Pseudocapacitance of rutile nickel fluoride in alkaline solution—a review

Rutile nickel fluoride NiF 2 has a theoretically high pseudocapacitance performance in alkaline aqueous solutions, while the actual pseudocapacitance performance of an actual NiF 2 electrode material is relatively low. Obviously, the actual NiF 2 electrode material’s chemical activity of Ni 2+ ions, crystal structure of NiF 2 , electron conductivity, and the amount of NiF 2 that contacts with OH − definitely affect the completeness and speed of the pseudocapacitance process or reaction and further the pseudocapacitance performance. Lots of researches devote to improve these structural factors through various strategies, such as synthesizing NiF 2 with large specific surface areas or excess F amount, introducing a heterogeneous metal atom (Co) to construct bimetallic fluoride NiCoF 2 , and introducing another heterogeneous metal atoms (Mn, Fe, Cu, Zn) to construct trimetallic fluorides, so as to benefit for the pseudocapacitance process and enhance the pseudocapacitance performance. The research status of these novel NiF 2 materials, including synthetic methods, pseudocapacitance parameter test, structure characterization results representing the above mentioned structural factors, and pseudocapacitance performance, is summarized and clarified in this review. A perspective is given. This review enriches the understanding of anion storage materials.