SYMMETRIC SUPERCAPACITOR OF MN3O4 AND ENHANCEMENT OF ELECTROCATALYTIC HYDROGEN EVOLUTION VIA RGO-MN3

Abstract

TITLE OF THE INVENTION Symmetric Supercapacitor of MnjC^and Enhancement of Electrocatalytic Hydrogen Evolution via rGO-MnaCh Composite Formation ABSTRACT Manganese oxide (Mn3O4) is an attractive candidate for electrocatalytic hydrogen evolution and supercapacitor studies, owing to its stable tetragonal spinel structure, where Mn2+ occupies tetrahedral units and Mn3+ octahedral units. Its low cost, environmental compatibility, and reduced toxicity make Mn3C>4 ideal for large-scale applications. M113O4 is a pseudocapacitive material with higher energy density and power density. We synthesized Mn3O4 nanoparticles through a simple and low-temperature hydrothermal method. The prepared nanoparticles were utilized to analyze the electrochemical performance in an aqueous electrolyte solution. The practical applicability of the electrode was further examined with the fabricated aqueous symmetric supercapacitor device. The prior study of Mn3O4 symmetric device delivered a specific capacitance of 68 Fg'1 at a current density of 1 Ag'! with an energy density of 9.34 W h kg'1. The cyclic stability was 72 % for 1000 cycles with a coulombic efficiency of 100 %. Thus, the Mn3O4 electrodes can be explored in symmetric supercapacitor device applications. Furthermore, integrating Mn3O4 with reduced graphene oxide (rGO) in composite electrodes enhances conductivity and surface area, improving efficiency for hydrogen evolution reactions (HER). This combination offers a sustainable, high-performance solution for hydrogen generation in electrochemical systems. In this study, the composite of Mn3C>4 and 20% rGO was also fabricated using hydrothermal method. A significant reduction in overpotential was observed, decreasing from 275 mV to 219 mV at a current density of 10 mA/cm2, demonstrating enhanced electrocatalytic efficiency. Additionally, the Tafel slope analysis revealed a marked improvement, with, values decreasing from 140.6 to 116.7 mV/dec, indicating faster hydrogen evolution kinetics. Further cyclic voltammetry (CV) analysis was performed at different scan rates for both pure Mm04 and the Mn3O4-rGO composite, revealing capacitance values of 5 pF/cm2 and 7.26 pF/cm2, respectively. The enhanced capacitance in the rGO composite highlights improved charge storage capacity and electrochemical surface area. Additionally, electrochemical impedance spectroscopy (E1S) studies exhibited semicircularNyquist plots for both samples, with the MnjO4-rGO composite showing a smaller semicircle, indicating significantly lower charge transfer resistance. This further confirms the superior conductivity and electrochemical performance of the composite for efficient hydrogen evolution reactions. These results confirm that the MnsCU and reduced graphene oxide (rGO) composite electrode offers superior performance in hydrogen evolution reactions (HER), supporting its potential for. efficient and scalable hydrogen generation in electrochemical systems.

Specification

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL/COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. TITLE OF THE INVENTION
Symmetric Supercapacitor of M113O4 and Enhancement of Electrocatalytic Hydrogen Evolution via rGO-Mn3O4 Composite Formation

2. APPLICANT(S)
Name Nationality Address
a) CHRISMA ROSE BAKU
b) ASLAM HOSSAIN
c) ANILA E I
INDIAN
INDIAN
INDIAN
CHRIST (Deemed to be University)
Hosur Road
Bangalore
Karnataka
India
560029
Smart Materials Research Institute
Southern Federal University
Sladkova 178/24
Rostov-on-Don
Russia
344090
CHRIST (Deemed to be University)
Hosur Road
Bangalore
Karnataka
India
560029

3. PREAMBLE TO THE DESCRIPTION

PROVISIONAL
The following specification describes
the invention.

COMPLETE
The following specification particularly
describes the invention and the manner in which
it is to be performed.

4. DESCRIPTION (Description shall start from next page.)
ATTACHED
5. CLAIMS (not applicable for provisional specification. Claims should start with the
preamble- "1/ We claim" on separate page)
ATTACHED

6. DATE AND SIGNATURE (to be given at the end of last page of specification)
Date: 24th October 2024
(1) CHR1SMA ROSE BABU
(2) ASLAM HOSSAIN
(3) AN1LA E I

7. ABSTRACT OF THE INVENTION (to be given along with complete specification on separate page)
ATTACHED
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TITLE OF THE INVENTION
Symmetric Supercapacitor of MinOt and Enhancement of Electrocatalytic Hydrogen Evolution via rGO-Mn3O4 Composite Formation

DESCRIPTION

FIELD OF THE INVENTION
[0001] The present study is focused on developing electrode material to enhance electrochemical performance within the realm of supercapacitor applications and an electrocatalyst for the hydrogen evolution reaction. Manganese oxide (Mn30«) is utilized for the symmetric supercapacitor configuration. The electrocatalyst involves manganese oxide and reduced graphene oxide-manganese oxide nanocomposite.

BACKGROUND OF THE INVESTIGATION
[0002] The emergence of nanomaterials has become a high-demand concern in energy storage and conversion research. The nanomaterials are defined if their dimension is within 100 nm, where many materials are developed for various applications. There are several techniques for the synthesis of nanomaterials, they are categorized into top-down and bottom- up approaches. Top-down synthesis methods include sputtering, laser ablation, electroexploitation, mechanical milling, and etching. The bottom-up approach includes spinning, cheriiical vapor deposition, chemical reaction, green synthesis, sol-gel process, laser pyrolysis, and solvothermal and hydrothermal methods. Some more unique factors that affect the formation of nanomaterials are temperature, time and pH value, etc. After the formation, its surface area, porosity, magnetic, structural, optical, electrical and electrochemical properties, etc, would identify the application of the material. Thus, nanomaterials can be selected for applications like supercapacitor electrodes, electrocatalysts, battery electrodes, drugs, and various other forms.

[0003] The present investigation considers a transition metal oxide for energy storage and conversion application. Manganese oxide, Mn3C>4 is selected as an electrode for fabricating a symmetric supercapacitor device. Mn3O4 has a theoretical specific capacitance of 1400 Fg'1. Manganese oxide (MnsCM) is an attractive candidate for electrocatalytic hydrogen evolution and supercapacitor studies, owing to its stable tetragonal spinel structure, where Mn2+

occupies tetrahedral units and Mn3+ octahedral units. Its low cost, environmental compatibility, and reduced toxicity make MnjO4 ideal for large-scale applications. Mn3O4 is a pseudocapacitive material with higher energy density and power density. We synthesized MmOi nanoparticles through a simple and low-temperature hydrothermal method. The prepared nanoparticles were utilized to analyze the electrochemical performance in an aqueous electrolyte solution. The practical applicability of the electrode was further examined with the fabricated aqueous symmetric supercapacitor device.

[0004] The inclusion of reduced graphene oxide (rGO), a two-dimensional material known for its excellent electrical conductivity and large surface area, into the matrix of Mn3O4 nanoparticles offers a promising strategy to enhance the electrocatalytic performance of pure manganese oxide. By forming a nanocomposite of rGO and Mn3O4, the material's intrinsic limitations, such as lower conductivity and surface exposure, can be addressed, resulting in improved charge transfer and reaction kinetics. Both the rGO-Mn3O4 nanocomposite and pure Mn3O4 were extensively studied for their performance in the hydrogen evolution reaction (HER). This composite material shows potential for scalable hydrogen production due to its cost-effectiveness, environmental compatibility, and superior electrochemical properties, making it an ideal candidate for use in water-splitting technologies and renewable energy applications.

MOTIVATION AND CONTRIBUTION
[0005] The primary motivation for this patent application is the development of an efficient electrode material for symmetric supercapacitor and electrocatalytic HER using a highly cost- effective synthesis method. This investigation focuses on addressing the growing demand for advanced electrocatalysts and electrode materials, particularly in energy storage and conversion applications. Traditionally, asymmetric supercapacitors have dominated practical applications due to their superior performance. However, the development of a transition metal oxide-based electrode material could significantly advance research in symmetric supercapacitor devices, providing both energy storage and catalytic functionalities. The inclusion of carbon-based materials, such as rGO, is a key aspect of this innovation, as it explores the synergistic effects between the transition metal oxide and carbon to improve both conductivity and catalytic activity. The composite material developed in this study is not only suitable for high-performance symmetric supercapacitors but also demonstrates exceptional electrocatalytic properties for hydrogen evolution. This dual functionality expands the potential applications of the material, offering a versatile, scalable, and cost-effective solution for renewable energy technologies.

BRIEF SUMMARY OF INVENTION
[0006] The present study investigates the fabrication of a symmetric supercapacitor device with manganese oxide as the electrode material. Also, the nanocomposite synthesized with reduced graphene oxide was observed as an electrocatalyst for hydrogen evolution reaction along with pure MnaO4. The above investigations are primarily studied with the manganese oxide and its nanocomposite with iGO. The electrochemical performances were studied to analyze their significance in both applications.

[0007] Mn3C>4 was synthesized using a simple, one-pot hydrothermal method at a lower temperature. The preparation of Mn3O4 involves 1 M manganese chloride and 2 M sodium hydroxide, and the pH was 12 in 50 ml of distilled water. The solution was stirred for a few minutes and transferred to a Teflon beaker. The beaker was then kept in a steel autoclave and allowed for hydrothermal treatment for 12 hours at 120* C. After the thermal treatment, the resultant solution was filtered and washed properly with distilled water. A brown color powder was obtained after drying at 60' C. The nanocomposite formation was also similar to the preparation of pure manganese oxide. Here, 20 wt. % of reduced graphene oxide powder is ultrasonicated in distilled water for one hour and transferred to the precursor solution of manganese oxide. Then, by applying the same synthesis parameters, we obtained a blackish brown powder. The prepared nanoparticles were drop-casted on a nickel foam substrate after pre-treatment with acetone, acid and alkaline solutions to analyze the supercapacitor performance. The active material, MnjO4 powder was taken in 80 wt. %, a binder of 10 wt. % - polytetrafluoroethylene (PTFE) and a conducting agent of 10 wt. %, activated carbon was mixed in an ethanol medium to prepare the solution for drop-casting. The drop-casted electrodes were dried for a few hours.

[0008] The electrochemical characteristics of drop-casted Mn3C>4 on nickel foam substrate were further investigated using a tri-electrode setup. The working electrode is the Mn3O4 electrode. Silver/silver chloride and platinum were used as the reference and counter
electrodes. The electrochemical investigations were conducted in an alkaline electrolyte
medium comprising 0.5 M NazSCh. Preliminary electrochemical analyses, encompassing
cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical
impedance spectroscopy (EIS), were performed on the electrodes. The CV curves investigated
the electrode material's electric double layer and pseudocapacitive behavior, which is evident
from the quasi-rectangular shape and weak oxidation and reduction features. GCD curves
exhibited rapid faradaic redox reactions at the electrode/electrolyte interface. The specific
capacitance (Csp) was determined using the formula:

Where At represents the discharging time, AV denotes the potential window, and l/m represents
the current density. The symmetry observed in the charging and discharging curves reflects the
reversibility of the electrode material. A specific capacitance value of 163 F/g was achieved at a current density of 4 A/g. From the electrochemical impedance spectral data, a Nyquist plot was analyzed to find the solution and charge-transfer resistance at the electrode/electrolyte
interface.

[0009] A prototype symmetric supercapacitor device was assembled following preliminary
investigations with similar MmCh electrodes separated by Whatman filter paper soaked in a
0.5 M NazSO4 electrolyte solution. Electrochemical assessments were conducted using a twoelectrode
setup to evaluate the stability of the electrode material. Notably, specific capacitance
measurements yielded a value of 68 F/g at a current density of 1 A/g. The innovation resulted
in impressive energy and power densities, calculated as 9 W h/kg and 500 W/kg, respectively,
utilizing the equations:

Energy density, ED = ~
Power density, PD - -tn
n = - x 100

Moreover, the electrode material exhibited exceptional stability over 1000 charge/discharge
cycles, with a remarkable capacitive retention rate of 72% compared to the initial cycle and
coulombic efficiency of 100 %. These findings underscore the potential of MnsCh as a highly efficient and durable electrode material for supercapacitor applications, promising significant advancements in the field.
[0010] The electrocatalytic HER was evaluated in a 1 M NaOH electrolyte solution at room temperature using an electrochemical workstation (PARSTAT 4000) with a three-electrode system (Hg/HgO/OH- reference electrode, Pt counter electrode, and the studied sample grown on a glassy carbon macrodisc electrode as the working electrode).

was obtained at a scan rate of 1 mVs'1. The galvanostatic charge-discharge curves were also studied after optimizing the potential window from the cyclic voltammetry technique. The redox behaviour of the electrode can be easily visualized from the GCD curves exhibiting a faradaic behaviour and representing a pseudocapacitive nature. The GCD analysis was conducted at different.current densities from 4 Ag'1 to 10 Ag'1. The highest specific capacitance obtained at 4 Ag'1 is 163 Fg*1. The nearly symmetrical nature of GCD curves shows the reversibility of the electrode. As the current density increases, the specific capacitance decreases. The Nyquist plot was plotted with the real part of impedance (Z5) versus the negative imaginary part (-Z")- it exhibits an ideal supercapacitor behaviour with a very small semicircle, representing very low charge-transfer resistance (Ret).

[0014| Figure 2 depicts the cyclic voltammetry (CV) plots, galvanostatic charge-discharge (GCD) curves and Nyquist plot of the fabricated symmetric prototype supercapacitor device. The CV curves obtained for the aqueous symmetric device with Mn3O4 electrode exhibit a quasi- rectangular shape with small redox characteristics. The potential window of the device was optimized to be 0 - 1 V. The cyclic voltammograms vary from 5 mVs*1 to 1000 mVs'!. The electrolyte used for the device construction was 0.5 M Na2SC>4. The Na2+ ions were intercalated into the electrode surface and the redox reactions occurred. At higher scan rates, the interaction of ions is very less compared to lower scan rates. The behaviour of GCD curves was different with more charging time. An IR drop was observed at each lower current density. This shows a faradaic characteristic. The highest specific capacitance attained for the device at 1 Ag'1 is 68 Fg*1. The cyclic stability was studied for 1000 cycles and a capacitive retention of 72 % was observed compared to the initial charge-discharge cycle. A coulombic efficiency of 100 % was aslo identified. The Nyquist plot also followed an ideal supercapacitor behaviour with no evident semicircle. The equivalent circuit diagram studied the internal resistances of the device. The equivalent series resistance, Rs was found to be 5 Q and a charge-transfer resistance, Ret as 0.35Q. The linear variation in the low-frequency region suggests the practical applicability of fabricating symmetric supercapacitor devices with Mn3C>4 electrodes.

[0015] Figure 3 illustrates the electrocatalytic performance of the synthesized materials consist of electrodes towards the HER was evaluated in a 1 M NaOH solution through polarization studies. LSV curves obtained a* a scan rate of 10 mV/s are presented in Figure 3a.

Analysis of the LSV curves reveals a trend in overpotential at a current density of 10 mA/cm2, with the Mn3C>4 nanomaterials exhibiting the highest overpotential (278 mV) and the lowestoverpotential observed for the rGO-MnaCM nanocomposite (217 mV). The lower overpotential observed for the composite suggests more favorable kinetics or higher activity for HER compared to the conventionally synthesized materials. The v-shape Tafel curve shows in Figure 5b and corresponding Tafel slope values of the materials (Figure 5b) follows the order MmCh nanomaterials (140.6 mV/dec) > rGO-MnjCM nanocomposite (116.7 mV/dec), further support the aforementioned observations. The electrochemical active surface area (ECS A) of the prepared electrode was determined to assess its surface accessibility. ECSA was estimated using CV curves obtained at various scan rates ranging from 5 to 50 mVs"1 in the non-faradic region, as illustrated in Figure 3(d-e). The calculated double-layer capacitance Cm value for all samples from scan rates of 5 to 50 mVs-1, is depicted in Figure 5f and the highest value obtained for rGO-MnjCU nanocomposite is 5.26 mF/cm2. From the EIS plot, it is observed that rGO-Mn3O4 nanocomposite exhibits a semicircle with the lowest radius, indicating faster charge transfer kinetics (Figure 5g). The EIS data were further analyzed by fitting with an equivalent circuit to .investigate the electrical properties related to the electrode-electrolyte interface (inset of Figure 5g). In the Bode plot (Figure 5h and 5i), support the EIS data.

PRODUCT EVALUATION
[0016] Supercapacitors have gained a significant attention for energy storage applications due to their high power density, rapid charging and discharging capabilities, long-lasting performance, and low maintenance cosis. These devices are produced using various electrode materials, including carbon-based substances, metal oxides, and conductive polymers. Among these, transition metal oxide nanoparticles, such as MnjO4, hold great promise for enhancing energy storage performance. Despite extensive research in this area, the development of a symmetric supercapacitor using Mn3C>4 electrodes that can deliver both high specific capacitance and extended cycle life remains unachieved.

[0017] In this patent, we present the electrochemical performance of a new supercapacitor using Mn3O4 as the electrode material. We tested its efficiency through cyclic voltammetry, charge-discharge cycles, and impedance analysis. MnaCh proves to be highly effective, showing long-lasting performance and excellent specific capacitance. We used hydrothermal hydrothermal method to synthesize M113O4 and a version with rGO-Mn3C>4. The resulting supercapacitor shows strong stability and impressive energy and power densities. The
comparison table highlights that no previous research has used this material for supercapacitors, making this a novel approach.

[0018] We also present a novel approach by incorporating rGO with MmCh to create a
composite electrode material. The composite material has been thoroughly evaluated through
techniques such as LSV, EIS, and CV demonstrating significantly reduced overpotential from
278 mV to 217 mV and enhanced Tafel slopes from 140.6 mV/dec to 116.7 mV/dec for HER.
These findings also represent the first report on the HER properties of MnaCh and rGO- Mn3O4,
showing the potential of this material not only in energy storage but also in electrocatalysis,
offering a dual-functional solution for next-generation energy devices.

(1) CHRISMA ROSE BABU (2) ASLAM HOSSAIN
(3) ANILA E 1

COMPLETE SPECIFICATION- DIAGRAMS

Figure 1: Cyclic voltammetry curves, galvanostatic charge-discharge curves and Nyquist plot
profiles of Mn3O4 electrode material in three-electrode configuration studies.

Figure 2: Cyclic voltammetry curves, galvanostatic charge-discharge curves, cyclic stability
assessment and Nyquist plot of a prototype symmetric supercapacitor device MibOV/MmO^

Figure 3: Electrocatalytic HER for the synthesized Mn3C>4 and Mn3Ch-rGO nanocomposites
(a) linear sweep voltammetry curves (b) Tafel plots (c) Tafel slope derived from the
corresponding polarization curves, (d-e) cyclic voltammetric curves, (f) Linear fit of the
capacitive current versus scan rates, (g) EIS curve, and (h) Bode phase angle (i) Bode
impedance curves.
-------imVii'
'------ IO t»V(i
-------IJmV/i
------- 20 mV/.
- 30 io V/.
■ 40 nV/i
-------JO mV/.
-------MH-1
-------M20G
logb(MA)] log[i(inA/cnf)|
0.5 0.6 0.7 0.8 0.9
E/V vs.RHE
£ 0.I
B 0.0
0.5 0.6 0.7 0.8 0.9
E/V vs.RHE Scan rale (mV/s)
MH-1
M20G MH-1
M20G

No prior reports exist on symmetric MnsCW/M^Cb supercapacitor device studies and the
electrocatalytic HER activity of MnjO4 and rGO-Mn3O4

(1) CHRISMA ROSE BABU (2) ASLAM HOSSAIN (3)ANILAEI




CLAIMS
[0011] We claim,
1. Synthesis of efficient electrode materials - manganese oxide, Mn3O4 for and reduced graphene oxide-MnjCU (rGO-Mn3O4) - by hydrothermal method.

2. Mn3O4 electrode was observed for supercapacitive energy storage applications; both Mn3O4 and rGO-Mn3O4 electrodes for hydrogen evolution reaction (HER).

3. Electrochemical investigations, including cyclic voltammetry, galvanostatic chargedischarge, and impedance studies, have been conducted on Mn3O4 nanoparticles for supercapacitors.

4. Linear sweep voltammetry, electrochemical impedance spectroscopy, and cyclic voltammetry were performed to evaluate the electrochemical performance of both Mn3C>4 and rGO-Mn3C>4 nanocomposites.

5. Fabrication of a symmetric prototype supercapacitor device with Mn3C>4 drop-casted on nickel foam, demonstrating an outstanding supercapacitive performance with a specific capacitance of 68 F/g at a current density of 1 A/g, along with an energy density of 9.34 W h/kg and power density of 500 W/kg.

6. Highly stable prototype supercapacitor device sustaining IK cycles at 5 A/g with a capacitive retention rate of 72% and a coulombic efficiency of 100 %.

7. First-time report of a symmetric prototype supercapacitor employing Mn3C>4 as the electrode.

8. This study represents the first report on the HER properties of Mn3C>4 and its composite with rGO, providing novel perceptions of their electrocatalytic performance.

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