Biofilm-engineered fabrication of Ag nanoparticles with modified ZIF-8-derived ZnO for a high-performance supercapacitor

The particle size, pore structure, and surface area of nanomaterials are critical characteristics that govern their effectiveness in energy storage applications. In addition, as the accessibility of the surface to ions or reactants has a significant impact on the performance of the supercapacitor, thus the properties of designed nanostructures are essential and need to be considered. In this study, a ZnO-based nanomaterial with a high surface area and electronic conductivity was synthesized by combining the thermal treatment of a zeolitic imidazolate framework-8 (ZIF-8) with a biofilm-assisted surface modification method. A nanocomposite of ZnO and carbon (ZnO/C) was prepared by the systematic N₂/O₂ thermal treatment of ZIF-8. The ZnO/C composite underwent additional modification through the direct synthesis of Ag nanoparticles (Ag@ZnO/C) on the ZnO/C surface. An electrochemically active biofilm (EAB) was used as the reducing tool to synthesize the Ag nanoparticles. The final product, Ag@ZnO/C, was used as the electrode in a supercapacitor. Ag@ZnO/C exhibited a specific capacitance of 368.4C g⁻¹ (921 F g⁻¹) at a current density of 1 A g⁻¹, which was remarkably higher than that of ZnO/C (383.5 F g⁻¹). The cyclability of Ag@ZnO/C was also evaluated, demonstrating a 95 % capacity retention over 9000 cycles. The significantly enhanced surface area and electronic conductivity of Ag@ZnO/C resulted in an excellent supercapacitor performance.