Hollow core-shell PANI-encapsuled Ni-Prussian blue analogue (H-NP@PANI) with omnidirectional conductive layer for efficient capacitive desalination

Abstract

Prussian blue analogue (PBA) as a typical Faraday electrode material has important application value in capacitive deionization (CDI) for its rigid open framework and unique ion storage properties. But poor electrical conductivity and deformation of crystal structure during the desalination process restrict its development. To enhance the stability of PBA and provide rapid charge transfer, a new composite hollow core-shell polyaniline-encapsuled Ni-Prussian blue analogue (H-NP@PANI) is constructed. Experiments illustrate that PANI formed an omnidirectional uniform and highly conductive layer on the crystal surface, which tremendously improved the electrochemical capacity of H-NP@PANI (242.24 F·g−1). In constant voltage mode, the adsorption capacity of AC║H-NP@PANI cell is 35.86 mg·g−1, which was the highest to H-NP (20.82 mg·g−1) and pure Ni-PBA (16.08 mg·g−1). The retention rate remains 96.1 % after 50 cycles. XRD tests show that superior cycle stability is due to the hollow structure and buffer space provided by PANI shell, which can effectively inhibit the degree of crystal transformation. Furthermore, DFT calculation confirms the existence of a highly stable tight electron coupling between H-NP and PANI, and the electron aggregation center around Fe atom facilitates the Fe3+/Fe2+ redox cycle. Hence, this work can provide a feasible strategy for designing stable and efficient electrodes.