#These authors contributed equally to this work
In this paper, the non-polluting, non-toxic, and eco-friendly material-MnO2 electrodes were deposited on three-dimensional porous nickel (Ni) foam by linear sweep voltammetry, and the entire electrodeposition process did not require sintering of the material, which was fast and convenient while avoiding unnecessary energy consumption and thus was environmentally friendly. Scanning electron microscopy (SEM) and transmission electron microscopy were used to examine the surface and microscopic characteristics of each sample (TEM). Chronoamperometry (CA), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) were then used to determine the electrochemical characteristics of the manufactured samples. The result suggests that the MnO2-sv80 electrode sample at a scan rate of 80 mV/s−1 has excellent performance for the supercapacitor electrode. The specific capacitance was as high as 531.4 F g−1 at a current density of 1 A g−1 and remained at 223.2 F g−1 at an ultra-high current density of 20 A g−1, with capacitance retention of 42%.
The discovery and consumption of fossil fuels have contributed to rapid social development. However, the rapid economic growth has brought about increasingly severe environmental pollution. The goals of peak carbon dioxide emissions and carbon neutrality have triggered a human desire for clean energy. Solar energy and wind energy are high-quality clean energy sources. However, they are often unstable sources due to geographical factors and weather. As a result of this wave of the energy revolution, new, green, safe, and efficient energy storage systems (ESS) have become a hot research and development topic [
Electrode materials are the core components directly affecting the performance of supercapacitors [
Combining the advantages of MnO2 in supercapacitor electrodes with the advantages of the electrochemical deposition method, such as its fast results, green and low-carbon features, and no need to introduce conductive agents, this paper presents a method of ultrasonic-assisted preparation of the non-polluting, non-toxic and high-performance nano-MnO2 electrode material on three-dimensional porous nickel (Ni) foam by linear sweep voltammetry with manganese acetate and sodium sulfate as raw materials.
For 15 min, Nickel foam (110 PPI, 1 mm thickness, 350 g m−2, 1.0 × 1.5 cm−2) was submerged in a solution of hydrochloric acid, ethanol, and deionized water to remove any oxides or impurities from the substrate surface [
Electrode | MnO2-sv40 | MnO2-sv60 | MnO2-sv80 | MnO2-sv100 |
---|---|---|---|---|
mass (mg) | 1.2 | 1.1 | 0.8 | 0.6 |
Scanning electron microscope (SEM, Zeiss ULTRA 55 SEM) and transmission electron microscope (TEM, FEI Tecnai G2 F20) were used to observe the microscopic morphology of the prepared MnO2 films.
Chronoamperometry (CA), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) were used to evaluate the electrochemical performance of the MnO2 thin film electrode in a three-electrode system (Each MnO2 electrode served as the working electrode, saturated Ag/AgCl served as the reference electrode, and Pt served as the counter electrode in the French BioLogic electrochemical workstation) at room temperature, using 1 M Na2SO4 solution as the electrolyte. According to the galvanostatic charge/discharge curve and cyclic voltammetry curve, obtained from the test, the following
In
In
The Faradaic redox reactions of sodium ions embedded and de-embedded on the surface of MnO2 during the charging and discharging process are shown in
Scanning electron microscopy (SEM) pictures of electrodes generated at various scan rates are shown in
In electron microscopy images at high magnification, the electrode samples at high scan rates showed a densely packed nanorod morphology with overlapping associations. This structure facilitated the rapid transfer and transport of electrons and ions, resulting in an increase in the number of active sites for electrochemical reactions and an increase in the materials’ specific capacitance. Additionally, at a scan rate of 40 mV/s, the aggregation of nanorods on the MnO2 electrode surface resulted in the formation of nanospheres which was because the longer electrode deposition time at low scan rates could lead to the growth of nanorods for a long time in a preferred orientation. However, the electrochemical redox reaction occurred mainly at the electrode surface. The active materials at the bottom of this structure were covered and cannot participate in the electrode reaction for capacitance provision. Thus, the material mass utilization was low.
To further understand the microstructure of the microstructure of the manganese dioxide electrode samples prepared, the prepared, the prepared samples were observed by using transmission electron microscopy (the selected samples were made at a scan rate of 80 mV/s for observation), as shown in
To conduct additional research on the sample surface’s oxidation state and chemical makeup, we characterized the MnO2-sv80 through the XPS technique. The results are shown in
Specific capacitance | Current density | Electrode | Reference |
---|---|---|---|
158 F g−1 | 1 A g−1 | δ-MnO2 | [ |
239 F g−1 | 1 A g−1 | SSM-MnO2/PPy | [ |
410 F g−1 | 1 A g−1 | GP/MnO2 | [ |
531.4 F g−1 | 1 A g−1 | MnO2-sv80 | Our work |
Additionally, cyclic voltammetry is a critical technique for determining the electrochemical properties of materials.
Chronoamperometry is an important technique used to study the electrode reaction process and the stability of electrode materials.
To further investigate the electrode materials’ electrochemical characteristics, we employed electrochemical impedance spectroscopy (EIS) to determine their charge transfer kinetics and chemical process. The electrode’s electrochemical reaction process is depicted in
Electrode | MnO2-sv40 | MnO2-sv60 | MnO2-sv80 | MnO2-sv100 |
---|---|---|---|---|
Rct (Ω) | 0.94 | 1.08 | 0.88 | 0.86 |
RΩ (Ω) | 1.27 | 1.21 | 1.25 | 1.24 |
In conclusion, in the preparation of the MnO2 thin-film electrode, the electrochemical deposition method could help better control the thickness of the film, avoiding needless waste of materials while improving the energy storage efficiency. Meanwhile, the entire electrodeposition process did not require sintering of the material, which avoided unnecessary energy consumption and was therefore environmentally friendly. We prepared MnO2 thin-film electrodes through modified ultrasound-assisted sweep voltammetry and four sets of samples were obtained by scan rate control to regulate the electrodeposition process. These measurements were employed to investigate the mechanism by which the scanning rate affects the growth of MnO2. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe each sample’s surface morphology and microscopic morphology. The electrochemical characteristics of the produced samples were then determined using chronoamperometry (CA), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The result suggests that the MnO2-sv80 electrode sample at a scan rate of 80 mV/s has excellent performance for the supercapacitor electrode. The specific capacitance was as high as 531.4 F g−1 at a current density of 1 A g−1, and remained at 223.2 F g−1 at an ultra-high current density of 20 A g−1, with capacitance retention of 42%.