Nonconductive two-dimensional metal−organic frameworks for high-performance electrochemical energy storage

Most metal-organic frameworks (MOFs) cannot be used as electrode materials due to their high cost, poor stability in aqueous solutions, inferior intrinsic electrocatalytic activity, and poor conductivity. The novel application of a nickel (II) cluster-based two-dimensional MOF, Ni-mba ([Ni(II)6Ni(III)2(mba)6(Cl)2(OH−)2(O2−)]n, H2mba is 2-mercaptobenzoic acid), is reported for use as electrode materials. Ni-mba is an insulator and H2mba is an inexpensive chemical raw material. The conductivity of Ni-mba is 2.180 × 10−9 Scm−1 at 30 °C. The electrocatalytic activity of Ni-mba is enhanced by the hexanuclear nickel (II) cluster subunit containing the sulfhydryl group and the mixed valence Ni2+/Ni3+ ions. Ni-mba shows excellent performance, stability in 6 M KOH, and a high inherent density (1.828 gcm−3) and specific capacity (704.4 Fg−1 at 1 Ag−1 and 1088.5 mAhg−1 at the first cycle) for lithium-ion batteries and supercapacitors. This paper provides a novel application of nonconductive two-dimensional MOFs in the energy storage field and the design recommendations of high-performance electrode materials for energy conversion and storage based on its structure and performance differences.