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Article

Cobalt Oxide-Decorated on Carbon Derived from Onion Skin Biomass for Li-Ion Storage Application

1
School of Metallurgy, Northeastern University, Shenyang 110819, China
2
College of Science, Northeastern University, Shenyang 110819, China
3
Institute of Biomedical Engineering, BoğaziçI University, 34684 Istanbul, Turkey
*
Author to whom correspondence should be addressed.
Metals 2024, 14(2), 191; https://doi.org/10.3390/met14020191
Submission received: 28 December 2023 / Revised: 22 January 2024 / Accepted: 29 January 2024 / Published: 2 February 2024
(This article belongs to the Special Issue Feature Papers in Metallic Functional Materials)

Abstract

:
Onion waste, particularly onion skin, is a widely generated waste material, and harnessing its potential for energy storage aligns with sustainable development goals. Despite the high specific surface area exhibited by biocarbon derived from onion skin, its Li-ion storage performance is not desirable. In this study, biocarbon derived from purple onion skin serves as the substrate for accommodating cobalt oxide (Co3O4) through a hydrothermal method, employing Co(NO3)2·6H2O at various concentrations, and with and without prior activation using KOH treatment. The resulting samples undergo comprehensive analyses, including phase, morphological, surface, and electrochemical characterizations. The Co3O4 decoration on activated carbon derived from onion skin, synthesized using Co(NO3)2·6H2O at a concentration of 1 M, reveals a porous structure with a surface area of 702 m2/g, featuring predominant pore sizes of less than 5 nm. Significantly, the Li-ion storage performance of this sample surpasses that of alternative samples, demonstrating a remarkable reversible capacity of 451 mAh/g even after 500 cycles at an elevated current density of 2000 mAh/g. The charge transfer resistance of the sample (110.3 Ω) is found to be substantially lower than that of the sample prepared using carbonized onion skin biomass without activation. This research introduces an innovative approach leveraging onion skin waste as a template for Co3O4 decoration, thereby fabricating high-performance anodes for lithium-ion batteries.

1. Introduction

Replacing fossil fuels with diverse clean and renewable energy sources is imperative to address the current energy crisis and environmental challenges [1]. In recent decades, lithium-ion electrochemical energy storage systems have experienced rapid advancements, achieving notable breakthroughs due to their compact size, extended life cycle, and lack of operational pollution [2,3]. Carbon materials play a prevalent role as the negative electrode in Li-ion batteries (LIBs) [4]. Nevertheless, their theoretical specific capacity is constrained to 372 mAh/g, limiting the overall performance [5]. Currently, developing electrode materials with both a highly specific capacity and robust cycle performance for LIBs remains a formidable task [6].
Biomass materials emerge as environmentally preferable alternatives to conventional electrode materials, owing to their low cost, widespread availability, and rapid regeneration. Various biomass materials derived from plants, animals, and microorganisms have been synthesized for diverse applications [7,8,9,10,11]. Notably, onions, the second most cultivated vegetable crop globally [12], contribute to this pool of biomass materials. Approximately 10% of onion products, mainly comprising onion skin, are discarded as waste directly into the environment [13]. This waste has found utility in the production of functional materials, such as bioactive agents [13], or as adsorbents for removing organic pollutants [14]. Furthermore, carbon derived from discarded onion skins exhibits a high specific surface area and mesoporous structure, making it advantageous for applications such as supercapacitors [15,16]. Surprisingly, despite these attributes, the exploration of onion skin as a negative electrode for Li-ion batteries (LIBs) has been absent in the literature, and this research aims to fill that gap.
Transition metal oxides, including Sn [17,18], Mo [19,20,21], Cu [22,23], and Fe [24,25], have been investigated as anode materials for LIBs due to their high theoretical capacities and availability. Among these, Co3O4 stands out as a promising oxide with a theoretical capacity of 890 mAh/g [26,27]. However, the practical utilization of Co3O4 faces challenges related to significant volume changes during Li-ion insertion and extraction processes, as well as the poor electronic conductivity of this transitional metal oxide [28,29]. Various methods have been developed to address these issues, such as the fabrication of Co3O4 nanoparticles and nanowires [30,31,32], often combined with additional materials to facilitate the charge transfer. This configuration helps reduce the material volume variation and enhance electrochemical properties [33,34,35]. Incorporating carbon as an additional component in Co3O4-based anodes can lead to composite materials benefiting from the highly specific capacity of the transition metal oxide and the electrical conductivity of the carbon component [36,37]. For example, Li et al. [38] synthesized a Co3O4/C composite material using sodium alginate cobalt fibers, calcium chloride, and cobalt chloride as the raw materials employing an acid (HCl) treatment, followed by calcination at 800 °C. The material exhibited a Li-ion storage capacity of 782 mAh/g after cycles, at the current density of 89 mA/g.
However, these strategies often involve a complex synthesis or relatively high production costs, posing challenges to their practical applications [39]. For example, Chen et al. [40] wrapped zeolitic imidazolate frameworks containing tetrahedral Co cations in polyacrylonitrile by electrospinning, and calcined the compound at 700 °C for 2 h to prepare the Co/carbon nanofibers. Then, the sample was further calcined at 300 °C (6 h) to obtain Co3O4/carbon nanofibers, which experienced a vulcanization process at 450 °C to introduce sulfur to the system. The final product provided a capacity of 325 mAh/g at 10 A/g.
The exploration of a facile method for producing Co3O4/carbon composites using onion skin waste represents a compelling avenue in this research. In this investigation, onion skin waste serves as the carbon template, onto which Co3O4 is intricately deposited through a straightforward hydrothermal approach utilizing Co(NO3)2‧6H2O. The resulting composite material is synthesized both without the activation of the carbonized onion skin (COS) and, alternatively, after the activation of the carbon material (A-COS). This leads to the preparation of two distinct materials, namely Co-COS and Co-A-COS. Subsequently, these materials are subjected to comprehensive characterization through various techniques. In particular, this study introduces a novel strategy for the utilization of onion skin waste in the fabrication of Co3O4 composites tailored for efficient Li-ion storage. By delving into the unexplored territory of utilizing onion skin waste, this research not only addresses environmental concerns related to waste biomass disposal but also offers a sustainable and cost-effective solution for the production of advanced materials for energy storage applications. The characterization of Co-COS and Co-A-COS materials aims to elucidate their structural, morphological, and electrochemical properties, contributing insights to the development of onion skin waste-derived materials for energy storage applications. Through these efforts, this research contributes to the ongoing exploration of green and sustainable approaches in material synthesis and energy storage technologies [41].
The novelty of the current work lies in the innovative approach of utilizing onion skin waste as a template for the decoration of cobalt oxide (Co3O4) crystals. This process involves a hydrothermal method, utilizing Co(NO3)2·6H2O at various concentrations, with and without prior activation using the KOH treatment. The resulting composite material, synthesized from the activated carbon derived from onion skin, demonstrates enhanced Li-ion storage electrochemical performances. The sample synthesized with Co(NO3)2·6H2O at a concentration of 1 M shows a superior Li-ion storage performance with a remarkable reversible capacity of 451 mAh/g, even after 500 cycles at an elevated current density of 2000 mAh/g.

2. Experimental Section

2.1. Material Synthesis

The purple onion skin biomass was washed by deionized water and dried in an oven at 60° for 24 h. The dried onion skins were then carbonized by heating in a tube furnace under a nitrogen protective gas at the heating rate of 5 °C/min to 700 °C with a dwell time at a maximum temperature of 2 h. Then, the carbonized onion skin (COS) and KOH were mixed by mass ratio of 1:4, and the mixture was dried for 24 h at 60°, before being thermally treated under nitrogen at 800 °C for 1 h at a heating rate of 5 °C/min. The solid material obtained (1 g) was added into 100 mL hydrochloric acid (1 M), and the suspension was stirred for 24 h. Subsequently, the suspension was filtered, and the filtrate was washed with deionized water to fully remove the acid, in order to prepare the activated carbonized onion skin (A-COS). Then, the A-COS was loaded with cobalt oxide. For this, COS and A-COS were separately added into a solution of Co(NO3)2·6H2O with varying concentrations of 0.5, 1, and 1.5 M. Then, the suspensions were heated in an autoclave at 180 °C for 20 h to prepare the final samples, namely Co-A-COS (0.5 M), Co-A-COS (1.0 M) and Co-A-COS (1.5 M). Figure 1 exhibits the method employed to fabricate various samples. Additionally, the COS sample was used without activation to interact with Co(NO3)2·6H2O (1 M) in the autoclave. This sample is called Co-COS (1 M).

2.2. Material Characterization

The phase characterization was conducted using an X-ray powder diffraction employing Cu-Kα radiation with a step size of 0.03 using an X’Pert Pro diffractometer (Panaco, The Netherlands). Thermogravimetric analysis (TGA) was conducted under nitrogen atmosphere at a heating rate of 5 °C/min using a thermal analyzer (Mettler Toledo, UK). A field emission scanning electron microscope (SSX-550, Shimadzu, Japan) was used for morphological characterization. A Micromeritics ASAP 2020 HD88 instrument (Germany) was used for surface characterizations.

2.3. Cell Assembling and Electrochemical Characterization

Li-ion half-cells were assembled using biocarbon-derived materials. For this, N-methylpyrrolidone (NMP) was used as solvent, using which a slurry was made employing the active material (80%), acetylene black (10%), and polyvinylidene fluoride (PVDF) binder (10%). To this end, PVDF was mixed with NPM in a mass ratio of 1:9, and the mixture was stirred vigorously until it became transparent. Then, the acetylene black and the active material were added; the suspension obtained was subjected to grinding using a mortar and pestle to make the slurry, which was subsequently coated on copper foil. For coating, a piece of copper foil was fixed onto a cleaned glass, and then, the slurry was evenly spread onto the copper foil using the doctor blade method. The coated foil was then dried in a vacuum oven at 120 °C for more than 8 h. The electrodes were assembled into 2032 coin cells using 1 M LiPF6 in EC:DMC (1:1 vol) as the electrolyte, as well as the polypropylene (PP) Celgard 2400 membrane as the separator, in an argon-filled glove box. The active material mass loading was measured to be 0.9 mg/cm2–1.3 mg/cm2. A CT2001A (LAND Electronic, Wuhan Jinnuo Electronics) was used for galvanostatic discharge-charge measurements within the range of 0.01–3 V. The cyclic voltammetry (CV) curves were measured using an electrochemical workstation (CHI760E) at the rate of 0.1 mv/S.

3. Results and Discussion

3.1. Structural, Morphological, Thermal, and Surface Characterization

Figure 2a represents the X-ray diffraction patterns of Co-COS (1 M) and Co-A-COS (1 M), prepared based on the method exhibited in Figure 1. The XRD pattern on Co-A-COS (1 M), shown in Figure 2a, confirms the presence of Co3O4 as the major phase. In particular, the diffraction peaks located at the two-theta values of 31.68°, 36.7°, 44.6°, 59°, and 65° could be assigned to the (202), (311), (500), (811), and (904) crystalline planes of the spinel-structured cubic Co3O4. Similarly, the XRD pattern of the Co-COS (1 M), shown in Figure 2a, demonstrates the presence of Co3O4. As can be observed, the diffraction peaks of Co3O4 in Co-A-COS (1 M) are sharper and narrower than those of Co-COS (1 M), indicating that the Co3O4 phase decorated on the activated carbonized onion skin (A-COS) has a greater crystallinity than the one fabricated using a non-activated material sample (COS).
The Raman spectra of both Co-COS (1 M) and Co-A-COS (1 M) are illustrated in Figure 2b. Notably, the initial prominent Raman peak detected at approximately 670 cm⁻1 in both samples can be attributed to the A1g phonon mode in Co3O4 [42,43]. Additionally, the Raman bands observed at approximately 1337 and 1559 cm⁻1 correspond to the D and G bands often observed in defective graphitic structures [44,45], indicative of the A1g and E2g vibrational modes of the biomass-derived carbon, respectively, within the Co3O4/C nanocomposites. The D band signifies the presence of sp3-hybridized, disordered carbon [46], along with other structural defects, while the G band represents the sp2 -hybridized carbon in an ordered graphite structure [47].
The ratio of the intensities of the D and G bands (ID/IG) serves as a metric for the degree of graphitization in carbon materials [48]. The ID/IG ratio for the Co-A-COS (1 M) and Co-COS (1 M) composite materials is recorded at 0.75 and 0.83, respectively, confirming the defective graphitic structure of the biocarbon in these materials. This carbon structure provides a conductive platform for the integration of Co3O4 nanoparticles, thereby enhancing the Li-ion storage performance of the composite material.
The scanning electron microscopy (SEM) micrographs of the samples depicted in Figure 2 are presented in Figure 3. As illustrated in Figure 3a,b, the carbonized onion skin (COS) exhibits a flaky structure, while the activated carbonized onion skin (A-COS) displays significantly greater porosity, resulting in a larger specific surface area (Figure 3b,c). These findings suggest that the activation process enhances the porosity and surface area of the resulting carbon material. This is in agreement with other studies confirming the formation of a highly carbon porous structure through a KOH activation step involving the melting and penetration of KOH into the carbon structure [49].
Figure 3e illustrates the SEM morphology of Co-COS (1 M), revealing the presence of Co3O4 crystals deposited in the carbon substrate. A similar morphology is observed for Co-A-COS (1 M), with the distinction that the carbon substrate in the latter is rougher than that in the former.
The improved porous structure in A-COS inevitably facilitates the ion and electron transfer across the electrode, thereby enhancing the Li-ion storage capacity of the material, as elaborated in the article. Such structures also offer the increased access to transition metal oxide nanoparticles, thereby improving the electrochemical properties of the hybrid structure. In other words, both the carbonized onion skin (COS) and the activated COS can serve as templates for the deposition of Co3O4 while maintaining their structural integrity. The enhanced porous structure increases accessibility to the structure for the electrolyte, specifically lithium cations, when utilized as the anode in Li-ion batteries.
Energy-dispersive X-ray spectroscopy (EDS) was utilized to examine the distribution of various elements in the materials, and the corresponding results are depicted in Figure 4. These findings validate the existence of cobalt oxide nanoparticles on the carbon phase, corroborating the XRD patterns presented in Figure 2. The micrographs further reveal the uniform distribution of these nanoparticles.
The surface characteristics of Co-COS (1 M) and Co-A-COS (1 M) are illustrated in Figure 5. Figure 5a displays the N2 adsorption-desorption isotherm hysteresis of Co-A-COS, revealing Type II isotherms with an H4 loop, according to the IUPAC classification [50]. Such isotherms are typically associated with physisorption on porous structures, indicating micro-mesoporous materials. The specific surface area of Co-A-COS (1 M) was determined to be 702 m2/g. Figure 6b indicates that the predominant pore sizes fall within the range of less than 5 nm. The N2 adsorption-desorption isotherms of Co-COS are presented in Figure 5c, displaying type III isotherms with H3-type hysteresis, indicating the presence of a porous structure. The majority of pore volume is attributed to pores with diameters in the range of 10–25 nm (Figure 5d). The specific surface area of Co-COS was found to be significantly smaller than that of Co-A-COS at 100 m2/g. These findings underscore the greater porosity of Co-A-COS, which is consistent with the microscopy observations. The substantial porosity of the sample, coupled with the presence of Co3O4 nanoparticles, can enhance the kinetics of the Li-ion insertion and extraction into/out of the material, as discussed in the following section.

3.2. Electrochemical Characterizations

The electrochemical performances of onion skin carbons decorated with Co3O4 as the anode in Li-ion batteries were assessed. Shown in Figure 6a, the Li-ion storage performances of Co-COS (1 M) and Co-A-COS (1 M) are compared at various current densities (100, 200, 500, 1000, 2000, and 5000 mA/g). Co-A-COS (1 M) demonstrates a discharge capacity of 1050 mAh/g at a current density of 100 mA/g after 5 cycles, surpassing the 502 mAh/g recorded for Co-COS (1 M) under the same conditions. Notably, the specific capacities of Co-A-COS (1 M) consistently outperform those of Co-COS (1 M) at higher current densities, reaching around 505 mAh/g after 30 cycles at 5000 mA/g, while that of Co-COS (1 M) is limited to approximately 90 mAh/g under this high current density.
Co-A-COS samples were synthesized through the hydrothermal treatment of A-COS and Co(NO3)2·6H2O with varying concentrations of 0.5, 1, and 1.5 M. The impact of these concentrations on the Li-ion storage performance of the resulting hybrid nanostructures is explored in Figure 6b. At the current density of 100 mA/g, the capacities after 5 cycles for A-COS, Co-A-COS (0.5 M), Co-A-COS (1 M), and Co-A-COS (1.5 M) were recorded as 491, 623, 1050, and 780 mAh/g, respectively. This trend persists at higher current densities, providing evidence for the superior performance of Co-A-COS (1 M) compared to other samples.
To further evaluate the electrochemical performance of Co-A-COS (1 M), the prolonged Li-ion storage cycling performance of the material was examined at the current density of 2000 mA/g (Figure 6c). As shown, the capacity of the sample experienced an initial decline which is due to the decomposition of the electrolyte onto the electrode, leading to the formation of the solid electrolyte interphase (SEI) [51]. Then, the capacity of the sample gradually increases to record a value of around 550 mAh/g after 220 cycles, after which the capacity gradually decreases to exhibit a value of 451 mAh/g after 500 cycles. Figure 7 shows the Coulombic efficiency (CE) of the Co-A-CoS (1M) electrode at the current density of 2 A/g. As can be observed, the CE at the first cycle is around 76.5%, which increases to around 90 and 95% at the second and third cycle cycles, respectively, and eventually to more than 98% after 20 Li-ion insertion/extraction cycles. This value is recorded to be 99.3% after 500 cycles. The lower CE at initial cycles can mainly be related to the formation of SEI layers. However, the initial Coulombic efficiency (76.5%) is still relatively high, indicating an appropriate degree of electrochemical stability right from the first cycle, which is an important parameter in practical applications [52].
As observed in Figure 6c, after around 20 cycles, the capacity of the electrode experiences a rising trend until the 220th cycle. This phenomenon can be attributed to the activation of electrode materials during the charge-discharge processes. This behavior has also been reported for the case of other oxide electrodes, where the detailed mechanism involved is still unclear [53]. However, the origin of this cycling-induced capacity-increase after a certain number of cycles [54] can be related to a combination of reasons, including the gradual amorphization of the electrode after cycling, and the formation of metallic components due to the partially irreversible conversion mechanism, lowering the activation overpotential involved in Li-ion insertion and extraction [54].
Moreover, the decrease in the capacity observed after 220 cycles (Figure 6c) can be related to various issues, including the large volume changes involved in Li-ion insertion/extraction into/out of the electrode [55].
To shed light on the Li-ion storage mechanism of Co-A-COS (1 M), cyclic voltameter measurements were performed at 0.01–3.00 V (Figure 6d).
During the first cathodic scan, three cathodic peaks can be observed at around 0.9, 0.4 V, and less than 0.1 V. The reduction peaks at 0.9 and 0.4 V are related to the combination of forming SEI and the reduction of Co3O4 to form Co [56]:
Co3O4 + 8Li+ + 8e → 3Co + 4Li2O
Accordingly, the anodic peak observed at around 2.2 V is related to the oxidation of Co to CoO:
Co + Li2O → CoO + 2Li+ + 2e
The cathodic peak observed in the first cycle below 0.1 V is accompanied by an anodic peak. This event can be related to the insertion and extraction of Li+ into/out of the activated carbon obtained by the carbonization of the biomass. The cathodic peak at 0.9 V moves to a greater potential of 1.2 V in the second cycle, corresponding to the reduction of CoO:
CoO + 2Li+ + 2e → Co + Li2O
However, the corresponding anodic peak does not move in comparison to that of the first cycle, confirming the occurrence of the oxidation reaction based on the reversible reaction (2). The curves of the second and third cycles correlate well, indicating the reversibility of the electrochemical reactions. This mechanism can be confirmed by considering the galvanostatic charge-discharge curves recorded at 100 mA/g (Figure 6e).
As can be observed, the specific capacities of the material at the first discharge and after 20 cycles could reach around 1100 and 800 mAh/g, respectively. In the first cycle, the specific capacities of the material under the charge and discharge were 960 and 1200 mAh/g, respectively, with the coulombic efficiency of around 80%. At the 20th cycle, the specific capacities of the charge and discharge processes were 760 and 800 mAh/g, respectively, with the coulombic efficiency of greater than 95%.
As shown in Figure 6, the enhanced performance of Co-A-COS (1 M) in comparison with that of Co-COS (1 M) is evident, and this enhancement was related to the greater porous structure of the earlier, brought about by the activation process. The greater prosity of Co-A-COS (1 M) could facilitate the ion transportation of the electrode/electrolyte interface, leading to a reduced charge transfer resistance, as demonstrated by the EIS curves shown in Figure 6f. The EIS curves show one high frequency semi-circle and a low frequency line corresponding to the charge-transfer process and the semi-infinite linear mass-transport of the ions, respectively [57]. The diameter of the semi-circle and slope of the line represent the charge transfer resistance and the diffusion resistance, respectively. It can be clearly observed from Figure 6f that the charge resistance of Co-A-COS (110.3 Ω) is significantly lower than that of Co-COS (245.1 Ω).
In this research, onion skin as a widely available biomass was used to extract carbon materials (COS) which were subsequently decorated with Co3O4 nanocrystals, using Co(NO3)2·6H2O of various concentrations, with and without being activated beforehand. The sample obtained using the activated carbon with a Co(NO3)2·6H2O concentration of 1 M (Co-A-COS (1M)) demonstrated an enhanced Li-ion storage performance, as illustrated by a capacity of 451 mAh/g even after 500 cycles at the enhanced current density of 2000 mA/g. This performance can be compared with the literature including the work of Huang et al. [56], who fabricated mesoporous Co3O4 nano-cubes. This sample could exhibit a capacity of 400 mAh/g at 2000 mAh/g after 60 cycles where the cycling was terminated. The electrochemical performance of Co-A-CoS (1 M), in contrast with alternative materials from the literature, is summarized in Table 1, highlighting the superior Li-ion storage performance of the CoA-CoS (1 M) composite material. As shown, at a high current density of 2000 mA/g and after 200 cycles, the electrode exhibits a capacity of 571 mAh/g, which is the highest value among the materials presented in the table tested at lower current densities in the range from 20 to 1000 mA/g. After 500 cycles, the CoA-CoS (1 M) electrode retains a high capacity of 450 mAh/g, which is indicative of its resilience and consistent energy delivery; this is critical for practical applications. From Table 1, at the current density of 100 mA/g, the capacity of pure Co3O4 decreases from an initial value of 1387 mA h g−1 to a limited capacity of 115 mAh/g after 100 cycles [58], providing evidence for the efficiency of carbon components in maintaining the capacity at prolonged cycles [59,60,61].
In the current work, CO3O4 crystals decorated on carbon were fabricated using onion skin waste, and the material obtained was employed to fabricate anode materials for Li-ion storage with a high capacity and stability over cycling. This strategy not only facilitates the preparation of high-performance energy materials but also actively contributes to ongoing research focused on the sustainable utilization of waste [62,63]. Along with the green utilization of natural resources [64,65], the successful implementation of waste-to-energy solutions [66,67] represents a crucial stride toward achieving the sustainable development goals, advocating for the efficient recycling and valorization of waste. Additional research can be directed to investigate the impact of carbon derived from onion skin on enhancing the electrochemical performance of hybrid nanostructures. Furthermore, exploring various applications of this biomass-derived carbon, such as water treatment [68,69], biomedical applications [70,71], modern metallurgical processes [72,73], and catalysis [74], merits attention in forthcoming research endeavors.
It should be noted that cobalt is recognized as a crucial element for various applications, including serving as the cathode in Li-ion batteries, as well as being utilized in electronics, superalloys, and hard metals. Consequently, effective cobalt recycling [75] can be considered a viable source for secondary applications, such as in the anode of Li-ion batteries, as discussed in this article. The Li-ion performance of Co-A-CoS (1 M) may be influenced by other parameters, such as the electrolyte components. Additionally, the presence of impurities in biomass and their variability depending on the environment warrants further investigation in future studies. Novel technologies, such as reserve lithium-ion batteries [76], and strategies developed to mitigate voltage hysteresis in reversed conversion reactions of transitional metal oxide anodes [77], could be utilized to enhance the performance of Co-A-CoS electrodes in future studies. Another application of the C-A-COS electrodes is their use as a lithiophilic magnetic host matrix, aiming to simultaneously mitigate uncontrolled dendritic lithium growth and substantial lithium volume expansion, which are common challenges in typical lithium-metal anodes used in LIBs [78].

4. Conclusions

In this investigation, carbon derived from onion skin biomass (COS) served as the template for adorning Co3O4, with and without the prior activation of the biocarbon. The resulting samples underwent comprehensive analyses, encompassing phase, morphological, surface, and electrochemical characterizations. The Co3O4 decoration on activated carbon derived from onion skin, synthesized using Co(NO3)2·6H2O with a concentration of 1 M, led to the production of a porous structure with the surface area of 702 m2/g with predominant pore sizes of less than 5 nm. Notably, the Li-ion storage performance of this sample outperformed alternative samples, exhibiting a remarkable reversible capacity of 451 mAh/g even after 500 cycles at an elevated current density of 2000 mAh/g. The charge transfer resistance of the sample (110.3 Ω) was found to be significantly lower than that of the sample prepared using carbonized onion skin biomass without activation. This research introduces an innovative approach utilizing onion skin waste as a template for Co3O4 crystal decoration, thereby fabricating high-performance anodes for lithium-ion batteries.

Author Contributions

Conceptualization, Y.L. and T.S.; methodology, Y.L. and T.S.; validation, Y.L., T.S. and A.R.K.; formal analysis, Y.L., T.S. and A.R.K.; investigation, Y.L., T.S. and A.R.K.; resources, Y.L., T.S., D.E. and A.R.K.; data curation, Y.L., T.S. and A.R.K.; writing—original draft preparation, Y.L. and A.R.K.; writing—review and editing, A.R.K.; visualization, Y.L. and A.R.K.; supervision, T.S. and A.R.K.; project administration, Y.L., T.S., D.E. and A.R.K.; funding acquisition, T.S. and A.R.K. All authors have read and agreed to the published version of the manuscript.

Funding

Financial support by National Natural Science Foundation of China (52250610222) is acknowledged.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic representation of the process employed to prepare samples.
Figure 1. Schematic representation of the process employed to prepare samples.
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Figure 2. (a) XRD patterns and (b) Raman spectra of Co-A-COS (1 M) and Co-COS (1 M).
Figure 2. (a) XRD patterns and (b) Raman spectra of Co-A-COS (1 M) and Co-COS (1 M).
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Figure 3. SEM micrographs of the (a,c) COS, (b,d) A-COS, (e) Co-COS (1 M), and (f) Co-A-COS (1 M).
Figure 3. SEM micrographs of the (a,c) COS, (b,d) A-COS, (e) Co-COS (1 M), and (f) Co-A-COS (1 M).
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Figure 4. (a) SEM and EDS mapping analysis of (ad) Co-COS (1 M) and (eh) Co-A-COS (1 M).
Figure 4. (a) SEM and EDS mapping analysis of (ad) Co-COS (1 M) and (eh) Co-A-COS (1 M).
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Figure 5. Nitrogen adsorption–desorption isotherm curves of (a) Co-A-COS and (c) Co-COS. Barret–Joyner–Halenda (BJH) pore size distribution curves of (b) Co-A-COS and (d) Co-COS.
Figure 5. Nitrogen adsorption–desorption isotherm curves of (a) Co-A-COS and (c) Co-COS. Barret–Joyner–Halenda (BJH) pore size distribution curves of (b) Co-A-COS and (d) Co-COS.
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Figure 6. (a,b) Rate performances of various samples. (c) Cycling performance at 2000 mA/g, (d) CV, and (e) GCD curves of Co-A-COS (1 M). (f) EIS curves of Co-A-COS (1 M) and Co-COS (1 M).
Figure 6. (a,b) Rate performances of various samples. (c) Cycling performance at 2000 mA/g, (d) CV, and (e) GCD curves of Co-A-COS (1 M). (f) EIS curves of Co-A-COS (1 M) and Co-COS (1 M).
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Figure 7. Coulombic efficiency of Co-A-CoS (1M) at the current density of 2 A/g.
Figure 7. Coulombic efficiency of Co-A-CoS (1M) at the current density of 2 A/g.
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Table 1. Electrochemical performance of samples prepared in the current study in contrast with alternative materials extracted from the literature.
Table 1. Electrochemical performance of samples prepared in the current study in contrast with alternative materials extracted from the literature.
Active MaterialCurrent Density (mA/g)Capacity (mAh/g)Cycle Reference
Co3O4100115100[58]
CNT/Co3O4200498100[59]
C/Co3O4-nanowires20534100[60]
Graphene/Co3O41000550100[61]
Co-A-CoS (1 M)2000578200This work
Co-A-CoS (1 M)2000451500This work
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Liu, Y.; Sun, T.; Ege, D.; Kamali, A.R. Cobalt Oxide-Decorated on Carbon Derived from Onion Skin Biomass for Li-Ion Storage Application. Metals 2024, 14, 191. https://doi.org/10.3390/met14020191

AMA Style

Liu Y, Sun T, Ege D, Kamali AR. Cobalt Oxide-Decorated on Carbon Derived from Onion Skin Biomass for Li-Ion Storage Application. Metals. 2024; 14(2):191. https://doi.org/10.3390/met14020191

Chicago/Turabian Style

Liu, Yunan, Ting Sun, Duygu Ege, and Ali Reza Kamali. 2024. "Cobalt Oxide-Decorated on Carbon Derived from Onion Skin Biomass for Li-Ion Storage Application" Metals 14, no. 2: 191. https://doi.org/10.3390/met14020191

APA Style

Liu, Y., Sun, T., Ege, D., & Kamali, A. R. (2024). Cobalt Oxide-Decorated on Carbon Derived from Onion Skin Biomass for Li-Ion Storage Application. Metals, 14(2), 191. https://doi.org/10.3390/met14020191

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