Influence of Capping Agents on the Synthesis of Mn₃O₄ Nanostructures for Supercapacitors

Abstract

Nanotechnology offers powerful strategies for the synthesis of advanced materials for supercapacitors. It is hypothesized that the size reduction of Mn 3 O 4 nanoparticles can eliminate time-consuming electrochemical activation and increase the electrochemical pseudocapacitance of this material. Moreover, due to the redox properties and specific features of its chemical synthesis procedure, Mn 3 O 4 can potentially outperform other promising cathode materials for energy storage in supercapacitors. A facile room temperature method to fabricate Mn 3 O 4 nanoparticles is described, which is based on the application of advanced capping agents (CAs) for nanofabrication. Building on the strong adsorption power of the catechol ligand, we utilize tetrahydroxy-1,4-quinone, catechin, and gallocyanine as CAs for the preparation of Mn 3 O 4 . The use of the catecholate molecules as CAs for chemical precipitation facilitates the preparation of Mn 3 O 4 platelet nanoparticles with a typical size of 5 nm. The reduction of the particle size allows the fabrication of advanced Mn 3 O 4 multiwalled carbon nanotube cathodes with 40 mg cm –2 active mass (AM), which show a significant increase in capacitance in a 0.5 M Na 2 SO 4 electrolyte. The highest capacitances of 7.03 F cm –2 (175.8 F g –1 ) at a potentiodynamic sweep rate of 2 mV s –1 and 9.13 F cm –2 (228.3 F g –1 ) at a constant current density of 3 mA cm –2 are obtained at a low impedance using gallocyanine as a CA. Obtained electrodes outperform MnO 2 -based cathodes of similar mass. Another important finding is the possibility to avoid the time-consuming activation process for Mn 3 O 4 -based electrodes. Analysis of the testing results provides evidence of the influence of the CA structure on the electrode performance. The results of this investigation pave the way for the application of Mn 3 O 4 in advanced high-AM supercapacitor cathodes.

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