates to pack two 5 cm 2 -sized membrane elements in a single module to increase the packing density. A cross-flow channel was created using slits on the side of the module (Figure ). Cu foil in the assembled module could be removed by flowing the etchant through the cross-flow slits (Figure ). This exposed graphene and generated a feed channel for gas permeation experiments.