Recyclable amphiphilic porous thin-films as electrodes for high-performance potassium-ion transport and storage

Abstract

Compared to lithium, potassium possesses abundant storage, a similar standard potential, and lower desolvation energy. However, the bulkier atom size seriously weakens its ionic kinetic properties, conductivity and storage in most of the traditional electrode materials, impeding its practical application in devices of energy conversion and storage. In this work, the two commercially available nanomaterials, one-dimensional (1D) nanofibrillated cellulose (NFC) and two-dimensional (2D) reduced graphene oxide (rGO), were assembled to one kind of porous thin-film, predominantly driven via van der Waals interactions. The nanoporous structures of these thin-films were significantly revealed by Brunauer–Emmett–Teller (BET) analysis, obtaining specific areas up to 120 m² g⁻¹. Meanwhile, substantial open amphiphilic nanochannels over the whole of the thin-film, and which are associated with the presence of coulombic repulsion of carboxylic groups on the backbones of NFC, were constructed. Moreover, their highly compact character was evaluated at a density of 1.6 g cm⁻³, providing them with excellent conductivity (up to 128 s cm⁻¹). Such porous thin-films can undergo reversible assembly and disassembly for several cycles without significant changes to their structural characters, thus allowing for recyclable utilization. The as-prepared porous thin-films enable rapid transportation of K⁺ with a diffusion coefficient range of 1.2 × 10⁻¹³ to 5.4 × 10⁻¹⁰ cm² s⁻¹, with voltages from 3 V to 0 V in galvanostatic intermittent titration technique (GITT) measurements. As the electrodes of the symmetry supercapacitor, they provided an excellent volumetric energy density of 68 W h L⁻¹ with KPF₆ electrolyte, and this is similar to the values of 70 W h L⁻¹ for LiPF₆ and 74 W h L⁻¹ for NaPF₆ electrolytes, but there is better stability in the former case. These results represent a reliable and sustainable strategy approach for green energy storage.