Enhanced energy storage ability of UIO66 active material on acid-treated carbon cloth for flexible supercapacitors

Metal organic framework, UIO66, has been regarded as one of potential electroactive materials for supercapacitors (SC), due to high surface area and tunable pore structures. To further improve electrochemical performance of UIO66-based SC, morphology design of UIO66 is necessary. In this work, it is the first time to study the effects of pH value of precursor solution on physical and electrochemical properties of UIO66. The pH values of 1, 2, 4 and 6 of precursor solution is prepared using acetic acid which is also acts as structure-directing agent. The different sizes of UIO66 are obtained by merely changing pH value of precursor solution. The UIO66 octahedron synthesized using pH values of 1 and 6 present the smallest size and similar dimensions to carbon black with irregular spherical morphology and size of around 75 nm which is also in paste. Carbon cloth (CC) substrate is also modified using acid to understand substrate influences on SC performance. The optimized pH value of 1 and 6 is respectively obtained for synthesizing UIO66 on acid-treated CC (ACC) and CC substrates. Due to the extra energy storage from substrate, the electrode with UIO66 prepared using pH value of 6 on ACC (M6/ACC) shows the highest areal capacitance (C_A) of 3.87 mF/cm² at 2.5 A/g. Also, the symmetric SC (SSC) fabricated using M6/ACC electrodes and aqueous medium-based electrolyte shows potential window of 0.9 V, maximum energy density of 36 mWh/kg at 89.94 W/kg, and C_A retention of 130% after 10000 times charging and discharging process.