Dual-metal sites enable conductive metal–organic frameworks with extraordinary high capacitance for transparent energy storage devices

Abstract

Two-dimensional (2D) conductive metal–organic frameworks (c-MOFs) with intrinsic electrical conductivity and framework structure have been considered promising electrode materials for flexible and transparent energy storage devices. However, balancing electrochemical properties and optical transmittance remains challenging. To address this issue, a strategy of dual-metal-sites 2D c-MOFs is proposed to expand 2D Cu-MOF to nanorod-combined 2D CuNi-HHTP (HHTP = 2, 3, 6, 7, 10, 11-hexahydroxy-triphenylene) with improved ion and charge transport to redox species for Faraday reactions in micro-supercapacitors. Density functional theory calculations reveal that the incorporation of Ni can optimize the insertion of pseudocapacitive cations (K⁺) on dual-metal sites, significantly enhancing electron transfer during the charge-storage process. Furthermore, a facile laser-scribing technique is adopted for the fabrication of the interdigital architecture, serving as a transparent platform with exceptional optoelectronic properties. As a result, the CuNi-HHTP MSC exhibits high optical transmittance (over 80%), ultrahigh areal capacitance (28.94 mF cm⁻²), high energy density (1.45 μW cm⁻²), high power density (61.38 mW cm⁻²) and decent cycle stability (over 5000 cycles). This work offers a means of rationally designing 2D c-MOFs for the advancement of flexible transparent portable electronics.