Three-dimensional hierarchical Na3Fe2(PO4)3/C with superior and fast sodium uptake for efficient hybrid capacitive deionization

Abstract

Using Faradaic electrodes instead of carbon electrodes to assemble hybrid capacitive deionization (HCDI) is an effective strategy to solve the shortcomings of traditional carbon-based CDI with low salt adsorption capacity (SAC). Herein, high HCDI desalination performance of Na3Fe2(PO4)3/Carbon-X (NFeP/C-X) is attested by designing and preparing three-dimensional (3D) hierarchical porous architecture via a sol-gel-calcination method. The NFeP nanoparticles with small size are uniformly embedded in interconnected carbon nanosheets, and then a convenient nanochannels and 3D conductive carbon framework is formed. This fine structure can not only improve the interface area between electrode and electrolyte, but also shorten the ion transmission distance and ensure the rapid transfer of ions and electrons, thus achieving ultra-high desalination performance. As expected, the as-prepared NFeP/C-750 shows an ultrahigh SAC of 94.5 mg g−1, an ultrarapid desalination rate of 22.5 mg g−1 min−1 and a stable regeneration desalination ability. In addition, the desalination mechanism and ion diffusion kinetics of the NFeP/C-750 was deeply studied by ex-situ structure analysis, electrochemical characterization and density functional theories (DFT) calculations. These results demonstrate that the NFeP/C-750 with excellent desalination ability is a feasible material and offers great potential for HCDI desalination.