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Article

Functional Sulfur-Doped Biocarbon for Hydrogen Storage: Development of Nanomaterials for Energy Applications

by
David Rosas
1,
B. Escobar
1,2,
Karina Suarez-Alcantara
3,
Carlos Pacheco
1 and
Romeli Barbosa
1,*
1
Centro de Investigación Científica de Yucatán, Carretera Sierra Papacal-Chuburná Puerto, Km 5, Sierra Papacal, Mérida C.P. 97302, Mexico
2
IxM-CONAHCYT, Centro de Investigación Científica de Yucatán, Carretera Sierra Papacal-Chuburná Puerto, Km 5, Sierra Papacal, Mérida C.P. 97302, Mexico
3
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro No. 8701, Col. Ex Hacienda de San José de la Huerta, Morelia C.P. 58190, Mexico
*
Author to whom correspondence should be addressed.
Processes 2024, 12(12), 2715; https://doi.org/10.3390/pr12122715
Submission received: 24 October 2024 / Revised: 19 November 2024 / Accepted: 28 November 2024 / Published: 1 December 2024
(This article belongs to the Special Issue Advances in Materials for Electrocatalytic, Photocatalytic and Thermocatalytic Applications)
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Abstract

This research focuses on the synthesis and characterization of advanced materials for hydrogen storage. Two biocarbon samples were synthesized from Sargassum spp. The first was activated with KOH (SKPT) and the second was doped with sulfur (SSKTP); both were obtained through pyrolysis at 900 °C. The sulfur-doped biocarbon (SSKTP), with its high specific surface area (2377 m2 gࢤ1), exhibited enhanced electrocatalytic properties, making it an efficient candidate for hydrogen storage applications. Various characterization techniques were employed to study the relationship between physicochemical properties and hydrogen uptake. The presence of micropores and sulfur doping significantly improved hydrogen uptake at 45 °C and 50 bar, where SSKTP achieved 0.40 wt%. In comparison, the non-doped biocarbon (SKPT) showed a lower hydrogen storage capacity of 0.33 wt%, with a specific surface area of 1620 m2 gࢤ1. The results highlight the potential of sulfur-doped activated biocarbon as a functional material in energy conversion systems, specifically for electrocatalytic hydrogen storage processes. This study demonstrates a sustainable approach to utilizing biomass waste for advanced electrocatalysts, contributing to renewable energy solutions.

1. Introduction

One of the main challenges of hydrogen storage is related to its low energy density; this feature is considered crucial for the boost of the hydrogen economy, as hydrogen storage is a viable technology for hydrogen produced by sustainable energy systems [1]. At present, the large-scale application of hydrogen requires higher storage capacity, facile storage technology, low-cost and safe storage, and near-zero carbon emissions [2]. The U.S. Department of Energy (DOE) has set a technical target for hydrogen storage system costs at $8/kWh [3]. Functional carbonaceous materials have been widely developed for hydrogen storage applications that require porous materials [4,5]. One of them, biocarbon, has gained important attention, attributable to its potential to operate at moderate temperatures and pressures. Biocarbon materials derived from renewable biomass offer a sustainable solution for the development of carbon-based storage technologies, aligning with global efforts toward greener energy systems [6]. Biocarbon or biochar can be obtained by various thermochemical methods, including torrefaction, gasification, and hydrothermal carbonization; however, it is usually obtained from the pyrolysis of biomass by-products, including crop residues from the agricultural and forestry sectors, food and animal manure, municipal solid waste, industrial waste, and marine products [7]. The advantages of using biomass feedstocks to make biocarbon materials are that they are plentiful in the environment, abundant in variety, eco-friendly, lower-cost, and offer an opportunity to develop better waste management strategies [8]. In particular, marine biomass like Sargassum spp. provides an attractive feedstock due to its high carbon availability, further contributing to environmental management by mitigating its overgrowth in coastal areas [9].
Biocarbon materials have been widely investigated in the areas of energy [10,11], hydrogen storage [12,13], and soil amendment [14,15], due to their reasonable price, highly specific surface area, pore structure, large surface area, good thermochemical stability, and superior electrical conductivity [16]. However, the use of biocarbon requires an understanding of the material properties and their behavior under different conditions. Given the rising demand for efficient and scalable hydrogen storage solutions, biocarbon offers a promising approach, especially when functionalized to enhance performance [17]. At present, the use of biocarbon for hydrogen storage is an area of important research, with several studies focusing on the potential of biomass-derived activated carbon. Biocarbon materials offer several advantages for hydrogen storage because molecular hydrogen can be stored or physisorbed on low-weight materials with a large specific surface area. However, the weak interaction between molecular hydrogen and the surface biocarbon walls still represents a challenge for hydrogen adsorption in functional carbonaceous materials at ambient temperatures [18]. There are various studies in the literature that detail how hydrogen can be stored in materials derived from carbon. Lazzarini et al. conducted a study on the potential of biochar for hydrogen storage. This study emphasized the importance of regulating the pore structure of biochar to enhance its storage capacity. The results indicated that biochar with a well-controlled, mesoporous pore structure could be a potentially valuable material for hydrogen storage [19]. In a review article by Rimza et al., the potential of carbon fiber for hydrogen storage applications was discussed. The article featured the low gas–solid interaction, tunable texture, high pore volume, and chemical stability of carbon fiber. It was further mentioned that the unique properties of carbon fiber make it a promising material for future research and development in hydrogen storage [20]. Moradi et al. conducted a study to assess different energy storage options for green hydrogen. The study focused on identifying technologies generated from renewable energy sources that could be used for hydrogen storage. According to the research, carbon-based materials, such as biochar, could substantially impact the development of hydrogen storage technology [21].
Recently, the possibility of introducing heteroatoms such as N, P, B, and S through doping has been explored. Doping functional carbonaceous materials with heteroatoms significantly enhances their catalytic properties, surface energy, and gas adsorption capacity, making them highly relevant in energy storage systems [19]. It is fascinating to assess the properties of sulfur-doped activated biocarbon since these materials are typically thermally stable, display good stability, and have improved adsorption capacities [22]. Unfortunately, there have been few investigations into the hydrogen storage capacity of sulfur-doped activated biocarbon. Based on the literature and our own experience of activated biocarbon, we performed sulfur doping and investigated how a higher surface area, porosity, and sulfur content can influence hydrogen uptake. Sulfur doping has been shown to introduce additional active sites on the carbon surface, which enhances interactions with hydrogen molecules, leading to improved adsorption performance. This approach aligns with current advancements in material science aimed at developing more efficient catalysts and storage materials [20].
Therefore, we reported the synthesis and hydrogen uptake of porous sulfur-doped biocarbon using Sargassum spp. (brown macroalgae) as raw biomass, commercial sulfur as an S source, and KOH as an activating agent. Sargassum spp. was selected because of (1) its high carbon content and (2) its high availability. The benefits of commercial sulfur are its low price and the lower use of reactive agents for its production, which increase its green chemistry applications. This work contributes to the ongoing development of sustainable hydrogen storage materials, supporting the global transition to renewable energy systems.

2. Materials and Methods

2.1. Synthesis of Biocarbon

Sargassum spp. (also named sargasso) was collected from the north coast of Quintana Roo (Playa del Carmen). The sargasso was washed with seawater to remove sand, cleaned thoroughly with tap water, and then cleaned with deionized water to eliminate any remaining minerals and impurities. In the drying process, the sargasso was open-sun-dried to remove as much moisture as possible, and then dried in an oven at 80 °C for 16 h. Once dry, it was ground through a 60-mesh sieve. A 10 g sample was mixed with KOH (90% Sigma Aldrich, Saint Louis, MO, USA)) in a 2:1 ratio to activate the sargasso. This solution was heated and stirred at 95 °C and 400 rpm for 4 h. Afterward, it was filtered and dried at 60 °C for 16 h. The sample was subjected to pyrolysis in a horizontal tubular oven at 700 °C for 2 h, at a heating rate of 10 °C min−1 with a nitrogen flow of 50 mL min−1. Next, the sample was mixed with 100 mL of 2 M HCl while stirring, and heated at 95 °C and 240 rpm for 1 h to remove the KOH impurities. It was then filtered and mixed with 200 mL of deionized water while stirring at 300 rpm to eliminate any remaining traces of HCl. The washing process was repeated with water until a neutral pH was reached, and this sample was named SKPT. Finally, the doping process was performed by mixing the SKPT sample with commercial sulfur (fertilizer-grade, from a local store) with 99.4% purity in a 1:1 ratio. The activation, washing, and pyrolysis processes described above were repeated for this sample, named SSKTP. Figure 1 illustrates the general diagram of the biochar preparation process, highlighting the weight percentage at each stage. The wet sargasso collected from the beach was sun-dried, and the sun-dried sargasso represented 100% by weight. The sargasso powder for the pyrolysis process decreased to 76.8% because of the grinding and sieving processes. The process concluded with the production of biochar, yielding 11.6% relative to the original sun-dried sargasso sample.

2.2. Physicochemical Characterization of Biocarbon

SKPT and SSKTP biocarbon samples were analyzed through BET, XRD, Raman, CHNS, FE-SEM, and XPS. All these techniques are used to evaluate the correlation between the physicochemical properties of biocarbon and its behavior toward hydrogen storage. The BET surface area of the biocarbon was measured by N2 sorption analysis at 77 K with a surface analyzer (Quantachrome Nova 2200 model) after being outgassed under a vacuum at 523 K for 5 h. A Brunauer–Emmett–Teller (BET) analysis was used to estimate the surface area. The XRD patterns were collected by a diffractometer (Bruker Phaser 2) with Cu-Kα radiation (λ = 1.54056 Å), operating conditions of 40 kV and 40 mA, a 2θ range of 10–100°, and a step size of 0.01°. Raman spectroscopy measurements were performed to evaluate the purity of the biocarbon, using a Raman microscope (Thermo Scientific) with a 633 nm laser at 2 mW of power. The total concentrations of C, H, S, and N were determined with an elemental analyzer (Thermo Scientific Flash 2000). HR-TEM and chemical mapping characterization were performed in an FEI Talos F200 operating at 30 kV accelerating voltage. The surface chemical composition was analyzed with a spectrophotometer (K-Alpha Thermo-Fisher Scientific) with an X-ray source (Al K-α) at 12 kV and 40 W; the XPS spectra were calibrated considering the C1s at 284.8 eV [23].

2.3. Hydrogen Uptake Measurements

Pressure-Composition Isotherm (PCI) was performed in a Quantachrome Isorb-100 machine. A sample of about 0.15 g of each material was transferred to the machine. Then, the materials were degassed by heating them to 200 °C in a dynamic high vacuum and this condition was maintained for 2 h. After degassing, the materials were cooled to 45 °C in a high vacuum, and the machine was calibrated for void volume in the sample holder. The calibration for void volume was performed with ultrahigh purity helium. Then, hydriding reactions were performed at 45 °C by a progressive increase in the hydrogen pressure from 0.01 to 50 bar (in 25 steps). Dehydriding reactions were performed by a progressive decrease of the hydrogen pressure from 50 to 0.01 bar (in 25 steps). PCI curves are required to be performed in equilibrium conditions; this translates to long testing times for real-world experiments. Equilibrium conditions were assumed when no changes in pressure superior to 0.1 × 10−3 bar were registered for 12 min, or a maximum duration of 240 min for each step. Reaching equilibrium directed the change to the next step. The hydrogen used during the PCI experiments was of chromatographic purity. All the reported pressures corresponded to the absolute pressure scale, with 0.8 bar being the average atmospheric pressure in our location.

3. Results and Discussion

3.1. Specific Surface Area and CHNS Elemental Analysis

It is well known that the use of KOH initiates changes in biochar surface area and porosity. However, sulfur can also produce a porogenic action. The textural properties of SKPT and SSKPT were examined using nitrogen sorption at −196 °C. Both the isotherms (adsorption and desorption) and pore distributions are displayed in Figure 2. The isotherms of SKPT and SSKPT presented in Figure 2 could be identified as type IV with an H4 hysteresis loop linked with the replacement of micropores, that are commonly present, with a mixture of micropores and mesopores in the biocarbon after treatment with KOH. The H4 hysteresis loop indicates slit-shaped pores, which suggests a complex pore structure often associated with layered or plate-like particle arrangements. This type of hysteresis is consistent with materials that have both micropores and mesopores, enhancing gas adsorption characteristics. Through the BET analysis, a surface area of 1670 m2 g−1 was calculated for the SKTP; this sample was activated with KOH. The BET surface area (SBET), average pore size, pore volume, and CHNS elemental analysis of the SKTP and SSKTP are completely detailed in Table 1. Several authors indicate that during the thermal treatment, K penetrates the biocarbon, and above 570 °C, the K2CO3 can be formed, expanding the carbon network and forming porosity [24]. In the case of the SKPH sample, a surface area of 2377 m2 g−1 was obtained. The increase in pore size after the activation process can be attributed to the action of KOH, which not only removes volatile substances, but also reacts with carbon to create additional porosity through gasification reactions. This reaction between KOH and carbon leads to the release of gases such as CO2 and H2O, which further etch and enlarge the existing pore structures. Additionally, sulfur plays a role by creating secondary porosity during the thermal treatment. The incorporation of sulfur can lead to the formation of sulfur-containing gases, which, upon release, contribute to expanding the pore volume and increasing the average pore size. These changes may also subtly influence the hysteresis type by enhancing mesoporous structures while retaining the characteristic H4 loop, indicative of slit-like pores. Consequently, the combined effect of KOH activation and sulfur-induced porogenic action results in a highly porous structure with larger and more interconnected pores, enhancing the specific surface area and textural properties of the biocarbon. It was found that the sulfur content can increase the specific surface area of biocarbon significantly [25,26].
Figure 2a insert displays the pore size distribution diagram (PSD) of SKPT. The results of the N2 adsorption isotherms and PSD curves indicate that SKPT is a nanoporous biocarbon with a relatively narrow PSD, with an average pore size of 1.904 nm and a pore volume of 0.795 cm3 g−1. It can be seen that the nanopore structure of SSKPT was developed after sulfur doping, obtaining a slight increase in average pore size of 2.519 nm and a pore volume of 1.078 cm3 g−1. Both biocarbon samples showed a large fraction of nanopores with diameters less than 2 nm, which is suitable for hydrogen storage [27] and electrochemical applications. The pore sizes obtained for the biocarbon samples, ranging from 1.9 to 2.5 nm, facilitate hydrogen and ion transport. The sulfur content of the SSKTP (17.45 wt%) was considerably higher than that of SKTP (0.85 wt%) due to the doping process. There were minor differences in carbon content since the same synthesis conditions were used.

3.2. X-Ray Diffraction Analysis

The crystalline structures of the materials and the change in the biocarbon after doping with S are depicted in Figure 3. According to the results, the diffractograms of the SKPT and SSKPT are very similar, with extended signals between 18° and 30° and 40° and 46°, corresponding to the (002) and (101) planes of graphitic carbon [28]. The broadening of the (002) peak centered around 24° suggests an amorphous carbon structure with incomplete graphitization, which can result from the pyrolysis conditions at 900 °C. This incomplete carbonization leads to a disordered arrangement of carbon atoms. Additionally, the sharp peaks at 15°, 28°, 31°, and 41° observed in the SKPT sample may be attributed to impurities in the Sargassum spp. biomass, which contains various minerals such as silicon. These mineral residues can form silica or silicate phases that persist through the pyrolysis process, contributing to the observed peaks. This result shows that the structure of lignocellulose was transformed during the thermal degradation by producing amorphous carbon with low graphitization [29].

3.3. Raman Analysis

A Raman spectroscopy analysis was carried out to determine the degree of graphitization of the biocarbon. Figure 4 shows the Raman spectra of SKTP and SSKTP. It is possible to observe two well-defined bands, one of them at 1328 cm−1, corresponding to the D band that is typical of amorphous carbon [30], like for activated carbon and biocarbon. Another band, called the G band, occurs at around 1587 cm−1, and is associated with graphic carbon [31]. Information regarding the various degrees of defects between these two bands was calculated using the relationship of ID/IG. It can be seen from Figure 4 that the ID/IG ratio of SKTP was 1.35, indicating that it had the highest graphitization degree compared with SSKPT (ID/IG = 1.46). This slight increase indicates a change in the level of defects in the material, confirming atomic doping of sulfur in the SSKPT sample, and this is corroborated by the results of elemental analysis, in which a sulfur content of 17.45 wt% was obtained. Furthermore, it is likely that the increased carbon content in the SKPH sample improved some of its structural characteristics, as noted from the Raman analyses [32].

3.4. XPS Analysis

The sulfur group of the SKTP and SSKTP was determined using X-ray photoelectron spectroscopy (XPS), analysis using a spectrophometer (K-Alpha, Thermo Scientific, East Grinstead, UK) equipped, as presented in Table 2. Figure 5a shows the XPS spectra of the SKPH sample, displaying S 2p signals split into two principal peaks. The first peak S 2p3/2 was intense and measured at 163.7 eV, while the second peak S 2p1/2 had lower intensity and was around 164.9 eV. This spin–orbit splitting corresponds to thiophenic sulfur atoms that have been incorporated into biocarbon [33]. The S content of 0.64 wt% at 168.9 eV suggests the presence of oxidized sulfur (S-O). This sulfur content found in sargasso may be naturally occurring. Throughout the deconvolution of the C1s carbon spectrum, peaks with binding energies of 284.8, 286.1, 287.5, and 289.1 eV were found, corresponding to the bond types of C=C, C-C, C-O, and O-C=O, respectively, as shown in Figure 5b.
Figure 5c shows the evolution of the S surface group after the doping process (SSKTP), and the specific peak-splitting results are shown in Table 2. Figure 5d shows that the C1s peak was split into four peaks based on the previous peak-splitting method, revealing apparent differences in the C peaks of SSKPT. The four peaks of C 1s are 284.6, 284.6, 285.9, 287.2 eV, and 288.7, representing C=C, C-C, C-O, and O-C=O bonds. The sulfur bonds in this sample are identical to those found in the SKPT sample. The main difference is the amount of S content, which is mostly in the form of thiophene type and reaches 20.16%. This amount is close to the values obtained in the CHNS elemental analysis, as shown in Table 1.

3.5. Morphology Studies

Figure 6 displays the surface microstructures and morphology characteristics of biocarbon, as determined by HR-TEM and chemical mapping. In the SEM images of SKTP and SSKTP in Figure 6a and Figure 6b, respectively, no defined structures are observed at a scale of 50 nm. This morphology is related to the X-ray diffraction results, in which an amorphous structure of the synthesized biocarbon was obtained. Heteroatoms of nitrogen, sulfur, and oxygen are distributed on the surface of biocarbon samples. In Figure 6b, the element mapping shows an increase in the amount of S, which means that the doping process achieved the introduction of S atoms into the structure of SSKTP. On the other hand, chemical mapping shows a uniform distribution of sulfur functional groups in SSKTP.

3.6. Hydrogen Storage Performance

Figure 7 shows the hydrogen adsorption and desorption isotherms of the SKTP and SSKTP samples. The hydrogen storage capacity achieved was 0.33 wt% and 0.40 wt% for SKTP and SSKTP, respectively. The shape of the PCI curves is close to a Type III isotherm of the IUPAC classification [34]. In this type of curve, the adsorbent–adsorbate interactions are relatively weak, and the adsorbed molecules are clustered around the most favorable sites on the surface of a nonporous or macroporous solid [35]. Cychosz et al. proposed that in functionalized carbon materials, the presence of groups and ions can affect the characteristics of gas (N2) sorption [36]. This idea can be extrapolated to the sorption of hydrogen in functionalized carbon materials; here, the presence of -C-S-C- or -C-SOX-C- functional groups can lead to a modification of the Type III curve. Figure 7b shows the effect of sulfur doping on hydrogen uptake capacity. The results show that SSKPH has a 20% higher hydrogen uptake capacity compared to SKPH under similar measurement conditions. Sulfur-doped activated biocarbon (SSKTP) displays a higher specific H2 uptake per surface area than the S-free sample (SKPT). This hydrogen adsorption onto porous carbon is facilitated by sulfur functional groups. The literature suggests that hydrogen adsorption in functional carbonaceous materials depends on their surface area or pore size [37]. The hydrogen storage capacities of carbon are generally associated with an increased BET surface area [38], and particularly micropore volumes. In both samples, the hydrogen adsorption curve matches its desorption curve, indicating that nearly all the hydrogen that was adsorbed and stored during depressurization was subsequently desorbed and released. This means that the material had low hysteresis.
In this work, the characterization temperature (45 °C) delimits the results of hydrogen storage applications at room temperature. However, given the obtained capacity of 0.4 wt%, it is possible to conclude that 250 kg of our SSKTP material is required to store 1 kg of hydrogen. Considering that the yield of our biomass conversion process is 11.6%, it is crucial to note that for every ton of dried sargasso, we can obtain 116 kg of SSKTP material, which can be used to achieve a reversible energy storage system in the form of hydrogen with a capacity of 18.3 kWh (hydrogen HHV = 39.39 kWh/kg).

4. Conclusions

In summary, we successfully synthesized sulfur-doped activated biocarbon using Sargassum spp. biomass, with commercial sulfur as the S source and KOH as the activating agent through pyrolysis. Sulfur doping is an inexpensive process that significantly enhances material properties, making it suitable for green chemistry applications. The surface areas of the SKTP and SSKTP were 1620 m2 gࢤ1 and 2377 m2 gࢤ1, respectively. CHNS and XPS analyses confirmed a uniform sulfur distribution, with the SSKTP having a sulfur content of 17.45 wt%, which proved effective for hydrogen uptake. The SSKTP exhibited a 20% improvement in hydrogen storage capacity (0.40 wt% at 50 bar and 45 °C) compared to the SKTP (0.33 wt%). These findings underscore the potential of sulfur doping for improving adsorption properties, presenting a promising path for developing sustainable hydrogen storage materials. The increase in hydrogen uptake capacity is closely linked to surface area, pore volume, and sulfur doping. Although sulfur-doped activated biocarbon is effective for hydrogen storage, there remains potential for optimization. Future research should explore co-doping strategies with other heteroatoms (e.g., nitrogen, phosphorus) to create additional active sites and further optimize the porous structure. Moreover, long-term stability studies and real-world evaluations will be essential for advancing the development of competitive hydrogen storage technologies.

Author Contributions

Conceptualization, R.B. and B.E.; methodology, K.S.-A. and D.R.; formal analysis, R.B., B.E. and C.P.; investigation, R.B., B.E. and K.S.-A.; writing—original draft preparation, D.R. and C.P.; writing—review and editing, C.P. and D.R.; supervision, R.B, B.E. and K.S.-A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Consejo Nacional de Humanidades, Ciencia y Tecnología (CONAHCYT) for the financial support provided through grants 253986, 254667 and for the postdoctoral research fellowship 2022(3), application number 4047288. K.S.-A. thanks to UNAM-DGAPA-PAPIIT-IN200122.

Data Availability Statement

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

Acknowledgments

They also extend their thanks to Jose Martin Baas Lopez for his valuable technical assistance.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. General diagram of the process of biochar preparation.
Figure 1. General diagram of the process of biochar preparation.
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Figure 2. Adsorption isotherms of the samples of SKPT and SSKTP.
Figure 2. Adsorption isotherms of the samples of SKPT and SSKTP.
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Figure 3. Powder XRD patterns of SKPT and SSKPT.
Figure 3. Powder XRD patterns of SKPT and SSKPT.
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Figure 4. Raman spectra of SKPT and SSKPT.
Figure 4. Raman spectra of SKPT and SSKPT.
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Figure 5. S 2p and C 1s peaks in the XPS spectra of the SKPT and SSKPT samples.
Figure 5. S 2p and C 1s peaks in the XPS spectra of the SKPT and SSKPT samples.
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Figure 6. HR-TEM images, dark field micrographs and corresponding elemental mappings of (a) SKTP and (b) SSKTP.
Figure 6. HR-TEM images, dark field micrographs and corresponding elemental mappings of (a) SKTP and (b) SSKTP.
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Figure 7. Hydrogen adsorption (empty circles) and desorption (filled circles) isotherms at 45 °C up to 50 bar for SKTP and SSKTP samples.
Figure 7. Hydrogen adsorption (empty circles) and desorption (filled circles) isotherms at 45 °C up to 50 bar for SKTP and SSKTP samples.
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Table 1. Porous textural and elemental compositions of SKTP and SSKTP samples derived from Sargassum spp.
Table 1. Porous textural and elemental compositions of SKTP and SSKTP samples derived from Sargassum spp.
SampleSBET
(m2 g−1)		Average Pore Size (nm)Pore Volume
(cm3 g−1)		C
(wt%)		H
(wt%)		N
(wt%)		S
(wt%)
SKTP16701.9040.79564.043.67ND0.85
SSKTP23772.5191.07861.961.13ND17.45
ND: Not detected.
Table 2. Chemical properties from the XPS and elemental analysis of the SKTP and SSKTP.
Table 2. Chemical properties from the XPS and elemental analysis of the SKTP and SSKTP.
SampleAnalysis Elemental CHNS
(% wt.)		XPS
Chemical Composition XPS
(% at.)		Sulfur Relative Content (% at.) and Binding Energy (eV)
CSC1sS 2p-C-S-C--C-SOX-C-
S 2p3/2S 2p1/2
SKTP64.040.8585.610.6446.75
(163.7)		29.10
(164.9)		24.15
(168.9)
SSKTP61.9617.4568.9320.1643.84
(163.7)		21.92
(165.0)		34.23
(168.9)
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Rosas, D.; Escobar, B.; Suarez-Alcantara, K.; Pacheco, C.; Barbosa, R. Functional Sulfur-Doped Biocarbon for Hydrogen Storage: Development of Nanomaterials for Energy Applications. Processes 2024, 12, 2715. https://doi.org/10.3390/pr12122715

AMA Style

Rosas D, Escobar B, Suarez-Alcantara K, Pacheco C, Barbosa R. Functional Sulfur-Doped Biocarbon for Hydrogen Storage: Development of Nanomaterials for Energy Applications. Processes. 2024; 12(12):2715. https://doi.org/10.3390/pr12122715

Chicago/Turabian Style

Rosas, David, B. Escobar, Karina Suarez-Alcantara, Carlos Pacheco, and Romeli Barbosa. 2024. "Functional Sulfur-Doped Biocarbon for Hydrogen Storage: Development of Nanomaterials for Energy Applications" Processes 12, no. 12: 2715. https://doi.org/10.3390/pr12122715

APA Style

Rosas, D., Escobar, B., Suarez-Alcantara, K., Pacheco, C., & Barbosa, R. (2024). Functional Sulfur-Doped Biocarbon for Hydrogen Storage: Development of Nanomaterials for Energy Applications. Processes, 12(12), 2715. https://doi.org/10.3390/pr12122715

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