Sulfur Vacancies Enriched Copper Sulfide Nanotubes Boost Desalination Efficiency of Hybrid Capacitive Deionization

Vacancy engineering is a promising approach to improve the performance of electrode materials in electrochemical desalination. However, common methods for introducing sulfur vacancies are difficult to avoid the disadvantages of requiring high temperature and pressure environments and complex synthesis conditions. Herein, an anion exchange is developed to synthesize hollow CuS nanotubes with tunable sulfur vacancies. Such a hollow structure with tunable sulfur vacancy enhances the electrical conductivity and mitigates the structural stress caused by electrochemical insertion, thereby boosting the electrochemical kinetic. The abundant sulfur vacancies can provide additional electrochemical adsorption pathways for capacitive deionization, leading to enhanced salt removal capacity. As a result, the optimized CuS nanotubes yield superior comprehensive desalination efficiency, with a salt adsorption capacity (SAC) of 42.32 mg g^-1, and a salt adsorption rate of 4.84 mg g^-1 min^-1. Moreover, the obtained CuS nanotube electrodes show a high efficiency in removing sodium ions in a 30 min simulated seawater experiment, resulting in an effective SAC of 41.33 mg g^-1 (as the sodium concentration of 1681.51 mg L^-1 NaCl, 50 mL) over 30 min. This study suggests a scalable method that highlights new insights for extending high desalination capacity materials with vacancies and hollow structures for energy conversion and storage.