Self-supporting honeycomb-like porous nickel phosphide microsphere with high atomic percentage of phosphorus for high performance supercapacitor

Transition metal phosphides (TMPs), especially those with high atomic percentages of phosphorus in TMPs, are attracting extensive attention in novel electrode materials for energy conversion and storage due to their metallization properties, desired electrical conductivity together with superior redox activity, and high theoretical capacity. Unfortunately, their inherent low surface electroactivity and poor structural integrity result in unsatisfactory capacity rates and low cycling stability. Herein, we propose a facile hydrothermal and subsequent low-temperature phosphating strategy to construct a self-supporting honeycomb-like porous Ni5P4 microsphere with a high atomic percentage of phosphorus. Benefiting from the unique porous structural peculiarities in the microsphere to reduce ion/electron diffusion paths and increased the accessible area of the electrolyte, as well as provide significant durability, the Ni5P4 microsphere provides a high specific capacity of 450.1 C g−1 at 1 A g−1 (about 6 times than corresponding NiO microsphere) and good rate capability. Moreover, an asymmetric supercapacitor assembled based on Ni5P4 microsphere and activated carbon (AC) electrodes delivers a high specific energy of 43.5 Wh kg−1 at the specific power of 820 W kg−1, and good cycling stability with 88 % capacity retention after 5000 cycles.