Molybdenum-incorporated zinc phosphate hydrate nanorods for enhanced electrochemical performance in potassium-ion capacitors

Electrode materials that concurrently provide high capacity, long cycling stability, and dependable performance for reusability are required in the expanding search for sustainable and scalable energy storage systems. The lack of high-capacity and kinetically efficient cathode materials continues to impede the advancement of aqueous electrochemical energy storage (EES) systems, despite their inherent safety, environmental compatibility, and affordable manufacture. Here, a chemically engineered (NH₄)ZnMoO₄PO₄ (ZMP) cathode with sugarcane-like interlocked nanorod bundles employing a Mo-intermediated zinc phosphate electrode is used to develop an aqueous-based potassium hydride ion capacitor (PHIC). The resulting ZMP integrates abundant electrochemically active sites for K⁺ and OH⁻ ions, interconnected porosity, and short radial diffusion pathways, thereby boosting ion transport and charge storage efficiency. The optimized ZMP electrode has a dominating diffusion-controlled contribution and low electrochemical resistances and exhibits a high specific capacity of 7.95 F/cm² (1.0 mAh/cm²) at 10 mA/cm². More significantly, the assembled PHIC device achieved a specific capacity of 560 mF/cm² along with an energy density of 174 μWh/cm² at a power delivery of 1.13 mW/cm², maintaining 95% of its initial capacity over prolonged cycling. Additionally, for size-dependent EES analysis, a solid-state PHIC device was designed. Results demonstrate that trimmed devices have a reliable storage capacity in the range of 146 to 160 mF/cm² at 20 mA/cm². This research establishes a practical approach to nanostructure optimization, enabling superior ZMP cathode performance and marking a step forward in the development of next-generation aqueous energy storage technologies.