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Article

Interfacial Engineering of V2O5 via Conductive Polyaniline for Accelerated Hydrogen Evolution Reaction

by
Chaitany Jayprakash Raorane
* and
Seong-Cheol Kim
School of Chemical Engineering, Yeungnam University, Gyeongsan 38541, Gyeongsanbuk-Do, Republic of Korea
*
Author to whom correspondence should be addressed.
Polymers 2026, 18(11), 1408; https://doi.org/10.3390/polym18111408
Submission received: 13 May 2026 / Revised: 4 June 2026 / Accepted: 4 June 2026 / Published: 5 June 2026
(This article belongs to the Special Issue Functional Polymers for Catalysts)
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Abstract

The hydrogen evolution reaction (HER) plays a pivotal role in electrochemical water splitting for sustainable hydrogen production. However, its practical implementation is hindered by sluggish kinetics and the reliance on costly noble-metal catalysts. In this work, a conductive polymer-inorganic hybrid electrode based on vanadium pentoxide (V2O5) and polyaniline (PANI) is rationally designed and fabricated on carbon cloth via a combined hydrothermal synthesis and electropolymerization strategy. Initially, hierarchical V2O5 nanoflowers were synthesized, followed by controlled PANI deposition through cyclic voltammetry at varying cycle numbers to tailor the interfacial architecture and electronic properties. Morphological and structural analyses reveal the formation of well-defined V2O5 nanoflowers uniformly decorated with PANI nanorods, establishing an interconnected conductive network. Among the prepared samples, the optimized V2O5-PANI-2 electrode exhibits superior interfacial integration and structural homogeneity. Electrochemical evaluation in 1.0 M KOH demonstrates that V2O5-PANI-2 achieves a low overpotential of 79.9 mV at −10 mA cm−2, accompanied by a small Tafel slope of 46.6 mV dec−1, indicating accelerated HER kinetics. Furthermore, the electrode shows reduced charge-transfer resistance and an enhanced electrochemically active surface area (ECSA), facilitating efficient charge transport and abundant active site exposure. The catalyst also delivers excellent durability, maintaining stable performance over 5000 CV cycles and prolonged 24 h operation. The enhanced HER performance is attributed to the synergistic interaction between V2O5 and the conductive PANI matrix, which promotes charge redistribution, improves electrical conductivity, and optimizes the adsorption/desorption energetics of hydrogen intermediates.

1. Introduction

The progress of clean and renewable energy resources is increasingly vital because of the rising global energy demands and the urgent requirement to reduce greenhouse gas emissions [1,2]. Hydrogen’s high energy density and the fact that its combustion generates only water as a by-product render it an effective energy carrier [3]. Electrocatalytic water splitting is recognized for its effectiveness and eco-friendliness among the various methods of hydrogen production. Nonetheless, the inadequate kinetics of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) present significant challenges to the widespread application of this method [4]. High-efficiency electrocatalysts can decrease energy usage in water electrolysis by enhancing reaction kinetics and minimizing the energy barrier [5]. At present, catalysts from the platinum (Pt) group, especially Pt/C and IrO2/RuO2, are mainly utilized in the production of hydrogen on an industrial scale. Nonetheless, the significant expense and restricted accessibility present considerable obstacles to expanding these technologies [6,7]. Consequently, the advancement of electrocatalysts based on transition metals is essential, since these substances not only exhibit potential performance but are also more cost-effective and plentiful for practical applications [8]. Thus, numerous research efforts have concentrated on the strategic design of various metal oxides to discover ideal candidates for enhancing HER performance.
Vanadium pentoxide (V2O5) has become a potential electrode material for various electrochemical applications due to its high activity and cost-effectiveness [9]. Significantly, V2O5 provides substantial benefits in electrochemical water splitting because of its natural structural stability and capacity to display various oxidation states, mainly V5+ and V4+, promoting effective redox reactions [10,11]. Additionally, V2O5 can facilitate HER kinetics by promoting the adsorption and desorption of hydrogen intermediates through its multivalent redox behavior and abundant surface V=O active sites [12,13]. Multiple synthesis approaches have been created to produce high-quality V2O5 nanostructures, such as hydrothermal routes [14], chemical vapor deposition techniques [15], spray pyrolysis methods [16], electrospinning techniques [17], and sol–gel route techniques [18]. Among these, hydrothermal synthesis is often favored because of it is easy to perform, affordable, and allows for superior control over morphology and crystallinity. In spite of these benefits, the direct application of bare V2O5 as an HER electrocatalyst typically shows restricted performance due to its low inherent electrical conductivity, inadequate electrochemically active sites, slow reaction kinetics, and quick charge recombination [19,20,21]. These constraints considerably impede effective electron flow and catalytic performance during HER. To address these limitations and improve the electrocatalytic efficiency of V2O5, different modification approaches have been investigated, including pairing with transition metal oxides/chalcogenides [22], combining with carbon-based materials [23], and conductive polymers [24]. For instance, Zn-doped vanadium oxide (Zn0.4V1.6O5) was developed to investigate the synergistic effect of transition-metal doping and oxygen vacancies, exhibiting an overpotential of 194 mV at a current density of 10 mA cm−2 in alkaline media [25]. In another study, a NiS2@V2O5/VS2 ternary heterojunction electrocatalyst was reported, delivering an overpotential of 216 mV at 10 mA cm−2, where the heterointerface played a crucial role in facilitating electron transport and catalytic activity [26]. Furthermore, a polypyrrole/V2O5/MnO2 hybrid electrocatalyst exhibited an HER overpotential of 192 mV at 10 mA cm−2, demonstrating the effectiveness of hybrid structure engineering for enhancing catalytic performance [24]. A carbon-dot-decorated silver-doped vanadium oxide (Ag/V2O5@C) demonstrated enhanced HER performance, requiring a low overpotential of 126 mV to achieve the same current density, owing to improved conductivity and charge-transfer characteristics [27].
Conductive polymers (CPs) have become highly effective supportive materials for a range of electrochemical energy conversion and storage applications [28,29,30]. Among the various conductive polymers, polyaniline (PANI) has garnered substantial interest because of its remarkable physicochemical characteristics, including straightforward synthesis, exceptional stability against environmental and chemical factors, high electrical conductivity, extensive surface area, minimal pore volume, and the utilization of inexpensive precursors. These benefits position PANI as one of the most promising materials for cutting-edge electrochemical systems [31,32]. Owing to these distinct features, PANI has been extensively applied in numerous technological fields, such as organic corrosion-resistant coatings [33], fuel cells [34], membranes [35], water splitting [36], and supercapacitors [32]. PANI is commonly used as a support material for electrocatalysts in devices related to electrochemical energy storage and conversion, including batteries, fuel cells, water splitting equipment and supercapacitors. Its simple preparation, high conductivity, affordable monomer source, and exceptional electrochemical stability greatly improve charge transfer, approachability of active sites, and overall performance of the device [31]. Recent studies have demonstrated that conductive PANI-based composite electrocatalysts exhibit promising HER activity in alkaline media. For instance, to improve the efficiency of electrochemical water splitting, a NiMnO3/PANI composite synthesized through a hydrothermal method exhibited an overpotential of 188 mV at a current density of −10 mA−2 [37]. Similarly, a NiFe2O4/PANI nanocomposite synthesized through a hydrothermal method achieved a low overpotential of 161 mV at a current density of −10 mA cm−2 [38]. In another study, PANI-coated nickel-cobalt phosphide nanowire arrays grown on nickel foam (NiCoP@PANI) exhibited excellent HER performance, requiring an overpotential of only 80.6 mV to deliver 10 mA cm−2 in 1.0 M KOH electrolyte [39]. Furthermore, a cobalt manganese oxide/polyaniline (CoMnO3/PANI) composite prepared via a hydrothermal route demonstrated an overpotential of 185 mV at 10 mA−2 [40].
In this work, a V2O5-PANI composite electrode was successfully developed on carbon cloth for enhanced HER in alkaline medium. Pristine V2O5 nanoflower structures were first synthesized through a hydrothermal method, followed by the electropolymerization of PANI with controlled deposition cycles to optimize the interfacial structure and catalytic performance. The conductive PANI layer was introduced to improve electrical conductivity, increase active site accessibility, and accelerate charge transfer kinetics. Among the prepared samples, the optimized V2O5-PANI-2 electrode exhibited superior HER activity with low overpotential, a small Tafel slope, reduced charge transfer resistance, and outstanding long-term stability.

2. Experimental Section

2.1. Chemicals

Ammonium metavanadate (NH4VO3 ≥ 99.0%) was acquired from Sigma-Aldrich, St. Louis, MO, USA. Anhydrous oxalic acid (C2H2O4, 98%) was obtained from Alfa Aesar, Gangnam-gu, Seoul, Republic of Korea. Aniline (C6H5NH2, 99.0%) and potassium hydroxide (KOH ≥ 85.0%) were provided by DaeJung Chemicals & Metals Co., Siheung-si, Republic of Korea. Sulfuric acid (H2SO4, ~95%) and hydrochloric acid (HCl, extra pure) was purchased from Duksan Reagents, Ansan-si, Republic of Korea. High-purity carbon cloth (CC), employed as the conductive substrate and current collector for electrode fabrication, was procured from NARA Cell-Tech Corporation, Seoul, Republic of Korea. All chemicals were of analytical grade and were used directly without any supplementary purification. Deionized (DI) water was used throughout all synthesis procedures and electrochemical experiments to ensure the consistency and purity of the reaction environment.

2.2. Synthesis of V2O5 and V2O5-PANI

Pristine V2O5 was directly synthesized on carbon cloth through a hydrothermal approach followed by thermal annealing. Initially, 10 mM of NH4VO3 was dissolved in 30 mL of ethanol under ultrasonication for 10 min to attain a homogeneous precursor solution. Subsequently, 3 mM of C2H2O4 was introduced into the solution to adjust the pH toward a mildly acidic condition and to facilitate precursor complexation. The resulting combination was again ultrasonicated for 10 min to ensure complete dissolution and uniform dispersion, followed by magnetic stirring for 30 min to achieve a stable reaction medium. The prepared precursor solution was then moved into a 50 mL Teflon-lined stainless-steel autoclave. Pre-cleaned carbon cloth, serving as the conductive substrate and current collector, was vertically immersed in the solution. The hydrothermal reaction was carried out at 180 °C for 24 h to promote the in situ growth of V2O5 nanostructures on the carbon cloth surface. After naturally cooling to room temperature, the obtained electrode was carefully washed with DI water to remove loosely attached particles and residual precursors, followed by drying at 70 °C for 8 h. The as-prepared sample was further annealed in air at 300 °C for 2 h.
The synthesized V2O5 electrode was subsequently employed as the working electrode for the direct electropolymerization of polyaniline (PANI). The electrolyte for electropolymerization was prepared by adding 0.93 mL of aniline monomer into an aqueous acidic medium containing the required amount of H2SO4. The solution was continuously stirred until complete dispersion of the monomer was achieved, ensuring a uniform polymerization environment. Electrodeposition of PANI was performed using cyclic voltammetry (CV) in the potential window of 0 to 0.95 V at a scan rate of 50 mV s−1. Different PANI loadings were controlled by varying the number of CV deposition cycles, specifically 5, 10, and 15 cycles, to ensure uniform film growth and optimized surface coverage. The resulting electrodes were designated as V2O5-PANI-1, V2O5-PANI-2, and V2O5-PANI-3, respectively, which correspond to increasing PANI deposition levels. After electropolymerization, the deposited electrodes were thoroughly rinsed with DI water. The electrodes were then dried at 70 °C for 10 h. A schematic illustration of the overall hydrothermal synthesis and subsequent PANI electrodeposition process is presented in Figure 1.

2.3. Material Characterization

The crystallographic structure and phase conformation of the prepared materials were examined using powder X-ray diffraction (XRD) with an X’Pert Pro diffractometer (PANalytical, Almelo, The Netherlands) employing Cu Kα radiation (λ = 1.5418 Å). Surface chemical composition, elemental valence states, and interfacial bonding characteristics were investigated by X-ray photoelectron spectroscopy (XPS) using a Thermo Scientific K-Alpha system (Cheshire, UK analysis system). The surface architecture and morphological characteristics of the electrodes were examined using field-emission scanning electron microscopy (FESEM) on a HITACHI S-4800 instrument (FESEM, HITACHI S-4800, Tokyo, Japan). Furthermore, the field-emission scanning electron microscopy (FESEM, HITACHI S-4800, Tokyo, Japan) system coupled with energy-dispersive X-ray spectroscopy (EDX) was used to regulate the elemental composition and to obtain elemental mapping images.

2.4. Electrochemical Analysis

All electrochemical measurements were performed at room temperature using a BioLogic VSP-300 electrochemical workstation, Gières, France, in a standard three-electrode system with 1.0 M KOH solution as the electrolyte. The active materials were directly grown on pre-cleaned carbon cloth, which functioned as both the working electrode substrate and current collector. Before synthesis, the carbon cloth was ultrasonically cleaned in 1 M HCl, deionized water, and ethanol for 20 min each, followed by overnight drying at 60 °C. An Ag/AgCl electrode and a Pt plate were used as the reference and counter electrodes, respectively. Linear sweep voltammetry was recorded at 5 mV s−1 to evaluate the HER activity of the prepared catalysts, and all potentials were converted to the reversible hydrogen electrode scale for accurate comparison. The electrochemical double-layer capacitance was obtained from cyclic voltammetry measurements conducted in the non-Faradaic region of 0.1–0.2 V vs. Ag/AgCl at scan rates of 5–25 mV s−1. The electrochemically active surface area was then estimated from the Cdl values using a specific capacitance, Cs, of 0.040 mF cm−2 [41,42]:
ECSA = Cdl/Cs
Electrochemical impedance spectroscopy (EIS) was performed from 100 kHz to 0.1 Hz with a 10 mV AC amplitude to examine charge-transfer behavior at the electrode/electrolyte interface. The durability of the optimized electrocatalyst was evaluated using 5000 continuous CV cycles at 50 mV s−1, followed by comparison of LSV curves before and after cycling. Long-term stability was further assessed by chronopotentiometry at a constant current density under continuous HER operation.

3. Results and Discussion

The X-ray diffraction (XRD) patterns presented in Figure 2a for the hydrothermally synthesized V2O5 and electrodeposited V2O5-PANI composite exhibit distinct diffraction peaks within the 2θ range of 10–50°. The prominent diffraction peaks located at 2θ values of 15.3°, 20.1°, 21.6°, 26.0°, 31.1°, 32.2°, 33.2°, 34.1°, and 41.1° were indexed to the (200), (001), (101), (110), (400), (011), (111), (310), and (002) crystal planes, respectively, confirming the successful formation of the V2O5 phase. These peaks are characteristic of the orthorhombic crystal phase of V2O5 and are in good agreement with the standard JCPDS card No. 00-009-0387 [43,44]. The presence of sharp and well-resolved diffraction peaks indicates the high crystallinity and well-developed crystal structure of the synthesized V2O5. In addition, two broad diffraction peaks observed at 2θ values of 25.2° and 43.3° were assigned to the (002) and (100) planes of carbon cloth, respectively, which are consistent with JCPDS card No. 75-1621 [45]. For the V2O5-PANI composite electrodes, no distinct crystalline peaks corresponding to PANI were observed in the XRD patterns. This behavior suggests that the deposited PANI mainly exists in an amorphous form [45,46]. Interestingly, with increasing PANI deposition cycles, the intensity of the broad diffraction peak at 25.2° gradually increased, further supporting the successful formation of amorphous PANI on the electrode surface. Simultaneously, the characteristic diffraction peak intensities of V2O5 showed a gradual decrease with increasing PANI loading. This reduction in peak intensity indicates that the PANI layer progressively covered the crystalline V2O5 surface, resulting in partial attenuation of the V2O5 diffraction signals. These observations collectively confirm the successful deposition of PANI onto the V2O5 framework and the effective formation of the V2O5-PANI composite structure.
The surface chemical composition and oxidation states of the V2O5-PANI-2 composite were analyzed using X-ray photoelectron spectroscopy (XPS). The full XPS survey spectrum (Figure 2b) confirms the presence of vanadium (V), oxygen (O), carbon (C), and nitrogen (N) elements within the composite. To further elucidate the chemical states of these elements, the XPS spectra were deconvoluted; the high-resolution spectra of V2p, O1s, C1s, and N1s are presented in Figure 2. The high-resolution V2p spectrum shown in Figure 2c confirms the coexistence of mixed vanadium oxidation states, namely V4+ and V5+. The deconvoluted peaks located at 516.3 eV and 523.4 eV are assigned to the V4+ species corresponding to the V2p3/2 and V2p1/2 spin–orbit components, respectively. In addition, the dominant peaks observed at 517.3 eV and 524.8 eV are attributed to the V5+ oxidation state in the V2p3/2 and V2p1/2 regions, respectively [43,47]. The O1s spectrum presented in Figure 2d consists of two major components. The dominant peak centered at 530.1 eV is assigned to lattice oxygen associated with the V-O bond in the V2O5 crystal framework, confirming the formation of metal-oxygen coordination. A second weaker peak located at 531.7 eV corresponds to surface hydroxyl species (V-OH) or adsorbed oxygen-containing groups, which may originate from surface adsorption during synthesis or exposure to ambient conditions [22,43,48]. The high-resolution C1s spectrum shown in Figure 2e confirms the successful incorporation of PANI on the V2O5 surface. The main peaks at 284.4, 285.5, and 288.1 eV are assigned to C-C/C=C, C-N, and O-C=O bonds, respectively [49,50]. The N1s spectrum displayed in Figure 2f provides direct evidence for the successful electropolymerization of PANI on the V2O5 surface. The broad peak around 399 eV was deconvoluted into three distinct nitrogen species located at 399.4, 401.3, and 403.3 eV. The peak located at 399.4 eV is attributed to benzenoid amine nitrogen (-NH-), which is present in the polyaniline backbone. The peak centered at 401.3 eV corresponds to nitrogen cationic radicals (=N+.), which are associated with the oxidized conductive state of PANI. In addition, the higher binding energy peak observed at 403.3 eV is assigned to protonated amine nitrogen (-N+-), indicating protonation of the polymer chain and enhanced electrical conductivity of the composite electrode. [51,52,53]. The presence of these nitrogen functionalities confirms the successful deposition of conductive PANI and suggests strong electronic interaction between PANI and V2O5, which contributes to improved HER performance.
The surface morphology and microstructural evolution of pristine V2O5 and the V2O5-PANI composite electrodes were investigated using field-emission scanning electron microscopy (FESEM), and the corresponding images are presented in Figure 3. The pristine V2O5 sample, shown in Figure 3(a1–a3), exhibits a well-defined nanoflower-like architecture composed of densely packed and interconnected nanosheets. After electropolymerization of PANI, significant morphological changes were observed in the composite electrodes. For V2O5-PANI-1 (Figure 3(b1–b3)), corresponding to 5 CV deposition cycles, the nanoflower structure of V2O5 remains clearly visible, while the initial growth of PANI nanorods can be observed on the surface. These rod-like structures are sparsely distributed and partially cover the V2O5 nanoflowers, indicating the early stage of PANI deposition. Although the conductive polymer improves surface conductivity, the relatively low PANI loading may limit the number of electrochemically active sites available for the HER. In the case of V2O5-PANI-2, presented in Figure 3(c1–c3), which was prepared with 10 CV deposition cycles, a more uniform and optimized hybrid structure is formed. The PANI nanorods are homogeneously distributed over the V2O5 nanoflower framework without causing severe aggregation or blocking of the active surface. The intimate interfacial contact between the nanoflower-like V2O5 and the conductive PANI nanorods creates a highly interconnected network that significantly enhances electron transport, improves electrolyte accessibility, and increases the density of catalytically active sites. For V2O5-PANI-3 (Figure 3(d1–d3)), synthesized using 15 CV deposition cycles, excessive PANI deposition leads to the formation of thicker and more densely packed nanorod structures, resulting in partial agglomeration and over coverage of the V2O5 nanoflowers. This excessive polymer layer can hinder electrolyte diffusion and block the accessibility of the intrinsic active sites of V2O5, thereby reducing catalytic efficiency. Among all samples, V2O5-PANI-2 exhibits the most desirable microstructure with an optimal balance between active site exposure, conductivity enhancement, and interfacial charge transport, which directly supports its superior HER performance.
The elemental composition and surface distribution of pristine V2O5 and the V2O5-PANI composite were further investigated using energy-dispersive X-ray spectroscopy (EDX), and the corresponding spectra and elemental mapping images are presented in Figure 4. For pristine V2O5, the EDX spectrum shown in Figure 4(a1) confirms the presence of only V and O, with weight percentages of 62.22 wt% and 37.78 wt%, respectively, indicating the successful formation of pure vanadium oxide without detectable impurity phases. The corresponding elemental mapping images in Figure 4(a2,a3) demonstrate a uniform spatial distribution of V and O throughout the analyzed region, confirming the homogeneous growth of V2O5 over the carbon cloth substrate. After electropolymerization of PANI, additional signals corresponding to C and N become clearly visible in the EDX spectra, confirming the successful deposition of the conductive polymer layer. For V2O5-PANI-1 (Figure 4(b1)), the composition consists of 54.60 wt% V, 23.81 wt% O, 20.50 wt% C, and 1.09 wt% N. The elemental mapping images in Figure 4(b2–b5) show that V, O, C, and N are uniformly distributed, confirming good interfacial contact between the oxide and polymer phases. For the V2O5-PANI-2 sample (Figure 4(c1)), the EDX results reveal a balanced composition of 53.29 wt% V, 23.23 wt% O, 21.25 wt% C, and 2.23 wt% N. This optimized elemental ratio suggests an ideal PANI loading that provides sufficient conductive coverage without excessive blockage of the intrinsic V2O5 active sites. The elemental mapping images shown in Figure 4(c2–c5) demonstrate a highly uniform dispersion of all constituent elements, indicating strong interfacial integration and effective hybridization between V2O5 and PANI. In contrast, V2O5-PANI-3 (Figure 4(d1)) exhibits a further increase in carbon and nitrogen content, with a composition of 50.46 wt% V, 20.80 wt% O, 23.73 wt% C, and 5.01 wt% N. The higher nitrogen content indicates excessive PANI deposition, which is consistent with the FESEM observations of dense polymer overgrowth. Although the conductivity may improve, excessive PANI coverage can hinder electrolyte diffusion and reduce the exposure of catalytically active V2O5 sites. The mapping images in Figure 4(d2–d5) still show uniform elemental dispersion; however, the thicker polymer coverage may negatively influence catalytic efficiency by limiting direct access to the oxide surface.
The electrocatalytic HER performance of the as-prepared catalysts was investigated in 1.0 M KOH electrolyte, and the corresponding electrochemical results are presented in Figure 5. All polarization curves were carefully calibrated to the RHE scale to ensure an accurate evaluation of the intrinsic catalytic activity of the electrodes. Figure 5a,c present the comparative HER polarization behavior of pristine V2O5 and the V2O5-PANI composite catalysts, namely V2O5-PANI-1, V2O5-PANI-2, and V2O5-PANI-3. Among all investigated samples, pristine V2O5 exhibited the highest overpotential of 207.0 mV at a current density of −10 mA cm−2, indicating relatively sluggish HER kinetics. Although V2O5 inherently provides redox-active sites that can participate in hydrogen evolution, its limited electrical conductivity and slower interfacial electron transfer significantly restrict its catalytic efficiency. Upon electro polymerization of PANI, a substantial enhancement in HER activity was observed for all composite catalysts. Specifically, V2O5-PANI-1, V2O5-PANI-2, and V2O5-PANI-3 exhibited significantly reduced overpotentials of 196.8, 79.9, and 186.0 mV, respectively, at the same current density of −10 mA cm−2. This remarkable improvement confirms the strong synergistic interaction between the V2O5 framework and the conductive PANI network, which effectively promotes charge transport and increases the accessibility of catalytically active sites. Among the series, V2O5-PANI-2 demonstrated the best HER performance with the lowest overpotential of 79.9 mV, indicating its optimized catalytic configuration. This superior activity can be attributed to the ideal PANI loading and its uniform distribution over the V2O5 surface, which collectively enhance electrical conductivity, facilitate rapid electron migration, and expose a larger number of active reaction centers. To further evaluate the HER kinetics, Tafel slope analysis was performed using the polarization data, as shown in Figure 5b,c. The V2O5-PANI-2 electrocatalyst exhibited the lowest Tafel slope of 46.6 mV dec−1, indicating the most favorable reaction kinetics and faster hydrogen adsorption–desorption processes. The Tafel slope values followed the order of V2O5-PANI-2 (46.6 mV dec−1) < V2O5-PANI-3 (68.2 mV dec−1) < V2O5-PANI-1 (77.3 mV dec−1) < V2O5 (89.3 mV dec−1). The significantly lower Tafel slope of V2O5-PANI-2 suggests that the HER proceeds more efficiently on this catalyst surface, with reduced kinetic barriers and accelerated charge-transfer processes. The Tafel slope is an important kinetic parameter for understanding the dominant reaction pathway of the HER. According to established electrochemical theory, the HER mechanism can be interpreted based on the obtained Tafel slope values. A Tafel slope in the range of 30–40 mV dec−1 generally indicates that the reaction proceeds through the Volmer-Tafel pathway, where the recombination of two adsorbed hydrogen intermediates (H*) is the rate-determining step [54,55].
The initial water dissociation and hydrogen adsorption process can be represented by the Volmer reaction:
H2O + e− → H* + OH− (Volmer reaction)
followed by the Tafel recombination step:
H* + H* → H2 (Tafel reaction)
On the other hand, Tafel slope values between 40 and 120 mV dec−1 suggest that the HER predominantly follows the Volmer-Heyrovsky mechanism, in which electrochemical desorption of adsorbed hydrogen acts as the rate-determining step [56]. This process is represented by the Heyrovsky reaction:
H* + H2O + e− → H2 + OH− (Heyrovsky reaction)
For the V2O5-PANI-2 electrocatalyst, the experimentally obtained Tafel slope of 46.6 mV dec−1 indicates that the HER mainly proceeds through the Volmer-Heyrovsky mechanism. This result suggests that the electrochemical desorption step governs the overall reaction kinetics, while the optimized interfacial interaction between V2O5 and the conductive PANI network facilitates rapid charge transfer and efficient hydrogen intermediate conversion, thereby enhancing HER performance. The intrinsic catalytic activity of the prepared electrodes was further evaluated by calculating the turnover frequency (TOF), which represents the number of hydrogen molecules generated per active site per second during the HER. The TOF values were estimated under anodic peak conditions, assuming that each electrochemically accessible metal center participates as an active catalytic site. The calculated TOF values for V2O5, V2O5-PANI-1, V2O5-PANI-2, and V2O5-PANI-3 were 1.64 × 10−5, 2.04 × 10−5, 1.21 × 10−4, and 3.89 × 10−5 s−1, respectively, as presented in Figure 5d. Among all the investigated samples, V2O5-PANI-2 exhibited the highest TOF value, indicating its superior intrinsic catalytic activity for the HER. This optimized electronic environment promotes efficient hydrogen intermediate adsorption (H*) and conversion, thereby enhancing HER kinetics and overall electrocatalytic activity [57]. Electrochemical impedance spectroscopy (EIS) was further employed to investigate the interfacial charge transfer characteristics during HER, and the corresponding Nyquist plots are shown in Figure 5e. The EIS data were fitted using an equivalent circuit model shown in inset figure, to quantitatively analyze the electrochemical resistance components. In the Nyquist plots, the diameter of the semicircle in the high-frequency region corresponds to the charge transfer resistance (Rct), which directly reflects the efficiency of electron transfer at the electrode-electrolyte interface [58]. Notably, V2O5-PANI-2 exhibited the smallest semicircle and the lowest Rct value of 3.2 Ω, demonstrating the fastest interfacial electron transfer and the most efficient HER kinetics among all samples. In comparison, pristine V2O5 showed a significantly higher Rct value of 11.7 Ω, while V2O5-PANI-1 and V2O5-PANI-3 displayed intermediate values of 9.6 and 6.3 Ω, respectively. The substantially reduced Rct value of V2O5-PANI-2 clearly indicates that the optimized incorporation of PANI effectively improves the electrical conductivity and interfacial charge transport behavior of the composite, thereby facilitating rapid electron injection and enhanced catalytic activity for hydrogen evolution.
The CV analysis of all the electrocatalysts were evaluated to investigate their surface electrochemical behavior and estimate the density of accessible active sites. Figure 6a–d presents the CV curves of pristine V2O5 and the V2O5-PANI composite catalysts recorded at various scan rates within the non-faradaic potential region, along with the corresponding current density versus potential profiles. A gradual increase in current response with increasing scan rate was clearly observed for all samples, which is characteristic of capacitive behavior and confirms the strong dependence of electrochemical activity on surface charge accumulation processes. To further understand the relationship between catalytic performance and the number of exposed active sites, the electrochemically active surface area (ECSA) was estimated from the double-layer capacitance (Cdl). The 2Cdl values (Figure 6e) were obtained by plotting the difference in anodic and cathodic current densities against the scan rate, where the slope of the linear fitting corresponds to the double-layer capacitance. Since Cdl is directly proportional to the available electrochemically active surface, it serves as an important indicator of catalytic site density and surface accessibility. The calculated Cdl values, shown in Figure 6f, for pristine V2O5, V2O5-PANI-1, V2O5-PANI-2, and V2O5-PANI-3 were 2.04, 2.14, 5.62, and 5.36 mF cm−2, respectively. Based on these values, the corresponding ECSA values were determined to be 51.12, 53.62, 140.50, and 134.12 cm2, respectively, as summarized in Figure 6g. Among all the catalysts, V2O5-PANI-2 exhibited the highest Cdl and ECSA values, indicating the largest electrochemically accessible surface area and the highest density of exposed active sites. The significant enhancement in both Cdl and ECSA after the incorporation of PANI demonstrates that the conductive polymer effectively modifies the surface architecture of V2O5, leading to improved interfacial contact, enhanced electrolyte penetration, and greater exposure of catalytically active centers.
A comparative assessment of the electrocatalytic performance of V2O5-PANI-2 with recently reported HER electrocatalysts is presented in Table 1. The summarized electrochemical parameters demonstrate the competitive HER activity of the developed catalyst, highlighting the effectiveness of the V2O5-PANI hybrid architecture for alkaline hydrogen evolution. The long-term electrochemical durability of the optimized V2O5-PANI-2 electrocatalyst was systematically evaluated under both dynamic and steady-state operating conditions to assess its structural and catalytic stability during the HER. To examine the durability under repeated redox cycling, accelerated stability testing was performed using continuous CV scanning for 5000 cycles. As presented in Figure 7a, the polarization curve of V2O5-PANI-2 after prolonged cycling shows an observable shift toward a higher overpotential region, indicating a certain degree of catalytic performance degradation. Specifically, the overpotential required to achieve a current density of −10 mA cm−2 increased to 180.7 mV compared to its initial value, suggesting partial deterioration of the catalytic interface during repeated electrochemical operation. This decline in HER activity can be attributed to repeated polarization, which may induce slight detachment of the active material from the substrate or changes in the conductive PANI network, which can negatively influence charge transfer efficiency. To further evaluate the operational stability under practical working conditions, chronopotentiometric analysis was carried out at a constant current density of −10 mA cm−2 for 24 h, as shown in Figure 7b. Unlike the CV cycling results, the potential-time profile during the long-term constant-current test exhibited a gradual decrease after several hours of operation, indicating an activation behavior rather than continuous degradation. These results demonstrate that although slight performance loss is observed under harsh accelerated CV cycling, the V2O5-PANI-2 electrocatalyst exhibits reasonable stability under practical continuous HER operation conditions. The post-stability FESEM images of V2O5-PANI-2 after 5000 continuous CV cycles (Figure 7(c1–c3)) reveal that the rod-like PANI structures remain largely preserved, indicating good structural stability of the conductive polymer framework under repeated electrochemical cycling. However, the V2O5 nanoflower-like structures show partial agglomeration and surface reconstruction, which may be attributed to repeated redox polarization and localized structural rearrangement during prolonged cycling. These morphological changes likely contribute to the increase in overpotential observed after the durability test.

4. Conclusions

In conclusion, a series of V2O5-PANI composite electrodes were successfully fabricated on carbon cloth through hydrothermal synthesis followed by controlled electropolymerization for efficient HER in alkaline medium. Pristine V2O5 exhibited a nanoflower-like morphology, while the electrodeposited PANI formed nanorod-like structures that effectively improved the surface conductivity and interfacial charge transfer. Among the prepared samples, V2O5-PANI-2 showed the most optimized architecture with uniform PANI distribution and strong interfacial interaction between V2O5 and the conductive polymer matrix. Electrochemical results demonstrated that V2O5-PANI-2 delivered the best HER performance with a low overpotential of 79.9 mV at −10 mA cm−2, a small Tafel slope of 46.6 mV dec−1, and the lowest charge transfer resistance of 3.2 Ω. In addition, the catalyst exhibited the highest double-layer capacitance of 5.62 mF cm−2 and an electrochemically active surface area of 140.50 cm2, confirming the presence of abundant accessible active sites. The electrode demonstrated reasonable electrochemical stability after 5000 CV cycles and sustained catalytic activity during 24 h chronopotentiometric testing. These findings confirm that the synergistic integration of V2O5 and PANI is an effective strategy to enhance HER activity and stability, offering a promising pathway for the development of cost-effective and high-performance electrocatalysts for sustainable hydrogen production.

Author Contributions

C.J.R.: Conceptualization, Methodology, Investigation, Writing—original draft; Software, Visualization, Writing—review and editing, Project administration. S.-C.K.: Formal analysis, Supervision, Writing—review and editing, Project administration, Funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2025-22222973).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Polymers 18 01408 g001
Figure 1. Schematic illustration of synthesis of V2O5 and V2O5-PANI electrocatalysts.
Figure 1. Schematic illustration of synthesis of V2O5 and V2O5-PANI electrocatalysts.
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Figure 2. (a) XRD spectra of all the electrocatalysts, (b) XPS survey spectra, and high-resolution XPS spectra of (c) V2p, (d) O 1s, (e) C1s, and (f) N1s of V2O5-PANI-2 composite.
Figure 2. (a) XRD spectra of all the electrocatalysts, (b) XPS survey spectra, and high-resolution XPS spectra of (c) V2p, (d) O 1s, (e) C1s, and (f) N1s of V2O5-PANI-2 composite.
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Figure 3. FESEM micrograph images of (a1–a3) V2O5, (b1–b3) V2O5-PANI-1, (c1–c3) V2O5-PANI-2, and (d1–d3) V2O5-PANI-3 electrocatalysts.
Figure 3. FESEM micrograph images of (a1–a3) V2O5, (b1–b3) V2O5-PANI-1, (c1–c3) V2O5-PANI-2, and (d1–d3) V2O5-PANI-3 electrocatalysts.
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Figure 4. Energy-dispersive X-ray spectroscopy analysis and elemental mapping data of (a1–a3) V2O5, (b1–b5) V2O5-PANI-1, (c1–c5) V2O5-PANI-2, and (d1–d5) V2O5-PANI-3.
Figure 4. Energy-dispersive X-ray spectroscopy analysis and elemental mapping data of (a1–a3) V2O5, (b1–b5) V2O5-PANI-1, (c1–c5) V2O5-PANI-2, and (d1–d5) V2O5-PANI-3.
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Figure 5. HER performances of all the electrocatalyst: (a) LSV curves at 5 mV/s scan rate, (b) equivalent Tafel slopes, (c) HER performance concerning overpotential at −10 mA cm−2 and Tafel slope, (d) TOF plot, and (e) EIS spectra (inset equivalent circuit) of all the electrocatalysts.
Figure 5. HER performances of all the electrocatalyst: (a) LSV curves at 5 mV/s scan rate, (b) equivalent Tafel slopes, (c) HER performance concerning overpotential at −10 mA cm−2 and Tafel slope, (d) TOF plot, and (e) EIS spectra (inset equivalent circuit) of all the electrocatalysts.
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Figure 6. Cyclic voltammetry analysis at different scan rates: (a) V2O5, (b) V2O5-PANI-1, (c) V2O5-PANI-2, and (d) V2O5-PANI-3. (e) 2Cdl graph, (f) Cdl graph, and (g) ECSA graph of all the electrocatalysts.
Figure 6. Cyclic voltammetry analysis at different scan rates: (a) V2O5, (b) V2O5-PANI-1, (c) V2O5-PANI-2, and (d) V2O5-PANI-3. (e) 2Cdl graph, (f) Cdl graph, and (g) ECSA graph of all the electrocatalysts.
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Figure 7. (a) LSV curves of V2O5-PANI-2 before and after 5000 CV cycles. (b) Chronopotentiometry analysis. (c1–c3) After stability FESEM images of V2O5-PANI-2 electrocatalyst.
Figure 7. (a) LSV curves of V2O5-PANI-2 before and after 5000 CV cycles. (b) Chronopotentiometry analysis. (c1–c3) After stability FESEM images of V2O5-PANI-2 electrocatalyst.
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Table 1. Comparison of HER results of developed electrocatalyst and other reported electrocatalysts.
Table 1. Comparison of HER results of developed electrocatalyst and other reported electrocatalysts.
ElectrocatalystElectrolyteOverpotential (mV @ 10 mA cm−2)Ref.
CdS-V2O5/g-C3N41 M KOH202[23]
PPy/V2O5/MnO21 M KOH192[24]
NiS2@V2O5/VS21 M KOH216[26]
NiMnO3/PANI1 M KOH188[37]
NiFe2O4/PANI1 M KOH161[38]
NiCoP@PANI1 M KOH80.6[39]
CoMnO3/PANI1 M KOH185[40]
V2O51 M KOH177[43]
VO/CoN1 M KOH80.5[59]
NdCoO3/PANI1 M KOH113[60]
V2O5-PANI-21 M KOH79.9Present work
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Raorane, C.J.; Kim, S.-C. Interfacial Engineering of V2O5 via Conductive Polyaniline for Accelerated Hydrogen Evolution Reaction. Polymers 2026, 18, 1408. https://doi.org/10.3390/polym18111408

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Raorane CJ, Kim S-C. Interfacial Engineering of V2O5 via Conductive Polyaniline for Accelerated Hydrogen Evolution Reaction. Polymers. 2026; 18(11):1408. https://doi.org/10.3390/polym18111408

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Raorane, Chaitany Jayprakash, and Seong-Cheol Kim. 2026. "Interfacial Engineering of V2O5 via Conductive Polyaniline for Accelerated Hydrogen Evolution Reaction" Polymers 18, no. 11: 1408. https://doi.org/10.3390/polym18111408

APA Style

Raorane, C. J., & Kim, S.-C. (2026). Interfacial Engineering of V2O5 via Conductive Polyaniline for Accelerated Hydrogen Evolution Reaction. Polymers, 18(11), 1408. https://doi.org/10.3390/polym18111408

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