Fungal hypha-derived freestanding porous carbon pad as a high-capacity electrode for water desalination in membrane capacitive deionization

Capacitive deionization (CDI) is an emerging technology for water desalination, especially low-salinity water. Freestanding porous carbon-based electrodes with rapid electron transfer rate and effective ion diffusion features are desired to achieve high desalination performance. Here, a porous carbon pad derived from the fungal hyphae of Aspergillus niger was prepared as a precursor of the electrode. After carbonization and activation, the intertwined and hierarchical porous structure of the fungal hypha pad was well-preserved, producing a freestanding fungal hypha activated carbon pad (FhACPad) electrode for MCDI. The interconnected carbon fibers and open pore structure of the FhACPad yielded an electrode with high electrical conductivity and rapid ion transport properties. The novel FhACPad exhibited a gravimetric salt adsorption capacity of 35.6 ± 2.3 mgNaCl/g with an average desalination rate of 1.2 mgNaCl/gelectrode/min from a 585 mg/L NaCl aqueous solution at a cell voltage of 1.2 V and a flow rate of 1 mL/min. As a result, the FhACPad outperformed conventional powdered activated carbon (PAC) electrodes and the most recently reported porous carbon electrodes under similar desalination conditions. This work also provides insights into the structure-performance relationships of CDI electrodes and shows a great potential of fungal biomass-derived porous carbon electrodes for high-performance MCDI applications.