Enhanced energy storage performance of advanced hybrid supercapacitors derived from ultrafine Ni–P@Ni nanotubes with novel three-dimensional porous network synthesized via reaction temperatures regulation

Nickel-phosphorus semimetallic compounds with an open-framework structure have attracted increasing interests as electrode materials for supercapacitor applications. In this work, ultrafine Ni–P@Ni nanotubes (NTs) with a novel three-dimensional network are synthesized by using a one-pot hydrothermal method under different temperatures to form the electrode material for hybrid supercapacitors. The energy storage performances of the Ni–P@Ni NTs electrodes are systematically investigated, and the results demonstrate that the Ni–P@Ni NTs possess a superior specific capacity of 771.8 C g⁻¹ at 1 A g⁻¹ in a three-electrode cell. Remarkably, a specific capacity of 350.2 C g⁻¹ can still be maintained when the current density increases up to 30 A g⁻¹. The energy storage performance of the as-prepared Ni–P nanowires (NWs) and Ni₁₁(HPO₃)₈(OH)₆@Ni nanoparticles (NPs) also are evaluated for comparison. Furthermore, a hybrid supercapacitor (HSC) is assembled with the Ni–P@Ni NTs as the positive electrode and activated carbon (AC) as the negative electrode. The as-assembled HSCs show a high energy density of 58.7 Wh kg⁻¹ at a relatively high-power density of 945 W kg⁻¹, outweighing most of the hybrid supercapacitors reported in the literature. Furthermore, such a hybrid supercapacitor displays an excellent cycling stability (91.2% after 6000 cycles at 5 A g⁻¹) under a voltage of 1.6 V.