Precisely controlling the nanostructure of bimetallic Mg/Zn MOFs to construct a high-performance material for supercapacitors and sodium-ion batteries†

Abstract

Precisely adjusting the specific surface area and mesoporosity, along with integrating the microporous structure of carbon materials, is key to constructing high-performance materials for supercapacitors and sodium-ion batteries (SIBs). The limited tunability of single metal–organic framework (MOF) derivatives makes it hard to precisely regulate their meso-/micropore ratio, resulting in low capacitance and rate performance. Herein, we propose a new bimetallic Mg/Zn MOF derivative with the expected performance through multiple precise regulations of Mg/Zn ratios, decarboxylation/volatile removal, acid etching, and KOH activation. Characterization and electrochemical tests reveal that a suitable Mg–Zn proportion, decarboxylic reaction, and removal of MgO nanoparticles contribute to the formation of a micro-pore structure, which significantly increases specific capacitance (SC) at low current density. The introduced KOH activation contributes to the conversion of micropores into mesopores, significantly enhancing specific capacitance at high current density. The optimized MZAPC-4 structure demonstrates an increased surface area (2127 m² g⁻¹) and SC (468 F g⁻¹ at 1 A g⁻¹) and excellent rate performance (366 F g⁻¹ at 100 A g⁻¹ and 268 F g⁻¹ at 300 A g⁻¹); these values are far superior to those of recently published porous carbons. Furthermore, it offers high specific capacity (401 mAh g⁻¹ at 0.05 A g⁻¹) in assembled SIBs, confirming its dual application in energy storage systems. The proposed precise regulation of the sub-nanopore structure of bimetallic MOF derivatives is a promising strategy for fabricating high-performance supercapacitors and SIBs.