Solid-state phase transformation of NiO into metallic Ni via ammonia reduction reaction for hybrid supercapacitors

NiO has the characteristics of low cost, good environmental compatibility and high theoretical specific capaci-tance, and it is a promising electrode material. However, the poor intrinsic electrical conductivity of NiO greatly hinders its practical application as a high-performance electrode material for energy storage. Herein, we report a facile ammonia reduction reaction method so as to realize solid-state phase transformation of NiO into metallic Ni for optimizing the conductivity and electrochemical character of NiO. By analyzing the evolution process of composition, structure, and morphology during the entire solid-state phase transition reaction, it is confirmed that the low-coagulation NiO precursor particles are successfully transformed into high-coagulation metallic Ni. It is also confirmed that the metallic Ni displays a higher electrical conductivity and more significant energy storage performance. Generally speaking, the present results provide a new strategy to improve the electrical conductivity of NiO, and the simple ammonia reduction reaction method is expected to be applied to other metal oxides.

Automated summary

By using a simple ammonia reduction reaction method, solid-state phase transformation of NiO into metallic Ni was achieved, resulting in improved electrical conductivity and energy storage performance. This approach provides a new strategy to enhance the electrical conductivity of NiO and is expected to be applicable to other metal oxides.