Substantial Electrocatalytic Oxygen Evolution Performances of Activated Carbon-Decorated Vanadium Pentoxide Nanocomposites

Sekar, Sankar; Ilanchezhiyan, Pugazhendi; Ahmed, Abu Talha Aqueel; Lee, Youngmin; Lee, Sejoon

doi:https://doi.org/10.1155/2024/9953038

International Journal of Energy Research

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Abstract Introduction Results and Discussion Conclusions Data Availability Conflicts of Interest Authors’ Contributions Acknowledgments Supplementary Materials References Copyright Related Articles

Research Article | Open Access

Volume 2024 | Article ID 9953038 | https://doi.org/10.1155/2024/9953038

Substantial Electrocatalytic Oxygen Evolution Performances of Activated Carbon-Decorated Vanadium Pentoxide Nanocomposites

Sankar Sekar,^1,2Pugazhendi Ilanchezhiyan,²Abu Talha Aqueel Ahmed,¹Youngmin Lee,^1,2and Sejoon Lee^1,2

Academic Editor: Suresh Kannan Balasingam

Received13 Mar 2024

Revised09 Apr 2024

Accepted20 Apr 2024

Published08 May 2024

Abstract

Developing the ecofriendly and high-fidelity electrocatalysts for the oxygen evolution reaction (OER) is essential to foster effective production of environmentally friendly hydrogen. Herein, we fabricated the highly efficient OER electrocatalysts of the activated carbon-decorated vanadium pentoxide (AC-V₂O₅) nanocomposites using a facile hydrothermal technique. The AC-V₂O₅ nanocomposites displayed an aggregated structure of the AC nano-sheet-anchored orthorhombic V₂O₅ nanorods. When performing the OER process in an alkaline electrolyte at 10 mA/cm², AC-V₂O₅ exhibited the low overpotential (~230 mV), small Tafel slope (~54 mV/dec), and excellent stability. These substantial OER performances of AC-V₂O₅ could be ascribed to the synergistic effects from both the electrochemically active V₂O₅ nanorods and the highly conductive AC nanosheets. The results infer that the AC-V₂O₅ nanocomposites possess a substantial aptitude as a high-performance OER electrocatalyst for production of the future green energy source—hydrogen.

1. Introduction

Recently, continuously escalating demands and concerns about the energy, environment, and exhaustion of fossil fuels have spurred the energy science and technology communities to explore the ecofriendly renewable energy sources [1–3]. Among various energy sources, due to its natural abundance, high energy density, and zero carbon radiation, hydrogen (H₂) has emerged as a prominent resource for future green energy technology [4, 5]. For effective H₂ production, the electrocatalytic water-splitting technique is promising because of its excellent recyclability, extraordinary sustainability, and absence of pollution [6, 7]. In the overall water-splitting process, the oxygen evolution reaction (OER) activity is of great importance because of its sluggish reaction kinetics, attributed to the four-electron oxidative half-reaction [8, 9]. Currently, IrO₂- and RuO₂-based nanocomposites have been secured as an excellent OER electrocatalyst because of their supreme active sites and high H₂ production rates. However, the high cost, rareness, and fast deactivation of those rare earth metal oxides forcefully impede their wide applications [10, 11]. Therefore, developing the cost-effective, earth-abundant, and nonnoble OER electrocatalysts with a high water-to-hydrogen conversion efficiency is crucial.

As an alternative to the rare earth metal oxides, the semiconductive transition metal oxides are promising because of their high specific surface areas, modified electronic structures, enhanced interface tunability, and high electrochemical activity [12, 13]. Among them, vanadium pentoxide (V₂O₅) is favorable for demonstrating high OER performances because of its cost-effectiveness, simple synthesis process, layered structure, high redox-active sites, and intrinsically nonexplosive safe characteristics [14–17]. To obtain the high-quality V₂O₅ nanostructures, there are several synthesis methods such as sonochemical [18, 19], sol-gel [20], acid leaching [21], electrospinning [22, 23], laser irradiation [24], spray pyrolysis [25], hydrothermal [26–28], and chemical vapor deposition [29, 30]. When using bare V₂O₅ alone as an OER electrocatalyst, however, OER activity is rather meager because of its fast electron transmission, low electrical conductivity, scarce electrochemically active sites, and sluggish kinetics [10, 11, 17]. To improve the electrocatalytic OER performance of V₂O₅, therefore, decorating the V₂O₅ nanostructures with different transition metal oxides/chalcogenides [31–33] or various carbonaceous materials (e.g., graphene [34], reduced graphene oxide [15, 35], carbon nanotubes [36], graphitic carbon [18], and activated carbon (AC) [37]) was employed. Among them, AC possesses several advantages such as a variety of morphological architectures, facile synthesis methods, large specific surface areas, and superior electrical conductivity. Furthermore, the high-quality AC nanostructures could be derived from various biomass waste resources [38–40]; hence, biomass AC provides more advantages such as mass production, low cost, fast supply, and ecofriendliness [41–43]. Moreover, the morphological characteristics of AC could be modified when obtaining it through carbonization and activation of the biomass materials [44, 45]. Despite the above benefits, biomass AC-incorporated V₂O₅ has not been used as an OER electrocatalyst.

All those backgrounds prompt us to investigate the electrocatalytic characteristics of the biomass AC-encapsulated V₂O₅ (AC-V₂O₅) nanocomposites. Herein, we fabricated the high-performance electrocatalytic OER catalyst of AC-V₂O₅ by the facile hydrothermal aggregation process using the hydrothermally disassembled V₂O₅ and the biomass rice husk-derived AC nanosheets. The prepared AC-V₂O₅ catalyst exhibited the excellent OER activities with a low overpotential (~230 mV) and a small Tafel slope (~54 mV/dec). In this article, the material characteristic-to-electrocatalytic performances are meticulously analyzed and discussed.

2. Experimental Section

2.1. Materials

For the hydrothermal synthesis of the V₂O₅ nanorods, the commercial bulk V₂O₅ powder, ethanol (C₂H₆O), and potassium hydroxide (KOH) were purchased from Sigma-Aldrich (St. Louis, MO, USA); and those were used with no additional purification. In the case of biomass AC, brown rice husks, which had been collected from Tamil Nadu (India), were used as a source material. In all the experiments, deionized (DI) water was employed to avoid chemical contamination.

2.2. Preparation of V₂O₅ Nanorods

Figure 1 represents the experimental steps for fabricating the AC-V₂O₅ nanocomposites. As a primary step, the V₂O₅ nanorods were prepared by the hydrothermal disassembly process using the bulk V₂O₅ power. Initially, 0.5 g of V₂O₅ was mixed in 70 ml of DI water by stirring for 20 min at room temperature (25°C). Next, the above aqueous solution was transferred to the Teflon autoclave (100 ml), and then, the hydrothermal disassembly was performed in an electric oven at 150°C for 6 h. Thereafter, the autoclave chamber was cooled to 25°C, and then, the hydrothermally disassembled V₂O₅ nanorods were gathered and rinsed with DI water and C₂H₆O to remove other contaminants that might be introduced during the sample manipulation. Finally, the V₂O₅ nanorods were obtained in nanopowder form by drying the above colloidal suspension at 120°C for 8 h.

2.3. Derivation of Biomass AC Nanosheets

The biomass AC nanosheets were derived from the brown rice husks through the following process. Firstly, the raw rice husks were cleaned with DI water and dehydrated for 100 h in an air atmosphere. Then, the dried rice husks were carbonized in a muffle furnace at 400°C for 1 h. After collecting 3 g of carbonized rice husk ashes in a mortar, 12 g of KOH was mixed to carry out the KOH activation process. The mixture was then put into the alumina crucible and annealed at 600°C for 2 h. Next, the KOH-activated rice husk ashes were stirred in 100 ml of DI water to get rid of other traces of potassium-related residues. Finally, the cleaned suspension was filtrated and dried at 100°C for 12 h to collect the AC nanosheets in powder form.

2.4. Fabrication of AC-V₂O₅ Nanocomposites

The AC-V₂O₅ composites were prepared by the hydrothermal reassembly process using the above V₂O₅ nanorods and AC nanosheets. Initially, 0.5 g of V₂O₅ nanorods was dissolved in 70 ml of DI water and stirred for 20 min at room temperature (25°C). Then, 0.25 g of biomass AC nanosheets was added into the V₂O₅-mixed aqueous solution. After stirring it for 20 min, the AC-V₂O₅ mixture solution was transferred to the Teflon autoclave (100 ml) to conduct the hydrothermal reassembly process. Soon after the hydrothermal treatment at 150°C for 6 h, the autoclave chamber was cooled to 25°C to collect the aggregated composites of AC-V₂O₅. The collected AC-V₂O₅ wet powder was filtered and cleaned three times by C₂H₆O and DI water to remove the unreacted traces. After drying the cleaned AC-V₂O₅ wet powder at 120°C for 8 h, finally, the nanopowder type of AC-V₂O₅ was obtained.

2.5. Material Characterization

The morphological and the compositional properties of V₂O₅ and AC-V₂O₅ were studied by means of field emission scanning electron microscopy (FE-SEM, Inspect-F50, FEI, Mahwah, NJ, USA) and in situ energy-dispersive X-ray (EDX) spectroscopy, respectively. The vibrational and the crystallographic characteristics were analyzed by Raman scattering spectroscopy (LabRAM HR-800, Jobin Yvon, Longjumeau, France) and X-ray diffractometry (XRD, D8-Advance, Bruker, USA), respectively. Furthermore, the chemical bonding states of AC-V₂O₅ were further investigated by X-ray photoelectron spectroscopy (XPS) using a ESCALab250Xi system (Thermo Fisher Scientific, USA).

2.6. Measurements of Electrocatalytic OER Characteristics

The electrocatalytic OER performances of V₂O₅ and AC-V₂O₅ were investigated through the electrochemical characterization using the three-electrode measurement setup with a VersaSTAT-3 workstation (Ametek Scientific Instruments, Berwyn, PA, USA). Initially, we fabricated two different working electrodes using V₂O₅ and AC-V₂O₅. For this, the prepared catalyst (i.e., either V₂O₅ or AC-V₂O₅) was blended with the N-methyl-2-pyrrolidinone solution and coated onto the nickel foam substrate (1 cm²). Then, each catalyst-coated nickel foam substrate was dried individually at 180°C for 6 h. The alkaline KOH (1 M) solution was used as an electrolyte source for the OER measurements. Additionally, the Pt mesh electrode and the saturated calomel electrode (SCE) were also used as a counter electrode and a reference electrode, respectively. After preparing all the required electrodes, the cyclic voltammetry (CV) characteristics were assessed at different scan rates of 10–100 mV/s within a potential range from 0 to 0.5 V. In addition, the linear sweep voltammetry (LSV) measurements were conducted in −0.1–1.0 V potential ranges at a constant scan rate of 1.0 mV/s. To investigate the electrical characteristics of V₂O₅ and AC-V₂O₅, the electrochemical impedance spectroscopy (EIS) responses were measured at 1 Hz–10 kHz with the 10 mV amplitude of the applied AC signal. Furthermore, the chronopotentiometric (CP) characteristics of the samples were examined by applying stepwise current (i.e., 10 ⟶ 20 ⟶ 30 ⟶ 40 ⟶ 50 ⟶ 100 mA/cm² (for 10 min at each step)).

3. Results and Discussion

Figure 2 displays the morphological features of V₂O₅ and AC-V₂O₅. The bare V₂O₅ nanorods exhibited the aggregated morphology with plenty of nanorods (Figures 2(a) and 2(b)). The formation of V₂O₅ nanorods can be explained by hydrothermal cleaving and dispersing the layer-structured V₂O₅ stacks [46–51]. Since bulk V₂O₅ is composed of bunch of stacked layers (Figure S1), they can be effectively broken into the smaller species. Namely, during the hydrothermal process in a closed autoclave medium, the hydroxyl (OH) and hydrogen (H) radicals will supply the boundaries of the layered V₂O₅ stacks with a sufficient energy to cleave themselves. Different from the bare V₂O₅ nanorods, the AC-V₂O₅ nanocomposites revealed the AC nanosheet-decorated V₂O₅ nanorods (Figures 2(c) and 2(d); see also Figure S2 for the morphological shape of the AC nanosheets). Namely, after hydrothermal hybridization of V₂O₅ and AC, most of the V₂O₅ nanorods were aggregated and encapsulated by the AC nanosheets. Next, the compositional properties of V₂O₅ and AC-V₂O₅ were confirmed by in situ EDX measurements. As shown in Figures 2(e) and 2(f), both samples displayed their own intrinsic species such as C, V, and O, indicating the high purity of the present materials. One additional peak from Au was arisen from the ultrathin coating layer utilized to minimize the electron charging behavior during the FE-SEM measurement of the oxide material.

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The structural characteristics of V₂O₅ and AC-V₂O₅ were investigated by XRD measurements. As depicted in Figure 3(a), the V₂O₅ nanorods exhibited the diffraction patterns at 15.3, 20.2, 21.7, 26.2, 31.0, 32.3, 33.3, 34.2, 37.3, 41.1, 42.0, 45.4, 47.1, 48.9, 49.9, 51.9, 55.5, 58.4, 60.1, 62.1, 66.1, 68.8, 71.1, 72.4, and 76.1°, corresponding to the (200), (001), (110), (101), (400), (011), (111), (301), (211), (020), (120), (411), (600), (021), (002), (610), (012), (421), (312), (701), (230), (330), (621), (322), and (331) crystal planes of orthorhombic V₂O₅ (JCPDS card no: 86-2248), respectively [52, 53]. For the AC nanosheets (see Figure S3), the two typical patterns of (002) and (100) were found at 21.8° and 43.1°, respectively. In the case of AC-V₂O₅, the (001) peak was red-shifted by 6.2° because of the aggregation of amorphous AC and crystalline V₂O₅ during the hydrothermal reassembly process [54, 55]. However, no AC-related patterns were detected from AC-V₂O₅ because of the relatively lower diffraction intensity of AC than that of V₂O₅ [56, 57].

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(b)

The molecular interactions of V₂O₅ and AC-V₂O₅ were further examined by Raman scattering spectroscopy. As can be seen from Figure 3(b), the V₂O₅ nanorods showed the ten structural vibrational bands at 102, 143, 197, 282, 300, 403, 482, 524, 700, and 995 cm⁻¹, associated with the orthorhombic structure of V₂O₅. The Raman modes at 102 and 143 cm⁻¹ might be ascribed to the stretching vibrations of the V–O bond and the layered V₂O₅ structure [58], respectively. The Raman modes at 197 and 282 cm⁻¹ could be accredited to the twisting vibrations of O–V–O with the chain translation in V₂O₅ [52]. The bands at 300 and 403 cm⁻¹ are known to originate from the twisting vibrations of the V=O bonds [59]. The Raman mode at 482 cm⁻¹ could be described as resulting from the elongating vibrations of the triply-coordinated V₃–O bonds, which are located on the oxygen atom edges shared by three pyramids. The Raman scattering modes at 524 and 700 cm⁻¹ could be correlated with the twisting and stretching modes of the doubly synchronized V–O–V bonds, comprising the corner-shared oxygen atoms [60, 61]. The vibrational band at 995 cm⁻¹ was sprouted from the elongating vibrations of the twofold V=O bonds, verifying the layered structure of V₂O₅ [62]. In the case of the AC nanosheets, we here note that two distinct Raman scattering modes were observed at 1354 and 1601 cm⁻¹, originating from the D and G bands of the layered AC nanosheets (see Figure S4) [40, 42, 57]. Consequently, the AC-V₂O₅ nanocomposites clearly revealed the relevant Raman features from both V₂O₅ and AC. Furthermore, the Raman bands of the AC-V₂O₅ nanocomposites were shifted to the lower wavenumber region than those of bare V₂O₅ because the incorporated amorphous AC led to the increase in the interlayer distance [10]. This specifies that V₂O₅ and AC were effectively hybridized in the AC-V₂O₅ nanocomposites system.

The hybridization of AC and V₂O₅ was further elucidated by the XPS measurements. As can be seen from the full-survey XPS spectra (Figure 4(a)), both catalysts revealed their own elements such as V, O, and C, whereas no other impurities were observed. In the case of bare V₂O₅, the core-level spectrum of V 2p exhibited the two peaks at 524.51 and 517.06 eV, corresponding to the V 2p_1/2 and V 2p_3/2 states, respectively (see Figure 4(b)) [36, 63]. Through deconvoluting these peaks, it was confirmed that V⁵⁺ and V⁴⁺ valence states coexisted in V₂O₅. Namely, the peaks at 515.28 and 522.64 eV could be attributed to the V⁴⁺ valence states, and the peaks at 516.99 and 524.47 eV could be ascribed to the V⁵⁺ valence state [36]. As can be confirmed from Figure 4(b), the portion of the pentaionized V⁵⁺ valence was dominant in V₂O₅, compared to V⁴⁺. This specifies that the bonding states of V₂O₅ are chemically stable. For the O 1s case in bare V₂O₅ (Figure 4(c)), there are three O-related bonding states of O_I (530.04 eV), O_II (531.32 eV), and O_III (533.03 eV), which are well-known to correspond to the oxygen atoms bonded with the vanadium metal ions in the host V₂O₅ lattice, oxygen vacancies, and chemically adsorbed oxygen atoms at the surface, respectively [64, 65]. Similar to those above in V₂O₅, the AC-V₂O₅ nanocomposites exhibited almost identical valence states in the V 2p core level (see Figure 4(d)). Compared to bare V₂O₅, however, there are two different features; i.e., one is the appearance of C-related bonds, and the other is the change in O-related bonds. As shown in Figure 4(e), AC-V₂O₅ clearly exhibited the existence of C-related bonds inside the composite material system. As deconvoluted, the C 1s involves the three bonding states centered at 288.93, 286.27, and 284.88 eV, attributing to the C=O, C−O, and C−C (sp² hybridized carbon) bonds, respectively [10, 57]. Furthermore, from the O 1s spectrum of AC-V₂O₅ (Figure 4(f)), one can clearly observe that the O-C bonds (i.e., O_IV at 532.17 eV [66]) were additionally included in the composite material system. Such an appearance of carbon-oxygen bonds (i.e., C=O and C−O in C 1s and O-C in O 1s) substantiates the effective hybridization of AC and V₂O₅ in the present composite system.

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After confirming the effective hybridization of AC-V₂O₅, we examined the effects of the AC incorporation on the OER performances of AC-V₂O₅ because the synergistic effects from AC (i.e., high electrical conductivity) and V₂O₅ (i.e., high ion diffusivity) could be beneficial for enhancing the electrocatalytic OER performance. Figures 5(a) and 5(b) display the CV curves for V₂O₅ and AC-V₂O₅, respectively, measured under various scan rates ranging from 10 to 100 mV/s. Both samples exhibited the distinctive oxidation and reduction peaks, representing the Faradic redox-based pseudocapacitive activities of the prepared catalysts. When increasing the scan rate, the current density increased because of the low diffusion resistance. Compared to bare V₂O₅, AC-V₂O₅ exhibited the larger integrated CV windows. Furthermore, the AC-V₂O₅ catalyst exhibited the increased redox peak intensities, indicative of the restricted redox reaction in AC-V₂O₅. Namely, when incorporating AC into V₂O₅, the electrocatalytic performances were improved. This is presumably because, compared to bare V₂O₅, the AC-V₂O₅ composites have a higher density of the active sites and a lower electrical resistance, as discussed later. To clarify the above hypothesis, firstly, we calculated and compared the electrochemically active surface areas (ECSA) for both samples using the below equations [8, 9, 67, 68]: where , , , , and are the non-Faradic capacitance, KOH electrolyte capacitance (0.04 mF/cm²), electrode area, double-layer charging current, and scan rate, respectively. The ECSA values could be determined from the non-Faradic regions from 0 to 0.1 V in the CV curves of the V₂O₅ and AC-V₂O₅ catalysts (see also Figures S5(a) and S5(b)). Figures 5(c) and 5(d) display the linear relationship between and for V₂O₅ and AC-V₂O₅, respectively, which were extracted from the non-Faradic CV region at the potential of 0.05 V. From the slopes in Figures 5(c) and 5(d), the magnitudes of were determined to be 7.16 and 11.40 mF/cm² for V₂O₅ and AC-V₂O₅, respectively. According to the above equations, the obtained values correspond to ECSA of 179 and 285 cm² for V₂O₅ and AC-V₂O₅, respectively. This validates that the AC-V₂O₅ nanocomposites have a higher density of electrochemically active sites than that of the bare V₂O₅ nanorods.

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Next, we assessed the electrocatalytic OER performances of V₂O₅ and AC-V₂O₅ by measuring their LSV characteristics. Figure 6(a) displays the -corrected LSV characteristic curves of V₂O₅ and AC-V₂O₅ measured under 1 mV/s (see Figure S6(a) for the bare AC case). From the LSV data, the magnitudes of overpotential () were calculated to be 310, 280, and 230 mV (at 10 mA/cm²) for V₂O₅, AC, and AC-V₂O₅, respectively, by using the following equations [5, 11]: where and are the standard potentials of the reversible hydrogen electrodes and the SCE at room temperature, respectively. Compared to bare V₂O₅, the AC-V₂O₅ nanocomposites exhibited a lower value because of their increased electrocatalytically active sites (i.e., higher ECSA). Furthermore, the AC-V₂O₅ nanocomposites chronicled to possess the lowest , compared to other metal oxide-based electrocatalysts (Table 1). The improved electrocatalytic OER kinetics could be further elucidated through calculating the magnitude of the Tafel slope () by using the following equation [9]: where and are the applied current density and the fitting parameter, respectively. As can be seen from Figure 6(b), the Tafel slope was more gentle for AC-V₂O₅ than those for V₂O₅ and AC (see Figure S6(b)). Accordingly, a smaller value was obtained from AC-V₂O₅ (i.e., 54 mV/dec), compared to V₂O₅ (i.e., 178 mV/dec) and AC (i.e., 68 mV/dec). Moreover, the value of AC-V₂O₅ was smaller than that of other metal oxide-based electrocatalysts (Table 1). The obtained value suggests that the AC-V₂O₅ catalyst follows the combined Volmer-Heyrovsky mechanism [32]. Compared to V₂O₅, AC-V₂O₅ exhibited the lower values of and because the AC-V₂O₅ hybridization in the composite system facilitates the enhanced catalytically active surface area and improves the material conductivity. Namely, the increased electrochemically active sites and the increased electrical conductivity eventually gave rise to the improved rate of the reaction kinetics. This hypothesis could also be corroborated by the ECSA-corrected LSV curve analysis (see Figure S7).

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The improved electrocatalytic OER characteristics can also affect the CP performances. Figure 6(c) displays the CP profiles of the prepared catalysts. Compared to bare V₂O₅, the AC-V₂O₅ nanocomposites exhibited the smaller values at every current density. This rarifies that the hybridization of AC with V₂O₅ could lead to improved catalytic activity because of the synergistic effects from both AC (i.e., high electrical conductivity) and V₂O₅ (i.e., high electrochemical activity). Additionally, AC-V₂O₅ showed better long-term stability than bare V₂O₅ (Figure 6(d)). Although both catalysts showed the stable potential profiles even after 20 h, AC-V₂O₅ revealed a smaller potential value, compared to bare V₂O₅. Furthermore, it was confirmed that the LSV curves were maintained to be nearly same before and after 20 h of the OER stability test (see Figure S8). Such a good long-term stability of AC-V₂O₅ could be attributed to the encapsulation of the V₂O₅ surface by AC. Namely, the chemically inert AC nanosheets that were physisorpted onto the V₂O₅ surface could improve the surface stability of V₂O₅ in the AC-V₂O₅ medium. This would eventually improve the long-term stability during the electrochemical reaction. All the above suggest that the AC-V₂O₅ composites hold superior electrocatalytic OER activity, compared to the bare V₂O₅ nanorods. After the OER stability test, we performed the Raman and FE-SEM measurements to observe the changes in both vibrational and microstructural characteristics of the catalysts. From FE-SEM measurements, the V₂O₅ catalyst showed the aggregated structure of the nanorods (see Figure S9(a)). However, the AC-V₂O₅ catalyst still maintained its original structure of the AC nanosheet-decorated V₂O₅ nanocomposites (see Figure S9(b)). From Raman measurements (see Figure S10), both V₂O₅ and AC-V₂O₅ showed the additional vibrational bands located at 294, 411, and 694 cm⁻¹, arising from the electrocatalytically active VOOH phase formed during the OER process [69].

Finally, we evaluated the resistive behaviors of the catalysts by means of the EIS measurements. Figures 7(a) and 7(b) show the Nyquist plots of the bare V₂O₅ nanorods and the AC-V₂O₅ composites, respectively. Both catalysts clearly revealed the linear features at the low frequency region, attributing to the electrolyte diffusion within the catalyst medium [10, 15]. At the high frequency region, however, the samples exhibited no clear semicircles but revealed only small parabolic curvatures, which are associated with the charge transfer resistance () [70]. By calculating the and values using an equivalent circuit model (Figure 7, insets), it was found out that, compared to V₂O₅ (: 0.86 Ω, : 83 mΩ), AC-V₂O₅ has smaller resistance values (: 0.84 Ω, : 51 mΩ; see also Table S1). Consequently, it can be inferred that the outstanding OER performances of AC-V₂O₅ were attributed to both higher electrical conductivity (i.e., smaller and ) and higher ion storage capacity (i.e., greater ECSA), both of which give rise to the vigorous electrocatalytic OER actions inside the AC-V₂O₅-hybridized nanocomposite system.

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4. Conclusions

The high-performance OER electrocatalyst of AC-V₂O₅ was fabricated by the facile hydrothermal reassembly process using the hydrothermally disassembled orthorhombic V₂O₅ nanorods and the rice husk-derived biomass AC nanosheets. The AC-V₂O₅ nanocomposites exhibited the outstanding OER performances in the 0.1 M KOH alkaline electrolyte. For example, a low of 230 mV and a small of 54 mV/dec were observed from the AC-V₂O₅ nanocomposites. These could be attributed to both higher ion storage capacity (ECSA: 285 cm²) and high electrical conductivity (: 0.84 Ω, : 51 mΩ), resulting from the synergistic hybridization of electrochemically active V₂O₅ and electrically conductive AC. Consequently, it can be concluded that the hydrothermally reassembled AC-V₂O₅ nanocomposites hold significant promise for future electrocatalytic water-splitting applications.

Data Availability

Data will be made available on request.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Authors’ Contributions

Sankar Sekar contributed to the investigation, formal analysis, methodology, and writing of the original draft. Pugazhendi Ilanchezhiyan assisted in the formal analysis and validation. Abu Talha Aqueel Ahmed carried out the investigation and formal analysis. Youngmin Lee made great contributions to the supervision, validation, and data curation. Sejoon Lee contributed to the conceptualization, supervision, and funding acquisition and wrote, reviewed, and edited the manuscript.

Acknowledgments

This research was supported by National Research Foundation (NRF) of Korea through the basic science research programs (2016R1A6A1A03012877 and 2023R1A2C1005421) funded by the Korean Government.

Supplementary Materials

Supplementary data includes the microstructural characteristics of the V₂O₅ bulk and AC nanosheets, the structural properties of the AC nanosheets, the electrocatalytic properties of V₂O₅ and AC-V₂O₅, the morphological properties of V₂O₅ and AC-V₂O₅ after the stability test, the structural properties of V₂O₅ and AC-V₂O₅ after the stability test, and the resistance parameters of V₂O₅ and AC-V₂O₅. Figure S1: FE-SEM image of the V₂O₅ bulk. Figure S2: FE-SEM image of the rice husk-derived biomass AC nanosheets. Figure S3: XRD pattern of the rice husk-derived biomass AC nanosheets. Figure S4: Raman spectra of the rice husk-derived biomass AC nanosheets. Figure S5: non-Faradic CV curves of the (a) V₂O₅ and the (b) AC-V₂O₅ catalysts. Figure S6: (a) LSV curve and (b) Tafel slope of the bare AC nanosheets. Figure S7: ECSA-normalized LSV curves of the (a) V₂O₅ and the (b) AC-V₂O₅ catalysts. Figure S8: LSV curves of the (a) V₂O₅ and the (b) AC-V₂O₅ before and after the OER stability test. Figure S9: FE-SEM images of the (a) V₂O₅ and the (b) AC-V₂O₅ catalysts after the stability test. Figure S10: Raman spectra of the (a) V₂O₅ and the (b) AC-V₂O₅ catalysts after the stability test. Table S1: fitted parameters from the Nyquist EIS curves of the V₂O₅ and AC-V₂O₅ catalysts. (Supplementary Materials)

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Copyright © 2024 Sankar Sekar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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International Journal of Energy Research

Substantial Electrocatalytic Oxygen Evolution Performances of Activated Carbon-Decorated Vanadium Pentoxide Nanocomposites

Abstract

1. Introduction

2. Experimental Section

2.1. Materials

2.2. Preparation of V2O5 Nanorods

2.3. Derivation of Biomass AC Nanosheets

2.4. Fabrication of AC-V2O5 Nanocomposites

2.5. Material Characterization

2.6. Measurements of Electrocatalytic OER Characteristics

3. Results and Discussion

4. Conclusions

Data Availability

Conflicts of Interest

Authors’ Contributions

Acknowledgments

Supplementary Materials

References

Copyright

2.2. Preparation of V₂O₅ Nanorods

2.4. Fabrication of AC-V₂O₅ Nanocomposites