Revealing the effects of functional group in organic linkers on properties of metal organic frameworks electrode and their performance in supercapacitors

Abstract

The history of developing supercapacitors with increased performance is inextricably linked to the exploration and design of suitable electrode materials. Metal-organic frameworks (MOFs) have attracted intensive attention for use in high-performance supercapacitors thanks to their large specific surface area, tuneable pore sizes and crystal structure. Understanding the influence of MOF structures and properties on the performance of supercapacitors is critical to enhancing their performance. However, so far researchers have been keen on exploring metal atoms in MOFs and have ignored the effects of organic ligands, especially the functional groups thereon, on supercapacitors. In this work, we have studied the impact of organic linkers’ functional groups on the properties of MOFs and how this influences their performance as supercapacitor electrode materials. We synthesized four MOFs with different functional groups, including hydroxyl, nitride and thiol groups and characterised their physicochemical properties and their performance as supercapacitor electrode materials. Characterisation of the specific surface area shows that the BET area decreases from 980.3 m² g⁻¹ for the original MOF to 12.2 m² g⁻¹ when the thiol group is incorporated. Furthermore the –OH, –NH, and −SH functionalities reduced the charge transfer resistance (< 1 Ω) and induced more pseudocapacitance, whereas the –OH group dramatically increased the hydrophilicity of the electrode and rate performance of supercapacitors. Although the MOFs without extra function group showed the highest specific capacitance of 1495F g⁻¹, analysis of the normalized areal specific capacitance only shows 1.5 F m⁻². The MOFs with the −SH group showed the highest normalized areal specific capacitance of 26F m⁻² as well as stable cycling performance of 80 % retention after 10,000 cycles.