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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.373

New Methods for the Fabrication of Composites for Supercapacitor Electrodes with High Active Mass Loading Aseeb M. Syed and Igor Zhitomirsky Department of Materials Science and Engineering, McMaster University ABSTRACT

MnO2-multiwalled carbon nanotube (MWCNT) supercapacitor electrodes with active mass loading of 30-45 mg cm-2 were prepared. In method 1, MnO2 and MWCNT were dispersed using 3,4-dihydroxybenzaldehyde (DHB) and toluidine blue (TD), respectively. The Schiff base formation between amino group of TD and aldehyde group of DHB facilitated improved mixing of MnO2 and MWCNT. In method 2, gallocyanine (GC) was used as a co-dispersant for MnO2 and MWCNT. The catecholate type bonding of DHB and GC allowed for adsorption of the dispersant molecules on MnO2 nanoparticles. The electrodes, prepared by method 1 showed higher capacitance, compared to the electrode, prepared by method 2. The highest capacitance of 7.8 F cm-2 (173 F g-1, 139 F cm-3) was obtained at a scan rate of 2 mV s-1 and active mass loading of 45 mg cm-2. INTRODUCTION MnO2 is currently under intensive investigation for energy storage applications in electrodes of supercapacitors (SC)[1-4]. The interest in application of MnO2 in SC electrodes is due to high theoretical capacitance of this material, nearly ideal capacitive charge-discharge behavior in a relatively large voltage window and low cost. MnO2 is usually combined with conductive additives in order achieve enhanced electronic conductivity of composites. MnO2 and composite electrodes showed [5-9] high gravimetric capacitances (Cm, F g-1) at low active mass loadings in the range of 0.005–1 mg cm-2. However, significantly higher active mass loadings above 10 mg cm-2 are necessary for practical applications[10,11]. It was found that Cm decreased drastically with increasing active mass due to poor electrolyte access to the active material and low electronic conductivity. Areal capacitance (CS, F cm-2) is another important parameter of SC, especially at high active mass loadings. The important task is to achieve good performance at high active mass loadings[11] and fabricate SC electrodes with high CS and Cm. The goal of this investigation was the development of colloidal strategies for the fabrication of MnO2-MWCNT electrodes with mass loadings in the range of 30-45 mg cm-2. The approach was based on the use of advanced dispersants for dispersion and mixing of MnO2 and MWCNT, which facilitated the fabrication of efficient SC electrodes with high CS and Cm.

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EXPERIMENTAL SECTION Toluidine blue (TD), 3,4-dihydroxybenzaldehyde (DHB), gallocyanine (GC), polyvinyl butyral (PVB), KMnO4, Na2SO4 (Aldrich, Canada), MWCNT (ID 4 nm, OD 13 nm, length 1-2 um, Bayer, Germany) and Ni foams (95 % p