Polyaniline-modified NiCo layered double hydroxide hollow nanocages for aqueous ammonium-ion supercapacitors

Aqueous ammonium ion supercapacitors have attracted extensive attention from researchers for their environmental friendliness, high safety, and low cost. Unfortunately, compared with other energy storage technologies, the research and development of high-performance ammonium storage electrode materials is lagging, which has seriously hindered its development. Here, we designed and prepared nickel-cobalt layered double hydroxide nanocages (HLDH@P) with a unique hollow structure and polyaniline (PANI) coating, and used them as ammonium ion energy storage hosts. The optimized HLDH@P electrode material exhibits a great specific capacity of up to 1248 F g^-1 at 1 A/g, while a high discharge plateau of 0.6 V is observed. The assembled asymmetric supercapacitor (A-HSC) has an energy density of 42 Wh kg^-1 and a corresponding power density of 623 W kg^-1, while also exhibiting excellent cycling stability. In addition, density functional theory (DFT) shows that the abundant nitrogen-containing groups in the composite material effectively increase the adsorption energy of NH₄⁺ ions, and the large number of hydrogen bonds formed thereby greatly improve the electrochemical performance of the composite material. The results of this study fully demonstrate the broad application prospects of surface engineering in designing high-performance ammonium storage electrode materials.