Synergistic effect of Co/Ni bimetallic metal–organic nanostructures for enhanced electrochemical energy storage

Introducing a secondary metal ion is an effective strategy to significantly enhance the electrochemical performance of monometallic metal-organic frameworks (MOFs). Herein, we synthesize a series of cobalt-nickel bimetallic MOFs (Co/Ni-MOFs) by the Co2+ substitution into Ni-MOF ({Ni3(OH)2(tdc)2(H2O)4}n, H2tdc = 2,5-thiophenedicarboxylic acid). The Co/Ni-MOF-2:1 with optimal Co/Ni ratio possesses improved electrical conductivity, intrinsic reactivity, and stability. Compared with the monometallic Ni-MOF, the bimetallic Co/Ni-MOF-2:1 with nanowire morphology achieves a higher specific capacitance (610 F g-1 at a current density of 0.5 A g-1), a better rate capacity (88 % capacitance retention at 5 A g-1) and cycling performance (72 % retention after 5000 cycles). Moreover, the asymmetric supercapacitor constructed with Co/Ni-MOF-2:1 and activated carbon exhibits a high specific capacitance (228 F g-1 at 0.5 A g-1) and excellent cycling stability (95.5 % of capacitance retention after 5000 circulations at 5 A g-1).