High-performance asymmetrical hybrid supercapacitor based on yolk-shell Ni₃P nanoparticles constructed by selective etching

A novel yolk-shell Ni₃P nanoparticle is fabricated through a facile solvothermal synthesis of amorphous Ni-P nanospheres under normal pressure, heat treatment to transform amorphous sample into crystalline Ni₃P/Ni, followed by the selective removal of metal nickel via washing with hydrochloric acid. The plausible formation mechanism is proposed. Due to the unique microstructure and the high intrinsic electrochemical activity of Ni₃P, the as-prepared yolk-shell Ni₃P nanosphere presents an outstanding specific capacity of 749.7 C g⁻¹ at 1 A g⁻¹. The asymmetric supercapacitor (ASC), employed yolk-shell Ni₃P nanoparticles and activated carbon (AC) as cathode and anode, can not only delivers high energy density of 34.2 Wh kg⁻¹ at 299.9 W kg⁻¹ but also exhibits preeminent cycling stability with 95.6% capacitance retention after 3500 cycles. Notably, two ASCs in series can power a small light emitting diode (LED) display screen or a remote control car robustly. These results demonstrate a great potential application of the yolk-shell Ni₃P nanospheres and may speed up the development of phosphide-based electrodes for asymmetric application.