Effective Utilization of Waste Red Mud for High Performance Supercapacitor Electrodes

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 (Fe 2 O 3 ), 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.

Recycled Red Mud–Decorated Porous 3D Graphene for High‐Energy Flexible Micro‐Supercapacitor

“…X‐ray photoelectron spectroscopy (XPS) was carried out to probe the presence of different elements in the composite assembly as shown in Figure 1f–h. The survey scan of the red‐mud embedded LIG structure shows the presence of Fe 2 O 3 and oxides of aluminum, silicon, sodium, and trace amounts of oxides of magnesium, titanium, and manganese in agreement with our previous work [ 36 ] and is also similar to the red‐mud XPS data taken by Xu et al and Liu et al, [ 40 ] respectively. The high‐resolution XPS graphs display the C 1s and Fe 2p spectra, and the presence of both components confirms the formation of the LIG‐RM nanocomposite.…”

“…The variation in the cyclic voltammogram data of the LIG‐RM sample as a function of scan rate (from 10 to 200 mV s −1 ) is shown in Figure 2b. The specific cell capacitance, C cell , is assessed from the CV graphs using Equations () and () [ 36 ] where I is the total current (in amperes) and v is the scan rate (in V s −1 ). The total current I can also be obtained from integration of the CV curve as [ 36,42 ] where V i and V f represent the upper and lower bounds of the voltage range.…”

“…The primary charge storage mechanism of an electrode is governed by the amalgamation of capacitive and intercalation. The appearance of both the processes can be evaluated and distinguished by monitoring the CV scans at different scan rates rendering to the following power law [ 36,44 ] …”

“…The b values between the potentials −1.2 and 1.5 V were obtained for LIG‐RM, and the variation of b with applied potential is plotted in Figure 2d with a considerable variation in “ b ” values from 0.3 to 0.85, which suggests that the charge storage mechanism is an amalgamation of both capacitive and diffusion, which arises from intercalation/de‐intercalation phenomena. [ 36,46 ]…”

“…In our previous work, [ 36 ] we have used RM from National Aluminium Company Limited (NALCO), India, and used ball‐milling to produce ≈30–50 nm diameter RM nanoparticles for use as supercapacitor electrodes. RM nanoparticles yielded a specific capacitance of ≈317 F g −1 , at 10 mV s −1 scan rate in 6 m aqueous KOH electrolyte, and cyclic stability of ≈97% after 5000 cycles, [ 36 ] demonstrating promising capability as supercapacitor electrodes.…”