Electrochemical-repaired porous graphene membranes for precise ion-ion separation

Abstract

The preparation of atom-thick porous lattice hosting Å-scale pores is attractive to achieve a large ion-ion selectivity in combination with a large ion flux. Graphene film is an ideal selective layer for this if high-precision pores can be incorporated, however, it is challenging to avoid larger non-selective pores at the tail-end of the pore size distribution which reduces ion-ion selectivity. Herein, we develop a strategy to overcome this challenge using an electrochemical repair strategy that successfully masks larger pores in large-area graphene. 10-nm-thick electropolymerized conjugated microporous polymer (CMP) layer is successfully deposited on graphene, thanks to a strong π-π interaction in these two materials. While the CMP layer itself is not selective, it effectively masks graphene pores, leading to a large Li⁺/Mg²⁺ selectivity from zero-dimensional pores reaching 300 with a high Li⁺ ion permeation rate surpassing the performance of reported materials for ion-ion separation. Overall, this scalable repair strategy enables the fabrication of monolayer graphene membranes with customizable pore sizes, limiting the contribution of nonselective pores, and offering graphene membranes a versatile platform for a broad spectrum of challenging separations.

The preparation of atom-thick lattices with Å-scale pores is desirable for achieving ion selectivity and high ion flux. Here authors present a cm-scale membrane made of atom-thick graphene film hosting zero-dimensional pores spanning only a few Å, repaired using an in situ electrochemical strategy, yielding high Li⁺/Mg²⁺ separation performance.