Co-Ln (Ln = Ce ∼ Yb) bimetal complexes: Syntheses, structures and their applications as supercapacitor anode materials

Abstract

In this present, 16 Co-Ln (Ln = Ce ∼ Yb) bimetallic complexes (named as complexes #1-#16 and abbreviated as CoLnPda) were synthesized. Among these complexes, complexes #1-#12 were two-dimensional layered, and complexes #13-#16 were three-dimensional block MOFs. Single crystal x-ray diffractometer (SXRD) and x-ray photoelectron spectrometer (XPS) were applied to confirm the components of the complexes and the oxidation state of the central atom. Optical microscopy, powder x-ray diffractometer (PXRD), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet–visible spectrum (Uv–vis) were used to characterize the complexes. Among these 12 kinds of two-dimensional layered complexes, the obtained pure complexes were evaluated by thermo gravimetric analysis (TG) to illustrate their thermal stability. Next, complex #2 (CoPrPda-n) was selected as an example to illustrate the use of such layered complexes as the precursors to prepare the energy storage materials. Under the atmosphere of nitrogen gas flow, the composite with blade structure (C/Pr2O2CO3/CoO/Co) was formed when the precursor was calcined at 800 °C for 2 h. The sample was used as the electrode material of the supercapacitor and when the current density was 2 A·g−1 in 6 M KOH electrolyte, it showed a specific capacity of 1440 F·g−1. The cycle tests showed that the specific capacitance retained well after 2000 cycles at the current density of 20 A·g−1.