Modifying Electronic Structure of Cation-Exchanged Bimetallic Sulfide/Metal Oxide Heterostructure through In Situ Inclusion of Silver (Ag) Nanoparticles for Extrinsic Pseudocapacitor

The inferior electrical conductivity of conventional electrodes and their slow charge transport impose limitations on the electrochemical performance of supercapacitors (SCs) using those electrodes, necessitating strategies to overcome the limitations. An in situ Ag ion-incorporated cation-exchanged bimetallic sulfide/metal oxide heterostructure (Ag-Co_9-xFe_xS₈@α-Fe_xO_y) is synthesized using a two-step hydrothermal method. The coordination bond formation and Ag nanoparticle (NP) incorporation improve the electrical conductivity and adhesion of the heterostructure and reduce its interface resistance and volume expansion throughout the charge/discharge cycles. Density functional theory investigations indicate that the remarkable interlayer and interparticle conductivities of the heterostructure resulting from Ag doping have changed its electronic states, leading to an enhanced electrical conductivity. The optimized electrode has an excellent specific capacity (213.6 mA h g⁻¹ at 1 A g⁻¹) and can maintain 93.2% capacity retention with excellent Coulombic efficiency over 20 000 charge/discharge cycles. A flexible solid-state extrinsic pseudocapacitor (EPSC) is fabricated using Ag-Co_9-xFe_xS₈@α-Fe_xO_y and Ti₃C₂T_X electrodes. The EPSC has specific and volumetric capacitances of 259 F g⁻¹ and 2.7 F cm⁻³ at 0.7 A g⁻¹, respectively, an energy density of 80.9 Wh kg⁻¹ at 525 W kg⁻¹, and a capacity retention of 92.8% over 5000 charge/discharge cycles.