Conjugated microporous polytriphenylamine as high-performance anion-capture electrode for hybrid capacitive deionization with ultrahigh areal adsorption capacity

Abstract

Conducting polymers with good electron conductivity and rich redox functional groups have attracted enormous attention as anode material for capacitive deionization (CDI) towards the relief of global freshwater scarcity. However, because of their intrinsically poor porosity and severe particle aggregation natures, previously used conducting polymers for CDI desalination have suffered from the disadvantage of rather low specific surface areas (<50 m²g⁻¹), sluggish ion diffusion kinetics, limited desalination capacities, and low mass loadings (~1 mg cm⁻²) on electrodes. Herein, we synthesized an amino group-rich conjugated microporous polytriphenylamine (m-PTPA) and demonstrated for the first time its great potential as a high-performance anion-capture electrode material in CDI applications. m-PTPA possesses reversible redox property, predominant <2 nm microporous characteristics, and ultrahigh specific surface area (506 m²g⁻¹), which ensured the fast ion transport within interconnected porous network, and maximized the exposure of electrochemical active sites to saline solution. Owing these novel features, the m-PTPA-based CDI device, with m-PTPA as anode at a high mass loading of 8.7 mg cm⁻²and activated carbon as cathode, exhibited high gravimetric/areal/volumetric-normalized salt adsorption capacities (47.21 mg g⁻¹, 0.41 mg cm⁻², 10.92 mg cm⁻³), fast adsorption rate (2.83 mg g⁻¹min⁻¹), low energy consumption, and excellent cycling stability. Besides, we also evaluated the competitive adsorption of some common anions existing in water, and probed the mechanism for Cl⁻adsorption on m-PTPA. We believe that this work paves a new way for the usage of conjugated microporous polymers as a new kind of CDI electrode materials.