Nanocellulose-based ion-selective membranes for an aqueous organic redox flow battery

The redox flow battery (RFB) has emerged as one of the promising rechargeable energy storage devices. Ion-selective membranes play a pivotal role in RFB regarding their capacity, cycle performance, and cost of production. However, to achieve large-scale commercialization of RFB, it is imperative but remains challenging to develop the next generation of economically efficient and environmentally friendly membranes with outstanding ion transport performance. Here, we report a renewable ion-selective membrane fabricated from wood-derived nanocellulose. The appropriate nanopore size combined with abundant surface charge realized by a chemical cross-linking approach enables membranes with ultralow permeability of redox molecules. As a result, this nanocellulose membrane demonstrates excellent feasibility in an aqueous organic redox flow battery (AORFB) by using 4,5-dihydroxybenzene-1,3-disulfonate as catholyte and alizarin red S as anolyte. More significantly, the nanocellulose membrane indeed outperforms the commercial Nafion 115 membrane including higher capacity and better cycle stability. In addition to the highlighted electrochemical performance of nanocellulose membranes in RFBs, the renewable nanocellulose materials will facilitate AORFB toward sustainable development.