Synthesis of two new polyoxometalate-based organic complexes from 2D to 3D structures for improving supercapacitor performance†

Abstract

As an emerging energy-storage technology, research on supercapacitors is vital for advancing new energy applications, which rely on the development of electrode materials with superior properties. In this study, two novel polyoxometalate-based metal–organic complexes (POMOCs), Ag₄(imbta)₄(PMo^VMo^VI₁₁O₄₀) (PMo₁₂-Ag-imbta, 1) (imbta = 1-imidazole-1-methylene-1H-benzotriazole) and Ag₄(pybta)₄(PMo^VMo^VI₁₁O₄₀)(PMo₁₂-Ag-pybta, 2) (pybta = 1-pyridine-3-methylene-1H-benzotriazole), were synthesized via a hydrothermal method utilizing Ag⁺, imbta/pybta and [PMo₁₂O₄₀]³⁻, respectively. In 1, Ag⁺, imbta, and [PMo₁₂O₄₀]³⁻ form 2D layers via coordination bonds. At the same time, Ag⁺ forms a 1D chain with [PMo₁₂O₄₀]³⁻. In 2, Ag⁺ and pybta form four separate Ag-pybta spiral chains. In addition, the coordination interaction between Ag⁺ and [PMo₁₂O₄₀]³⁻ not only induces the construction of the Ag-PMo₁₂ 2D network that promotes electron transport in 2 but also facilitates the development of the 3D structure characterized by the four-helix winding. Meanwhile, there are many holes in 2, which are conducive to ion transport. In a three-electrode system, 2-GCE demonstrated superior capacitive performance (668 F g⁻¹ at 1 A g⁻¹) compared to 1-GCE (420 F g⁻¹ at 1 A g⁻¹), along with excellent cycling stability (91.4% retention after 1000 cycles). Notably, the specific capacitance of 2-GCE at 5 A g⁻¹ was four times higher than that of PMo₁₂. This study advances the development of novel crystalline electrode materials for energy storage applications.