Cr-doped Ni-MOF nanosheet array structure anchored on nickel foam with specific orientation for high performance supercapacitors

Metal-organic frameworks (MOFs) gain the popularity among studies due to their exclusive modular and buildable structure, tunable pore size distribution and diversity of functions, which provide tremendous possibilities for the production of high-performance supercapacitors and are considered as one of the vital energy storage materials. Among MOFs, Ni-MOF shows great application outlooks of the energy storage field because of its big specific capacitance and the ability to provide active sites during the reaction. However, the shortcomings of conductivity, rate performance and cycle stability are not very outstanding. This study uses one simple hydrothermal method to synthesize a three-dimensional bimetallic metal nanosheet structure by doping different ratios (including Ni: Cr=1:1, 2:1, 3:1, 4:1, 5:1 and 6:1) in Ni-MOF structure on nickel foam to improve electrochemical performance. Cr-doped materials have abundant active sites due to their large specific surface area. It promotes the reaction of the material surface in the electrolyte, thus enhancing the particular capacitance. At the same time, Cr3+ can also strengthen the lattice stability and gives a more stable nanostructure, effectively promoting conductivity and cycling stability. Therefore, after a series of tests, the obtained electrode material with the optimal ratio of Ni: Cr=4: 1 in Ni-MOF (NC4M@NF) reaches high specific capacity up to 853.00 C g-1 at 1 A g-1, better rate capacity of 64.48 % at 10 A g-1 with 3 M KOH in three-electrode system. Besides, the assembled NC4M@NF//AC ASC supplies an energy density of 64.41 Wh kg- 1 at 850.31 W kg- 1, and exceptional cycling stability with only decays 17.89 % after 5000 cycles.