A novel ε-MnO2/MXene composite as an electrode with excellent conductivity and ultrahigh capacitive deionization

Manganese dioxide (MnO2) holds great promise as an electrode material for capacitive deionization (CDI); but its low electrical conductivity considerably restricts its desalination capacity. Nevertheless, its electrochemical performance can be enhanced by augmenting its conductivity. Hence, we propose a novel strategy for constructing a strongly coupled ε-MnO2/MXene composite, in which, MXene (Ti3C2Tx) serves as a network of electron conduction highways that enhance the charge transfer of ε-MnO2 and activates the underutilized electrochemically active sites of ε-MnO2. Based on these advantages, an ε-MnO2/MXene composite is prepared for the first time, comprising spherical ε-MnO2 nanoparticles grown on MXene layers. As demonstrated, ε-MnO2/MXene composite demonstrates exceptional desalination performance, exhibiting a maximum deionization rate of 17.54 mg g−1 min−1 and an ultrahigh desalination capacity of 114.66 mg g−1 in 1000 mg/L NaCl solution at 1.2 V, which is considerably higher than those observed for ε-MnO2 (74.93 mg g−1), MXene (29.26 mg g−1) and recently reported electrode materials. Such an outstanding CDI performance can be ascribed to a considerably high specific capacitance ε-MnO2/MXene composite of approximately 337.2F g−1 at a specific current of 1 A/g, which is approximately 2.16 times that of an ε-MnO2 electrode. The excellent performance of ε-MnO2/MXene composite makes it a potential practical application of CDI.