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. 2024 Nov 2;14:26408. doi: 10.1038/s41598-024-77252-6

Electrochemical study of an enhanced platform by electrochemical synthesis of three-dimensional polyaniline nanofibers/reduced graphene oxide thin films for diverse applications

Fares Fenniche 1,2,✉, Yasmina Khane 1,3, Djaber Aouf 4, Salim Albukhaty 5,6,✉, Fatima Zohra Nouasria 7, Makhlouf Chouireb 8, Nesrine Harfouche 9, Abdellah Henni 4, Ghassan M Sulaiman 10,✉, Majid S Jabir 10, Hamdoon A Mohammed 11, Mosleh M Abomughaid 12
PMCID: PMC11531504  PMID: 39488583

Abstract

This work reports the electrochemical fabrication of thin films comprising polyaniline nanofibers (PANI) in conjunction with graphene oxide (GO) and reduced graphene oxide (rGO) on ITO substrate, along with examining the electrochemical properties, with a focus on the influence of the substrate and electrolyte in the electrodeposition methods. The study explores the electrochemical characteristics of these thin films and establishes a flexible framework for their application in diverse sectors such as sensors, supercapacitors, and electronic devices. It analyzes the impact of the substrate and electrolyte in electrodeposition techniques. The effects were studied using techniques such as cyclic voltammetry and chronoamperometry. The fabrication process of PANI/GO and PANI/rGO thin films involved the integration of rGO within PANI via electropolymerization, conducted under sulfuric acid. GO was synthesized by modifying the well-known Hummers’ method and characterized by X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). SEM showed the diameters of the formed PANI were between 40 and 150 nm, which helped to intertwine the rGO nanosheets with PANI nanofibers to form thin films. The electrochemical behavior of the PANI/rGO thin films was examined using cyclic voltammetry (CV) and chronoamperometry in different electrolytes, including sulfuric acid (H₂SO₄) and potassium nitrate (KNO₃). The CV profiles exhibited distinct oxidation and reduction peaks, with variations in the voltammogram morphology attributed to the nature of the electrolyte and the substrate employed during the electrodeposition process. These results highlight the critical role of both the substrate and electrolyte in governing the electrochemical performance of PANI/rGO thin films. The findings from this study demonstrate a versatile approach for the fabrication of PANI/graphene-based thin films with tunable electrochemical properties, and such a strategy has great application to fabricating other thin film composites for supercapacitors or other control source frameworks requiring enhanced charge storage and electrochemical responsiveness.

Keywords: Polyaniline, Electrodeposition, Electrochemical techniques , Reduced graphene oxide, Cyclic voltammetry

Subject terms: Graphene, Electrochemistry

Introduction

Industries relying on electrochemical technologies have become widespread and highly significant in the present time, drawing considerable interest from researchers and scientists. These industries encompass various applications, including the production of sensors1, supercapacitors2, electrochromic boards3, electrochemical packaging4, batteries5, and more. Significant advancements have been made to produce highly sensitive devices and utilize cost-effective materials to replace more expensive alternatives.

Among the inexpensive materials, conducting polymers have gained extensive use in both chemical and electrochemical applications6. Polyaniline (PANI) and polypyrrole (PPy) are two of the most extensively utilized conducting polymers7–13. PANI, characterized by its strong conductivity, high stability, and ease of preparation, stands out as one of the most commonly utilized conducting polymers in these sensitive electronic devices14,15.

Protonated polyaniline (PANI), an electrochromic polymer, undergoes redox reactions and internal changes when in contact with protonic acids, resulting in modified properties such as high conductivity and color variation16. These changes and characteristics serve as a fundamental basis for producing electronic devices, whether through chemical or electrochemical methods, as they occur when a material interacts with other chemical entities, converting them into optical and electrical signals. Several of these materials have been mentioned, including metal oxides17, carbon nanotubes (CNTs)18, graphene (G)19, graphene oxide (GO)20, and reduced graphene oxide (rGO)21,22. These materials are commonly integrated into the fabrication of PANI-based devices to enhance the required platform for efficient electron transfer and to augment electrocatalytic properties.

Numerous studies23–26 have reported the synergistic interplay between polyaniline and carbon derivatives, including reduced graphene oxide (rGO), showcasing their extensive utility across various applications. Reduced graphene oxide, in particular, stands out as one of the most remarkable and widely employed materials due to its exceptional mechanical, physical, and electrical properties27,28, which contribute significantly to enhancing electron transfer in polyaniline-based platforms.

Previous studies have predominantly employed chemical methods29,30. Rather than electrochemical methods. However, the current focus among scientists is on the electrochemical synthesis of nanocomposites based on polyaniline or reduced graphene oxide due to the ease of processing and synthesis offered by electrochemical techniques31,32. The synthesis of nanocomposites in the form of thin films33 Leads to high efficiency in various applications, unlike other forms such as powders or gels. Thin films, for instance, are cost-effective and exhibit complete formation, free from the defects and drawbacks associated with chemical synthesis. Moreover, they require fewer chemical materials, further contributing to their cost-effectiveness34. NR Tanguy et al.35 Have reported the high efficiency of reduced graphene oxide based on polyaniline films concerning their application in high-capacitance supercapacitors, where they exhibit strong performance. Additionally, in another study by F Mazzara et al.36 Mentioned the exceptional sensing capabilities of these thin films. However, it is worth noting that the electrochemical synthesis of thin films remains a recent development at present, therefore, thin films have a high capacity in many applications.

In this paper, we successfully synthesized graphene oxide (GO) and reduced graphene oxide (rGO) through a modified Hummers’ method. Graphene oxide was chemically reduced using hydrazine and electrochemically reduced through cathodic scanning of PANI/GO films. The synthesized GO and rGO were characterized by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Thin films of PANI/rGO were successfully produced via the mentioned electrochemical methods. We systematically investigated the electrochemical behavior of these films by studying their electrochemical deposition on different substrates in the presence of various electrolytes. Furthermore, we examined the influence of electrolytes on these films, along with tracking their excellent performance in photo-electrochemical applications. The results demonstrated high responsiveness in this application. This comprehensive study presents the electrochemical production of thin PANI /rGO films, which can be considered promising platforms for numerous applications, including sensors, biosensors, high-capacitance super-capacitors, and high-performance batteries. Despite the extensive research on PANI/rGO composites, one area that has remained largely underexplored is the influence of different substrates and electrolytes on the electrodeposition process and the resultant thin film properties. Most existing studies have focused on optimizing the composite materials themselves, with less attention given to how substrate-electrolyte interactions during electrodeposition can influence the electrochemical behavior and stability of the films. This study aims to address this gap by systematically investigating the effects of two distinct substrates—gold electrodes and indium tin oxide (ITO)—in combination with various electrolytes, such as sulfuric acid (H₂SO₄) and potassium nitrate (KNO₃), during the electrodeposition of PANI/rGO thin films. By exploring these under-researched variables, we seek to provide a deeper understanding of how the substrate and electrolyte choices impact the electrochemical performance of these composites, which could lead to better-tailored materials for specific electrochemical applications. Furthermore, the comprehensive approach adopted in this work, which examines substrate and electrolyte effects, sets it apart from previous studies primarily focused on single factors or general electrochemical behavior. Exploring the interplay between electrodeposition parameters and thin film characteristics offers new insights that could significantly enhance the design and optimization of PANI/rGO composites for practical applications in energy storage and electronic devices.

Experimental

Chemicals

All analytical reagents and aqueous solutions used were of high purity grades, with distilled (DI) water. Graphite (size < 150 μm), aniline (C6H5NH2) (99%), sulfuric acid (H2SO4) (96%), potassium permanganate (KMnO4), hydrazine hydrate (N2H4), hydrochloric acid (HCl) (37%), hydrogen peroxide (H2O2) (30%), acetone (C3H6O), and ethanol (C2H5OH) were purchased from Sigma-Aldrich. KCl (0.1 M) solution was prepared in the laboratory.

Chemical synthesis of GO and rGO

The initial synthesis of GO was accomplished utilizing the modified Hummer procedure37. Subsequently, a chemical reduction process was employed to obtain reduced graphene oxide (rGO), which consists of few-layer graphene. The synthesis steps for rGO and GO are illustrated in Figs. 1 and 2.

Fig. 1.

Fig. 1

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A scheme showing GO synthesis steps.

Fig. 2.

Fig. 2

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A scheme showing rGO synthesis steps.

After the synthesis of GO, rGO is obtained through chemical reduction using hydrazine (in this part, rGO was obtained through chemical reduction, while it can also be obtained through electrochemical reduction, as we will mention in the electrochemical study of thin films).

Electrochemical synthesis of PANI/GO and PANI/rGO thin films

Electrochemical measurements were conducted at ambient temperature using a potentiostat/galvanostat Autolab PGSTAT 204. A three-electrode electrochemical cell with multiple necks was employed for both deposition and measurement processes. The ITO substrates served as the working electrode, while the saturated calomel electrode (SCE) and a platinum plate functioned as the reference and counter electrodes, respectively. Before preparing thin films, the ITO-coated glass substrates (dimensions: 20 mm × 10 mm × 1 μm) were meticulously cleaned using acetone and deionized water in an ultrasonic bath. The PANI/GO and PANI/rGO films are formed on ITO substrates through electropolymerization/electrodeposition in a solution containing aniline dissolved in sulfuric acid and graphene oxide (GO) or reduced graphene oxide (rGO), using the cyclic voltammetry technique by performing multiple scans and applying specific potentials concerning the SCE reference. After the formation of these thin films, they are gently rinsed with distilled water to remove any residual sulfuric acid and then left to dry for 12 h at room temperature.

Results and discussion

Characterization of GO and rGO by XRD and FTIR

Figure 3 illustrates the X-ray diffraction (XRD) patterns of graphene oxide (GO) produced using the modified Hummers synthesis technique and the reduced graphene oxide (rGO) produced by chemically reducing GO. The XRD study reveals the differences in patterns formed by graphene oxide (GO) and reduced graphene oxide (rGO). A significant peak at 10.4° corresponds to the (001) plane with noticeable interlayer spacing, indicating the successful oxidation of graphite into graphene oxide (GO)38. In their study, SN Alam et al.39 attribute the increase in interlayer spacing in graphene oxide (GO) to the incorporation of various functional groups during the oxidation of pure graphite. The emergence of a clearly defined peak at 25° in reduced graphene oxide (rGO) is ascribed to the diffraction plane (002), indicating the existence of interlayer separation along the specified axis. A tiny diffraction peak detected suggests the disturbance of the periodic structure present in graphene oxide (GO), indicating the effective creation of decreased graphene nanosheets. However, the tightly packed structures of these decreased graphene nanosheets result in a wide peak in X-ray diffraction (XRD)40.

Fig. 3.

Fig. 3

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X-ray diffraction pattern of GO and rGO.

Figure 4 corresponds to the Fourier-transform infrared spectroscopy (FTIR) spectra of both graphene oxide (GO) and reduced graphene oxide (rGO). While notable peaks were observed for both materials, graphene oxide exhibited several absorption bands that are indicative of oxygen-containing functional groups, thereby affirming the success of the graphite oxidation process. A broad peak spanning the range between 3000 and 3500 cm− 1 emerged, which can be ascribed to the OH stretching vibrations arising from hydroxyl groups and water molecules. Additionally, the FTIR bands observed at 2927 cm− 1 and 2849 cm− 1 are attributed to the asymmetric and symmetric stretching of CH2 in GO41. The GO spectrum also manifests bands corresponding to C-O at 1048 cm− 1, C-O-C at 1223 cm− 1, and C = O functionalities present in carboxylic acid and carbonyl moieties. Notably, these functional groups are predominantly localized along the sheet edges but are also present on the basal plane of graphene layers at 1725 cm− 142.

Fig. 4.

Fig. 4

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FTIR spectra of GO and rGO.

In the spectrum of reduced graphene oxide (rGO), discernible peaks are observed at 1160 cm− 1 (C–O-H) and 1550 cm− 1 (C = C), providing compelling evidence of the successful reduction of graphene oxide (GO) during the process. The subtle upward shifts of these two bands to higher energy levels indicate the restoration of the π-conjugated network. Moreover, a notable observation is a significant decrease in the intensities of absorption bands associated with oxygen-containing functional groups in rGO42. Notably, the disappearance of C = O carbonyl bands results in the persistence of a broad absorption band centered at 3400 cm− 1 in the rGO spectrum, which is attributed to the remaining O-H groups in the reduced graphene oxide structure.

Synthesis of PANI/GO and PANI/rGO thin films

Through the synthesis procedure described in Fig. 5, thin films of PANI/GO and PANI/rGO were produced using the electrodeposition method. Prior to commencing the thin film synthesis, ITO substrates measuring 20 mm x 10 mm x 1 m were thoroughly cleaned in an ultrasonic bath using a series of solvents composed of acetone, ethanol, and distilled water.

Fig. 5.

Fig. 5

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Schematic representation of the preparation method for PANI/GO and PANI/rGO thin films.

Electrodeposition of PANI/GO thin films

Thin films are synthesized on ITO substrates by electropolymerization/electrodeposition in a solution containing aniline dissolved in sulfuric acid and graphene oxide. This is achieved using the cyclic voltammetry technique, where specific potentials are applied relative to the SCE reference at a predetermined scan rate. Once these thin films have been formed, they are delicately washed with distilled water to eliminate any remaining sulfuric acid and then subjected to a 12-hour drying process. GO has oxygen-based groups that can interact with nitrogen atoms of PANI through hydrogen bonding -OH.N and -O.H-N41. Therefore, PANI could more easily intercalate between the graphene oxide layers.

Electrodeposition by cyclic voltammetry

PANI/GO thin films were synthesized electrochemically on an ITO substrate utilizing cyclic voltammetry (CV) methods. The development of these films was investigated in the presence of a solution including aniline, GO, and sulfuric acid.

To facilitate the electropolymerization process for the production of PANI/GO, the ITO substrates were submerged in a 1.0 M sulfuric acid solution that included 0.5 M aniline and 0.5 mg/mL of graphene oxide (GO). The PANI/GO electropolymerization was performed using cyclic voltammetry, over a potential range of -0.6 to 1.2 V at a scan rate of 50 mV/s, over 15 cycles. Next, the PANI/GO thin films were meticulously washed with distilled water to remove any remaining sulfuric acid contaminants.

Figure 6a and b show the cyclic voltammograms obtained from the ITO substrate submerged in an H2SO4 solution including aniline and graphene oxide. These voltammograms were obtained to support the electropolymerization procedure used for the production of PANI/GO thin films. An informative characteristic of the polymer development rate in electropolymerization processes is the gradual increase of peak current density or charge density in the voltammograms, as a function of the number of scans. Figure 6a displays the observed cumulative charge associated with the anodic peaks in the voltammetric trace, which is expressed as a function of the scan number. The cyclic voltammetry used in the production of PANI/GO thin films on the ITO substrate is shown in Fig. 6a. This figure illustrates the evolution of oxidation and reduction peaks during the scanning process, with oxidative peaks represented as a1 and a2, and reductive peaks shown as b1 and b2. The consistent increase in current density strongly supports the accumulation of PANI on the surface of ITO in combination with GO nanosheets. Moreover, the use of scanning enables the detection of changes in film color, therefore facilitating the identification of transitions between different oxidation states of PANI during the deposition process.

Fig. 6.

Fig. 6

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Voltammograms recorded for (a) PANI/GO thin film. (b) the 4 cycles of voltammograms (1st, 2nd, 5th and 9th ).

The voltammograms exhibit the same redox peaks that were seen during the development of PANI films. These peaks begin at 0.2 V and occur throughout the initiation of PANI oligomer formation, and then distinctly appear at 0.3 V, 0.6 V, and 0.9 V during the first cycle. Furthermore, these peaks increase with the number of cycles and current density. One can also detect a rise in current density in comparison to the earlier ITO/PANI films43. The redox peak pairs are associated with the oxidative and reductive processes of PANI molecules, namely from their semiconducting state (leucoemeraldine) to their conducting state (emeraldine) and from emeraldine to their fully oxidized state (pernigraniline) respectively44. Figure 6b displays the voltammograms of PANI/GO thin film development obtained from extended potential scans, specifically highlighting a set number of cycles to clearly demonstrate the redox peaks. The voltage voltammogram for PANI/GO film growth has a distinct shape compared to the ITO/PANI film in the previous work43. The redox peaks stay consistent during continuous scanning, and this difference is ascribed to the incorporation of GO nanosheets with polymer fibers to create a homogeneous thin film. A unique irreversible anodic current peak labeled as “1” (first cycle) is found during the first positive potential scan of aniline, at about 0.95 V. Furthermore, the intensity of peak “1” gradually decreases until it ultimately vanishes. Repeated voltammogram cycles, obtained by continuous scanning, show a progressive increase in current intensity with each subsequent cycle, suggesting the ongoing and consistent development of the polymer layer in conjunction with graphene oxide (GO). The redox peaks seen at 2, 2’, 3, 3’, and 4, 4’ may be ascribed to the conversion of polyaniline (PANI) into its many oxidation and reduction states. With an increasing number of voltammogram cycles, the substrate becomes saturated with film particles and GO nanosheets are deposited in combination with PANI, resulting in the fabrication of the PANI/GO composite film.

Electrodeposition by chronoamperometry

The synthesis of PANI/GO thin films is achieved by the chronoamperometry method, where a constant applied potential is maintained for certain duration, as seen in Fig. 7. Figure 7 displays the i(t) transitions that correlate to the growth rate of the PANI/GO film at the first moments measured at 1.0 V vs. the electrochemical conductivity slope (ECS). This image illustrates that the form of the curves produced is mostly same, thus independent of the concentration of graphene oxide (GO) in the electrolyte and the duration of film deposition. Nevertheless, there are noticeable distinctions, namely with the manifestation of minimum and maximum current densities in absolute terms and their corresponding time points of occurrence.

Fig. 7.

Fig. 7

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Evolution of the chronoamperometry (CA) curve linked to the formation of PANI/GO under the imposed potential of 1.0 V vs. SCE.

The curves acquired are shown in Fig. 7, depicting the immediate and gradual three-dimensional thickness development of PANI/GO films. The gradual rise in current density following the first instantaneous nucleation spike may be attributed to the subsequent development of film particles, which leads to a progressive increase in current density over time. Subsequently, PANI nuclei are generated on the surface of the ITO, and a GO nanosheet is fused with these nuclei, leading to an enlarged contact surface area between the electrode and electrolyte. This, in turn, enhances the flow of electric current at this interface.

Instantaneous nucleation in electrodeposition refers to a procedure in which the number of nuclei stays constant throughout the deposition process, and growth occurs only at the original nucleation sites, without the production of new nuclei. Therefore, this kind of nucleation results in the formation of nuclei with greater radii, which gives rise to a coarse surface morphology. In contrast, progressive nucleation refers to the ongoing production of new nuclei throughout the process of electrodeposition. Consequently, growth occurs on both newly generated and originally assembled nuclei, resulting in a surface structure that is generally flatter. Regarding growth properties, 3D growth is a mode in which the rate of development of nuclei is consistent in both the parallel and perpendicular directions to the surface of the electrode. In contrast, during 2D development, the nuclei demonstrate a faster lateral expansion (i.e., in the direction parallel to the electrode) until they come into contact and overlap with adjacent nuclei45.

Electrochemical study of PANI/GO thin films

Effect of the electrolyte

Figure 8 shows the voltammograms recorded for PANI/GO on the ITO substrate at a scan rate of 50 mV/s for 25 cycles. The electrodeposition was performed in a solution containing potassium nitrate (KNO3), aniline, and GO. This electrolyte was prepared by dissolving 0.25 M aniline in 0.1 M H2SO4 adding 5 mL of KNO3 solution as the first solution (1), and then preparing a second solution (2) of GO (1.25 mg/mL) with KNO3 (1.5 M). The two solutions (1) and (2) were mixed in a 1:1 ratio to obtain the final electrolyte used in the electrodeposition.

Fig. 8.

Fig. 8

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Voltammograms recorded of PANI/GO on ITO substrate for 25 cycles at − 0.56 and 1.6 V in an aqueous solution of KNO3 (1.5 M) containing 0.25/1.25 M of aniline and GO at a scan rate 50 mV/s.

The voltammogram of the figure shows distinct oxidation and reduction peaks. Red arrows indicate an increase in these peaks as the number of cycles during scanning increases. The electrolyte significantly influences the shape of the voltammogram while preserving the redox peaks, which indicate the formation of a PANI film coupled with GO layers. This observation aligns with the findings reported in the literature46,47. With each scanning cycle, the size of the voltammogram grows, emphasizing the oxidation peaks that originated at 0.4 V and reached their highest point at 0.8 V. This process maintains the same pattern of thin film development on the substrate, eventually leading to the production of a coherent and defect-free thin film.

Effect of the substrate

To investigate the effect of the substrate on the growth of PANI/GO thin films, we deposited them on the gold electrode in the presence of a standard electrolyte containing sulfuric acid, while on the other side; an electrolyte containing KNO3 was used. Figure 6 shows two voltammograms, where the first and second figures (a and b) represent the evolution of PANI/GO film electrodeposition on the gold electrode in the electrolyte without KNO3, and the third figure (c) represents the evolution of PANI/GO film electrodeposition on the gold electrode in the electrolyte with the presence of KNO3.

In Fig. 9a, the first cycle of the voltammogram at 1.0 V represents the initial nucleation for the formation of the PANI/GO nanocomposite, followed by subsequent cycles that exhibit normal redox peaks indicating the electropolymerization process of aniline. These peaks maintain the same shape and size until the last cycle, as shown in Fig. 9b, which demonstrates a good formation of oxidation and reduction peaks, with a clear difference between the first and last cycles. It is worth noting that the shape of the voltammogram on the gold electrode is completely different from the voltammogram on the ITO substrate, along with a significant difference in current density. This difference is attributed to the variation in surface properties between the gold electrode and the ITO substrate.

Fig. 9.

Fig. 9

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Voltammograms recorded of PANI/GO (a) on the gold electrode at a scan rate of 50 mV/s for 10 cycles, (b) the first and the last PANI/GO voltammogram cycle, and (c) voltammograms in KNO3 electrolyte at a scan rate 100 mV/s for 15 cycles.

On the other hand, on the same electrode, the PANI/GO film is electrodeposited in the presence of an electrolyte containing KNO3 (Fig. 9c), with the number of cycles increased to 15 instead of 10 cycles. It can be observed that the shape of the voltammogram is quite similar to that of the voltammogram in Fig. 9a, from the first cycle to the redox peaks. The increase in the number of cycles can be explained by stating that the growth of thin films in the electrolyte containing KNO3 is somewhat slower compared to its absence in the first electrolyte. Additionally, when comparing the gold electrode to the ITO substrate, it is evident that the film growth on the ITO substrate is faster, which is attributed to the properties of the substrate’s surface.

Electrochemical reduction of PANI/GO

To investigate the electrochemical conversion of graphene oxide (GO) into reduced graphene oxide (rGO), voltammograms were obtained for cathodic scanning of PANI/GO thin films placed on an ITO substrate (Fig. 10a) and a gold electrode (Fig. 10b) within a potential range of 0.0 to -1.2 V under inert atmosphere.

Fig. 10.

Fig. 10

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Voltammograms recorded of PANI/GO deposited on ITO substrate (a) and gold electrode (b) in a buffer solution (PBS) saturated with nitrogen gas at a scanning speed of 50 mV/s.

Upon comparing the early potential cycles of Fig. 10a and b, it becomes apparent that the reduction current is greater in these first cycles, with only minor variations seen after the third cycle. This observation suggests that the reduction reaction is progressing accurately and efficiently. Thus, the electrochemical reduction of graphene oxide (GO) in polyaniline/graphene oxide (PANI/GO) films takes place rapidly and irreversibly49.

Both figures of the voltammogram exhibit a cathodic wave ranging from − 0.8 to -0.9 V. Subsequently, the waves gradually decrease as the number of scanning cycles increases. An electrochemical reduction of graphene oxide (GO) yields reduced graphene oxide (rGO), which exhibits a significant enhancement in electrical conductivity. This enhancement is shown by measurements of electrical conductivity, which suggest an increased capacity of charge carriers to migrate50. The observed decline in cathodic waves as the number of scans increases may be ascribed to the reduction of electrochemically active oxygen-containing groups present on the surface of graphene oxide (GO). Further evidence suggests that the current density at the ITO substrate surpasses that at the gold electrode, therefore underscoring the significance of the surface.

Electrodeposition of PANI/rGO thin films

Figure 11 corresponds to the recorded voltammograms of PANI/rGO thin films synthesized by the cyclic voltammetry method on the ITO substrate for 10 cycles, ranging from − 0.56 to 1.2 V vs. SCE, with a scan rate of 50 mV/s to promote the growth of nanocomposite.

Fig. 11.

Fig. 11

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Voltammograms recorded of (a) PANI/rGO thin film on ITO substrate for 10 cycles at -0.56 and 1.2 V at a scan rate of 50 mV/s. (b) the 2 cycles of voltammograms (1st, and 10th ).

Figure 11a shows the biphasic voltammograms of ITO at the onset of PANI/rGO development. Following ion exchange across 10 consecutive scans within the range of possibilities, reduced graphene oxide (rGO) was produced in situ using PANI on the ITO substrate. By virtue of the transition between quinone/hydroquinone groups in reduced graphene oxide (rGO), a characteristic feature of carbon-based materials, it displays two sets of redox peaks that consistently increase with each cycle51. The presence of functional groups in reduced graphene oxide (rGO) allows aniline monomers to attract and attach to rGO nanosheets. Furthermore, reduced graphene oxide (rGO) nanosheets exhibit high conductivity, resulting in a significant enhancement in current in voltammogram cycles and current density compared to the previously used PANI and PANI/GO thin films.

The cyclic voltammograms profile in Fig. 11b reveals that the oxidation peak of PANI/rGO occurs at 0.3 V and 0.5 V versus SCE. The reduction peak is measured at 0.05 V and 0.3 V versus SCE for the first and last cycles, respectively. The significant difference between the first and last cycles indicates that the PANI/rGO film development on the ITO surface is more electroactive compared to earlier voltammograms. This confirms the film’s exceptional conductivity and improved film formation. While PANI has notable conductivity, the inclusion of reduced graphene oxide (rGO) nanosheets enhances the contact between PANI and the electrolyte, leading to a higher surface area that is responsive to electrochemical reactions. When a PANI/rGO film with a significant surface area is produced, the enhancement results in changes in the voltammogram profiles, which suggest enhanced charge transfer mechanisms52.

SEM was used to characterize the morphologies of rGO, PANI, and PANI/rGO thin films, as shown in Fig. 12. The SEM images in Fig. 12a display the surface appearance of rGO and confirm the deposition of rGO nanosheets on the ITO substrate. The cluster design of reduced graphene oxide (rGO) results in a three-dimensional structure characterized by wrinkled layers that are distributed randomly. The average thickness of these layers is few nanometers, which greatly enhances the effective surface area of the thin film. This phenomenon may also be ascribed to the chemical reduction of graphene oxide (GO) to produce reduced graphene oxide (rGO) by anhydrazine hydrate37.

Fig. 12.

Fig. 12

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SEM images of thin films (a) rGO, (b) PANI, (c) PANI/rGO on ITO substrate.

In contrast, Fig. 12b depicts the surface morphology of the PANI thin film, including a network of interconnected nanofibers and exhibiting a uniform and well-structured polymer chain arrangement. The electron transport at the electrolyte-thin film interface is facilitated by this network53,54. The diameter of the PANI is around 100 nm, and its length is consistently around 1 μm. Consequently, this leads to a more consistent and homogeneous microstructure.

The surface morphology of the PANI/rGO thin film and an expanded view of this film are shown in Fig. 12c. A remarkable observation is that the layers of reduced graphene oxide (rGO), which were covered with PANI nanofibers, have a highly organized and evenly distributed structure. When seen under magnification, it is evident that PANI nanofibers completely envelop the rGO layers and intertwine with them, creating interactive connections. The practical melting point of a material provides a favorable environment for electron transport, thereby enhancing the electrical responsiveness55,56.

Photoelectrochemical performance of PANI/rGO thin film

The assessment of photoelectric performance is often conducted by examining the capacity to absorb light, since this directly and effectively impacts the optical holes and free electrons. The photocurrent-time characteristics of PANI and PANI/rGO thin films were investigated in a 0.1 M KCl solution under intermittent light, with progressively higher applied potential values used. The relationship between the applied voltage and the photocurrent for the synthesised PANI/rGO hybrids is diagrammed in Fig. 13. Transient exposure to light directly stimulates the generation of electron-hole pairs inside the semiconductors. To investigate the photocurrent characteristics of these thin films, we used several applied potential ranges. While the current density remains constant and very insignificant in the absence of light, it exhibits a substantial rise with a rectangular vertical response when exposed to light.

Fig. 13.

Fig. 13

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Photocurrent response curves of PANI and PANI/rGO films.

Rapid and uniform photocurrent responses were detected for all instances of light activation and deactivation for all electrodes, with positive values elucidating the properties of p-type and n-type semiconductors. This phenomenon may be ascribed to the existence of charge carriers that undergo transfer from the valence band (VB) to the conduction band (CB) when subjected to UV light stimulation. The PANI electrode exhibits a photocurrent of 0.47 mA/cm2 at a voltage of only 1.5 V. This phenomenon may be ascribed to the recombination of electron-hole pairs inside the electrode and the sluggish transit of electric charge. As the accumulation of electrons and holes occurs, leading to the recombination of charges under continuous illumination, the generation of photo-excited electrons counteracts the internal electric field57. Evidence indicates that the photocurrent intensity of the PANI/rGO electrodes was much greater than that of the pure PANI electrodes. Following modification with reduced graphene oxide (rGO), the PANI/rGO photoelectrode demonstrated increased photocurrent (around 0.53 mA/cm2 at 1.8 V) and attained satisfactory values. The excellent electrical conductivity of reduced graphene oxide (rGO) enables efficient electron transport and inhibits electron-hole recombination, leading to a much higher photocurrent and faster photoreaction58. A study by A. Henni et al.37 suggests that rGO might have expanded the bandgap of PANI/rGO by enhancing the abundance of carriers in the valence band. Furthermore, it has been measured that the photocurrent intensity of PANI/rGO electrodes exhibits a significant rise as the potential rises (around 0.57 mA/cm2 at 2.4 V).

Conclusion

This study presents the synthesis of thin films of PANI/GO and PANI/rGO nanocomposites on ITO substrates by electrochemical methods. The electrodeposition of these films was carried out using the cyclic voltammetry approach. The integrated reduced graphene oxide (rGO) networks containing polyaniline were obtained by chemically reducing graphene oxide (GO) using hydrazine and electrochemically using cathodic scanning under inert gas. Due to their importance in many applications, we focused primarily on PANI/rGO films.

Using scanning electron microscopy (SEM), surface inspection of the oxide layers showed that the films produced are composed of fused polyaniline nanofiber networks that are embedded with reduced graphene oxide nanosheets. Furthermore, we performed an extensive electrochemical investigation of these thin films, taking into account variables such as the characteristics of the substrate and the impact of electrolytes during the process of electrodeposition. In addition, the PANI/rGO films demonstrate exceptional performance in photoelectrochemical applications, using improved light absorption and effective charge separation characteristics. Polyaniline fibers and reduced graphene oxide nanosheets may be combined synergistically to provide a versatile platform for many applications, including energy storage in supercapacitors and the production of sensors and biosensors. As shown in the literature, this phenomenon is ascribed to the rapid electron transfer rate in this nanocomposite.

Acknowledgements

The authors are thankful to the Deanship of Graduate Studies and Scientific Research at the University of Bisha for supporting this work through the Fast-Track Research Support Program.

Author contributions

Conceptualization and methodology, Fares Fenniche., Djaber Aouf., Fatima Zohra Nouasria., Abdellah Henni., and Yasmina Khane; formal analysis, Makhlouf Chouireb., and Nesrine Harfouche.; investigation and data curation Salim Albukhaty.,and Ghassan M. Sulaiman.; validation Majid S. Jabir., Hamdoon A. Mohammed, and Mosleh M. Abomughaid.; Visualization, original draft preparation, Fares Fenniche., Yasmina Khane., and Djaber Aouf.; writing—review and editing, Salim Albukhaty., Ghassan M. Sulaiman., Fatima Zohra Nouasria, and Yasmina Khane.; supervision, Fares Fenniche., and Salim Albukhaty.; project administration, Yasmina Khane., and Fares Fenniche. All authors gave approval to the final version of the manuscript.

Funding

The authors state no funding is involved.

Data availability

Data availabilityThe datasets generated and/or analysed during the current study are available upon reasonable request from the corresponding author (Fares Fenniche).

Declarations

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Fares Fenniche, Email: fennichefares@yahoo.fr.

Salim Albukhaty, Email: albukhaty.salim@uomisan.edu.iq, Email: albukhaty.salim@uomanara.edu.iq.

Ghassan M. Sulaiman, Email: ghassan.m.sulaiman@uotechnology.edu.iq

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

Data availabilityThe datasets generated and/or analysed during the current study are available upon reasonable request from the corresponding author (Fares Fenniche).

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