Self-supporting Prussian blue@CNF based battery-capacitor with superhigh adsorption capacity and selectivity for potassium recovery

Prussian blue (PB), due to its abundant interstitial sites and high theoretical specific capacity, offers a great possibility in battery and capacitive deionization application. Herein, we developed a facile strategy for in-situ growth of PB on an electrospun flexible Fe-rich porous carbon nanofiber (Fe-CNF) to obtain the self-supporting PB-inlaid CNF (PB@CNF). By simple incubation of Fe-CNF in a K-4[Fe(CN)(6)] aqueous solution with the slow addition of acid, a large number of PB particles were evenly and tightly confined inside the pores of fibers with good stability. Being directly used as a self-supporting battery electrode, the PB@CNF delivered an excellent specific capacity of 318.4 F.g(-1) owing to the uniform distribution of PB particles along the conductive CNF matrix. This self-supporting PB@CNF electrode has been applied successfully in battery-capacitor deionization device for selective potassium adsorption with a super-high adsorption capacity of 2.55 mmol.g(-1) (equivalent of 190.1 mg.g(-1) KCl adsorption) and excellent stability. In the synthetic seawater containing the coexistent Na+, Ca2+ and Mg2+, the recovery of K+ achieved 73.4%. This synthesis approach shows great potential for designing the flexible electrode for use in capacitor and batteries.