Optimization of Ti₃C₂T_x performance through synergistic enhancement of GeO_x/Ti₃C₂T_x heterostructures for ammonium-ion storage

Aqueous energy storage systems with non-metallic ion charge carriers, ammonium (NH₄⁺) ions, are most promising compared to metal-ion batteries, owing to their high safety and performance, as well as their sustainability. Here, we first report the germanium oxides (GeO_x) coupled with Ti₃C₂T_x MXenes nanosheets (denoted as GeO_x@Ti₃C₂T_x) composite cathode material for ammonium-ion hybrid supercapacitor (AHSC). This research focused on addressing the limitations of conventional cathode materials while examining the intercalation behaviour of ammonium ions within the GeO_x@Ti₃C₂T_x framework. GeO_x and Ti₃C₂T_x were integrated through a precise synthesis process, leading to defect engineering within the composite material. This approach enhanced the structural stability, increased the specific surface area, and improved ion transport properties. The postmortem ex-situ XRD, XPS and TEM investigations show that GeO_x@Ti₃C₂T_x maintained its structural integrity and electrochemical stability during the charge/discharge process. The assembled GeO_x@Ti₃C₂T_x//AC-AHSC device exhibits high specific capacitance, excellent rate capability, and remarkable cycling stability. The device exhibits a high energy density of 51.4 Wh/kg at a power density of 800.6 W/kg, which is superior to many existing MXene-based devices. These findings highlight the promise of GeO_x@Ti₃C₂T_x composites as candidates for high-performance, environmentally friendly energy storage solutions.