Enhanced capacitive deionization via modulating local electron of electro-adsorption sites in a Trace-Fe-modified carbon framework

In order to alleviate the crisis of freshwater resources, it is essential to explore a clean, efficient, and low-consumption water treatment technology. As a kind of electro-adsorption water purification technology, capacitive deionization (CDI) has drawn continuously growing attention because of its advantages. The ion adsorption capability of CDI is closely related to the electrodes. Unfortunately, the ion adsorption capacity of common carbon materials is limited and far from reaching the rapidly increasing requirements of fresh water treatment. In this study, Fe-N-HPC electrode materials with trace Fe uniformly dispersed in N-doped hollow carbon polyhedral frameworks were tactfully prepared by a simple in-situ growth and pyrolysis method. The structure and morphology of the heterostructure material were verified by various analysis. Electrochemical tests showed the Fe-N-HPC electrode had an enhanced performance with a higher specific capacitance and fast ions diffusion coefficient. The Fe-N-HPC showed excellent CDI performance, with an enhanced desalinization capacity (34.38 mg/g, 500 mg/L NaCl solution, 1.2 V), and regenerative stability after 100 adsorption–desorption cycles. In addition, it also exhibited higher charge efficiency, energy efficiency and lower specific energy consumption. The removal mechanism of Na+ on the electrode and the participation of trace Fe can modulate the local electron of the electro-adsorption sites were reasonably verified by ex-situ XRD, Raman, and XPS characterizations, which finally facilitated the electro-adsorption property. This work presents a promising scheme for the advance of high efficiency capacitive desalination system.