Graphene is a promising candidate for an ideal membrane material. Its ultralow (one‐atomic) thickness potentially provides high permeation and at the same time high selectivity. Here, it is shown that these properties can be used to create a confined, two‐dimensional electrochemical environment between a graphene layer and a single‐crystal Pt(111) surface. The well‐defined fingerprint voltammetric characteristics of Pt(111) provide an immediate information about the penetration and intercalation of ions into the confined space. These processes are shown to be highly selective.
