Three-dimensional coated CuNiFe-Prussian blue analogue@MXene heterostructure for capacitive deionization to slow down the damage of MXene by dissolved oxygen

[Display omitted] •CuNiFe-PBA is coated as a functional layer on the surface of MXene.•The well combination of dual pseudocapacitive materials gives better performance.•CuNiFe-PBA@MXene heterostructure slows down the damage of MXene by dissolved oxygen. Within the capacitive deionization (CDI) realm, the two-dimensional (2D) layered material T3C2Tx MXene has drawn lots of attention because of its excellent electrical conductivity, reversible ionic intercalation/deintercalation capacity, and extensive active sites. However, the performance of MXene is compromised by the fact that its surface is susceptible to oxidation by dissolved oxygen and has inherent defects of self-stacking. In this paper, CuNiFe-Prussian blue analogue@MXene (CuNiFe-PBA@MXene) with three-dimensional (3D) coated heterostructure is successfully prepared by the in-situ coprecipitation. CuNiFe-PBA is uniformly coated on the MXene surface as a functional layer to avoid the re-stacking of MXene, to enlarge their layer spacing, and to slow down the damage of MXene by dissolved oxygen. Based on a coated structure constructed by a good combination of dual pseudocapacitive materials, the CuNiFe-PBA@MXene electrode has excellent electrochemical performance (250F g−1). The composed MXene//CuNiFe-PBA@MXene hybrid cell in 500 mg/L NaCl has higher desalination capacity (44.94 mg/g), lower energy consumption (0.66 kWh kg−1), and excellent desalination capacity retention (93.46 % after 40 adsorption/desorption cycles). Furthermore, the lower oxidation degree of CuNiFe-PBA@MXene after 40 desalination cycles compared to MXene indicates that the constructed 3D heterogeneous structure can protect MXene and slow down the oxidation of MXene by dissolved oxygen.