Interface engineering of Ni-MOF/NiCoFe-Prussian blue analogue composite with enhanced Na+ storage kinetics for high-performance hybrid capacitive deionization

Prussian blue faces challenges, including a tendency for particle agglomeration and limited charge transfer, which limit their application in hybrid capacitive deionization (CDI) technology. Herein, we develop a Ni-MOF/NiCoFe-Prussian blue analogue (NiCoFe-PBA) heterostructure by employing an in-situ growth of NiCoFe-PBA on a 2D Ni-MOF substrate. The formation of this heterogeneous interface significantly enhances charge transfer efficiency. Additionally, the in-situ growth of PBA on the MOF surface effectively mitigates the stacking of 2D Ni-MOF sheets, thereby increasing the exposure of active sites. Furthermore, Ni improves the structural stability of the composite during Na⁺ ion embedding/de-embedding, while Co doping introduces additional electrochemically active sites, significantly boosting the desalination capacity. Therefore, the Ni-MOF/NiCoFe-PBA composite exhibits an excellent desalination capacity of 63.19 mg g⁻¹ in a 500 μS cm⁻¹ NaCl solution, along with good cycling stability. The Na⁺ ion storage mechanism of the Ni-MOF/NiCoFe-PBA composite is thoroughly investigated. This study provide a new approach for developing high-performance electrodes for hybrid CDI technology.