Electrochemical Investigation of Pure and Nitrogen-Doped Graphene Aerogels for Supercapacitor Applications

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However, enhancing their electrochemical kinetics in a more realistic device setting is still a major challenge. In this work, the effects of nitrogen incorporation on the electrochemical performance of graphene aerogels were systematically examined by direct comparison of the electrochemical performance of pristine graphene aerogel (GA) and nitrogen-doped graphene aerogel (NGA). The materials were synthesized by hydrothermal reduction of graphene oxide and freeze-drying, and the nitrogen doping was made by a post-treatment modification step. Electrochemical characterization was carried out in the form of cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) with a symmetric two-electrode setup and 6M KOH electrolyte. Both the electrodes showed quasi-rectangular CV profiles as well as symmetrical triangular GCD curves, thus representing a predominantly electric double-layer capacitance behavior. The specific capacitance was found to moderately increase from 174.18 F/g for GA to 187.54 F/g for NGA at 5 mA. More importantly, N modification significantly decreased the charge transfer resistance from 9.55 to 2.37 \(\:{\Omega\:}\) and the electrochemical relaxation time constant, leading to improved rate capability. These results show that the nitrogen incorporation mainly leads to an improvement in interfacial charge transfer kinetics and does not result in significant pseudocapacitive contributions to the supercapacitor kinetics, which is a useful insight for the design of high-rate graphene-based supercapacitor electrodes. Supercapacitor Graphene Aerogel Nitrogen-doped EDLC Capacitance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction The recent explosion of the world electric vehicle market, as well as the portable electronic and large-scale renewable energy system markets, has made a strong demand for eco-friendly and effective electrochemical energy storage devices [ 1 ]. Supercapacitors (SCs), or ultracapacitors, with their high power density, high charge-discharge speeds, and long cycle life of more than hundreds of thousands of cycles, have become an important technology for filling the gap between conventional batteries and dielectric capacitors [ 2 ]. These advantages make them appealing for use in hybrid energy storage systems and also for backup power applications [ 3 , 4 ]. SCs are able to store energy by two main mechanisms: electric double layer capacitance (EDLC), which is due to electrostatic accumulation of ions at the electrodes-electrolyte interface, and pseudocapacitance, which is due to reversible Faradaic redox reactions at the electrode surface. [ 5 , 6 ]. Among the different electrode materials that have been studied, graphene has received a lot of attention because of its outstanding theoretical specific surface area, high electrical conductivity, and mechanical stability [ 7 ]. Despite all these inherent benefits, the application of pristine graphene for supercapacitors is often impaired by the intense \(\:{\pi\:}\) - \(\:{\pi\:}\) stacking interaction between single sheets, which results in severe agglomeration and thus reduced accessible surface area for ion adsorption [ 8 ]. To overcome this problem, the fabrication of three-dimensional graphene aerogels (GAs) has been proposed as a good alternative to inhibit restacking and preserve a highly porous network to enhance electrolyte penetration [ 9 – 11 ]. GAs have low density and high specific surface area, which are very critical when seeking to maximize the volumetric and gravimetric capacitance of device performance [ 12 ]. However, the pure GAs electrochemical performance is usually restricted due to the intrinsic hydrophobicity of graphene and a shortage of active sites for the faradaic reactions, which will give a capacitance value lower than the theoretical values [ 13 , 14 ]. One potential way of addressing these drawbacks comes from heteroatom doping of the graphene lattice, in this case with nitrogen, in order to create defects on its surface and alter its electronic structure, allowing for improved charge storage properties [ 15 , 16 ]. Nitrogen atoms can be introduced into the graphene framework in various manners, e.g., pyridinic, pyrrolic, and graphitic-N, which have a different impact on the electronic properties and surface reactivity of the carbon matrix [ 17 ]. Nitrogen doping can improve the wettability and conductivity, introduce defect sites, and enhance the overall capacitance owing to the contribution from pseudocapacitance [ 18 ]. Theoretical and experimental studies suggest that the enhancement in capacitance brought by the nitrogen doping is attributed to causes such as reversible redox reactions, capacitance enhancement by quantum capacitance through Fermi level shifts, and enhanced electrode-electrolyte interactions [ 19 ]. In several comparative studies, synthesis parameters between pure and nitrogen-doped graphene aerogels are often inconsistent, making it hard to isolate the specific effects of nitrogen functionalization on electrochemical behavior [ 20 ]. Consequently, this study employs a controlled synthesis methodology to ensure that the only variable between the two materials is the presence of nitrogen dopants and thus opens direct and rigorous evaluation of how nitrogen functionalization regulates the charge storage kinetics and overall electrochemical efficiency [ 21 ]. In this study, pure and nitrogen-doped graphene aerogels were synthesized using the hydrothermal reduction method under comparable preparation conditions to enable a direct evaluation of the performance differences attributable solely to nitrogen incorporation [ 22 ]. The study provides a systematic comparison of the electrochemical properties of pure and N-doped graphene aerogels to elucidate the particular significance of N functional groups in enhancing capacitive behavior. 2. Materials and Experimental Procedures 2.1. Reagents and Materials Graphene oxide (GO) dispersion (2 mg/mL) was procured from Graphenea (Spain). Hydrazine monohydrate (64–65%) and ethanol (95%) were obtained from LabChem (Malaysia). Potassium hydroxide (6M KOH) solution was obtained from Sigma-Aldrich (USA) and utilized as the electrolyte. All chemicals were utilized exactly as supplied, without additional purification. All experimental protocols employed deionized water for the cleaning and solution preparation stages. Hydrothermal reactors (50 mL Teflon-lined stainless-steel autoclaves) were purchased from Evergreen Engineering & Resources, Malaysia. Freeze-drying was performed in a SCANVAC lyophilizer (Chemopharm Group, Malaysia). A Gamry Interface 1000 potentiostat (Gamry Instruments, USA) was used to perform electrochemical experiments. 2.2. Synthesis of Pure and Nitrogen-Doped Graphene Aerogels Graphene aerogels (GAs) were synthesized via a hydrothermal reduction approach followed by freeze-drying. An aqueous suspension of graphene oxide (2 mg/mL) was used as the precursor solution. 35 mL of the suspension was ultrasonicated for 30 minutes to ensure homogeneous dispersion, after which it was transferred into a 50 mL Teflon-lined stainless-steel autoclave and heated at 200 \(\:^\circ\:\text{C}\) for 16 hours to facilitate the self-assembly into a three-dimensional network driven by \(\:{\pi\:}\) - \(\:{\pi\:}\) interactions and reduction of GO to a reduced GO hydrogel. After the completion of the hydrothermal reaction, the autoclave was allowed to cool naturally to room temperature for 3 hours, resulting in the formation of a cylindrical reduced GO hydrogel. The resulting hydrogel was carefully washed with deionized water for 72 hours, with the water replaced every 6 hours to remove residual impurities and unreacted precursors. Subsequently, the purified hydrogel was freeze-dried under vacuum at -107 \(\:^\circ\:\text{C}\) for 72 h to obtain the pure GAs. Nitrogen-doped GAs (NGAs) were prepared as a post-treatment modification of the pure GAs by mechanically sectioning the synthesized pure GA into smaller pieces and dispersing them into a mixed solution of hydrazine monohydrate and ethanol. The mixture was subjected to magnetic stirring for 30 minutes, followed by ultrasonication for another 30 minutes to form a homogeneous slurry. 2.3. Electrochemical Characterization Techniques Electrochemical measurements were carried out on a symmetric two-electrode configuration to evaluate the capacitive performance of the fabricated electrodes under conditions that are very much like the real working of devices. The NGA slurry, synthesized earlier, was coated onto current collectors of nickel foams with a geometric area of 4 cm² and was subsequently dried in a vacuum oven at 70 \(\:^\circ\:\text{C}\) for 12 h in order to ensure complete solvent evaporation and adhesion. The electrodes were then compressed at a pressure of 10 MPa for 20 minutes to increase the quality of the electrical contact between the active material and the current collector. Circular sections with a diameter of 1 cm were punched from the compressed nickel foam to be used as the working electrodes in the assembled cells with a mass loading of approximately 9 mg/cm². No binders or conductive additives (such as carbon black) were used in the electrode fabrication to separate the intrinsic electrochemical properties of the active materials. A cellulose separator was used to prevent electrical shorting between the two identical electrodes, which were then assembled into a test cell configuration and filled with 6M KOH electrolyte. Cyclic voltammetry (CV) was performed within a potential range of 0–1.0 V at different scan rates (from 5 to 50 mV/s) in order to assess the electrochemical behavior and the charge capacities of both non-doped and nitrogen-doped GAs. Galvanostatic charge-discharge (GCD) measurements with current densities ranging from 0.2 to 3 A/g were conducted to investigate the rate capability of the electrodes in order to assess the specific capacitance of the electrodes. The specific capacitance ( \(\:{\text{C}}_{\text{c}\text{e}\text{l}\text{l}}\) ) of the device was calculated by applying the following equation to the GCD curves of discharge [ 23 ]: $$\:{\text{C}}_{\text{c}\text{e}\text{l}\text{l}\:}(\text{F}/\text{g})=\:\frac{\text{I}\varDelta\:\text{t}}{\text{m}\varDelta\:\text{V}}$$ In the above expression, I denotes the discharge current (A), \(\:\varDelta\:\text{t}\) refers to the discharge time (s), \(\:\varDelta\:\text{V}\) corresponds to the potential window (V), and \(\:\text{m}\) is the total mass of active material in both electrodes (g). For the symmetric two-electrode case, the specific capacitance of one of the symmetric electrodes was determined by multiplying the capacitance of the device by a factor of four [ 24 , 25 ]. Both energy and power densities of the supercapacitor devices were further calculated from the GCD curves with the following expressions [ 26 , 27 ]: $$\:\text{E}\:(\text{W}\text{h}/\text{k}\text{g})=\:\frac{1}{2}{\text{C}}_{\text{c}\text{e}\text{l}\text{l}\:}\frac{{\varDelta\:\text{V}}^{2}}{3.6}$$ $$\:\text{P}\:\left(\text{W}/\text{k}\text{g}\right)=\:\frac{3600\text{E}}{\varDelta\:\text{t}}$$ In the above equation, the 3.6 value is used to convert the J/kg to Wh/kg, which is the standard unit used for energy storage devices. Electrochemical impedance spectroscopy measurements were performed in the frequency range of 100 kHz to 10 mHz with a sinusoidal amplitude of 10 mV to analyze the internal resistance and ion transport kinetics of the electrodes [ 28 ]. 3. Results and Discussion 3.1 Comparative Analysis of Cyclic Voltammetry Figure 2 shows the cyclic voltammetry curves for both the pristine and nitrogen-doped GAs obtained at scan rates from 5 to 50 mV/s for a potential window from 0 to 1.0 V. For both GAs and NGAs, the CV curves present a quasi-rectangular shape, which is an indication of typical electric double-layer capacitive behavior with good charge propagation in the porous structure. The lack of large redox peaks indicates that there is little pseudo-capacitive contribution based mostly on non-faradaic charge storage mechanisms. As the scan rate rises to 5 to 50 mV/s, the current density is increased proportionally for both aerogels in accordance with a good rate capability. However, rectangular-shaped distortions are more apparent at a higher scan rate (20 and 50 mV/s), especially for the pure GA, indicating limitations in ion accessibility and diffusion kinetics inside the interior pore structure. Importantly, the NGA electrode has a significantly higher current response at all scan rates than the pristine GA, which can be attributed to the enhanced charge storage capacity due to the nitrogen doping. The specific capacitance as a function of potential, in Fig. 3 , gives additional information about the charge storage mechanisms. The pure GA electrode exhibits scan-rate-dependent capacitance variation with increased capacitance values for low scan rates (5 and 10 mV/s). In contrast, the NGA electrode shows a more stable profile of capacitance over the whole potential window and has higher total capacitance values even at high scan rates (50 mV/s), showing partial kinetic limitation. In contrast, the NGA electrode exhibits a more stable capacitance profile across the entire potential window and maintains a higher overall capacitance, even at elevated scan rates. The relatively larger area enclosed by the CV curves for NGA is a further confirmation of their superior capacitance compared to the pristine GA counterparts. The relatively smooth capacitance voltage curves (without clear or sharp redox peaks) indicate that the storage of charge is mostly driven by EDLC, with only a little contribution of pseudo-capacitive effects. Notably, the improved capacitance in the NGA electrode is explained by the reduced internal resistance, demonstrated in the following GCD analysis, and improved ion transport kinetics provided by nitrogen functional groups. In order to further clarify the impact of N doping on the electrochemical performance, CV profiles of GA and NGA at 5 mV/s and 50 mV/s were directly compared with each other, as shown in Fig. 4 . At 5 mV/s, both electrodes exhibit well-defined quasi-rectangular profiles with good symmetry of the forward and reverse scans. However, the NGA has a much higher enclosed area, which supports the higher specific capacitance that was observed because of the incorporation of nitrogen. At 50 mV/s, the difference between the two electrodes becomes even more significant, with NGA maintaining a more rectangular shape and having a considerably larger nominal area of integration, which indicates its better rate ability and reduced diffusion limiting for electrolyte ions at higher scan rates. Overall, the NGA is consistently found to have a stronger electrochemical performance in terms of charge storage capacity and kinetics at different scan rates in symmetric device-level conditions compared to the undoped GA. This proves that nitrogen incorporation positively influences interfacial charge transfer and ion transport behavior within the aerogel framework. 3.2 Comparative Analysis of Galvanostatic Charge-Discharge Figure 5 shows the GCD curves for both pure and nitrogen-doped GAs at different current densities spanning from 0.2 to 3 A/g (5, 10, 20, and 50 mA) in a symmetric two-electrode setup cell. The GCD curves for both materials exhibit nearly triangular and symmetric profiles, affirming their predominantly capacitive behavior. The linear voltage-time response observed during charging and discharging further supports the efficient storage and release of charge. The absence of significant voltage plateaus further supports EDLC behavior, with minimal contribution from distinct Faradaic redox processes, consistent with the CV results. At 5 mA, the discharge time for pristine GA is approximately 170 s, whereas for NGA, it is slightly lower at 162 s. At 10 mA, the discharge duration for pure GA reduces to approximately 74 s, while NGA shows an almost identical discharge time of approximately 76 s. However, the difference becomes more evident at higher constant currents. At 20 mA, pristine GA has a discharge time of about 27 s, while the NGA has a discharge time of about 34.6 s. At 50 mA, the improvement is even greater, with NGA showing a discharge time of about 10.7 s to the 3.3 s of the pristine GA, a more than threefold increase in discharge time. The comparative GCD curves obtained at 5 mA and 50 mA are seen in Fig. 6 , which further illustrates the rate capability of the electrodes. At 5 mA, both electrodes show similar charge-discharge symmetry and similar discharge slope, indicating that the diffusion of ions in the porous network happens efficiently. Notably, the voltage drop ( \(\:{\text{V}}_{\text{d}\text{r}\text{o}\text{p}})\) seen at the start of the discharge curve, called the IR drop, is much smaller for NGA compared to pristine GA. This lowered IR drop in the NGA confirms a low internal resistance and improved electrical conductivity that is important in efficient energy delivery and power density in supercapacitors. This smaller IR drop helps to explain the enhanced performance and specific capacity of NGA despite having a slightly shorter discharge time at lower current densities as a result of improved charge transfer kinetics facilitated by the nitrogen functional groups. In contrast, at 50 mA, the NGA evidently outperforms the pristine GA and has a much longer discharge time as well as a smaller IR drop, indicating a better rate ability and a better energy preservation capability at high currents. Importantly, the enhancement is not only due to low current enhancement but can be more clearly observed under high current stress, hence proving that the incorporation of nitrogen mainly contributes to the performance enhancement of kinetic characteristics and reduction of internal resistance, instead of significant enhancement of the pseudocapacitance. The electrochemical performance parameters of pure GA and NGA electrodes at different currents are summarized in Table 1 . Table 1 Calculated Specific Capacitance, ESR, and Energy Density of NGA. Constant Current (mA) GA Specific Capacitance (F/g) NGA Specific Capacitance (F/g) GA ESR ( \(\:{\Omega\:}\) ) NGA ESR ( \(\:{\Omega\:}\) ) GA Energy Density (Wh/kg) NGA Energy Density (Wh/kg) 5 174.18 187.54 9.04 3.66 6.04 6.51 10 155.43 178.27 8.17 3.12 5.39 6.18 20 125.32 167.47 8.06 3.14 4.35 5.81 50 54.65 143.84 7.96 2.94 1.89 4.99 3.3 Comparative Analysis of Electrochemical Impedance Spectroscopy To further investigate the charge transfer kinetics and ion diffusion characteristics of both GA and NGA electrodes, EIS measurements were performed. The resulting Nyquist plots, shown in Fig. 7 , reveal distinct differences in their impedance characteristics, particularly in the high-frequency and low-frequency regions, which correspond to charge transfer resistance and ion diffusion resistance, respectively. In the high-frequency range, the solution resistance was nearly identical for both electrodes, with a value of approximately 0.18 Ω. This similarity is expected since the same 6 M KOH aqueous electrolyte and identical cell configuration were used for both systems. The comparable \(\:{\text{R}}_{\text{s}}\) values indicate that the intrinsic electrolyte and contact resistance contributions are consistent between the two devices. However, a clear distinction emerges in the semicircle diameter within the high-frequency region, with NGA exhibiting a significantly smaller semicircle compared to GA, indicating lower charge transfer resistance ( \(\:{\text{R}}_{\text{c}\text{t}}\) ) at the electrode-electrolyte interface, approximately 2.37 Ω versus 9.55 Ω. In the low-frequency region, NGA shows a more vertical slope compared to GA. This steeper slope for NGA suggests a more efficient ion-diffusion process within its framework, which is crucial for high-rate performance [ 29 ]. The frequency-related impedance magnitude of the pure GA and NGA is shown in Fig. 8 a. At low frequencies, both electrodes show higher capacitive behavior, with NGA presenting a consistently lower impedance magnitude across the frequency spectrum as compared to pristine GA. The lower frequencies in the middle to high frequencies for NGA provide further evidence of superior charge transfer kinetics and ionic transport characteristics. The real part of the impedance (Z') as a function of frequency plot, in Fig. 8 b, gives further evidence that NGA retains a low Z' over the frequency range, showing a reduced energy dissipation and resistance during cycling. At high frequencies, Z' for both the GA and NGA approaches each other, indicating similar solution resistance as in the Nyquist plot analysis. The reduced values of Z' of NGA over most of the frequency domain confirm the reduction of the \(\:{\text{R}}_{\text{c}\text{t}}\) . The imaginary part of the impedance is shown in Fig. 8 c. Both electrodes show a relaxation peak in the mid-frequency range, with the NGA having a peak shifted towards the high-frequency part of the spectrum, indicating shorter relaxation time, faster ion response, and charge propagation in the electrode material [ 30 – 32 ]. The phase angle plot for NGA, shown in Fig. 8 d, shows a shift towards the capacitive region at higher frequencies compared to the pure GA. This observation indicates an accelerated change to capacitive behavior by an increase in charge transfer kinetics [ 33 , 34 ]. The wider phase angle response of pure GA in the mid-frequency region reflects the lower electrochemical response kinetics. The frequency-dependent complex capacitance measurement helps to understand the charge storage dynamics of both electrodes. As can be seen from Figs. 8 e and 8 f, the real part of the complex capacitance for NGA is always higher than that of GA over a wide range of frequencies, especially at low frequencies, indicating a larger stored charge capability [ 35 ]. In addition, the imaginary part of the complex capacitance shows that NGA exhibits higher capacitance at higher frequencies, which implies that NGA exhibits a more stable capacitive response and enhances its charge retention ability at higher charge/discharge speeds. Overall, the EIS analysis shows that the incorporation of nitrogen is able to significantly improve the charge-transfer resistance and the electrochemical relaxation processes, which improve the ion transport kinetics and rate performance of the electrode. 4. Conclusion In this work, a systematic comparative study between pristine GA and NGA was performed in order to assess the role of nitrogen incorporation on the electrochemical performance of graphene-based supercapacitor electrodes under realistic device conditions. Both materials showed typical electric double-layer capacitive behavior, as supported by the quasi-rectangular cyclic voltammetry profiles and the symmetric triangular charge-discharge profiles obtained in electrochemical testing. Despite the similar charge storage mechanism, the introduction of nitrogen was able to significantly enhance the electrochemical kinetics and rate capability of the aerogel electrodes. At low current conditions, nitrogen incorporation led to a moderate improvement of the electrochemical performance with a specific capacitance increase of about 8% higher than that of pristine GA. However, the beneficial effect of nitrogen modification became much more significant at increased current densities. At intermediate current conditions, the capacitance improvement was about 34%, whereas at high current operation, the NGA electrode showed an enhancement of nearly 160% compared to GA. A similar trend was observed for the energy storage capability, where the energy density increased by about 8% for low current and increased by more than 160% under high current conditions, which implies a far superior rate capability. Electrochemical analysis also showed that the addition of nitrogen strongly enhanced the charge transport properties of the electrodes. The equivalent series resistance obtained using the GCD measurements decreased by about 71%, and electrochemical impedance spectroscopy measurements showed that the charge-transfer resistance decreased by about 75%. In addition, complex capacitance analysis indicated a shift to higher relaxation frequencies for NGA, which indicated a short electrochemical response time and rapid ion transport dynamics. Interestingly, even though no particularly strong pseudocapacitive features were found in the CV profiles, the overall capacitance and electrochemical performance were enhanced. This observation implies that the influence of nitrogen doping in the present system is not so much related to the contribution of additional Faradaic reactions but rather to electrochemical kinetics improvements. Nitrogen incorporation likely results in improved electronic properties of the carbon framework and better interactions between the electrode surface and electrolyte ions, which are responsible for improved charge transfer and ion transport within the porous aerogel structure. Overall, these results have shown that nitrogen incorporation is an effective approach to improve the kinetics and rate capability of the graphene aerogel electrodes, which enables nitrogen doping as a potential strategy for the improvement of high-frequency operation of graphene-based supercapacitor systems. Declarations Author Contribution All authors reviewed the manuscript.Khaled Abdou Ahmed Abdou Elsehsah: Wrote the main manuscript, Methodology, Validation, Supervision, Investigation.Zulkarnain Noorden Ahmad: Wrote the main manuscript, Methodology, Validation, Supervision, Investigation.Norhafezaidi Mat Saman: Edit the main manuscript, Validation, Supervision.Ayaz Ahmed Sahito: Supervision, Validation.Mohd Aizam Talib: Supervision.Sharin AB Ghani: Supervision . Acknowledgments The authors would like to acknowledge the financial support from Universiti Teknologi Malaysia under UTM Flagship CoE/RG Research Grants (Q.J130000.5009.10G17). Conflict of Interest The authors declare no conflict of interest. Data Availability All data needed to evaluate the conclusions in the paper are present in the paper. Any additional data related to this paper may be requested from the authors. 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Available from: https://doi.org/10.1038/srep43104 Mutuma, B.K., Sylla, N.F., Bubu, A., Ndiaye, N.M., Santoro, C., Brilloni, A., et al.: Valorization of biodigestor plant waste in electrodes for supercapacitors and microbial fuel cells. Electrochimica Acta [Internet]. [cited 2025 Aug];391:138960. (2021). Available from: https://doi.org/10.1016/j.electacta.2021.138960 Zhao, Y., Zhang, X.: In situ activation graphitization to fabricate hierarchical porous graphitic carbon for supercapacitor. Scientific Reports [Internet]. 2021 [cited 2025 Oct];11. Available from: https://doi.org/10.1038/s41598-021-85661-0 Sylla, N.F., Ndiaye, N.M., Ngom, B.D., Mutuma, B.K., Momodu, D., Chaker, M., et al.: Ex-situ nitrogen-doped porous carbons as electrode materials for high performance supercapacitor. Journal of Colloid and Interface Science [Internet]. 2020 [cited 2025 Oct];569:332. Available from: https://doi.org/10.1016/j.jcis.2020.02.061 Zhang, Y., Liang, W., Liu, X., Ma, W., Wang, J., Fan, S.: N/O co-enriched graphene hydrogels as high-performance electrodes for aqueous symmetric supercapacitors. RSC Advances [Internet]. [cited 2025 Aug];11:19737. (2021). Available from: https://doi.org/10.1039/d1ra01863a Mi, H., Yang, X., Hu, J., Zhang, Q., Liu, J.: Carbothermal Synthesis of Nitrogen-Doped Graphene Composites for Energy Conversion and Storage Devices. Frontiers in Chemistry [Internet]. [cited 2025 Oct];6. (2018). Available from: https://doi.org/10.3389/fchem.2018.00501 Adsorption Technology for Water and Wastewater Treatments [Internet]: MDPI eBooks. 2023 [cited 2025 Oct]. Available from: https://doi.org/10.3390/books978-3-0365-8584-0 Benitto, J.J., Vijaya, J.J., Saravanakumar, B., Al-Lohedan, H.A., Bellucci, S.: Microwave engineered NiZrO3@GNP as efficient electrode material for energy storage applications. RSC Advances [Internet]. [cited 2025 Sep];14:8178. (2024). Available from: https://doi.org/10.1039/d4ra00621f Liu, Z., Tao, Y., Song, X., Bao, M., Tan, Z.: A three dimensional N-doped graphene/CNTs/AC hybrid material for high-performance supercapacitors. RSC Advances [Internet]. [cited 2025 Sep];7:6664. (2017). Available from: https://doi.org/10.1039/c6ra27420j Liu, T., Zhao, Q., Zhou, H., Zhang, S., Li, Y., Sui, Z.: Porous graphene with high porosity derived from nitrogen-doped graphene aerogel for vapor adsorption and lithium–sulfur batteries. Research Square (Research Square) [Internet]. 2024 [cited 2025 Sep]; Available from: https://doi.org/10.21203/rs.3.rs-4260095/v1 Bundaleska, N., Henriques, J., Abrashev, M.V., Rego, A.M.B., do, Ferraria, A.M., Almeida, A., et al.: Large-scale synthesis of free-standing N-doped graphene using microwave plasma. Scientific Reports [Internet]. [cited 2025 Aug];8. (2018). Available from: https://doi.org/10.1038/s41598-018-30870-3 Banda, H.: Development of graphene-based composite materials for electrochemical storage applications. HAL (Le Centre pour la Communication Scientifique Directe) [Internet]. [cited 2025 Jun]; (2018). Available from: https://theses.hal.science/tel-02003297 Singh, K.P., Bhattacharjya, D., Razmjooei, F., Yu, J.: Effect of pristine graphene incorporation on charge storage mechanism of three-dimensional graphene oxide: superior energy and power density retention. Scientific Reports [Internet]. [cited 2025 Oct];6. (2016). Available from: https://doi.org/10.1038/srep31555 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 26 Apr, 2026 Reviewers agreed at journal 15 Apr, 2026 Reviewers agreed at journal 14 Apr, 2026 Reviewers agreed at journal 08 Apr, 2026 Reviewers invited by journal 08 Apr, 2026 Editor assigned by journal 02 Apr, 2026 Submission checks completed at journal 02 Apr, 2026 First submitted to journal 01 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9289593","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":623360454,"identity":"fd784074-c14f-405b-9686-26a4573d17d7","order_by":0,"name":"Khaled Abdou Ahmed Abdou Elsehsah","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIiWNgGAWjYDACCSDmYWCQ42eAMIjXYizZAGGA+IwNxGhJ3HCAWC38s7sTH7xhsGPcfH7tww9v2+zq+Bl4zB/dYNiWiEufxJ2zmw3nMCQzm914biw5ty1ZQrKBx7A5h+E2Ti0MN3K3SfP+Y2Yzu3GMQZq3jVnC4AABLfI3crf/5mGo5zGecYz5N29bvYQ9IS0GQFuYeRgOSxjwt7EBbQEyGAhoMbyRu1lyDsNxA4kbbGyWc84dl5xxmK1wdo7BbWNcWuRu5G788Iahur6//xjzjTdl1fz87c0bPudU3JbF6X04kEiAMpjBDmZwJKyF/wAq356gjlEwCkbBKBgpAAByileGRnmU2QAAAABJRU5ErkJggg==","orcid":"","institution":"University of Technology Malaysia","correspondingAuthor":true,"prefix":"","firstName":"Khaled","middleName":"Abdou Ahmed Abdou","lastName":"Elsehsah","suffix":""},{"id":623360455,"identity":"1f7bcd68-5a37-474a-8f99-1268707d3279","order_by":1,"name":"Zulkarnain Ahmad Noorden","email":"","orcid":"","institution":"University of Technology Malaysia","correspondingAuthor":false,"prefix":"","firstName":"Zulkarnain","middleName":"Ahmad","lastName":"Noorden","suffix":""},{"id":623360456,"identity":"7fd35d84-2beb-49af-88e3-0886d7450ec8","order_by":2,"name":"Norhafezaidi Mat Saman","email":"","orcid":"","institution":"University of Technology Malaysia","correspondingAuthor":false,"prefix":"","firstName":"Norhafezaidi","middleName":"Mat","lastName":"Saman","suffix":""},{"id":623360457,"identity":"5f737b88-624e-40b4-b7a6-b17f98887d75","order_by":3,"name":"Ayaz Ahmed Sahito","email":"","orcid":"","institution":"University of Technology Malaysia","correspondingAuthor":false,"prefix":"","firstName":"Ayaz","middleName":"Ahmed","lastName":"Sahito","suffix":""},{"id":623360458,"identity":"5db6ad09-d958-4532-8823-48d0e49c2c62","order_by":4,"name":"Mohd Aizam Talib","email":"","orcid":"","institution":"Tenaga Nasional Berhad (Malaysia)","correspondingAuthor":false,"prefix":"","firstName":"Mohd","middleName":"Aizam","lastName":"Talib","suffix":""},{"id":623360459,"identity":"6b03c1c9-957d-47ca-8a15-7b42476be9dc","order_by":5,"name":"Sharin AB Ghani","email":"","orcid":"","institution":"Technical University of Malaysia Malacca","correspondingAuthor":false,"prefix":"","firstName":"Sharin","middleName":"AB","lastName":"Ghani","suffix":""}],"badges":[],"createdAt":"2026-04-01 09:23:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9289593/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9289593/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107481474,"identity":"3fd5b3dc-8718-48a8-9364-c973a5c39a6d","added_by":"auto","created_at":"2026-04-22 02:18:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":936814,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the experimental workflow for the preparation and electrochemical evaluation of GA and NGA electrodes\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/74c47a8edb34e5750db6ffc6.png"},{"id":107480475,"identity":"2fc00175-5826-408d-8c16-a5c1d05fe6dd","added_by":"auto","created_at":"2026-04-22 02:11:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":222279,"visible":true,"origin":"","legend":"\u003cp\u003eCV curves of (a) pristine GA and (b) NGA recorded at scan rates of 5, 10, 20, and 50 mV/s\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/eb815d1f9a0cc618b68b79cf.png"},{"id":107065334,"identity":"cd811543-5a05-482a-a483-1fd0c38dc9dd","added_by":"auto","created_at":"2026-04-16 10:58:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":276350,"visible":true,"origin":"","legend":"\u003cp\u003ePotential-dependent specific capacitance profiles derived from CV measurements for (a) pristine GA and (b) NGA at scan rates of 5, 10, 20, and 50 mV/s\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/00f797217dda5fad4f6dbaad.png"},{"id":107065341,"identity":"2de69c7e-87da-4c89-bd9d-aab43bc4dc4a","added_by":"auto","created_at":"2026-04-16 10:58:01","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":106245,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of CV responses of pristine GA and NGA electrodes measured at (a) 5 mV/s and (b) 50 mV/s\u003c/p\u003e","description":"","filename":"image4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/37ed04d70454a23223504965.jpeg"},{"id":107065337,"identity":"3ecb431c-1928-408d-8295-7cf66b2bdaf9","added_by":"auto","created_at":"2026-04-16 10:58:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":178265,"visible":true,"origin":"","legend":"\u003cp\u003eGCD curves of (a) pristine GA and (b) NGA recorded at constant currents of 5, 10, 20, and 50 mA\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/f687f21d7d910324e8ea9b98.png"},{"id":107480685,"identity":"1a187777-c4ae-4e2f-8178-8399faa4983f","added_by":"auto","created_at":"2026-04-22 02:13:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":139912,"visible":true,"origin":"","legend":"\u003cp\u003eGCD curves of (a) pure GA and (b) NGA recorded at constant currents of 5, 10, 20, and 50 mA\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/aafd49f267113a066f69a0e0.png"},{"id":107065339,"identity":"05c65ad9-ef9e-48ca-8498-235c06641972","added_by":"auto","created_at":"2026-04-16 10:58:01","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":33442,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots of pure GA and NGA\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/2cf917372033c93f571a7f36.png"},{"id":107480697,"identity":"872f3f8b-1155-4d02-a5e2-7cc3afede678","added_by":"auto","created_at":"2026-04-22 02:13:07","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":335169,"visible":true,"origin":"","legend":"\u003cp\u003eEIS analysis of pristine GA and NGA SCs. (a) Impedance magnitude vs frequency, (b) real impedance vs frequency, (c) imaginary impedance vs frequency, (d) phase angle vs frequency, (e) real capacitance vs frequency, and (f) imaginary capacitance vs frequency\u003c/p\u003e","description":"","filename":"image8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/bd2838f55db9968770499e61.jpeg"},{"id":108005896,"identity":"0cf9b4f5-0aa8-43d6-9728-e35ce188cd11","added_by":"auto","created_at":"2026-04-28 12:50:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2336790,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9289593/v1/93858fb6-bb53-4cea-9a7d-0336c87a32a2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electrochemical Investigation of Pure and Nitrogen-Doped Graphene Aerogels for Supercapacitor Applications","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe recent explosion of the world electric vehicle market, as well as the portable electronic and large-scale renewable energy system markets, has made a strong demand for eco-friendly and effective electrochemical energy storage devices [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Supercapacitors (SCs), or ultracapacitors, with their high power density, high charge-discharge speeds, and long cycle life of more than hundreds of thousands of cycles, have become an important technology for filling the gap between conventional batteries and dielectric capacitors [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. These advantages make them appealing for use in hybrid energy storage systems and also for backup power applications [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. SCs are able to store energy by two main mechanisms: electric double layer capacitance (EDLC), which is due to electrostatic accumulation of ions at the electrodes-electrolyte interface, and pseudocapacitance, which is due to reversible Faradaic redox reactions at the electrode surface. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Among the different electrode materials that have been studied, graphene has received a lot of attention because of its outstanding theoretical specific surface area, high electrical conductivity, and mechanical stability [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite all these inherent benefits, the application of pristine graphene for supercapacitors is often impaired by the intense \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\pi\\:}\\)\u003c/span\u003e\u003c/span\u003e- \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\pi\\:}\\)\u003c/span\u003e\u003c/span\u003e stacking interaction between single sheets, which results in severe agglomeration and thus reduced accessible surface area for ion adsorption [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. To overcome this problem, the fabrication of three-dimensional graphene aerogels (GAs) has been proposed as a good alternative to inhibit restacking and preserve a highly porous network to enhance electrolyte penetration [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. GAs have low density and high specific surface area, which are very critical when seeking to maximize the volumetric and gravimetric capacitance of device performance [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. However, the pure GAs electrochemical performance is usually restricted due to the intrinsic hydrophobicity of graphene and a shortage of active sites for the faradaic reactions, which will give a capacitance value lower than the theoretical values [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. One potential way of addressing these drawbacks comes from heteroatom doping of the graphene lattice, in this case with nitrogen, in order to create defects on its surface and alter its electronic structure, allowing for improved charge storage properties [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Nitrogen atoms can be introduced into the graphene framework in various manners, e.g., pyridinic, pyrrolic, and graphitic-N, which have a different impact on the electronic properties and surface reactivity of the carbon matrix [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Nitrogen doping can improve the wettability and conductivity, introduce defect sites, and enhance the overall capacitance owing to the contribution from pseudocapacitance [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Theoretical and experimental studies suggest that the enhancement in capacitance brought by the nitrogen doping is attributed to causes such as reversible redox reactions, capacitance enhancement by quantum capacitance through Fermi level shifts, and enhanced electrode-electrolyte interactions [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn several comparative studies, synthesis parameters between pure and nitrogen-doped graphene aerogels are often inconsistent, making it hard to isolate the specific effects of nitrogen functionalization on electrochemical behavior [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Consequently, this study employs a controlled synthesis methodology to ensure that the only variable between the two materials is the presence of nitrogen dopants and thus opens direct and rigorous evaluation of how nitrogen functionalization regulates the charge storage kinetics and overall electrochemical efficiency [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In this study, pure and nitrogen-doped graphene aerogels were synthesized using the hydrothermal reduction method under comparable preparation conditions to enable a direct evaluation of the performance differences attributable solely to nitrogen incorporation [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The study provides a systematic comparison of the electrochemical properties of pure and N-doped graphene aerogels to elucidate the particular significance of N functional groups in enhancing capacitive behavior.\u003c/p\u003e"},{"header":"2. Materials and Experimental Procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Reagents and Materials\u003c/h2\u003e \u003cp\u003eGraphene oxide (GO) dispersion (2 mg/mL) was procured from Graphenea (Spain). Hydrazine monohydrate (64\u0026ndash;65%) and ethanol (95%) were obtained from LabChem (Malaysia). Potassium hydroxide (6M KOH) solution was obtained from Sigma-Aldrich (USA) and utilized as the electrolyte. All chemicals were utilized exactly as supplied, without additional purification. All experimental protocols employed deionized water for the cleaning and solution preparation stages. Hydrothermal reactors (50 mL Teflon-lined stainless-steel autoclaves) were purchased from Evergreen Engineering \u0026amp; Resources, Malaysia. Freeze-drying was performed in a SCANVAC lyophilizer (Chemopharm Group, Malaysia). A Gamry Interface 1000 potentiostat (Gamry Instruments, USA) was used to perform electrochemical experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Synthesis of Pure and Nitrogen-Doped Graphene Aerogels\u003c/h2\u003e \u003cp\u003eGraphene aerogels (GAs) were synthesized via a hydrothermal reduction approach followed by freeze-drying. An aqueous suspension of graphene oxide (2 mg/mL) was used as the precursor solution. 35 mL of the suspension was ultrasonicated for 30 minutes to ensure homogeneous dispersion, after which it was transferred into a 50 mL Teflon-lined stainless-steel autoclave and heated at 200 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\text{C}\\)\u003c/span\u003e\u003c/span\u003e for 16 hours to facilitate the self-assembly into a three-dimensional network driven by \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\pi\\:}\\)\u003c/span\u003e\u003c/span\u003e-\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\pi\\:}\\)\u003c/span\u003e\u003c/span\u003e interactions and reduction of GO to a reduced GO hydrogel.\u003c/p\u003e \u003cp\u003eAfter the completion of the hydrothermal reaction, the autoclave was allowed to cool naturally to room temperature for 3 hours, resulting in the formation of a cylindrical reduced GO hydrogel. The resulting hydrogel was carefully washed with deionized water for 72 hours, with the water replaced every 6 hours to remove residual impurities and unreacted precursors. Subsequently, the purified hydrogel was freeze-dried under vacuum at -107 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\text{C}\\)\u003c/span\u003e\u003c/span\u003e for 72 h to obtain the pure GAs.\u003c/p\u003e \u003cp\u003eNitrogen-doped GAs (NGAs) were prepared as a post-treatment modification of the pure GAs by mechanically sectioning the synthesized pure GA into smaller pieces and dispersing them into a mixed solution of hydrazine monohydrate and ethanol. The mixture was subjected to magnetic stirring for 30 minutes, followed by ultrasonication for another 30 minutes to form a homogeneous slurry.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Electrochemical Characterization Techniques\u003c/h2\u003e \u003cp\u003eElectrochemical measurements were carried out on a symmetric two-electrode configuration to evaluate the capacitive performance of the fabricated electrodes under conditions that are very much like the real working of devices. The NGA slurry, synthesized earlier, was coated onto current collectors of nickel foams with a geometric area of 4 cm\u0026sup2; and was subsequently dried in a vacuum oven at 70 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\text{C}\\)\u003c/span\u003e\u003c/span\u003e for 12 h in order to ensure complete solvent evaporation and adhesion. The electrodes were then compressed at a pressure of 10 MPa for 20 minutes to increase the quality of the electrical contact between the active material and the current collector. Circular sections with a diameter of 1 cm were punched from the compressed nickel foam to be used as the working electrodes in the assembled cells with a mass loading of approximately 9 mg/cm\u0026sup2;. No binders or conductive additives (such as carbon black) were used in the electrode fabrication to separate the intrinsic electrochemical properties of the active materials. A cellulose separator was used to prevent electrical shorting between the two identical electrodes, which were then assembled into a test cell configuration and filled with 6M KOH electrolyte.\u003c/p\u003e \u003cp\u003eCyclic voltammetry (CV) was performed within a potential range of 0\u0026ndash;1.0 V at different scan rates (from 5 to 50 mV/s) in order to assess the electrochemical behavior and the charge capacities of both non-doped and nitrogen-doped GAs. Galvanostatic charge-discharge (GCD) measurements with current densities ranging from 0.2 to 3 A/g were conducted to investigate the rate capability of the electrodes in order to assess the specific capacitance of the electrodes. The specific capacitance (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{C}}_{\\text{c}\\text{e}\\text{l}\\text{l}}\\)\u003c/span\u003e\u003c/span\u003e) of the device was calculated by applying the following equation to the GCD curves of discharge [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{\\text{C}}_{\\text{c}\\text{e}\\text{l}\\text{l}\\:}(\\text{F}/\\text{g})=\\:\\frac{\\text{I}\\varDelta\\:\\text{t}}{\\text{m}\\varDelta\\:\\text{V}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn the above expression, I denotes the discharge current (A), \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:\\text{t}\\)\u003c/span\u003e\u003c/span\u003e refers to the discharge time (s), \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:\\text{V}\\)\u003c/span\u003e\u003c/span\u003e corresponds to the potential window (V), and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{m}\\)\u003c/span\u003e\u003c/span\u003e is the total mass of active material in both electrodes (g).\u003c/p\u003e \u003cp\u003eFor the symmetric two-electrode case, the specific capacitance of one of the symmetric electrodes was determined by multiplying the capacitance of the device by a factor of four [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Both energy and power densities of the supercapacitor devices were further calculated from the GCD curves with the following expressions [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\text{E}\\:(\\text{W}\\text{h}/\\text{k}\\text{g})=\\:\\frac{1}{2}{\\text{C}}_{\\text{c}\\text{e}\\text{l}\\text{l}\\:}\\frac{{\\varDelta\\:\\text{V}}^{2}}{3.6}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\text{P}\\:\\left(\\text{W}/\\text{k}\\text{g}\\right)=\\:\\frac{3600\\text{E}}{\\varDelta\\:\\text{t}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn the above equation, the 3.6 value is used to convert the J/kg to Wh/kg, which is the standard unit used for energy storage devices. Electrochemical impedance spectroscopy measurements were performed in the frequency range of 100 kHz to 10 mHz with a sinusoidal amplitude of 10 mV to analyze the internal resistance and ion transport kinetics of the electrodes [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Comparative Analysis of Cyclic Voltammetry\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the cyclic voltammetry curves for both the pristine and nitrogen-doped GAs obtained at scan rates from 5 to 50 mV/s for a potential window from 0 to 1.0 V. For both GAs and NGAs, the CV curves present a quasi-rectangular shape, which is an indication of typical electric double-layer capacitive behavior with good charge propagation in the porous structure. The lack of large redox peaks indicates that there is little pseudo-capacitive contribution based mostly on non-faradaic charge storage mechanisms. As the scan rate rises to 5 to 50 mV/s, the current density is increased proportionally for both aerogels in accordance with a good rate capability. However, rectangular-shaped distortions are more apparent at a higher scan rate (20 and 50 mV/s), especially for the pure GA, indicating limitations in ion accessibility and diffusion kinetics inside the interior pore structure. Importantly, the NGA electrode has a significantly higher current response at all scan rates than the pristine GA, which can be attributed to the enhanced charge storage capacity due to the nitrogen doping.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe specific capacitance as a function of potential, in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, gives additional information about the charge storage mechanisms. The pure GA electrode exhibits scan-rate-dependent capacitance variation with increased capacitance values for low scan rates (5 and 10 mV/s). In contrast, the NGA electrode shows a more stable profile of capacitance over the whole potential window and has higher total capacitance values even at high scan rates (50 mV/s), showing partial kinetic limitation. In contrast, the NGA electrode exhibits a more stable capacitance profile across the entire potential window and maintains a higher overall capacitance, even at elevated scan rates. The relatively larger area enclosed by the CV curves for NGA is a further confirmation of their superior capacitance compared to the pristine GA counterparts. The relatively smooth capacitance voltage curves (without clear or sharp redox peaks) indicate that the storage of charge is mostly driven by EDLC, with only a little contribution of pseudo-capacitive effects. Notably, the improved capacitance in the NGA electrode is explained by the reduced internal resistance, demonstrated in the following GCD analysis, and improved ion transport kinetics provided by nitrogen functional groups.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to further clarify the impact of N doping on the electrochemical performance, CV profiles of GA and NGA at 5 mV/s and 50 mV/s were directly compared with each other, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. At 5 mV/s, both electrodes exhibit well-defined quasi-rectangular profiles with good symmetry of the forward and reverse scans. However, the NGA has a much higher enclosed area, which supports the higher specific capacitance that was observed because of the incorporation of nitrogen. At 50 mV/s, the difference between the two electrodes becomes even more significant, with NGA maintaining a more rectangular shape and having a considerably larger nominal area of integration, which indicates its better rate ability and reduced diffusion limiting for electrolyte ions at higher scan rates. Overall, the NGA is consistently found to have a stronger electrochemical performance in terms of charge storage capacity and kinetics at different scan rates in symmetric device-level conditions compared to the undoped GA. This proves that nitrogen incorporation positively influences interfacial charge transfer and ion transport behavior within the aerogel framework.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Comparative Analysis of Galvanostatic Charge-Discharge\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the GCD curves for both pure and nitrogen-doped GAs at different current densities spanning from 0.2 to 3 A/g (5, 10, 20, and 50 mA) in a symmetric two-electrode setup cell. The GCD curves for both materials exhibit nearly triangular and symmetric profiles, affirming their predominantly capacitive behavior. The linear voltage-time response observed during charging and discharging further supports the efficient storage and release of charge. The absence of significant voltage plateaus further supports EDLC behavior, with minimal contribution from distinct Faradaic redox processes, consistent with the CV results.\u003c/p\u003e \u003cp\u003eAt 5 mA, the discharge time for pristine GA is approximately 170 s, whereas for NGA, it is slightly lower at 162 s. At 10 mA, the discharge duration for pure GA reduces to approximately 74 s, while NGA shows an almost identical discharge time of approximately 76 s. However, the difference becomes more evident at higher constant currents. At 20 mA, pristine GA has a discharge time of about 27 s, while the NGA has a discharge time of about 34.6 s. At 50 mA, the improvement is even greater, with NGA showing a discharge time of about 10.7 s to the 3.3 s of the pristine GA, a more than threefold increase in discharge time.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe comparative GCD curves obtained at 5 mA and 50 mA are seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, which further illustrates the rate capability of the electrodes. At 5 mA, both electrodes show similar charge-discharge symmetry and similar discharge slope, indicating that the diffusion of ions in the porous network happens efficiently. Notably, the voltage drop (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{V}}_{\\text{d}\\text{r}\\text{o}\\text{p}})\\)\u003c/span\u003e\u003c/span\u003e seen at the start of the discharge curve, called the IR drop, is much smaller for NGA compared to pristine GA. This lowered IR drop in the NGA confirms a low internal resistance and improved electrical conductivity that is important in efficient energy delivery and power density in supercapacitors. This smaller IR drop helps to explain the enhanced performance and specific capacity of NGA despite having a slightly shorter discharge time at lower current densities as a result of improved charge transfer kinetics facilitated by the nitrogen functional groups. In contrast, at 50 mA, the NGA evidently outperforms the pristine GA and has a much longer discharge time as well as a smaller IR drop, indicating a better rate ability and a better energy preservation capability at high currents. Importantly, the enhancement is not only due to low current enhancement but can be more clearly observed under high current stress, hence proving that the incorporation of nitrogen mainly contributes to the performance enhancement of kinetic characteristics and reduction of internal resistance, instead of significant enhancement of the pseudocapacitance. The electrochemical performance parameters of pure GA and NGA electrodes at different currents are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculated Specific Capacitance, ESR, and Energy Density of NGA.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConstant Current (mA)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGA Specific Capacitance (F/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNGA Specific Capacitance (F/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGA ESR\u003c/p\u003e \u003cp\u003e(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\Omega\\:}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNGA ESR (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\Omega\\:}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGA Energy Density (Wh/kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNGA Energy Density (Wh/kg)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e174.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e187.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e155.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e178.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e125.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e167.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e5.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e54.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e143.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e4.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Comparative Analysis of Electrochemical Impedance Spectroscopy\u003c/h2\u003e \u003cp\u003eTo further investigate the charge transfer kinetics and ion diffusion characteristics of both GA and NGA electrodes, EIS measurements were performed. The resulting Nyquist plots, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, reveal distinct differences in their impedance characteristics, particularly in the high-frequency and low-frequency regions, which correspond to charge transfer resistance and ion diffusion resistance, respectively. In the high-frequency range, the solution resistance was nearly identical for both electrodes, with a value of approximately 0.18 Ω. This similarity is expected since the same 6 M KOH aqueous electrolyte and identical cell configuration were used for both systems. The comparable \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{R}}_{\\text{s}}\\)\u003c/span\u003e\u003c/span\u003e values indicate that the intrinsic electrolyte and contact resistance contributions are consistent between the two devices. However, a clear distinction emerges in the semicircle diameter within the high-frequency region, with NGA exhibiting a significantly smaller semicircle compared to GA, indicating lower charge transfer resistance (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{R}}_{\\text{c}\\text{t}}\\)\u003c/span\u003e\u003c/span\u003e) at the electrode-electrolyte interface, approximately 2.37 Ω versus 9.55 Ω. In the low-frequency region, NGA shows a more vertical slope compared to GA. This steeper slope for NGA suggests a more efficient ion-diffusion process within its framework, which is crucial for high-rate performance [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe frequency-related impedance magnitude of the pure GA and NGA is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea. At low frequencies, both electrodes show higher capacitive behavior, with NGA presenting a consistently lower impedance magnitude across the frequency spectrum as compared to pristine GA. The lower frequencies in the middle to high frequencies for NGA provide further evidence of superior charge transfer kinetics and ionic transport characteristics. The real part of the impedance (Z') as a function of frequency plot, in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb, gives further evidence that NGA retains a low Z' over the frequency range, showing a reduced energy dissipation and resistance during cycling. At high frequencies, Z' for both the GA and NGA approaches each other, indicating similar solution resistance as in the Nyquist plot analysis. The reduced values of Z' of NGA over most of the frequency domain confirm the reduction of the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{R}}_{\\text{c}\\text{t}}\\)\u003c/span\u003e\u003c/span\u003e. The imaginary part of the impedance is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec. Both electrodes show a relaxation peak in the mid-frequency range, with the NGA having a peak shifted towards the high-frequency part of the spectrum, indicating shorter relaxation time, faster ion response, and charge propagation in the electrode material [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The phase angle plot for NGA, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ed, shows a shift towards the capacitive region at higher frequencies compared to the pure GA. This observation indicates an accelerated change to capacitive behavior by an increase in charge transfer kinetics [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The wider phase angle response of pure GA in the mid-frequency region reflects the lower electrochemical response kinetics. The frequency-dependent complex capacitance measurement helps to understand the charge storage dynamics of both electrodes. As can be seen from Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ee and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ef, the real part of the complex capacitance for NGA is always higher than that of GA over a wide range of frequencies, especially at low frequencies, indicating a larger stored charge capability [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. In addition, the imaginary part of the complex capacitance shows that NGA exhibits higher capacitance at higher frequencies, which implies that NGA exhibits a more stable capacitive response and enhances its charge retention ability at higher charge/discharge speeds.\u003c/p\u003e \u003cp\u003eOverall, the EIS analysis shows that the incorporation of nitrogen is able to significantly improve the charge-transfer resistance and the electrochemical relaxation processes, which improve the ion transport kinetics and rate performance of the electrode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, a systematic comparative study between pristine GA and NGA was performed in order to assess the role of nitrogen incorporation on the electrochemical performance of graphene-based supercapacitor electrodes under realistic device conditions. Both materials showed typical electric double-layer capacitive behavior, as supported by the quasi-rectangular cyclic voltammetry profiles and the symmetric triangular charge-discharge profiles obtained in electrochemical testing. Despite the similar charge storage mechanism, the introduction of nitrogen was able to significantly enhance the electrochemical kinetics and rate capability of the aerogel electrodes. At low current conditions, nitrogen incorporation led to a moderate improvement of the electrochemical performance with a specific capacitance increase of about 8% higher than that of pristine GA. However, the beneficial effect of nitrogen modification became much more significant at increased current densities. At intermediate current conditions, the capacitance improvement was about 34%, whereas at high current operation, the NGA electrode showed an enhancement of nearly 160% compared to GA. A similar trend was observed for the energy storage capability, where the energy density increased by about 8% for low current and increased by more than 160% under high current conditions, which implies a far superior rate capability.\u003c/p\u003e \u003cp\u003eElectrochemical analysis also showed that the addition of nitrogen strongly enhanced the charge transport properties of the electrodes. The equivalent series resistance obtained using the GCD measurements decreased by about 71%, and electrochemical impedance spectroscopy measurements showed that the charge-transfer resistance decreased by about 75%. In addition, complex capacitance analysis indicated a shift to higher relaxation frequencies for NGA, which indicated a short electrochemical response time and rapid ion transport dynamics. Interestingly, even though no particularly strong pseudocapacitive features were found in the CV profiles, the overall capacitance and electrochemical performance were enhanced. This observation implies that the influence of nitrogen doping in the present system is not so much related to the contribution of additional Faradaic reactions but rather to electrochemical kinetics improvements. Nitrogen incorporation likely results in improved electronic properties of the carbon framework and better interactions between the electrode surface and electrolyte ions, which are responsible for improved charge transfer and ion transport within the porous aerogel structure.\u003c/p\u003e \u003cp\u003eOverall, these results have shown that nitrogen incorporation is an effective approach to improve the kinetics and rate capability of the graphene aerogel electrodes, which enables nitrogen doping as a potential strategy for the improvement of high-frequency operation of graphene-based supercapacitor systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors reviewed the manuscript.Khaled Abdou Ahmed Abdou Elsehsah: Wrote the main manuscript, Methodology, Validation, Supervision, Investigation.Zulkarnain Noorden Ahmad: Wrote the main manuscript, Methodology, Validation, Supervision, Investigation.Norhafezaidi Mat Saman: Edit the main manuscript, Validation, Supervision.Ayaz Ahmed Sahito: Supervision, Validation.Mohd Aizam Talib: Supervision.Sharin AB Ghani: Supervision .\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors would like to acknowledge the financial support from Universiti Teknologi Malaysia under UTM Flagship CoE/RG Research Grants (Q.J130000.5009.10G17).\u003c/p\u003e \u003cp\u003eConflict of Interest\u003c/p\u003e \u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data needed to evaluate the conclusions in the paper are present in the paper. 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Available from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://theses.hal.science/tel-02003297\u003c/span\u003e\u003cspan address=\"https://theses.hal.science/tel-02003297\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh, K.P., Bhattacharjya, D., Razmjooei, F., Yu, J.: Effect of pristine graphene incorporation on charge storage mechanism of three-dimensional graphene oxide: superior energy and power density retention. Scientific Reports [Internet]. [cited 2025 Oct];6. (2016). Available from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/srep31555\u003c/span\u003e\u003cspan address=\"10.1038/srep31555\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"materials-for-renewable-and-sustainable-energy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Materials for Renewable and Sustainable Energy](https://link.springer.com/journal/40243)","snPcode":"40243","submissionUrl":"https://submission.springernature.com/new-submission/40243/3","title":"Materials for Renewable and Sustainable Energy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Supercapacitor, Graphene Aerogel, Nitrogen-doped, EDLC, Capacitance","lastPublishedDoi":"10.21203/rs.3.rs-9289593/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9289593/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGraphene aerogels have been a promising electrode material for high-power supercapacitors due to their three-dimensional porous structure and good conductivity. However, enhancing their electrochemical kinetics in a more realistic device setting is still a major challenge. In this work, the effects of nitrogen incorporation on the electrochemical performance of graphene aerogels were systematically examined by direct comparison of the electrochemical performance of pristine graphene aerogel (GA) and nitrogen-doped graphene aerogel (NGA). The materials were synthesized by hydrothermal reduction of graphene oxide and freeze-drying, and the nitrogen doping was made by a post-treatment modification step. Electrochemical characterization was carried out in the form of cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) with a symmetric two-electrode setup and 6M KOH electrolyte. Both the electrodes showed quasi-rectangular CV profiles as well as symmetrical triangular GCD curves, thus representing a predominantly electric double-layer capacitance behavior. The specific capacitance was found to moderately increase from 174.18 F/g for GA to 187.54 F/g for NGA at 5 mA. More importantly, N modification significantly decreased the charge transfer resistance from 9.55 to 2.37 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\Omega\\:}\\)\u003c/span\u003e\u003c/span\u003e and the electrochemical relaxation time constant, leading to improved rate capability. These results show that the nitrogen incorporation mainly leads to an improvement in interfacial charge transfer kinetics and does not result in significant pseudocapacitive contributions to the supercapacitor kinetics, which is a useful insight for the design of high-rate graphene-based supercapacitor electrodes.\u003c/p\u003e","manuscriptTitle":"Electrochemical Investigation of Pure and Nitrogen-Doped Graphene Aerogels for Supercapacitor Applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-16 10:57:53","doi":"10.21203/rs.3.rs-9289593/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-26T11:33:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"238191870354749374990391476530801720994","date":"2026-04-15T05:52:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"43974331665594237048275634333979444311","date":"2026-04-14T08:58:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"69184180621260316574919952419900610879","date":"2026-04-08T17:35:44+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-08T16:28:23+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-02T08:55:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-02T08:54:12+00:00","index":"","fulltext":""},{"type":"submitted","content":"Materials for Renewable and Sustainable Energy","date":"2026-04-01T09:05:38+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"materials-for-renewable-and-sustainable-energy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Materials for Renewable and Sustainable Energy](https://link.springer.com/journal/40243)","snPcode":"40243","submissionUrl":"https://submission.springernature.com/new-submission/40243/3","title":"Materials for Renewable and Sustainable Energy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"419a7fc5-9463-466f-8026-621332b381d4","owner":[],"postedDate":"April 16th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-16T10:57:53+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-16 10:57:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9289593","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9289593","identity":"rs-9289593","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}