Curvature-induced ion docking effect in capacitive deionization

Abstract

Traditional capacitive deionization (CDI) materials usually exhibit low salt adsorption capacities due to the limitations in optimizing their specific surface area and chemical composition. Here we introduced the curvature parameter as a new variable for designing high-performance CDI electrodes. On the basis of a comprehensive surface curvature/electric field model, we found that smaller surface curvature radii may result in higher-concentration ion distributions. As a typical experimental example, bicontinuous mesoporous polypyrrole with saddle-shaped high-curvature surfaces demonstrated an enhanced ion docking effect, which provided high salt adsorption capacity values of 262.7 mg g−1 at 1.2 V and 312.5 mg g−1 at 100 mA g−1, along with an ultra-long cycling life of over 2,000 cycles. This CDI performance surpassed those of all previously reported CDI electrodes. This study provides a new design paradigm based on curvature structural engineering for next-generation CDI materials and demonstrates a promising approach for developing large-scale and sustainable high-performance CDI devices. A design principle based on the curvature parameter provides important guidance for the design of capacitive deionization electrodes.