Ultrafine Ag/AgCl heterostructures confined in the MXene nanosheets for enhanced chloride ion storage

Silver-based materials are recognized as highly efficient electrodes for chloride ion storage in capacitive deionization (CDI), owing to their superior theoretical capacity and exceptional selectivity for Cl⁻ ions. However, their chloride ion capture capacity and cycling stability are significantly limited by volume expansions during the ion capturing process. Herein, the silver/silver chloride/MXene (Ag/AgCl/Ti 3 C 2 T x ) was successfully synthesized using a combination of a Lewis acidic etching and a redox replacement strategy. The highly-dispersed Ag/AgCl heterostructures are confined within the MXene nanosheets, which improves the structural stabilities of both Ag and MXenes, and further promotes chloride ion capture capacity and long-term cycling stability. Benefiting from these superiorities, the Ag/AgCl/Ti 3 C 2 T x as a promising CDI anode achieves large Cl - capturing capacity (156.4 mg g -1 at 1.2 V; and 218.5 mg g -1 at 1.6 V), low energy consumption (0.58 W h g -1 ), and impressive cycling performance (90.8% retention after 120 cycles). Furthermore, the possible Cl - capturing mechanisms involved were elaborated by the systematical characterizations, density functional theory calculations and finite element simulations. This study provides inspirations for the design and construction of high-performance CDI electrodes for chloride ion capture technologies. • Ag/AgCl/Ti 3 C 2 T x was synthesized by the confined growth of Ag/AgCl within MXene. • Ag/AgCl/Ti 3 C 2 T x achieves a large Cl - capturing capacity of 218.5 mg g -1 . • Ag/AgCl/Ti 3 C 2 T x exhibits low energy consumption and superior cycling stability.