Aluminum sulfate—an electrolyte for MnO₂ hybrid supercapacitor

Abstract

Manganese oxide is an important emerging electrode material for use in supercapacitor applications. Herein, we propose a new aqueous electrolyte, Al₂(SO₄)₃, for use with this type of supercapacitor. We hypothesize that the trivalent aluminum ion will demonstrate higher specific capacities because of its higher charge. We show that β-MnO₂, which usually demonstrates low specific capacity (∼10 F g⁻¹), is highly active in this electrolyte. At a scan rate of 2 mV s⁻¹, a specific capacity of 185 F g⁻¹ is demonstrated. An asymmetric cell is constructed from a positive β-MnO₂ electrode and an activated carbon (AC) negative electrode. The cell exhibits an initial specific capacity of 42 F g⁻¹ (calculated for the total AC and MnO₂ mass), and a steady coulombic efficiency (97–98%), operating for 2500 cycles, after which a 20% drop from its initial capacity is measured. The cell displays higher values of specific capacitance when compared to a sodium sulfate electrolyte.