Bimetallic Fe, Ni-PBA on hollow graphite tube for capacitive deionization with exceptional stability

Abstract

Faradic materials become more and more attractive for capacitive deionization (CDI) due to their high ion adsorption capacity. However, it is still a great challenge to design a stable and high charge-transfer rate material for high-performance desalination. Herein, we report a bimetallic Fe, Ni-doped Prussian blue analogue (PBA)-packed hollow graphite tube (FeNiHCF@HGT) electrode for boosting the CDI performance. The high conductivity of HGT and the tight adhesion of PBA crystals on HGT endow the FeNiHCF@HGT electrode with fast charge-transfer, excellent redox activity and high stability through buffering the crystal deformation of PBAs in the ion-intercalation/deintercalation process. In addition, the bimetallic Fe, Ni-doping in PBA at the high-spin (HS) sites enhances the redox activity of FeIIC6/ FeIIIC6 in FeNiHCF with Ni substitution for partial HS Fe. Under the optimal Ni-doping condition, the obtained Fe1Ni1HCF@HGT delivers a high specific capacity and superior rate performance (364F g−1 at 1 A g−1, 88.2% retention at 20 A g−1), with an ultra-high surface capacitance contribution (92.3% at 20 mV s−1). The CDI results demonstrate its outstanding salt adsorption capacity (60.2 mg g−1 in 100 mM NaCl) and exceptional cycle stability (106.6% retention after 100 cycles). This new strategy with the synergy of conductive tube matrix and Ni substitution at PBA lattice sites fully achieves the high-performance CDI.