Nickel cobalt bimetallic metal-organic frameworks with a layer-and-channel structure for high-performance supercapacitors

Using L-malic and 4,4′-bipyridine as linkers and Ni and Co as metal centers, a series of bimetallic metal-organic frameworks (MOFs; NinComMOFs, n:m = 4:1, 2:1, 1:1 and 1:2) with a layer-and-channel structure were hydrothermally synthesized. Owing to the joint action of Co and Ni as well as internal crystal properties, the NinComMOFs presented a remarkable capacitive performance. The capacitance of Ni1Co1MOF could reach up 1333 F•g−1 at 2 A•g−1 and even at 10 A•g−1, the capacitance retained 83% of its performance, which was higher than that of its corresponding monometallic MOFs (NiMOF and CoMOF). Meanwhile, an asymmetric supercapacitor Ni1Co1MOF//activated carbon (AC) was developed. It had an outstanding capacitance of 97 F•g−1 at 0.5 A•g−1. Moreover, 83% retention capacitance after 2000 cycles suggested an excellent cycling lifespan. Ni1Co1MOF//AC also exhibited a high energy density of 28 Wh•kg−1 at 444 W•kg−1. To summarize, the bimetallic MOFs were promising electrode materials for supercapacitors owing to their excellent electrochemical properties.