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. 2025 Oct 25;10(43):51512–51523. doi: 10.1021/acsomega.5c07179

Enhanced Supercapacitor Performance through Synergistic BaCO3 Doping of Graphene Nanoplate Electrodes

Abdel-Menem Elnemr †,*, Eslam Sheha ‡, Ahmed M Ghander †, Hytham Elbohy †,§,*
PMCID: PMC12593138  PMID: 41210747

Abstract

Barium carbonate (BaCO3) is a stable inorganic compound with a high ionic conductivity and thermal stability, making it valuable for electrochemical applications. This study develops BaCO3-doped graphene nanoplate (GPL) electrodes and compares them to pure GPL electrodes. The BaCO3/GPL composite exhibits a lower surface area and altered pore distribution but achieves a higher surface potential, enhancing the electrolyte penetration and ion transport. Its superior electrochemical performance makes it a strong candidate for energy storage. Using a 1.0 M Na2SO4 electrolyte, Cyclic voltammetry (CV) measurements revealed that at a scan rate of 0.03 V s–1, the BaCO3/GPL composite exhibited markedly enhanced capacitance compared to pristine GPL, attaining 164.524 F g–1 versus 59.724 F g–1 in the anodic sweep and 943.95 F g–1 versus 510.124 F g–1 in the cathodic sweep. The enhanced capacitance is attributed to the greater negative surface potential, improving charge storage. The BaCO3/GPL electrode displays great cycling stability, still maintaining 91.17% and 90.08% of the initial capacitance in the negative and positive directions, respectively, after 1200 charge–discharge cycles. Structural and electrochemical properties were analyzed using XRD, FT-IR, Raman, AFM, XPS, and EIS at different cycling stages and SEM before and after cycling, confirming the material’s stability and efficiency for supercapacitor applications.

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1. Introduction

The need for sustainable, renewable energy storage results from global urbanization and the exhaustion of conventional energy resources. For meeting the growing energy needs, innovative and efficient energy storage technologies are needed. Historically, electrochemical storage devices like batteries and capacitors have been used for this purpose. − Supercapacitors (SCs) are increasingly being identified for energy storage applications because of their enhanced characteristics over conventional capacitors, thus making them valuable components in contemporary electronic systems. − Supercapacitors (SCs) offer a promising solution because they exhibit fast charging/discharging, high power density, and excellent cycling performance. − Supercapacitors (SCs) are supplemental power sources in diverse applications, including wearable and consumer electronics, smart grids, memory backup systems, portable healthcare devices, and military technology. In supercapacitors, two electrodes are separated by ion-permeable mechanism, where the electrolyte facilitates charge transport between them. − An ion-permeable mechanism acts as a barrier between two electrodes in supercapacitors, and the electrolyte facilitates the transfer of charge between these electrodes. − There are two types of SCs: Faradaic pseudocapacitors (PCs) and newer electric double-layer capacitors (EDLCs). Electric double-layer capacitors (EDLCs) store charge via separated electrodes made from inert and highly conductive carbon materials. Conversely, faradaic pseudocapacitors utilize conducting polymers, transition metal oxides (TMOs), and other electroactive materials for charge storage via surface redox reactions. − Current research aims to enhance supercapacitor production to satisfy the stringent requirements of contemporary energy storage. The performance of a supercapacitor in terms of energy storage heavily depends on the synthesis techniques and characteristics of the electrode materials (morphology and electrochemical properties). Supercapacitor electrodes utilize transition metal compounds, carbonaceous materials, and conducting polymers as key materials, thus significantly improving energy storage efficiency. Supercapacitors (PCs) use carbon derivatives as electrode materials due to their enhanced conductivity, superior charge density, expanded electrochemical potential window, and exceptional stability. Carbon fibers, reduced graphene oxide (rGO), carbon aerogels, activated carbon, graphitic carbon nitride (g-C3N4), and graphene nanoplates (GNP) are among the different carbon materials used. − These compounds feature active sites that readily adsorb reactants but exhibit reduced binding affinity due to electrostatic repulsion. Electrochemical oxygen gas reduction is key to fuel cells, metal-air batteries, and supercapacitors. − To improve the efficiency of supercapacitors, metal-air batteries, and fuel cells, catalysts are often needed to speed up the ORR’s slow kinetics. − Conversely, spinel-structured transition metal (TM) oxides, such as Co3O4, MnCo2O4, and CoFe2O4, along with their carbon-based hybrids, demonstrate superior catalytic activity for oxygen reduction reactions (ORR) in alkaline solutions. A four-electron process using the redox couples of TM2+/TM3+ within the spinel structure speeds up the ORR, thus improving the reaction kinetics. Recent research has shown that carbon-based materials doped with heteroatoms exhibit better performance for oxygen electroreduction. Incorporation of hetero atoms such as nitrogen (N), phosphorus (P), boron (B), and sulfur (S) into the carbon matrix has led to changes in charge density and spin density. The doping process significantly boosts the number of active sites for the oxygen reduction reaction (ORR). Barium carbonate (BaCO3), a widely used and affordable compound, finds application in diverse manufacturing and industrial processes. Recent work has shown that BaCO3 nanoparticles are the perfect catalysts for high-temperature oxygen reduction in solid oxide fuel cells (SOFCs). We benchmarked the electrochemical performance of our BaCO3/GPL composite electrode against those of GPL-based and metal-oxide/graphene composites reported in the literature. The chemically activated graphene nanoplatelet (CGnP) electrodes showed specific capacitance improvement from ∼123 F/g to ∼180 F/g (≈+46%) and excellent cycle stabilityonly ∼6.1% capacitance loss after 10,000 cycles. Composites of graphene with metal oxides like Ni­(OH)2 nanoplates grown on graphene showed remarkable specific capacitances (∼1335 F/g at 2.8 A/g; ∼953 F/g at 45.7 A/g) and exceptional stability. Asymmetric supercapacitors based on Ni­(OH)2/graphene and RuO2/graphene demonstrated energy densities of up to ∼48 Wh/kg and power densities of up to ∼21 kW/kg. For comparison, while BaCO3-based electrode data in the literature are limited, our BaCO3/GPL composite shows drastically improved ion-transport and charge-transfer propertiesas reflected in the very low R ct (∼7–8 Ω) and Warburg impedance W (∼36–48 Ω·s–0.5) throughout cyclingindicative of its competitive performance and prospects as an alternative electrode supported by the synergistic interaction between the conductive graphene network and BaCO3.

In this study, we synthesized a novel electrode made of barium carbonate/graphene nanoplates for supercapacitor devices that showed higher specific capacitance, energy, and power densities as well as better oxygen reduction reaction (ORR) activity. Further insights into the materials were gained through a BET analysis. The electrochemical properties of pure and barium-carbonate-modified graphene nanoplates were thoroughly investigated. Based on the reported stability of the capacitive wallet after cycling 1000 times charge–discharge, we further examined the electrochemical properties following cycling, as described in the manuscript.

2. Experimental Section

2.1. Materials

Graphene nanoplates, 6–8 nm (thick), and 5 μm (wide) were purchased from the Tokyo Chemical Industry (TCI). Poly­(vinylidene fluoride) and N-methyl-2-pyrrolidone were purchased from Merck. Fluorine-doped tin oxide (FTO) substrates used as current collectors with a sheet resistance of 7 Ω/sq, barium carbonate (99.98% trace metals basis), and sodium sulfate were purchased from Sigma-Aldrich.

2.2. Preparation of GPL and BaCO3/GPL Thick Electrodes

The electrode was entirely made of graphene nanoplates (GPL), comprising 100 wt % of the total composition. Conversely, a second formulation of the electrode was prepared with a composition of 75 wt % graphene nanoplates (GPL) and 25 wt % barium carbonate (BaCO3). The chosen weight proportion in which BaCO3 constituted 25% of the entire mixture weight was determined from its better electrochemical performance, indicated by the results of cyclic voltammetry curves depicted in Figures S1 and S2. These mixtures were ground in two independent mortars for 15 min. 10 wt % PVDF was partially added to a vial containing 7 mL of NMP and subjected to stirring using a magnetic stirrer at 350 rpm. When the solution (PVDF and NMP) was clear, we divided the solution into two equal halves in two vials. Each vial contained 3.5 mL. A GPL droplet in vial and mixture (BaCO3 and GPL) droplet in other vial were subjected to stirring by using a magnetic stirrer for a duration of 24 h.

2.3. Fabrication GPL and BaCO3/GPL Electrodes

The FTO substrates were cleaned using a sonication system with DI water and soap, DI water, acetone, and 2-propanol, respectively, for 20 min each. The FTO substrates were exposed to UV–Ozone treatment for 30 min for further cleaning. The resultant slurry from the solutions GPL and BaCO3/GPL was coated on FTO substrates by using an MC-20 mini-coater and was left in a dry oven for 2 h at 70 °C.

2.4. Characterization of the Prepared Materials

Scanning electron microscopy (SEM) and energy-dispersive spectroscopy were carried out by using the JEOL JMS-700. Using a Rigaku MiniFlex 600 X-ray diffractometer, the materials’ lattice constants were obtained. Jasco FT/IR-410 174 Fourier-transform infrared (FT-IR) spectrometer was used to specify the functional groups. In an alkaline electrolyte solution, we assessed the supercapacitive properties of GPL and BaCO3/GPL electrodes utilizing galvanostatic charge–discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. These experiments were conducted in an electrochemical station with a three-electrode setup by Metrohm Autolab (PGSTAT204). The working electrode used in this technique was deposited FTO, while the counter electrode was platinum), and the reference electrode was Ag/AgCl. In electrochemical studies, an aqueous 1 M Na2So4 alkaline solution was used as the electrolyte. The zeta potential was measured using the ZTS1240 device, as detailed in the Malvern Panalytical report. XPS data were collected on a K-ALPHA (Thermo Fisher Scientific, USA) with monochromatic X-ray Al K-alpha radiation (10 to 1350 eV), a spot size of of 400 μm, and a pressure of 10–9 mbar, with a full spectrum pass energy of 200 eV and a narrow spectrum pass energy of 50 eV. The Brunauer–Emmett–Teller (BET) surface area and the porosity of the sample were obtained using the N2 adsorption–desorption apparatus of Microtrac’s BELSORP MINI X (BET specific surface areas from 0.01 m²/g and pore size distribution from 0.7 to 500 nm). Atomic force microscopy was performed using the SPM-9700.

3. Results and Discussion

X-ray diffractogram analysis was used to study the structural behavior of GPL and BaCO3/GPL electrodes in supercapacitors. Figure a illustrates the XRD pattern of GPL and BaCO3/GPL, displaying distinct and sharp peaks at specific 2θ values for GPL (27.35° and 55.39°), corresponding to the hkl planes (002) and (004), respectively, according to card number DB Card Number 9000046. On the other hand, the specific angles for BaCO3/GPL (20.36°, 20.75°, 24.78°, 25.069°, 27.37°, 30.48°, 34.97°, 35.42°, 40.33°, 41.26°, 42.84°, 43.77°, 45.22°, 45.69°, 47.63°, 49.78°, 50.00°, 54.48°, 55.45°, 56.46°, 57.05°, and 61.66°) conform to the hkl planes (110), (020), (111), (021), (002 “graphite”), (121), (031), (112), (220), (040), (032), (041), (031), (202), (141), (231), (222), (004 “graphite”), (150), (232), and (311), respectively, based on card numbers DB Card Number 9000046, 1539129, and 9006843. Interestingly, the composite’s peak GPL intensity gradually increases by adding BaCO3 as shown in Figure b, indicating that the addition of BaCO3 affects the GPL polymerization process. Furthermore, after hybridizing with BaCO3, the peak at 27.32° changes significantly to a higher angle, suggesting a decrease in the layer spacing of GPL. The presence of GPL crystalline planes was indicated by the diffraction angles of 27.32° and 55.39°, proving that the crystal-like planes of GPL precisely corresponded to the XRD patterns of BaCO3/GPL. Thus, the Scherrer equation can be found in eq .

D=KλB⁡cos(θ) 1

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Physicochemical analysis of GPL and BaCO3/GPL electrodes. (a) X-ray diffractogram patterns of GPL and BaCO3/GPL. (b) Shift in the X-ray diffraction (XRD) patterns of GPL and BaCO3/GPL. (c) FT-IR spectra of GPL and BaCO3/GPL. (d) Raman spectra of GPL and BaCO3/GPL. (e) EDS spectra of GPL and BaCO3/GPL. (f) Mass percentage of elements in the GPL electrode quantified by EDS. (g) Mass percentage of elements in the BaCO3/GPL electrode quantified by EDS. (h) SEM image of the GPL electrode illustrating surface morphology. (i) SEM image of the BaCO3/GPL electrode revealing microstructure.

It was used to measure the higher intensity peaks in order to determine the regular crystallite size of BaCO3/GPL. The X-ray wavelength, represented by λ, the full width at half-maximum B, and the diffraction angle, represented by θ, were all clearly stated. In this particular case, the form factor was K. The crystallite sizes of GPL and BaCO3/GPL are 25.872 and 18.539 nm, respectively. The FT-IR spectrum for BaCO3 shows the in-plane bending and out-of-plane bending modes of CO3 2– are represented by sharp peaks at 695.26 and 854.95 cm–1, respectively. The symmetric stretching vibration of the C–O bond is assigned to the weak band at 1054.98 cm–1, and the infrared bands at 1440.32 cm–1 are assigned to the asymmetric stretching mode of the C–O bond , as demonstrated in Figure c. The infrared spectrum of GPLs reveals that the C–H stretching band appears at 826.34 cm–1, whereas the CC stretching bands appear at 976.58 cm–1, 1609.28 cm–1, and 1669.08 cm–1. The carbonyl (OC) functional group is responsible for the characteristic absorption band at 1722.56 cm–1, according to BaCO3/GPL analysis. The bands at 1591 cm–1 and 1671 cm–1 are likewise caused by the slight vibrations that occur for CC bonds. The carbonate ion (CO3 2–) is represented by the band at 1435.1 cm–1. Additionally, the acute v2 vibrational mode of BaCO3 is responsible for the peak with the maximum intensity at 841.71 cm–1, whereas its v4 vibrational mode is responsible for the peak at 711.95 cm–1. The Raman spectrum of pure graphene nanoplates (GPL) shows the typical carbon bands as displayed in Figure c: the D-band (∼1340 cm–1), due to structural disorder and edge defects; the G-band (∼1580 cm–1), due to the in-plane vibration mode of sp2-hybridized carbon atoms; and the 2D-band (∼2680 cm–1), which is a proof of the graphitic character of the nanoplates and gives evidence of a multilayered structure. The I D/I G ratio, which is relatively moderate, suggests an even balance between structural order and defect density, qualities that are desirable for electrochemical activity. Conversely, the BaCO3/GPL composite displays more spectral features as illustrated in Figure c. A new Raman band at ∼1122 cm–1 appears, which is attributed to the ν1 symmetric stretching vibration of the CO3 2– anion, attesting to the existence of BaCO3 in the composite. Furthermore, minor D- and G-band position shifts are noticed relative to those of pristine GPL. These shifts are indicative of interfacial interactions, charge transfer, and strain effects between BaCO3 particles and the graphene lattice. These changes indicate that BaCO3 nanoparticles not only decorate the graphene surface but also modulate its electronic environment and defective structure, which may increase the availability of active sites and enhance electrochemical performance. The spectrum of BaCO3/GPL, as depicted in Figure e, reveals the presence of three elements: carbon (C), oxygen (O), and barium (Ba). In contrast, the energy-dispersive spectroscopy (EDS) spectrum of GPL indicates only two elements, carbon and oxygen, thereby confirming that GPL is composed solely of these two elements. Figure f,g presents the elemental mass percentages in the GPL and BaCO3/GPL electrodes, respectively, as determined by EDS analysis. Additionally, insights into the catalytic activity of BaCO3 for the oxygen reduction reaction (ORR) are presented in Figure e, demonstrating that BaCO3 effectively facilitates the reduction of oxygen sites. As seen in Figure h,i, the SEM images of GPL and BaCO3/GPL illustrate the differences in their morphologies. Interestingly, because solid rod-like BaCO3 exerts a blocking effect on GPL, it is interesting to note that the GPL image (Figure h) has higher porosity than the BaCO3/GPL (Figure i).

The X-ray photoelectron spectroscopy (XPS) of the BaCO3/GPL electrode offers compelling evidence in favor of powerful chemical interactions. The survey spectrum reveals the existence of barium (Ba), carbon (C), oxygen (O), and fluorine (F), hence confirming the successful deposition of BaCO3 on the graphene surface, as shown in Figure a. Figure b shows the high-resolution deconvolution of the C 1s region shows typical peaks at ∼284.5 eV (sp2 carbon), ∼285.6 eV (C–O/C–OH), and ∼288.5–289 eV (CO3 2–), indicating the presence of graphitic carbon and carbonate functionalities. Figure d shows the O 1s spectrum displays peaks for Ba–O bonds, carbonate oxygen, and adsorbed species, confirming the formation of BaCO3 and interfacial bonding with graphene. Figure c shows the Ba 3d spectrum exhibits spin–orbit split peaks in agreement with Ba2+ in a carbonate environment, which confirms the chemical state of barium. An important observation is that the shifts and broadening of the C 1s and O 1s peaks suggest electronic interactions or charge transfer between GPL and BaCO3 at their interface, likely mediated by oxygen-containing functional groups on the graphene surface as nucleation and anchoring sites. The observation of F 1s signalsattributed to ionic and covalently bonded fluorinemay suggest the presence of fluorinated species either introduced during the synthesis or serving as functional groups, which may alter the electronic properties of the composite (from the binder), as indicated in Figure e. Figure f illustrates the pore diameter distribution and nitrogen adsorption–desorption isotherms for GPL and BaCO3/GPL. Both materials exhibit mesoporous structures, characterized by a Type IV isotherm and an H3 hysteresis loop, consistent with IUPAC classifications. The BET-specific surface areas for GPL and BaCO3/GPL are measured at 3.8955 and 1.3702 m2/g, respectively. The incorporation of solid rod-like BaCO3 into GPL leads to a reduction in the specific surface area due to its mesoporous nature. Correspondingly, the pore volume of BaCO3/GPL is also diminished. It is noteworthy that enhanced electrocatalytic performance is influenced by factors beyond the specific surface area and pore size. Atomic Force Microscopy (AFM) was employed to analyze the surface morphology of BaCO3, GPL, and BaCO3/GPL composite. AFM images of BaCO3 showed smooth crystalline particles that manifested the lowest surface roughness among the samples tested, reflecting its dense structure and minimal surface irregularities, as shown in Figure g. In contrast, pristine GPL showed higher roughness due to its inherent wrinkled nature, step edges, and interlayer stacking of graphene sheets, leading to an open, porous structure, as illustrated in Figure h. Functionalization of GPL with BaCO3 significantly altered the topography of the composite, where BaCO3 was dispersed over the graphene surfaces, thus clogging the open pores of GPL partially, as shown in Figure i. This deposition enhanced overall surface uniformity and reduced the depth of surface valleys, resulting in a morphology that is smoother but denser compared to pristine GPL. The pore blockage effect is anticipated to reduce the accessible surface area and alter electrolyte infiltration and, in turn, the electrochemical performance of the composite electrodes. These findings corroborate the conclusions derived from the Brunauer–Emmett–Teller (BET) surface area analysis. Relevant parameters obtained from AFM spectroscopy for BaCO3, GPL, and BaCO3/GPL composite are summarized in Table S1. To investigate the charge on the surface electrodes, zeta potential measurements were conducted for GPL and BaCO3/GPL. The observed zeta potentials were −26.05 mV for GPL and −31.35 mV for BaCO3/GPL. The increased negative potential of BaCO3/GPL contributes to enhanced catalytic properties compared to GPL. We assessed the supercapacitive properties of GPL and BaCO3/GPL in an alkaline electrolyte solution using cyclic voltammetry (CV) spectroscopy techniques within a three-electrode electrochemical setup. The working electrode was made of a deposited FTO substrate, while a platinum wire served as the counter electrode, and a Ag/AgCl electrode was used as the reference. The electrolyte used in these electrochemical experiments was a 1.0 M Na2SO4 aqueous solution.

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An extensive characterization of GPL and BaCO3/GPL electrodes: (a) XPS full spectrum and high-resolution XPS spectra of BaCO3/GPL, (b) high-resolution C 1s XPS spectrum, (c) high-resolution Ba 3d XPS spectrum, (d) high-resolution O 1s XPS spectrum, (e) high-resolution F 1s XPS spectrum, (f) nitrogen adsorption–desorption isotherms and corresponding pore size distribution curves (inset) of GPL and BaCO3/GPL, (g) AFM spectrum of BaCO3, (h) AFM spectrum of GPL, and (i) AFM spectrum of BaCO3/GPL.

The capacitive values of the materials were calculated using eq .

Cs=∫vcvaI⁡dVm×S×ΔV 2

Equation states that the variables are the integral current area of the CV curve (∫vcvaI⁡dV) , specific capacitance (C s), scan rate (S), active mass (m), and potential window (ΔV). The CV plots obtained over a potential range of 0–0.7 V in the positive direction and from −0.8 to 0 V in the negative direction are displayed in Figures and . The storage capacity of the synthesized electrodes was evaluated by using these CV plots at sweep rates ranging from 0.03 to 0.2 V·s–1 for both directions. From Figures and , the area under the CV curve for BaCO3/GPL is greater than that for GPL. This difference is attributed to the enhanced catalytic properties of BaCO3/GPL, resulting from the addition of BaCO3 to GPL. We observed that the specific capacitance in the negative direction is more than eight times greater than that in the positive direction, as illustrated in Figures f and f, which plot specific capacitance against scan rate.

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Charge storage analysis of GPL and BaCO3/GPL electrodes in the positive direction: (a) cyclic voltammetry for GPL and BaCO3/GPL electrodes at 0.2 V·s–1, (b) 0.15 V·s–1, (c) 0.1 V·s–1, (d) 0.05 V·s–1, and (e) 0.03 V·s–1. (f) Specific capacitance versus scan rate.

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Charge storage analysis of GPL and BaCO3/GPL electrodes in the negative direction: (a) cyclic voltammetry for GPL and BaCO3/GPL electrodes at 0.2 V·s–1, (b) 0.15 V·s–1, (c) 0.1 V·s–1, (d) 0.05 V·s–1, and (e) 0.03 V·s–1. (f) Specific capacitance versus scan rate.

Using a 1.0 M Na2SO4 electrolyte solution across potential ranges of 0–0.7 V in the positive direction and −0.8 to 0 V in the negative direction, GCD characterization was employed to evaluate the storage capacity of the synthesized samples. Figures and present the GCD plots for pristine GPL and BaCO3/GPL produced as working electrodes at varying current densities.

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Charge storage characterization of GPL and BaCO3/GPL in the positive direction: (a) GCD for GPL and BaCO3/GPL at 0.0014 A, (b) 0.0015 A, (c) 0.0016 A, (d) 0.0017 A, and (e) 0.0018 A. (f) Specific capacitance as a function of scan rate, (g) energy and power density of BaCO3/GPL in the positive direction, (h) GCD for GPL and BaCO3/GPL at 0.0025 A in the negative direction, and (i) GCD for GPL and BaCO3/GPL at 0.0026 A in the negative direction.

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Charge storage characterization of GPL and BaCO3/GPL in the direction: (a) GCD for GPL and BaCO3/GPL at 0.0027 A, (b) 0.0028 A, (c) 0.0029 A. (d) Specific capacitance as a function of scan rate in the negative direction, (e) energy and power density of BaCO3/GPL in the negative direction, (f) EIS of GPL and BaCO3/GPL, (g) cyclic stability of BaCO3/GPL in the positive direction, and (h) cyclic stability of BaCO3/GPL in the negative direction.

The plotted GCD curves confirmed the reversibility of the electrochemical characteristics of the fabricated electrodes with the composite displaying a triangular shape and linear edges. Hence, Figures f and d display the measured specific capacitance at different current densities for both the unmodified (GPL) and modified (BaCO3/GPL) material. Moreover, Figures g and e illustrate the energy density versus power density relation, plotting data in the positive and negative directions, respectively. The CV and GCD curves demonstrate that as the doping level increases, both the area and discharge time in their respective cases also increase. This is likely due to an enhancement in conductivity attributed to the doping effect. In our work, the charge storage mechanism of the BaCO3/GPL composite electrode is largely controlled by the electric double-layer capacitance (EDLC) behavior instead of faradaic redox processes. This is evidenced from the quasi-rectangular cyclic voltammetry (CV) profiles and symmetric galvanostatic charge–discharge (GCD) curves, both of which are hallmarks of capacitive storage dominated by electrostatic ion adsorption at the electrode/electrolyte interface. Additionally, the lack of well-defined redox peaks in CV curves attests to the fact that faradaic reactions make a negligible contribution to the overall capacitance. These results confirm that BaCO3 is primarily a structural and conductive modifier to create increased surface area and ion accessibility, with the energy storage stemming principally from EDLC mechanisms.

Furthermore, the cycling stability and capacitance retention behavior of the BaCO3/GPL electrodes under both anodic and cathodic polarization are presented in Figure g,h. The electrodes exhibited outstanding electrochemical durability, maintaining capacitance retention values of 90.08% in the positive direction and 91.17% in the negative direction after 1200 consecutive charge–discharge cycles, thereby underscoring their robust long-term operational stability.

The electrochemical impedance spectroscopy (EIS) is employed to identify the different types of internal resistance within the system and to evaluate the frequency response of the supercapacitor electrode. EIS is useful for analyzing the physical and interfacial characteristics of the electrode. Ultimately, the EIS results demonstrate the favorable performance of the materials. The EIS test was performed in a 1.0 M Na2So4 solution at frequencies ranging from 0.1 Hz to 100 kHz, and the results are presented in Figure f. A suitable equivalent circuit for supercapacitor devices was chosen, which included electrolyte resistance (R s), Warburg impedance (W), constant phase element (CPE), and charge transfer resistance (R ct). As shown in Table S2, the pristine GPL electrode exhibits a relatively high charge-transfer resistance (R ct = 32.82 Ω) and large Warburg impedance (W = 421.7 Ω·s–0.5, which correspond to a pronounced semicircle in the high-frequency region and a shallow slope in the low-frequency domain of the Nyquist plot. These results indicate sluggish charge-transfer kinetics and limited ionic diffusion. By contrast, the BaCO3/GPL composite displays a much smaller semicircle diameter, consistent with its significantly lower R ct value (7.859 Ω), confirming faster interfacial electron transfer. Furthermore, the composite shows a steep oblique line in the low-frequency region, which agrees well with the substantially reduced W value (48.21 Ω·s–0.5. This decrease in Warburg impedance reflects an enhanced ionic diffusion rate through the electrode structure, facilitated by the synergistic interaction between the BaCO3 particles and the conductive graphene framework. Thus, the quantitative interpretation demonstrates that BaCO3 functionalization not only improves charge-transfer efficiency but also accelerates ion transport, which together account for the superior electrochemical performance of the BaCO3/GPL electrode compared with pristine GPL. To gain a comprehensive understanding of the mechanisms and high retention energy within a supercapacitor following the cycling process of the BaCO3/GPL electrode, we conducted electrochemical impedance spectroscopy (EIS) analysis before, after 10, 100, and after 1000 cycles. Additionally, we performed X-ray diffraction (XRD) analysis on the electrodes prior to cycling and after 1000 cycles and SEM before and after cycling. The XRD patterns for BaCO3/GPL, which are both deposited on FTO, are shown in Figure a, both before and after cycling. The XRD pattern of BaCO3/GPL after cycling shows new, shifted, and reduced peaks, resulting in an amorphous appearance as illustrated in Figure a. The shift and alteration of the major peaks before and after cycling for BaCO3/GPL are attributed to the incorporation of sulfate ions (SO4 2–) into the cathode framework (BaCO3/GPL) electrodes during discharge/charging, where they establish a bond with sulfur atoms through a conversion reaction. Where the SO4 2– ions result from the dissolution of salt in condensed water according to eq .

Na2SO4(s)+H2O(l)→2Na+(aq)+SO42−(aq) 3

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(a) XRD of substrate “FTO” and BaCO3/GPL on FTO before and after cycling, (b) FT-IR for BaCO3/GPL before and after 1000 cycles, , (c) EIS of GPL before and after 10 cycles, (d) EIS of GPL before and after 1000 cycles, (e) EIS of BaCO3/GPL before and after 10 cycles, and (e) EIS of BaCO3/GPL before and after 1000 cycles.

Based on the FT-IR analysis conducted before and after 1000 cycles, as depicted in Figure b, the emergence of a new peak at 1106.812 cm–1 was observed. This peak is assigned to the asymmetric stretching mode (v3) of sulfate ions (SO4 2–), which provides experimental evidence supporting the validity of our hypothesis.

Figure c–f demonstrates the EIS measurements for the pristine GPL electrode and the enhanced BaCO3/GPL electrode before cycling, after 10 cycles, and after 1000 cycles. The results indicate that the charge transfer resistance (R ct) of GPL electrodes decreases with an increasing number of cycles, which can be attributed to the incorporation of sulfur ions into the GPL matrix. Specifically, R ct values are measured at 32.82, 12.95, and 9.56 Ω for the pristine electrode, after 10 cycles, and after 1000 cycles, respectively, as summarized in Table S3. R s was nearly unchanged for all of the samples, indicating stable electrode/electrolyte contact during cycling. However, the charge transfer resistance (R ct) and Warburg impedance (W) exhibited large differences in accordance with the Nyquist plots. Pristine GPL displayed a large semicircle in the high-frequency region with an R ct of 32.82 Ω, demonstrating slow charge-transfer kinetics, while the BaCO3/GPL composite presented a very small semicircle corresponding to a greatly decreased R ct of 7.859 Ω, indicating improved interfacial conductivity. After 10 and 1000 cycles, both electrodes showed smaller semicircle diameters compared with their pristine states; however, BaCO3/GPL always displayed the lowest R ct (∼7.5 Ω), confirming its better structural stability. In the low-frequency region, the GPL electrode displayed high Warburg impedance values (421.7 Ω·s–0.5 before cycling and 136.9 Ω·s–0.5 after 1000 cycles), demonstrating slow ion diffusion. By contrast, BaCO3/GPL presented much lower W values (48.21 Ω·s–0.5 before cycling and 35.99 Ω·s–0.5 after 1000 cycles), which agrees with the steeper slope in the Nyquist plot and confirms facilitated ionic diffusion. These findings clearly indicate that BaCO3 functionalization not only lowers charge-transfer resistance but also enhances ionic diffusion, thus leading to the enhanced electrochemical performance and long-term cycling stability of the BaCO3/GPL composite over pristine GPL. As is evident from the EIS spectra in Figure e–f, very minimal changes in impedance response are observed, indicating very active electrochemical behavior and excellent stability of the electrode system under repeated charge–discharge cycling. This is largely a consequence of the gradual buildup and interaction of ions at the electrode–electrolyte interface, facilitated by continuous cycling, that enhances interfacial compatibility and retains performance integrity. SEM micrographs of the BaCO3/GPL electrode prior to and following 1200 charge–discharge cycles reveal that the surface is intact with no cracks or delamination. This supports the high structural durability and long-term stability of the electrode under successive cycling as illustrated in Figure S3.

4. Conclusion

The rising demand for high-efficiency energy storage drives advancements in supercapacitors due to their superior cycle stability and power density. This study investigates the electrochemical performance of pristine GPL and BaCO3/GPL electrodes synthesized via a coating process on an FTO substrate. Structural and chemical characterization using XRD, FT-IR, SEM, XPS, AFM, and EDS confirms material integrity. Cyclic voltammetry (CV) analysis shows that at 0.03 V·s–1, BaCO3/GPL exhibits significantly higher capacitance than GPL: 164.524 F/g vs 59.724 F/g (positive direction) and 943.95 F/g vs 510.124 F/g (negative direction). Galvanostatic charge–discharge (GCD) results further validate this, with BaCO3/GPL achieving 669.263 F/g (negative) and 126.084 F/g (positive), compared to 93.87 F/g and 45.204 F/g for GPL. Both materials demonstrate capacitance retention after cycling: 91.17% and 90.08% of the initial capacitance in the negative and positive directions, respectively. To understand the electrolyte–electrode interaction behind this stability, XRD, FT-IR, and EIS analyses were conducted before and after cycling, confirming the robust electrochemical performance of BaCO3/GPL for high-performance energy storage.

Supplementary Material

ao5c07179_si_001.pdf (532.3KB, pdf)

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c07179.

  • Statistical analysis chart in the positive and negative directions for a set of five concentrations of BaCO3 added to GPL (Figures S1 and S2); SEM of electrode before and after cycling (Figure S3); surface and structure parameters derived from AFM characterization (Table S1); findings from the electrochemical impedance equivalent circuit analysis (Table S2); results of the electrochemical impedance equivalent circuit analysis for BaCO3/GPL electrodes across various cycles (Table S3) (PDF)

A.-M.E.: writingoriginal draft, methodology, investigation, data curation, conceptualization. E.S.: writing, investigation, supervision, data curation. A.M.G.: supervision, review. H.E.: investigation, data curation, writingreview and editing.

The authors declare no competing financial interest.

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