Polyoxometalate Imide-Linked Molecules, Covalent Organic Polymers, and Frameworks: Dimensionality Effects on Supercapacitors Performance

Abstract

Efficient and durable energy storage materials are essential to meet the increasing demand for renewable energy technologies. However, existing materials often encounter trade-offs among energy density, power density, and cycling stability. To overcome these limitations, a 2D imide-linked polyoxometalate-covalent organic framework (i-POCOF) is introduced. This hybrid material combines the redox activity of polyoxometalates (POMs) with the structural adaptability of covalent organic frameworks (COFs). Complementarily, 0D imide-functionalized POM-molecule and 1D POM-polymer systems are investigated, enabling a systematic evaluation of how dimensionality affects their physicochemical properties and electrochemical performance. By increasing dimensionality, the hybrids exhibit improved surface area ranging from 107 m² g⁻¹ for 0D to 257 m² g⁻¹ for 2D, and optimized porosity (average pore size from 1.9 nm for 0D to 3.7 nm for 2D), resulting in enhanced ion diffusion and charge transport. In particular, 2D i-POCOF exhibits remarkable electrochemical performance, achieving a specific capacitance of 132 F g⁻¹, energy density of 73.3 Wh kg⁻¹, and power density of 0.9 kW kg⁻¹, with only 6% capacitance loss after 5000 cycles. These findings highlight the potential of POM hybrids as high-performance and stable energy storage hybrids, providing a promising pathway to overcome current limitations in electrode materials.