A novel “butter-sandwich” Ti₃C₂T_x/PANI/PPY electrode with enhanced adsorption capacity and recyclability toward asymmetric capacitive deionization

Capacitive deionization (CDI) is an environmentally-friendly-water-treatment technology, whereas its wide application has been limited by the low salt adsorption capacity and poor recyclability of electrode materials. In this study, a novel Ti₃C₂T_x/PANI/PPY electrode is invented with a “butter-sandwich” microstructure, where bread-like Ti₃C₂T_x slices are intercalated by polypyrrole (PPY) spheres, and then glued by butter-like polyaniline (PANI). Thus, the negatively charged PPY is fastened inside Ti₃C₂T_x slices by positively charged PANI for a superhigh structural stability and elevated specific surface area. When Ti₃C₂T_x/PANI/PPY is used as the electrode for CDI, a high salt adsorption capacity (39.62 mg g⁻¹), a fast salt adsorption rate (2.64 mg g⁻¹ min⁻¹) and a high cycling stability of almost 100% for 30 times are obtained, surpassing those of the Ti₃C₂T_x electrodes and many other related materials in literature. Such an outstanding CDI performance can be ascribed to the intercalation of PPY, which enlarges the layer spacing of Ti₃C₂T_x as well as the ion storage space, and the binding of them by PANI, which provides more paths for electron transport and improves the ion adsorption rate. This work provides a new direction to enhance the performance of capacitive deionization by an attentive “butter-sandwich” new microstructural design strategy.