Next Article in Journal
Evaluation and Experiment of High-Strength Temperature- and Salt-Resistant Gel System
Previous Article in Journal
Constructive Neuroengineering of Axon Polarization Control Using Modifiable Agarose Gel Platforms for Neuronal Circuit Construction
Previous Article in Special Issue
Tannic Acid-Enhanced Gelatin-Based Composite Hydrogel as a Candidate for Canine Periodontal Regeneration
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Catalytic Interface of rGO-VO2/W5O14 Hydrogel for High-Performance Electrochemical Water Oxidation

School of Chemical Engineering, Yeungnam University, 280 Daehak-ro, Gyeongsan 712-749, Republic of Korea
*
Author to whom correspondence should be addressed.
Gels 2025, 11(8), 670; https://doi.org/10.3390/gels11080670
Submission received: 11 July 2025 / Revised: 18 August 2025 / Accepted: 19 August 2025 / Published: 21 August 2025
(This article belongs to the Special Issue Properties and Structure of Hydrogel-Related Materials (2nd Edition))

Abstract

The continuous increase in global energy demand necessitates the development of sustainable, clean, and highly efficient methods of energy generation. Electrochemical water splitting, comprising hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), represents a promising strategy but remains hindered by sluggish reaction kinetics and limited availability of highly active electrocatalysts especially under alkaline conditions. Addressing this challenge, we successfully synthesized a rGO-VO2/W5O14 (rG-VO2/W5O14) hydrogel electrocatalyst through a facile hydrothermal approach. The prepared composite distinctly reveals an advantageous hierarchical microstructure characterized by VO2 nanoflakes uniformly distributed on the surface of rGO nanosheets, intricately integrated with W5O14 nanorods. Evaluated in a 1.0 M KOH electrolyte, the optimized rG-VO2/W5O14-2 catalyst demonstrates remarkable electrocatalytic performance towards OER, achieving a low overpotential of 265.8 mV and a reduced Tafel slope of 81.9 mV dec−1. Furthermore, the catalyst maintains robust stability with minimal performance degradation, exhibiting an overpotential of only 273.0 mV after 5000 cyclic stability tests. The superior catalytic activity and durability are attributed to the synergistic combination of enriched chemical composition, effective electron transfer, and abundant catalytic active sites inherent in the well-optimized rG-VO2/W5O14-2 composite.

1. Introduction

Electrochemical water splitting has emerged as a promising and efficient approach for sustainable hydrogen production. This process involves two key half-cell reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) [1,2,3,4,5,6,7,8,9,10,11]. Among these, the OER represents a significant bottleneck due to its complex reaction pathway, which includes a sluggish four-electron transfer mechanism [12]. This inherently slow kinetics results from the need to break O-H bonds and form O=O bonds, thereby necessitating the application of a substantial overpotential to initiate and sustain the reaction efficiently [13]. To overcome these kinetic limitations, extensive research over the past few decades has focused on the rational design and engineering of electrocatalysts. Enhancing catalytic performance has largely depended on tailoring the morphology, crystal structure, and electronic configuration of these materials. Various synthetic strategies have been employed for this purpose, including hydrothermal synthesis, electrodeposition, sol-gel processing, co-precipitation, and anion exchange methods, among others. These techniques aim to optimize surface area, active site exposure, and conductivity, thereby improving the overall efficiency of water splitting systems [14,15]. While noble-metal-based catalysts, such as those incorporating iridium (Ir) and ruthenium (Ru), exhibit exceptional performance in accelerating inherently sluggish catalytic processes still their widespread industrial adoption is significantly constrained by their scarcity, prohibitive costs, and limited availability [16,17,18]. Consequently, considerable research efforts are now dedicated to designing and developing cost-effective, abundant, and efficient alternative materials that can effectively replace these precious metals, thereby facilitating sustainable advancements in renewable energy technologies.
Graphene oxide (GO) is a promising carbon-based nanomaterial characterized by a two dimensional honeycomb lattice consisting primarily of sp2-hybridized carbon atoms. Composite materials that integrate graphene with various metals have demonstrated notable energy storage capacities and enhanced cyclic stability. However, the transformation of graphene oxide into reduced graphene oxide (rGO) significantly alters its electrical properties, resulting in electrical conductivity ranging broadly from approximately 2.98 × 104 to 0.1 Sm−1 [19]. Among various carbonaceous materials, rGO stands out as particularly advantageous for electrocatalytic applications. Its demand originates from distinctive attributes, including an expanded surface area, superior electron and mass transfer efficiencies, minimized catalyst poisoning, and enhanced charge carrier mobility. The elevated electronic conductivity of rGO is attributed to the efficient transport of delocalized electrons within its conjugated molecular orbitals [19]. Furthermore, the ability of rGO to establish synergistic interactions with other catalytic materials significantly amplifies overall catalytic performance [20,21]. Current research efforts have concentrated extensively on developing non-precious, hierarchical, and heterostructured electrocatalysts with superior catalytic performance, particularly targeting the HER and OER. Prominent candidates include transition-metal-based compounds such as oxides [22,23,24,25,26,27], sulfides [28,29,30,31], nitrides [32,33], and phosphides [34,35]. Among these materials, Vanadium oxides, as a class of transition metal oxides have garnered significant attention in the realm of energy storage and conversion technologies owing to their diverse oxidation states, structural versatility, and rich electrochemical properties. Particularly, the integration of vanadium oxides with carbon-based materials has demonstrated notable synergistic effects resulting in enhanced electrical conductivity, improved structural stability, and superior electrochemical performance. Such vanadium oxide-carbon heterostructures are highly promising candidates for next-generation batteries and supercapacitors, as well as for advanced electrocatalytic applications [36]. Among the various vanadium oxide phases, vanadium dioxide (VO2) stands out due to its unique polymorphism and its reversible monoclinic-to-rutile structural phase transition near 67 °C, which imparts intriguing electrical and optical properties [36,37,38,39]. For instance, Usmani et al. synthesized a VO2/graphite composite in which VO2 was uniformly anchored onto graphite sheets. This heterostructure exhibited an OER overpotential of 470 mV in alkaline electrolyte, indicating considerable catalytic activity [36]. Similarly, Cui et al. reported the fabrication of a Co3O4/VO2 nanohybrid, constructed by anchoring VO2 nanoparticles onto Co3O4 nanocages via a straightforward hydrothermal and subsequent calcination approach. The resulting hybrid demonstrated remarkable electrocatalytic activity, achieving a low OER overpotential of 433 mV at a current density of 10 mA cm−2 [40]. In another study, Gowrisankar et al. developed a β-MnO2-VO2 (M)/2D-rGO composite catalyst, which delivered an overpotential of 334 mV at 10 mA cm−2, further highlighting the beneficial role of vanadium oxide-carbon interfaces [41].
In this study, we present the design and synthesis of rGO-VO2/W5O14 nanostructured electrocatalysts, highlighting their superior electrocatalytic performance toward the OER in alkaline media. The strategic incorporation of W5O14, derived from rGO-VO2 was intended to enhance the intrinsic catalytic activity by promoting favorable structural and electronic interactions within the composite (Figure 1). Comprehensive spectroscopic and microscopic analyses verified the successful formation of the rGO-VO2/W5O14 hybrid, revealing well-dispersed W5O14 nanorods intimately interconnected with rGO-VO2 nanosheets and nanoflakes. Among the series of compositions evaluated, the rG-VO2/W5O14-2 sample exhibited the most outstanding electrochemical performance, achieving a notably low overpotential of 265.8 mV at a current density of 10 mA cm−2, accompanied by a Tafel slope of 81.9 mV·dec−1. This exceptional activity can be attributed to the enlarged electrochemically active surface area and the pronounced synergistic effects between the constituent phases, which collectively facilitate more efficient charge and mass transfer during OER. Moreover, the robust durability of the rG-VO2/W5O14-2 electrocatalyst was demonstrated through extended cyclic voltammetry and chronopotentiometry tests, confirming its stability under prolonged operational conditions.

2. Result and Discussion

The structural integrity, crystallinity, and phase purity of the synthesized materials were thoroughly examined using X-ray diffraction (XRD) analysis. All data were measured at room temperature and recorded in the 2θ range of 10–60°. Figure 2a presents the XRD spectra of rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4 composites providing critical insights into their phase composition. The diffraction pattern of rGO exhibits a big hump ranging from 22° to 26° corresponding to the (002) plane and one more peak appeared at 42.5° which shows (111) crystal plane [42]. For the VO2, the peaks are assigned at 15.3°, 17.3°, 25.5°, and 31.6°, which correspond to the (200), (−201), (110), and (400) lattice planes. The VO2 diffraction peaks provide the confirmation of monoclinic structure which is well matched with the JCPDS No. 00-031-1438 [43]. Additionally, the presence of W5O14 within the composite is indicated by prominent diffraction peaks observed at 20.5°, 23.3°, 27.4, and 29.6° which are attributed to the (520), (001), (640), and (650) lattice planes. The W5O14 phase exhibits a tetragonal crystal structure consistent with JCPDS card No. 01-071-0292 [44]. A noticeable trend in the XRD patterns reveals that as the concentration of W5O14 increases the intensity of the corresponding diffraction peaks also intensifies further validating the successful incorporation of W5O14 into the composite matrix. These findings confirm the successful formation of the rG-VO2/W5O14 nanocomposite with well-defined crystallinity and phase purity. The structural characteristics as revealed by XRD support the potential applicability of this composite in electrocatalytic processes where well crystallized phases contribute to enhanced catalytic activity and stability. To elucidate the molecular interactions and structural characteristics of the rG-VO2/W5O14-2 nanocomposite, Raman spectroscopy was conducted, as presented in Figure 2b. The Raman spectrum displays, for rGO, two characteristic peaks appear at 1356 and 1586 cm−1 corresponding to the D and G bands, respectively [45,46,47]. The D band is indicative of the presence of sp3-hybridized carbon atoms and lattice defects, whereas the G band originates from the in-plane vibration of sp2-bonded carbon atoms in the graphitic domains. Notably, in the rGO-VO2/W5O14-2 composite, the intensity of the D band surpasses that of the G band suggesting a higher concentration of structural defects and disorder in the rGO lattice. This increased D/G intensity ratio further confirms the partial reduction of GO and the introduction of defect sites which are beneficial for facilitating electron transfer and enhancing the electrocatalytic properties of the composite [46]. In the case for VO2, the signal at 164 cm−1 corresponds to both V-O-V bending and external wagging modes, while a band observed at 429 cm−1 is attributed to the V-O-V stretching mode [37,48]. A peak at 829 cm−1 assigned to the V=O stretching vibration of distorted octahedral and distorted square-pyramids, characteristic of VO2 [39]. For the W5O14, the spectrum also exhibits a peak at 254 cm−1, representing the bending vibration of O-W-O units and a distinct feature at 916 cm−1 which can be ascribed to the terminal W=O bond [49].
X-ray photoelectron spectroscopy (XPS) was employed to meticulously elucidate the chemical states and surface compositions of the synthesized composites. The full XPS survey spectrum (Figure 3a) confirms the presence of carbon (C), oxygen (O), vanadium (V), and tungsten (W) elements within the composite. Figure 3b presents the high-resolution XPS spectrum of C1s, which upon careful deconvolution reveals three distinctive peaks at binding energies of 284.5, 285.6, and 287.5 eV. These peaks are assigned to sp3/sp2 hybridized C-C/C=C bonds (pink colored line), C-O bonds (green colored line), and (C=O) (Blue colored line), respectively, indicating diverse functional groups present on the rGO surface [50,51]. The high-resolution O1s spectrum depicted in Figure 3c similarly displays multiple oxygen-related species. Precise peak fitting clearly distinguishes characteristic binding energy positions at approximately 530.2 eV (lattice oxygen bonded to V and W atoms, that is V-O/W-O) (pink colored line) (violet colored line), 532.8 eV (surface-adsorbed oxygen species) (orange colored line), and 533.3 eV (C=O functionalities present on the rGO framework), (dark cyan colored line) [43,50,52,53]. Moreover, the detailed V2p core-level spectrum in Figure 3d provides critical insight into the oxidation states of vanadium within the composite structure. Two distinct sets of peaks were identified: one pair centered at 517.4 eV (V2p3/2) (green colored line) and 524.6 eV (V2p1/2) (green colored line) indicative of V5+ oxidation states typical of the VO2 lattice, and a second pair located at lower energies, 516.0 eV (V2p3/2) and 523.6 eV (V2p1/2) attributed to V4+ species. This coexistence of multiple vanadium oxidation states implies an enhanced electron transfer capability, essential for effective catalytic activity [41,43]. The W4f high-resolution spectrum (Figure 3e) clearly reveals peaks at binding energies of 36.6 eV (W4f7/2) and 42.2 eV (W5p3/2). These peaks correspond explicitly to tungsten in its stable W6+ oxidation state, confirming successful integration of W atoms into the composite matrix [54,55].
The morphology and microstructure of the synthesized rGO-VO2/W5O14 nanocomposites with varying tungsten concentrations were systematically examined using scanning electron microscopy (SEM), as depicted in Figure 4. The SEM images clearly illustrate the notable morphological variations across the different compositions, corresponding to rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4. In the rG-VO2/W5O14-1 (Figure 4 (a1–a3)), rGO nanosheets appear as thin and wrinkled structures that act as substrates providing large surface areas and pathways for charge mobility. The nanosheets host small, scattered VO2 nanoflakes and sparsely distributed W5O14 nanorods. Here, the relatively lower concentration of tungsten results in a limited number of W5O14 nanorods with poor dispersion, thus offering fewer catalytic active sites. The morphology significantly improves at an optimized tungsten concentration in rG-VO2/W5O14-2 as displayed in Figure 4 (b1–b3). This composite distinctly demonstrates a highly favorable hierarchical structure, wherein VO2 nanoflakes densely and uniformly decorate the surface of the rGO nanosheets simultaneously interlaced with well-defined, elongated, and abundant W5O14 nanorods. Such uniform integration of VO2 nanoflakes and high-density W5O14 nanorods on rGO nanosheets substantially enhances the available surface active sites, facilitates efficient electron transfer, and ensures effective electrolyte penetration. These structural attributes collectively contribute to the superior electrocatalytic OER activity observed for this particular composition. Further increase in tungsten content, as depicted in rG-VO2/W5O14-3 (Figure (c1–c3)), leads to excessive growth and partial aggregation of thicker W5O14 nanorods, overwhelming the VO2 nanoflakes and resulting in morphological irregularities. In the rG-VO2/W5O14-4 (Figure (d1–d3)), the microstructure exhibits a noticeable decrease in W5O14 nanorod density. The fewer, relatively isolated, shorter nanorods along with sparsely distributed VO2 nanoflakes on the rGO nanosheets may lead to limited catalytic active site availability, restricted interfacial interactions, and inefficient charge transport, all negatively influencing the electrocatalytic efficiency of this sample.
Elemental composition and distribution within the optimized rG-VO2/W5O14-2 composite were systematically investigated using EDAX analysis, as demonstrated in Figure 5a and Table 1 exhibit the EDAX data of all the samples. The EDAX spectra clearly validated the presence of C, O, V, and W quantitatively establishing their weight percentages as 38.35%, 28.97%, 31.80%, and 0.88%, respectively. To further examine the uniformity and spatial distribution of these constituent elements EDAX elemental mapping was employed, as depicted in Figure 5b–f. The elemental mapping distinctly illustrated a homogeneous dispersion of C, O, V, and W across the entire composite. Such a uniformly distributed elemental configuration promotes efficient interactions between active catalytic sites, potentially facilitating rapid charge transfer pathways and enhanced electrolyte accessibility. Consequently, this homogeneous elemental dispersion significantly contributes to the superior electrocatalytic activity and stability observed in the rG-VO2/W5O14-2 composite during OER processes.
To systematically evaluate the oxygen evolution reaction performance of the synthesized electrocatalysts, electrochemical measurements were carried out in a standard three-electrode configuration using 1 M KOH aqueous electrolyte. The LSV was employed to determine the overpotential (η), a key indicator of catalytic activity, with a scan rate of 5 mV s−1 and iR compensation applied to all measurements. The LSV profiles of the rG-VO2/W5O14 composites namely rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4 are presented in Figure 6a and data presented in Figure 6c. Among them, the rG-VO2/W5O14-2 sample exhibited the most remarkable OER activity, achieving a low overpotential of 265.8 mV at a benchmark current density of 10 mA cm−2. In contrast, higher overpotentials were observed for rG-VO2/W5O14-1 (286.3 mV), rG-VO2/W5O14-3 (278.3 mV), and rG-VO2/W5O14-4 (282.1 mV) indicating inferior electrocatalytic performance under identical conditions. The superior performance of rG-VO2/W5O14-2 can be attributed to the optimized composition and synergistic integration of W5O14 which enhances the density of active sites and facilitates faster electron transfer. This trend suggests a direct correlation between W5O14 concentration in the hybrid material and OER efficiency. To further elucidate the reaction kinetics, Tafel slope analysis was conducted, as shown in Figure 6b,c. The rG-VO2/W5O14-2 catalyst recorded the lowest Tafel slope of 81.9 mV dec−1, reflecting more favorable charge transfer kinetics. This value was lower than those obtained for rG-VO2/W5O14-1 (96.7 mV dec−1), rG-VO2/W5O14-3 (87.1 mV dec−1), and rG-VO2/W5O14-4 (93.8 mV dec−1), confirming the enhanced intrinsic electrocatalytic activity of rG-VO2/W5O14-2. Electrochemical impedance spectroscopy (EIS) was employed to investigate the charge transfer properties and interfacial resistance of the catalysts during OER. The Nyquist plots displayed in Figure 6d reveal that rG-VO2/W5O14-2 exhibits the smallest semicircle diameter, signifying reduced charge transfer resistance (Rct) and accelerated interfacial electron transport. This behavior is further supported by the inset of Figure 6d, where the real impedance (Zre) trends toward lower values. The extracted Rct values for rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4 were 0.16, 0.12, 0.13, and 0.14 Ω, respectively. The notable decrease in Rct for rG-VO2/W5O14-2 underscores its superior electrochemical performance, which is primarily attributed to enhanced conductivity and the presence of abundant surface-active sites facilitated by the rGO-VO2/W5O14 integration. This synergistic effect promotes efficient electron transport pathways and increases the rate of oxygen evolution, making rG-VO2/W5O14-2 a promising electrocatalyst for OER applications.
Figure 7 illustrates the cyclic voltammetry (CV) profiles of the rG-VO2/W5O14 composites with varying W5O14 ratios, recorded at different scan rates. The CV curves for rG-VO2/W5O14-1 (Figure 7a), rG-VO2/W5O14-2 (Figure 7b), rG-VO2/W5O14-3 (Figure 7c), and rG-VO2/W5O14-4 (Figure 7d) reveal a progressive increase in current response with increasing scan rate. This trend underscores the dependence of electrocatalytic behavior on scan rate, suggesting improved charge transport kinetics across all samples. To quantify the electrochemically active surface area (ECSA), the double-layer capacitance (Cdl) was evaluated from the CV curves at varying scan rates, as shown in Figure 7e. The calculated Cdl values for rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4 were found to be 46.19, 57.94, 48.26, and 47.23 mF cm−2, respectively. These values directly reflect the extent of surface area available for electrochemical reactions. Subsequently, the ECSA values were estimated using the relation ECSA = Cdl/Cs, where Cs represents the specific capacitance of a flat surface (typically ~0.040 mF cm−2 for KOH) [56]. As depicted in Figure 7f, the corresponding ECSA values for rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4 were calculated to be 1154.63, 1448.38, 1206.38, and 1180.63 cm2, respectively. Among the samples, rG-VO2/W5O14-2 exhibited the highest ECSA indicating a greater number of electrochemically accessible active sites. This enhancement is attributed to the optimal incorporation of W5O14 within the composite matrix, which promotes a more effective interface between the rGO, VO2, and W5O14 nanostructures. The expanded active surface area plays a critical role in facilitating charge transfer and catalytic efficiency, thereby contributing to the improved overall electrochemical performance of the OER.
The long term stability of electrocatalysts is a crucial factor in electrochemical performance evaluation, particularly for potential commercial applications. To assess the structural and electrochemical durability of the heterostructured rG-VO2/W5O14-2 electrocatalyst in a 1.0 M KOH electrolyte, CV studies and chronopotentiometry measurements were conducted. The CV cycling test was performed at a scan rate of 50 mV s−1 in a 1.0 M KOH electrolyte to monitor the durability of the electrocatalyst under prolonged operational conditions. As depicted in Figure 8a, the polarization curve of rG-VO2/W5O14-2 was recorded before and after 5000 CV cycles to analyze its performance retention. After undergoing 5000 cycles, the electrocatalyst maintained an overpotential of 273.0 mV at a current density of 10 mA cm−2 which closely matches the initial values obtained before cycling, demonstrating excellent electrochemical stability. Furthermore, a chronopotentiometry experiment was conducted at a current density of 10 mA cm−2 over a continuous for 9 h (Figure 8b) to further examine the catalyst’s endurance. At the start of the chronopotentiometry test, the electrode surface conditions itself, its outer layer becomes more oxidized and oxygen bubbles temporarily cover parts of the surface. Both effects briefly make the reaction harder, so the cell voltage rises. Once the surface and wetting stabilize and bubbles detach regularly, the potential levels off and stays steady. The rG-VO2/W5O14-2 electrocatalyst exhibited remarkable stability. However, a slight loss in performance could be attributed to several factors, including the minor leaching of active materials from the electrode’s surface, or potential structural degradation due to oxidation under high potentials [57,58]. Figure 8c,d shows the before and after analysis SEM images. The SEM micrographs reveal that the hierarchical nanostructure VO2 nanoflakes anchored on rGO and intertwined with W5O14 nanorods remains intact after, indicating negligible structural degradation. Consistently, EDX (inset) of the C, O, V, and W exhibiting weight percentage of 29.02%, 25.94%, 44.27%, and 0.76 shows a vanadium increasing from that is no loss of V from the surface; thus, oxidation to V5+ manifests as a benign surface reconstruction rather than vanadate leaching.

3. Conclusions

In this study, we have successfully synthesized a novel rGO-VO2/W5O14 electrocatalyst via a facile hydrothermal method, showcasing remarkable potential for OER applications. The synthesized rGO-VO2/W5O14 composite demonstrates a homogeneous and uniform integration of its constituents which significantly contributes to its enhanced electrocatalytic activity. Among the prepared samples, the rG-VO2/W5O14-2 composition exhibited exceptional catalytic performance requiring a notably low overpotential of 265.8 mV to achieve a current density of 10 mA cm−2. This superior electrocatalytic performance is primarily attributed to the synergistic effects arising from the optimized structural interactions among rGO nanosheets, VO2 nanoflakes, and W5O14 nanorods, which effectively facilitate electron transport and amplify catalytic activity. Furthermore, all synthesized rGO-VO2/W5O14 composites displayed significantly reduced charge transfer resistance, promoting rapid electron and OH ion movement across the electrode interface, thereby accelerating OER kinetics. This work presents an efficient approach to developing advanced electrocatalysts with superior charge transfer dynamics and elevated electrochemical performance. Consequently, the rGO-VO2/W5O14 hydrogel-based materials exhibit considerable potential for practical utilization in advanced energy conversion and storage technologies.

4. Experimental Section

4.1. Chemicals

Sodium tungstate dihydrate (Na2WO4·2H2O, ≥99%), ammonium metavanadate (NH4VO3, ≥99%), polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP, ≥99%) were procured from Sigma-Aldrich St. Louis, MO, USA. Hydrochloric acid (HCl, extra pure), ammonia (NH3, extra pure), and ethanol (EtOH, C2H5OH, 94.5%) were sourced from Duksan Chemicals, Gyeonggi-do, Republic of Korea. Potassium hydroxide (KOH, >85%) was supplied by DaeJung Chemicals & Metals, Gyeonggi-do Republic of Korea. Acetylene black (99.9+%) was obtained from Thermo Scientific, Seoul, Republic of Korea. The carbon cloth utilized in this study was acquired from NARA Cell-Tech Corporation, Seoul, Republic of Korea. All chemicals were used without further purification, and deionized (DI) water was exclusively employed in all experimental procedures to ensure consistency and reliability in the study.

4.2. Preparation of rGO-VO2/W5O14 Composite

The rGO-VO2/W5O14 electrocatalyst was synthesized via a facile one-step hydrothermal approach, as schematically illustrated in Figure 1. Initially, 100 mg of graphene oxide (GO) was dispersed in 20 mL of DI water through ultrasonication to achieve a homogeneous suspension. Subsequently, 4.5 mL of ammonia solution and 150 μL of hydrazine hydrate were introduced into the mixture under continuous stirring to facilitate reduction and pH adjustment.
Following this, 0.043 g of NH4VO3 was added to the GO dispersion, and the mixture was further ultrasonicated for 10 min to ensure thorough mixing and precursor dissolution. To this solution, four distinct concentrations of Na2WO4·2H2O specifically 0.088, 0.176, 0.3525, and 0.52887 g were successively introduced. The total volume of the reaction mixture was then adjusted to 30 mL by the addition of 10 mL DI water. The resulting suspension underwent a further 10 min of ultrasonication, followed by magnetic stirring for 1 h to promote precursor interaction. The fully prepared solution was subsequently transferred into a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at 160 °C for 24 h, enabling the formation of a self-supporting hydrogel. After the hydrothermal process, the resulting hydrogel was subjected to freeze-dried for 24 h to obtain the final composite. For the preparation of rGO-VO2/W5O14 composites, the aforementioned procedure was repeated with the same four concentrations of Na2WO4·2H2O. The resulting samples were denoted as rG-VO2/W5O14-1, rG-VO2/W5O14-2, rG-VO2/W5O14-3, and rG-VO2/W5O14-4, corresponding to increasing sodium tungstate precursor amounts.

4.3. Material Characterization

The structural properties of the synthesized nanomaterials were examined using an X-ray diffractometer (X’Pert Pro, PAN Analytical, Almelo, The Netherlands) equipped with a Cu Kα radiation source. Raman spectroscopy was carried out with an XploRA Plus system (HORIBA Jobin Yvon S.A.S, Paris, France) to analyze the vibrational characteristics. The surface chemical composition and oxidation states were investigated through X-ray photoelectron spectroscopy (XPS) using a Thermo Scientific K-Alpha surface analysis system. Additionally, the surface morphology, particle size distribution, elemental composition, and elemental mapping were evaluated using scanning electron microscopy (SEM, HITACHI S-4800, Tokyo, Japan) integrated with an energy-dispersive X-ray (EDX) analysis system.

4.4. Electrochemical Analysis

Electrochemical measurements were systematically conducted using a Biologic Instrument WBCS3000 battery cycler (Gières, France) to comprehensively evaluate electrocatalytic performance. A conventional three-electrode configuration was adopted, consisting of carbon cloth (CC) as the working electrode, a Hg/HgO reference electrode, and a platinum plate as the counter electrode. Prior to catalyst deposition, the carbon cloth substrates underwent rigorous pretreatment involving successive sonication steps in 1 M HCl, deionized water, and ethanol, each for 20 min, followed by overnight drying at 70 °C to ensure cleanliness and optimal surface properties.
The electrocatalyst slurry was meticulously prepared using an optimized weight ratio of 80% active material, 10% polyvinylidene fluoride (PVDF), and 10% acetylene black dispersed uniformly in N-methyl-2-pyrrolidone (NMP) solvent. This slurry was evenly coated onto the pretreated carbon cloth substrates (1 × 1 cm2) and subsequently dried overnight at 60 °C to ensure robust adhesion and homogeneity.
Electrochemical characterization was executed in a nitrogen-saturated 1 M KOH aqueous electrolyte. Cyclic voltammetry (CV) measurements were performed within a non-Faradaic potential window of 0.1 to 0.2 V at various scan rates (5, 10, 15, 20, and 25 mV s−1) to investigate the electrochemical active surface area (ECSA) and capacitive behavior. Linear sweep voltammetry (LSV) analysis, conducted at a scan rate of 5 mV s−1 across a potential range of 0 to 1 V, was employed to determine the overpotential required for the OER. The measured potentials versus Hg/HgO reference electrode were accurately converted to the reversible hydrogen electrode (RHE) scale using the following Nernst equation:
ERHE = EHg/HgO + E°Hg/HgO + 0.0591 × (pH)
where E°Hg/HgO represents the standard electrode potential of the Hg/HgO reference electrode, and the pH of a 1 M KOH solution is approximately 13.9. LSV was utilized to relate the optimized electrocatalysts stability before and after 5000 cycles of CV study.

Author Contributions

M.B.: Writing-original draft, Methodology, Investigation. R.U.A.: Review & editing, Software. P.J.M.: Software and formal analysis. C.-W.J.: Supervision, Writing—review & editing, Project administration, Funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Technology development Program (RS-2024-00523443) funded by the Ministry of SMEs and Startups (MSS, Korea).

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zhou, N.; Wang, Q.; Zhu, J.; Zhou, N.; Chai, X.; Li, M.; Pei, Z.; Hu, K.; Huang, Z.; Chen, B. Interface engineering of Ni3S2 coupled NiFe-LDH heterostructure enables superior overall water splitting. Mater. Today Chem. 2025, 43, 102510. [Google Scholar] [CrossRef]
  2. Chen, B.; Kim, D.; Zhang, Z.; Lee, M.; Yong, K. MOF-derived NiCoZnP nanoclusters anchored on hierarchical N-doped carbon nanosheets array as bifunctional electrocatalysts for overall water splitting. Chem. Eng. J. 2021, 422, 130533. [Google Scholar] [CrossRef]
  3. Zhou, N.; Liu, R.; Wu, X.; Ding, Y.; Zhang, X.; Liang, S.; Deng, C.; Qin, G.; Huang, Z.; Chen, B. One-spot autogenous formation of crystalline-amorphous Ni3S2/NiFeOxHy heterostructure nanosheets array for synergistically boosted oxygen evolution reaction. J. Power Sources 2023, 574, 233163. [Google Scholar] [CrossRef]
  4. Kang, L.; Li, J.; Wang, Y.; Gao, W.; Hao, P.; Lei, F.; Xie, J.; Tang, B. Dual-oxidation-induced lattice disordering in a Prussian blue analog for ultrastable oxygen evolution reaction performance. J. Colloid Interface Sci. 2023, 630, 257–265. [Google Scholar] [CrossRef]
  5. Cao, S.; Qi, J.; Lei, F.; Wei, Z.; Lou, S.; Yang, X.; Guo, Y.; Hao, P.; Xie, J.; Tang, B. Reduction-induced surface reconstruction to fabricate cobalt hydroxide/molybdenum oxide hybrid nanosheets for promoted oxygen evolution reaction. Chem. Eng. J. 2021, 413, 127540. [Google Scholar] [CrossRef]
  6. Yang, X.; Kang, L.; Wei, Z.; Lou, S.; Lei, F.; Hao, P.; Xie, J.; Tang, B. A self-sacrificial templated route to fabricate CuFe Prussian blue analogue/Cu(OH)2 nanoarray as an efficient pre-catalyst for ultrastable bifunctional electro-oxidation. Chem. Eng. J. 2021, 422, 130139. [Google Scholar] [CrossRef]
  7. Xie, J.; Li, J.; Kang, L.; Li, J.; Wei, Z.; Lei, F.; Hao, P.; Tang, B. Molten-salt-protected pyrolytic approach for fabricating borate-modified cobalt–iron spinel oxide with robust oxygen-evolving performance. ACS Sustain. Chem. Eng. 2021, 9, 14596–14604. [Google Scholar] [CrossRef]
  8. Xie, J.; Yang, X.; Wang, Y.; Kang, L.; Li, J.; Wei, Z.; Hao, P.; Lei, F.; Wang, Q.; Tang, B. “Pit-dot” ultrathin nanosheets of hydrated copper pyrophosphate as efficient pre-catalysts for robust water oxidation. Chem. Commun. 2021, 57, 11517–11520. [Google Scholar] [CrossRef] [PubMed]
  9. Guo, Y.; Lei, F.; Qi, J.; Cao, S.; Wei, Z.; Lou, S.; Hao, P.; Xie, J.; Tang, B. Molten-salt-protected pyrolysis for fabricating perovskite nanocrystals with promoted water oxidation behavior. ACS Sustain. Chem. Eng. 2020, 8, 16711–16719. [Google Scholar] [CrossRef]
  10. Xie, J.; Zhang, X.; Zhang, H.; Zhang, J.; Li, S.; Wang, R.; Pan, B.; Xie, Y. Intralayered Ostwald ripening to ultrathin nanomesh catalyst with robust oxygen-evolving performance. Adv. Mater. 2017, 29, 1604765. [Google Scholar] [CrossRef]
  11. Sun, W.; Wei, Z.; Qi, J.; Kang, L.; Li, J.; Xie, J.; Tang, B.; Xie, Y. Rapid and scalable synthesis of Prussian blue analogue nanocubes for electrocatalytic water oxidation. Chin. J. Chem. 2021, 39, 2347–2353. [Google Scholar] [CrossRef]
  12. Xie, J.; Xin, J.; Wang, R.; Zhang, X.; Lei, F.; Qu, H.; Hao, P.; Cui, G.; Tang, B.; Xie, Y. Sub-3 nm pores in two-dimensional nanomesh promoting the generation of electroactive phase for robust water oxidation. Nano Energy 2018, 53, 74–82. [Google Scholar] [CrossRef]
  13. Zhang, W.; Kong, S.; Wang, W.; Cheng, Y.; Li, Z.; He, C. Enhanced electrocatalytic performance of LCO-NiFe-C3N4 composite material for highly efficient overall water splitting. J. Colloid Interface Sci. 2025, 680, 787–796. [Google Scholar] [CrossRef]
  14. Li, M.; Ma, D.; Feng, X.; Zhi, C.; Jia, Y.; Zhang, J.; Zhang, Y.; Chen, Y.; Shi, L.; Shi, J.W. Design and Modification of Layered Double Hydroxides-Based Compounds in Electrocatalytic Water Splitting: A Review. Small 2025, 21, 2412576. [Google Scholar] [CrossRef]
  15. Farhan, A.; Khalid, A.; Maqsood, N.; Iftekhar, S.; Sharif, H.M.A.; Qi, F.; Sillanpää, M.; Asif, M.B. Progress in layered double hydroxides (LDHs): Synthesis and application in adsorption, catalysis and photoreduction. Sci. Total Environ. 2024, 912, 169160. [Google Scholar] [CrossRef]
  16. Zhai, P.; Xia, M.; Wu, Y.; Zhang, G.; Gao, J.; Zhang, B.; Cao, S.; Zhang, Y.; Li, Z.; Fan, Z. Engineering single-atomic ruthenium catalytic sites on defective nickel-iron layered double hydroxide for overall water splitting. Nat. Commun. 2021, 12, 4587. [Google Scholar] [CrossRef]
  17. Wu, Z.-Y.; Chen, F.-Y.; Li, B.; Yu, S.-W.; Finfrock, Y.Z.; Meira, D.M.; Yan, Q.-Q.; Zhu, P.; Chen, M.-X.; Song, T.-W. Non-iridium-based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane water electrolysis. Nat. Mater. 2023, 22, 100–108. [Google Scholar] [CrossRef] [PubMed]
  18. Li, C.; Ye, B.; Ouyang, B.; Zhang, T.; Tang, T.; Qiu, Z.; Li, S.; Li, Y.; Chen, R.; Wen, W. Dual Doping of N and F on Co3O4 to Activate the Lattice Oxygen for Efficient and Robust Oxygen Evolution Reaction. Adv. Mater. 2025, 37, 2501381. [Google Scholar] [CrossRef]
  19. Qasim, M.; Atta, M.S.; Makasana, J.; Rekha, M.; Kumar, G.S.; Al-Anber, M.A.; Das, S.N.; Chaudhary, R.; Kumar, A.; Oza, A.D. Enhancement in performance of CuMnO2 anchored over rGO for water splitting. J. Phys. Chem. Solids 2025, 206, 112838. [Google Scholar] [CrossRef]
  20. Nemiwal, M.; Zhang, T.C.; Kumar, D. Graphene-based electrocatalysts: Hydrogen evolution reactions and overall water splitting. Int. J. Hydrogen Energy 2021, 46, 21401–21418. [Google Scholar] [CrossRef]
  21. Baby, N.; Thangarasu, S.; Murugan, N.; Kim, Y.A.; Oh, T.-H. MOF derived Fe3O4/NiO decorated rGO-BN for efficient electrochemical water splitting. Int. J. Hydrogen Energy 2025, 130, 127–138. [Google Scholar] [CrossRef]
  22. Han, G.-Q.; Liu, Y.-R.; Hu, W.-H.; Dong, B.; Li, X.; Shang, X.; Chai, Y.-M.; Liu, Y.-Q.; Liu, C.-G. Three dimensional nickel oxides/nickel structure by in situ electro-oxidation of nickel foam as robust electrocatalyst for oxygen evolution reaction. Appl. Surf. Sci. 2015, 359, 172–176. [Google Scholar] [CrossRef]
  23. Zhang, K.; Luo, Y.; Wang, H.; Li, J.; Wang, Y.; Du, X.; Liu, G. Transition metal induced metal oxide lattice strain for efficient and stable alkaline water splitting. Chem. Eng. J. 2025, 511, 161686. [Google Scholar] [CrossRef]
  24. Kao, Y.-T.; Young, C. Trimetallic oxide catalysts from metal-organic frameworks on Ti3C2Tx MXene for enhanced water splitting. Int. J. Hydrogen Energy 2025, 100, 704–712. [Google Scholar] [CrossRef]
  25. Fester, J.; Makoveev, A.; Grumelli, D.; Gutzler, R.; Sun, Z.; Rodríguez-Fernández, J.; Kern, K.; Lauritsen, J.V. The structure of the cobalt oxide/Au catalyst interface in electrochemical water splitting. Angew. Chem. 2018, 130, 12069–12073. [Google Scholar] [CrossRef]
  26. Xie, J.; Zhang, X.; Xie, Y. Preferential microstructure design of two-dimensional electrocatalysts for boosted oxygen evolution reaction. ChemCatChem 2019, 11, 4662–4670. [Google Scholar] [CrossRef]
  27. Yang, X.; Sun, X.; Qi, J.; Zhang, J.; Zheng, X.; Zhang, X.; Lei, F.; Sun, X.; Tang, B.; Xie, J. Two-dimensional confined topotactic transformation to produce Co-Pi/Co3O4 hybrid porous nanosheets for promoted water oxidation. J. Colloid Interface Sci. 2025, 677, 406–416. [Google Scholar] [CrossRef]
  28. Cummins, D.R.; Martinez, U.; Sherehiy, A.; Kappera, R.; Martinez-Garcia, A.; Schulze, R.K.; Jasinski, J.; Zhang, J.; Gupta, R.K.; Lou, J. Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction. Nat. Commun. 2016, 7, 11857. [Google Scholar] [CrossRef]
  29. Shang, X.; Chi, J.-Q.; Liu, Z.-Z.; Dong, B.; Yan, K.-L.; Gao, W.-K.; Zeng, J.-B.; Chai, Y.-M.; Liu, C.-G. Ternary Ni-Fe-V sulfides bundles on nickel foam as free-standing hydrogen evolution electrodes in alkaline medium. Electrochim. Acta 2017, 256, 241–251. [Google Scholar] [CrossRef]
  30. Dong, B.; Zhao, X.; Han, G.-Q.; Li, X.; Shang, X.; Liu, Y.-R.; Hu, W.-H.; Chai, Y.-M.; Zhao, H.; Liu, C.-G. Two-step synthesis of binary Ni–Fe sulfides supported on nickel foam as highly efficient electrocatalysts for the oxygen evolution reaction. J. Mater. Chem. A 2016, 4, 13499–13508. [Google Scholar] [CrossRef]
  31. Zhong, X.; Tang, J.; Wang, J.; Shao, M.; Chai, J.; Wang, S.; Yang, M.; Yang, Y.; Wang, N.; Wang, S. 3D heterostructured pure and N-Doped Ni3S2/VS2 nanosheets for high efficient overall water splitting. Electrochim. Acta 2018, 269, 55–61. [Google Scholar] [CrossRef]
  32. Xing, Z.; Li, Q.; Wang, D.; Yang, X.; Sun, X. Self-supported nickel nitride as an efficient high-performance three-dimensional cathode for the alkaline hydrogen evolution reaction. Electrochim. Acta 2016, 191, 841–845. [Google Scholar] [CrossRef]
  33. Balogun, M.-S.; Huang, Y.; Qiu, W.; Yang, H.; Ji, H.; Tong, Y. Updates on the development of nanostructured transition metal nitrides for electrochemical energy storage and water splitting. Mater. Today 2017, 20, 425–451. [Google Scholar] [CrossRef]
  34. Li, W.; Gao, X.; Wang, X.; Xiong, D.; Huang, P.-P.; Song, W.-G.; Bao, X.; Liu, L. From water reduction to oxidation: Janus Co-Ni-P nanowires as high-efficiency and ultrastable electrocatalysts for over 3000 h water splitting. J. Power Sources 2016, 330, 156–166. [Google Scholar] [CrossRef]
  35. Wan, H.; Li, L.; Chen, Y.; Gong, J.; Duan, M.; Liu, C.; Zhang, J.; Wang, H. One pot synthesis of Ni12P5 hollow nanocapsules as efficient electrode materials for oxygen evolution reactions and supercapacitor applications. Electrochim. Acta 2017, 229, 380–386. [Google Scholar] [CrossRef]
  36. Usmani, A.B.S.; Rana, S.; Arora, A.; Yadav, K.K.; Sammi, H.; Sardana, N.; Jha, M. Electrochemical oxygen generation from VO2 nanoflakes decorated onto graphite sheet. J. Alloys Compd. 2024, 976, 173058. [Google Scholar] [CrossRef]
  37. Karahan, O.; Tufani, A.; Unal, S.; Misirlioglu, I.B.; Menceloglu, Y.Z.; Sendur, K. Synthesis and morphological control of VO2 nanostructures via a one-step hydrothermal method. Nanomaterials 2021, 11, 752. [Google Scholar] [CrossRef]
  38. Goodenough, J.B. The two components of the crystallographic transition in VO2. J. Solid State Chem. 1971, 3, 490–500. [Google Scholar] [CrossRef]
  39. Sreekanth, T.; Tamilselvan, M.; Yoo, K.; Kim, J. Microwave-assisted in situ growth of VO2 nanoribbons on Ni foam as inexpensive bifunctional electrocatalysts for the methanol oxidation and oxygen evolution reactions. Appl. Surf. Sci. 2021, 570, 151119. [Google Scholar] [CrossRef]
  40. Cui, R.; Yu, S.; Han, P.; Wu, Y.; Li, Y.; Dang, Y.; Zhou, Y.; Zhu, J.-J. Novel vacancy-rich Co3O4/VO2 nanohybrids for enhanced electrocatalytic performance and application as oxygen evolution electrocatalysts. J. Alloys Compd. 2021, 876, 160129. [Google Scholar] [CrossRef]
  41. Gowrisankar, A.; Thangavelu, S. Effect of β-MnO2 on controlled polymorphism of VO2(x) (x= A, B, M polymorphs) microstructures anchored on two-dimensional reduced graphene oxide nanosheets for overall water splitting. J. Phys. Chem. C 2022, 126, 3419–3431. [Google Scholar] [CrossRef]
  42. Madhura, T.R.; Kumar, G.G.; Ramaraj, R. Reduced graphene oxide supported 2D-NiO nanosheets modified electrode for urea detection. J. Solid State Electrochem. 2020, 24, 3073–3081. [Google Scholar] [CrossRef]
  43. Kumar, N.; Upadhyay, S.; Chetana, S.; Joshi, N.C.; Priyadarshi, N.; Hossain, I.; Sen, A. Hydrothermal growth of 1D VO2 for oxygen evolution reaction. Mater. Lett. 2023, 335, 133810. [Google Scholar] [CrossRef]
  44. Saqib, M.; Jelenc, J.; Pirker, L.; Škapin, S.D.; De Pietro, L.; Ramsperger, U.; Knápek, A.; Müllerová, I.; Remškar, M. Field emission properties of single crystalline W5O14 and W18O49 nanowires. J. Electron. Spectrosc. Relat. Phenom. 2020, 241, 146837. [Google Scholar] [CrossRef]
  45. Le, T.K.; Kang, M.; Kim, S.W. Relation of photoluminescence and sunlight photocatalytic activities of pure V2O5 nanohollows and V2O5/RGO nanocomposites. Mater. Sci. Semicond. Process. 2019, 100, 159–166. [Google Scholar] [CrossRef]
  46. Bhosale, M.; Thangarasu, S.; Magdum, S.S.; Jeong, C.; Oh, T.-H. Enhancing the electrocatalytic performance of vanadium oxide by interface interaction with rGO and NiO nanostructures for electrochemical water oxidation. Int. J. Hydrogen Energy 2024, 54, 1449–1460. [Google Scholar] [CrossRef]
  47. Bhosale, M.; Thangarasu, S.; Murugan, N.; Kim, Y.A.; Oh, T.-H. Engineering 2D heterostructured VS2-rGO-Ni nanointerface to stimulate electrocatalytic water splitting and supercapacitor applications. J. Energy Storage 2023, 73, 109133. [Google Scholar] [CrossRef]
  48. Wu, X.; Tao, Y.; Dong, L.; Wang, Z.; Hu, Z. Preparation of VO2 nanowires and their electric characterization. Mater. Res. Bull. 2005, 40, 315–321. [Google Scholar] [CrossRef]
  49. Huang, C.; Zhu, Q.; Zhang, W.; Qi, P.; Xiao, Q.; Yu, Y. Facile preparation of W5O14 nanosheet arrays with large crystal channels as high-performance negative electrode for supercapacitor. Electrochim. Acta 2020, 330, 135209. [Google Scholar] [CrossRef]
  50. Zhao, Z.; Xu, X.; Wang, H.-E. Enhanced pseudocapacitive lithium-ion storage in a coherent rGO/VO2-R heterojunction. Energy Fuels 2024, 38, 4689–4698. [Google Scholar] [CrossRef]
  51. Yang, M.; Wang, J.; Dai, P.; Tang, X.; Li, G.; Yang, L. RuNi single-atom alloy anchored on rGO as an outstanding bifunctional catalyst for efficient electrochemical water splitting. New J. Chem. 2024, 48, 3942–3951. [Google Scholar] [CrossRef]
  52. Zhou, W.; Li, X.; Li, X.; Shao, J.; Yang, H.; Chai, X.; Hu, Q.; He, C. Crafting amorphous VO2–crystalline NiS2 heterostructures as bifunctional electrocatalysts for efficient water splitting: The different cocatalytic function of VO2. Chem. Eng. J. 2023, 470, 144146. [Google Scholar] [CrossRef]
  53. Yu, W.; Shen, Z.; Peng, F.; Lu, Y.; Ge, M.; Fu, X.; Sun, Y.; Chen, X.; Dai, N. Improving gas sensing performance by oxygen vacancies in sub-stoichiometric WO3−x. RSC Adv. 2019, 9, 7723–7728. [Google Scholar] [CrossRef]
  54. Remškar, M.; Kovac, J.; Viršek, M.; Mrak, M.; Jesih, A.; Seabaugh, A. W5O14 Nanowires. Adv. Funct. Mater. 2007, 17, 1974–1978. [Google Scholar] [CrossRef]
  55. Cogal, G.C.; Karaca, G.Y.; Uygun, E.; Kuralay, F.; Oksuz, L.; Remskar, M.; Oksuz, A.U. RF plasma-enhanced conducting Polymer/W5O14 based self-propelled micromotors for miRNA detection. Anal. Chim. Acta 2020, 1138, 69–78. [Google Scholar] [CrossRef]
  56. Pan, U.N.; Singh, T.I.; Paudel, D.R.; Gudal, C.C.; Kim, N.H.; Lee, J.H. Covalent doping of Ni and P on 1T-enriched MoS2 bifunctional 2D-nanostructures with active basal planes and expanded interlayers boosts electrocatalytic water splitting. J. Mater. Chem. A 2020, 8, 19654–19664. [Google Scholar] [CrossRef]
  57. Tang, C.; Zhong, L.; Xiong, R.; Xiao, Y.; Cheng, B.; Lei, S. Regulable in-situ autoredox for anchoring synergistic Ni/NiO nanoparticles on reduced graphene oxide with boosted alkaline electrocatalytic oxygen evolution. J. Colloid Interface Sci. 2023, 648, 181–192. [Google Scholar] [CrossRef] [PubMed]
  58. Ma, L.; Sui, S.; Zhai, Y. Preparation and characterization of Ir/TiC catalyst for oxygen evolution. J. Power Sources 2008, 177, 470–477. [Google Scholar] [CrossRef]
Figure 1. Schematic illustration of synthesis of rGO-VO2/W5O14 hydrogel.
Figure 1. Schematic illustration of synthesis of rGO-VO2/W5O14 hydrogel.
Gels 11 00670 g001
Figure 2. (a) XRD spectra of all the composite and (b) Raman spectra of rG-VO2/W5O14-2 composite.
Figure 2. (a) XRD spectra of all the composite and (b) Raman spectra of rG-VO2/W5O14-2 composite.
Gels 11 00670 g002
Figure 3. (a) XPS survey spectra, high resolution XPS spectra of (b) C1s, (c) O1s, (d) V2p, and (e) W4f of rG-VO2/W5O14-2 composite.
Figure 3. (a) XPS survey spectra, high resolution XPS spectra of (b) C1s, (c) O1s, (d) V2p, and (e) W4f of rG-VO2/W5O14-2 composite.
Gels 11 00670 g003
Figure 4. SEM micrograph images of (a1a3) rG-VO2/W5O14-1, (b1b3) rG-VO2/W5O14-2, (c1c3) rG-VO2/W5O14-3, and (d1d3) rG-VO2/W5O14-4 electrocatalyst.
Figure 4. SEM micrograph images of (a1a3) rG-VO2/W5O14-1, (b1b3) rG-VO2/W5O14-2, (c1c3) rG-VO2/W5O14-3, and (d1d3) rG-VO2/W5O14-4 electrocatalyst.
Gels 11 00670 g004
Figure 5. (a) Energy-dispersive X-ray spectroscopy analysis of rG-VO2/W5O14-2, and (bf) elemental mapping data of rG-VO2/W5O14-2 electrocatalyst.
Figure 5. (a) Energy-dispersive X-ray spectroscopy analysis of rG-VO2/W5O14-2, and (bf) elemental mapping data of rG-VO2/W5O14-2 electrocatalyst.
Gels 11 00670 g005
Figure 6. Electrochemical characterizations of electrocatalyst OER performances: (a) LSV curves at 5 mV/s scan rate, (b) analogous Tafel slopes, (c) assessment of the OER performance concerning overpotential at 10 mA cm−2 and Tafel slope, and (d) EIS spectra of all the electrocatalysts.
Figure 6. Electrochemical characterizations of electrocatalyst OER performances: (a) LSV curves at 5 mV/s scan rate, (b) analogous Tafel slopes, (c) assessment of the OER performance concerning overpotential at 10 mA cm−2 and Tafel slope, and (d) EIS spectra of all the electrocatalysts.
Gels 11 00670 g006
Figure 7. Cyclic voltammetry analysis at different scan rate (a) rG-VO2/W5O14-1, (b) rG-VO2/W5O14-2, (c) rG-VO2/W5O14-3, and (d) rG-VO2/W5O14-4, (e) Cdl graph, and (f) ECSA graph of all the electrocatalysts.
Figure 7. Cyclic voltammetry analysis at different scan rate (a) rG-VO2/W5O14-1, (b) rG-VO2/W5O14-2, (c) rG-VO2/W5O14-3, and (d) rG-VO2/W5O14-4, (e) Cdl graph, and (f) ECSA graph of all the electrocatalysts.
Gels 11 00670 g007
Figure 8. (a) LSV curves of rGO-VO2/W5O14-2 before and after 5000 CV cycles, (b) Chronopotentiometry analysis, SEM images (c) Before analysis, and (d) After analysis (inset EDAX analysis).
Figure 8. (a) LSV curves of rGO-VO2/W5O14-2 before and after 5000 CV cycles, (b) Chronopotentiometry analysis, SEM images (c) Before analysis, and (d) After analysis (inset EDAX analysis).
Gels 11 00670 g008
Table 1. EDAX analysis data of all the electrocatalysts.
Table 1. EDAX analysis data of all the electrocatalysts.
ElectrocatalystsC (Wt%)O (Wt%)V (Wt%)W (Wt%)
rG-VO2/W5O14-139.7729.730.130.40
rG-VO2/W5O14-238.3528.9731.800.88
rG-VO2/W5O14-337.7829.9130.761.55
rG-VO2/W5O14-438.1530.7928.262.8
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Bhosale, M.; Amate, R.U.; Morankar, P.J.; Jeon, C.-W. Catalytic Interface of rGO-VO2/W5O14 Hydrogel for High-Performance Electrochemical Water Oxidation. Gels 2025, 11, 670. https://doi.org/10.3390/gels11080670

AMA Style

Bhosale M, Amate RU, Morankar PJ, Jeon C-W. Catalytic Interface of rGO-VO2/W5O14 Hydrogel for High-Performance Electrochemical Water Oxidation. Gels. 2025; 11(8):670. https://doi.org/10.3390/gels11080670

Chicago/Turabian Style

Bhosale, Mrunal, Rutuja U. Amate, Pritam J. Morankar, and Chan-Wook Jeon. 2025. "Catalytic Interface of rGO-VO2/W5O14 Hydrogel for High-Performance Electrochemical Water Oxidation" Gels 11, no. 8: 670. https://doi.org/10.3390/gels11080670

APA Style

Bhosale, M., Amate, R. U., Morankar, P. J., & Jeon, C.-W. (2025). Catalytic Interface of rGO-VO2/W5O14 Hydrogel for High-Performance Electrochemical Water Oxidation. Gels, 11(8), 670. https://doi.org/10.3390/gels11080670

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop