Surface redox pseudocapacitance boosting Fe/Fe3C nanoparticles-encapsulated N-doped graphene-like carbon for high-performance capacitive deionization

The practical application of carbon anode in capacitive deionization (CDI) is greatly hindered by their poor adsorption capacity and co-ion effect. Herein, an N-doped graphene-like carbon (NC) decorated with Fe/Fe3C nanoparticles composite (Fe/Fe3C@NC) with large specific surface area and plentiful porosity is fabricated via a facile and scalable method, namely sol-gel method combined with Fe-catalyzed carbonization. As expected, it exhibits superior CDI performance as a Cl-storage electrode, with Cl- adsorption capacity as high as 102.3 mg g-1 at 1000 mg L-1 Cl- concentration and 1.4 V voltage, and a stable capacity of 68.5 mg g-1 for 60 cycles in 500 mg L-1 Cl- concentration and 100 mA g-1 current density. More importantly, on the basis of electrochemical tests, ex-situ X-ray diffraction, ex-situ X-ray photoelectron spectroscopy (XPS), and XPS analysis with argon ion depth etching, it is revealed that the chlorine storage mechanism of the Fe/Fe3C@NC electrode is dominated by the surface-related redox pseudocapacitance behavior of Fe2+/Fe3+ couple occurring on or near the surface, enabling fast and reversible ion storage. This work proposes an economical and environmentally friendly general method for the design and development of high-performance Cl-storage electrodes for CDI, and offers an in-depth insight into the Cl- storage mechanism of Fe decorated carbon electrodes, further promoting the development of CDI technology.