Overcoming Challenges in Development of Manganese Oxide Supercapacitor Cathodes by Alkali-Free Hydrothermal Synthesis

Abstract

This investigation is motivated by the need in the development of manganese oxide cathodes for supercapacitors with high capacitance at high charge–discharge rates and enhanced capacitance retention in a wide range of charge–discharge rates. It also addresses the challenge of eliminating the time-consuming activation procedure, which limits the applications of Mn3O4 cathodes. The new approach is based on the use of environmentally friendly and biocompatible pH modifiers–dispersants, such as polyethylenimine (PEI) and meglumine (MG) for hydrothermal synthesis. In this approach, the use of inorganic alkalis is avoided. We demonstrate the benefits of this approach for the fabrication of manganese oxide nanoparticles, such as Mn-PEI and Mn-MG. Electrodes with a high active mass of 40 mg cm−2 are fabricated and electrochemically tested in 0.5 M Na2SO4 electrolyte. The method of electrode material fabrication offers benefits for the accelerated electrode activation procedure, which is practically eliminated for Mn-MG electrodes. The Mn-MG electrodes showed a remarkably high capacitance of 3.68 F cm−2 (93.19 F g−1) at a sweep rate of 100 mV s−1 and a high capacitance retention of 90.6% in the CV sweep range of 1–100 mV s−1.

The effect of nickel oxide in the direct growth of MnOx on Ni foam by chemical vapor deposition

“…Transition metal oxides have garnered intense interest in this field as electrode materials due to their high electrochemical performance and cyclic stability [5][6][7][8][9][10][11][12][13]. Due to their diverse chemical properties, rich redox chemistry, and multitude of valance states, the manganese oxide (MnO x ) materials, including MnO, MnO 2 , Mn 2 O 3 , and Mn 3 O 4 , have become promising candidates as electrode materials [14][15][16][17]. MnO 2 and MnO have been theoretically predicted to produce exceptionally large specific capacitances of 1110 F g −1 [18] and 1350 F g −1 [19,20], respectively, at a voltage range of 1 V, while experimentally determined specific capacities are smaller but still high, on the order of a few hundred F g −1 [21][22][23].…”