Abstract
In recent years, metal oxide‐based, inexpensive, stable electrodes are being explored as a potent source of high performance, sustainable supercapacitors. Here, the employment of industrial waste red mud as a pseudocapacitive electrode material is reported. Mechanical milling is used to produce uniform red mud nanoparticles, which are rich in hematite (Fe2O3), and lower amounts of other metal oxides. A comprehensive supercapacitive study of the electrode is presented as a function of ball‐milling time up to 15 h. Ten‐hour ball‐milled samples exhibit the highest pseudocapacitive behavior with a specific capacitance value of ≈317 F g−1, at a scan rate of 10 mV s−1 in 6 m aqueous potassium hydroxide electrolyte solution. The modified electrode shows an extraordinary retention of ≈97% after 5000 cycles. A detailed quantitative electrochemical analysis is carried out to understand the charge storage mechanism at the electrode–electrolyte interface. The formation of uniform nanoparticles and increased electrode stability are correlated with the high performance. This work presents two significant benefits for the environment; in energy storage, it shows the production of a stable and efficient supercapacitor electrode, and in waste management with new applications for the treatment of red mud.
Highlights
The exploitation of non-conventional renewable energy sources is of significant worldwide interest due to the increasing global demand for energy, the rapid exhaustion of fossil fuels and other nonrenewable energy resources, and environmental concerns such as global warming and climatechange [1]
Carbon-based materials such as activated carbon [16], carbon nanotubes [17], graphene [18, 19], reduced graphene oxide [20, 21] have been explored as electrical double layer capacitance (EDLC) materials whilst conducting polymers [22, 23] and transition metal oxides [24, 25] have been utilised as pseudocapacitive supercapacitor electrodes
The present work successfully validated the suitability of mechanically activated red mud as a potent source of energy storage material
Summary
The exploitation of non-conventional renewable energy sources is of significant worldwide interest due to the increasing global demand for energy, the rapid exhaustion of fossil fuels and other nonrenewable energy resources, and environmental concerns such as global warming and climatechange [1]. The charge storage mechanism in a supercapacitor is governed either by electrical double layer capacitance (EDLC) [7, 8] or by pseudocapacitance [9, 10]. In EDLC, the charge is stored electrostatically through reversible adsorption of electrolytes onto a high surface area and electrochemically-stable electrodes. The phenomena is related to a potential-dependent accumulation of charges at the electrode-electrolyte interface [11, 12]. The capacitance is faradic in origin [13] whereby an ultra-fast redox reaction takes place at or near the electrode and a faradic charge is passed as a function of electrode potential [14, 15]. Carbon-based materials such as activated carbon [16], carbon nanotubes [17], graphene [18, 19], reduced graphene oxide [20, 21] have been explored as EDLC materials whilst conducting polymers [22, 23] and transition metal oxides [24, 25] have been utilised as pseudocapacitive supercapacitor electrodes
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