Combining Bismuth nanoclusters embedded 3D carbon nanofiber Aerogels: Towards fast and ultra-durable faradic capacitive deionization

Faradic-based capacitive deionization (FDI) has been recognized as one of the most promising technologies to solve the freshwater crisis, yet was hindered mostly by the relatively low desalination rate and sluggish long-term stability of its anode materials. Through careful analysis, the origin of the slow desalination rate was determined to be the faradic diffusion and mass transfer, while the poor cycling stability could be originated from the volumetric expansion of the redox-active material as well as structural damage caused by the uneven stress during multicycle operation. Herein, we developed a Bi nanocluster (NCs) embedded in carbon nanofiber aerogels (Bi NCs@CNFAs) nanostructure as chloride-capturing electrodes for FDI. The essence of this work lies in the design of the "multi-layer protection" shell that could not only limit the volumetric expansion of the Bi NCs (inner protection layer) but also alleviate the stress caused by potential structure changes (outer buffer layer). As a result, the Bi NCs@CNFAs-based FDI display ultra-fast desalination kinetics (0.524 mg g−1 s−1) with remarkable long-term stability (only 8 % reduction over 250 cycles), significantly outperformed the highest value reported in the literature so far. This study is interesting because it exemplifies the significance of problem-driven strategy (nanocluster-induced surface-driven capacitance to address slow desalination kinetics; rigid carbon shell to suppress the volumetric expansion of Bi NCs; CNFAs scaffold to address potential structural damage and aggregation) to improve the desalination performance of FDI, which could further motivate advancements of highly effective desalination systems in the future.