Embedment of graphene in binder-free fungal hypha-based electrodes for enhanced membrane capacitive deionization

Freestanding carbon electrodes that do not use binders are suitable for realizing high-performance capacitive deionization (CDI). Herein, we developed a freestanding and binder-free electrode derived from the fungal hyphae of Aspergillus niger with embedded graphene (G-FhEld) or activated carbon (AC-FhEld) for CDI. The carbonized fungal hypha fibers provided a stable 3D carbon framework with a hierarchical structure, and the embedded graphene or AC increased the conductivity, specific surface area, and amount of adsorption sites of the electrodes. When used in CDI cycles for desalination, the G-FhEld exhibited a gravimetric electrosorption capacity of 32.3 +/- 1.7 mg/g and an average salt adsorption rate of 1.1 mg/(g center dot min) from low-salinity water (10 mM NaCl), outperforming AC-FhEld and the electrodes without graphene or AC. These values were considerably higher than those of most existing carbon electrodes. Fungal hyphae can be mass-produced from food waste and separated by simple filtration to prepare the precursors of the electrodes, and thus, G-FhEld is highly scalable for large-scale CDI applications. This research presents a facile, effective, and low-cost technique to fabricate carbon electrodes to realize enhanced desalination by CDI.