# Enhanced hydrogen storage and release capacities when using HKUST-1@activated carbon hybrids obtained by resonant acoustic mixing

Laura Jimenez-Lopez, Rafael Morales-Ospino, Jimena Castro-Gutiérrez, Alain Celzard, Vanessa Fierro

► To cite this version:

Laura Jimenez-Lopez, Rafael Morales-Ospino, Jimena Castro-Gutiérrez, Alain Celzard, Vanessa Fierro. Enhanced hydrogen storage and release capacities when using HKUST-1@activated carbon hybrids obtained by resonant acoustic mixing. Chemical Engineering Journal, 2025, 520, pp.165834. 10.1016/j.cej.2025.165834. hal-05220963

HAL Id: hal-05220963

https://hal.univ-lorraine.fr/hal-05220963v1

Submitted on 24 Aug 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

# Enhanced hydrogen storage and release capacities when using HKUST-1@activated carbon hybrids obtained by resonant acoustic mixing

Laura Jimenez-Lopez<sup>a, ID</sup>, Rafael Morales-Ospino<sup>a, ID</sup>, Jimena Castro-Gutiérrez<sup>a, ID</sup>, Alain Celzard<sup>a, b</sup>, Vanessa Fierro<sup>a, *</sup>

## ARTICLE INFO

**Keywords:**

Metal-organic frameworks (MOFs)

Hydrogen storage

Adsorption

Activated carbons

MOF hybrids

Microporosity

## ABSTRACT

This study highlights the significant benefits of incorporating activated carbon (AC) into HKUST-1 matrix to reduce its hydrophilic nature while enhancing its hydrogen storage and release capacities. The integration of MSC30 commercial AC into HKUST-1 ([Cu₃(BTC)₂(H₂O)₃]ₙ; BTC = 1,3,5-benzenetricarboxylate) to form hybrid materials was achieved using Resonant Acoustic Mixing (RAM) as a mechanical mixing method. The hybrids demonstrated a significantly reduced affinity for water, with the hybrid containing 33 wt% AC exhibiting up to 50 % lower water uptake than pure HKUST-1. The AC's high specific surface area and narrow pore size distribution also contributed to improved H₂ adsorption in all hybrids. The hybrid containing 33 wt% AC exhibited a 26 % increase in excess adsorption compared to pure HKUST-1, although still lower than that of pure AC (4.8 vs. 5.8 wt% at 77 K and 25 bar, respectively). In terms of volumetric capacity, the higher tapped density of HKUST-1 improved the performance of the hybrid materials, with that containing 33 wt% AC achieving 39.4 kg m⁻³, an increase of 6 % compared to pure AC (37.0 kg m⁻³) and 28 % compared to the empty vessel (30.8 kg m⁻³). Additionally, this hybrid material reached a usable release capacity of 37.4 kg m⁻³, surpassing that of pure AC by 7 % (35.0 kg m⁻³) and that of the empty vessel by 23 % (30.4 kg m⁻³).

## 1. Introduction

Current research on hydrogen as an energy source primarily focuses on increasing its volumetric energy density [1]. While hydrogen has an exceptionally high specific energy density of 131.76 MJ kg⁻¹, its volumetric energy density is extremely low, 0.0108 MJ L⁻¹ [2], i.e., 300 times less dense than gasoline [3]. Therefore, hydrogen compression is of paramount importance in promoting the growth and effectiveness of hydrogen storage technologies.

Compressing hydrogen to pressures in excess of 700 bars is one of the most widely used physical methods for hydrogen storage [4,5]. Another approach is to store H₂ in liquid form at cryogenic temperatures of around 20 K [6], but evaporation of some of the hydrogen, known as “boil-off”, is unavoidable, resulting in process inefficiencies and energy losses [7]. Both techniques require extreme conditions and may raise public safety concerns. A promising alternative to these approaches is the physisorption of hydrogen on porous materials [8], a process in which hydrogen molecules are reversibly adsorbed onto the surface of a

material by weak van der Waals forces [9]. Although it is necessary to reach cryogenic temperatures (typically 77 K) and high pressures (100–140 bar) to increase storage capacity in porous materials, these conditions are less extreme than those required for compressed or liquid H₂.

The physisorption of hydrogen is significantly enhanced in porous materials with high microporosity and extremely narrow pores, typically between 0.6 and 0.7 nm in diameter. Therefore, to boost hydrogen adsorption capacity at 77 K, it is essential to increase both specific surface area and micropore volume in porous materials. Nanostructured carbon materials [10,11], activated carbon (AC) [12,13] and zeolites [14,15] are being extensively researched for hydrogen storage due to their large surface area and highly porous characteristics. On the other hand, metal-organic frameworks (MOFs) hold great promise for hydrogen storage due to their adjustable porosity, large surface area and the possibility of customizing their properties to particular uses [16–18]. For instance, HKUST-1 is a copper-based MOF linked by 1,3,5-benzenetricarboxylate (BTC) groups, resulting in a 3D square structure [19].

<footnote><sup>a</sup> Université de Lorraine, CNRS, IJL, F-88000 Epinal, France</footnote>

<footnote><sup>b</sup> Institut Universitaire de France (IUF), F-75231 Paris, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: Vanessa.Fierro@univ-lorraine.fr (V. Fierro).</footnote>
HKUST-1 is commonly employed in adsorption-related applications due to its high surface area, significant pore volume and ability to interact easily with various molecules [20].

Fig. S1 presents a schematic representation of the cluster and linker components, illustrating their assembly into the 3D framework structure of HKUST-1. HKUST-1 is generally coordinated with water molecules that complete the top of the cluster pyramids, resulting in the final coordination cage formula: [Cu₂ (COO)₄ + (H₂O)₂] [21]. In order to maximize its surface area, HKUST-1 can undergo an activation procedure in which water is removed from the initial coordination cage, allowing the recovery of metal sites that become available for other gases, such as hydrogen [22–24]. However, exposure of HKUST-1 to an aqueous environment can lead to its irreversible structural degradation, as water molecules can replace the metal-coordinated ligands [25,26]. Incorporation of an AC into a MOF matrix has been shown to increase the specific surface area of the resulting hybrid materials [27,28]. For example, Liu et al. synthesized HKUST-1 with various carbon-based materials, including ordered mesoporous carbon, activated carbon, and nitrogen-doped microporous carbon, which led to an overall increase in surface area and improved CO₂ adsorption capacity of the resulting MOF hybrids [29]. Similarly, Yu et al. incorporated AC into the synthesis of MIL-101(Cr), improving the textural properties of the samples and consequently boosting their H₂ adsorption capacity [30].

Several studies have investigated HKUST-1/carbon hybrids for hydrogen storage enhancement. For instance, Petit et al. [31] reported that incorporating 5 wt% of graphite oxide into HKUST-1 slightly increased the H₂ uptake from 2.2 to 2.4 wt%, while the surface area remained nearly unchanged (~990 m²·g⁻¹), attributing the improvement to the formation of additional small pores. Farrando-Pérez et al. [32] developed HKUST-1@graphite flakes monoliths and observed an enhanced H₂ uptake of 1.7 wt% for the hybrid with 10 wt% graphite flakes, compared to 1.25 wt% for the pure HKUST-1 monolith. These studies show that the integration of carbon-based materials can moderately improve hydrogen storage performance through changes in texture or thermal conductivity.

MOF hybrids can be prepared using several approaches, the most common being in situ growth, where the carbon-based material is added at the beginning of the synthesis, along with the MOF precursors. This means that the MOF forms in the presence of the carbon-based material, allowing strong interactions to develop between them. However, this approach typically requires long synthesis times (12–24 h) [16,32,33]. An alternative strategy is post-synthetic modification, which involves starting with a pre-synthesized MOF and then hybridizing it with another material to improve its properties [34–36]. Post-hybridization not only reduces synthesis times, but also ensures that the MOF is fully formed prior to hybridization, improving reproducibility and structural integrity.

This study aims to improve the hydrogen storage performance of HKUST-1 by combining AC and MOF, using resonant acoustic mixing (RAM) as a novel synthesis route to create hybrids through a post-synthetic approach. RAM is a technique that uses low-frequency, high-intensity movements to create a zone of uniform micro-mixing inside the vessel, facilitating material flow and ensuring homogeneous mixing of components and, sometimes, chemical reactions. For these reasons, it requires short mixing times (15 min) to achieve effective results using a fast, solvent-free and scalable technique. In this context, RAM stands out as an efficient method that enables rapid and uniform dispersion of additives into MOF structures without applying shearing or grinding forces. Unlike conventional methods such as ball milling, RAM preserves the crystallinity and porosity of the material, facilitating homogeneous hybrid formation while minimizing structural damage. The hybrids produced in this work were subjected to exhaustive characterization, including XRD, FTIR, TGA, SEM, textural properties analysis, and water affinity measurements. The hydrogen storage capacity of the materials was evaluated at high pressures (up to 140 bars) and 77 K, determining gravimetric and volumetric storage capacities and calculating the deliverable capacity under different conditions (usable hydrogen) in order to take a further step in representing and quantifying the system under more realistic operating conditions.

## 2. Materials and methods

### 2.1. Materials

The MOF selected was HKUST-1, commercially available under the name BASOLITE C 300 (particle size ~15 µm), provided by BASF (Germany), and the activated carbon (AC) employed was MSC 30 (particle size ~100 µm) provided by Kansai Coke (Japan). HKUST-1 was chosen for its high surface area and predominantly microporous nature, making it a suitable candidate for H₂ adsorption. Additionally, scalable synthesis techniques have been developed, allowing it to be commercialized. MSC-30 was selected due to its high surface area and well-developed microporosity, which are crucial for efficient hydrogen adsorption. Moreover, it is one of the most extensively studied ACs for hydrogen storage, making it a well-established reference material in this field [37].

### 2.2. Hybrid materials preparation

The preparation process of the hybrid materials is schematized in Fig. 1. HKUST-1 (1.5 g) and AC in various proportions were added (in powder form without further treatment) to a 20 mL glass vial and mixed using a LabRAM II resonant acoustic mixer (Resodyn, UK) for 15 min at 95 times the acceleration of gravity (95 g). As the mixing was produced in dry form, the samples were ready to use (without drying or washing steps). Samples were labelled HK-AC p, where “p” stands for the percentage of AC in the mixture, ranging from 5 to 50 %. The percentages of AC employed for the hybrids were calculated in relation to the amount of HKUST-1 present in the resulting material. For example, a sample labelled HK-AC 50 indicates that for every 1 g of HKUST-1, 0.5 g of AC was incorporated into the mixture, giving a final AC weight percentage of 33.3.

Eq. 1 below is the classical mixing rule that allows the calculation of theoretical values for a given property of the prepared hybrids:

$$X_n = X_{AC} \times wt.\%_{AC} + X_{HKUST-1} \times wt.\%_{HKUST-1} \quad (1)$$

where “Xn” is the theoretical property for a specific hybrid; “XAC” and “XHKUST-1” are the measured properties for pure AC and pure HKUST-1, respectively, and “wt%AC” and “wt%HKUST-1” are the weight fractions of AC and HKUST-1 present in the hybrid considered. This calculation is performed to compare the evaluated properties of the hybrids with those of their parent materials (pure HKUST-1 and MSC-30) based on a physical mixing rule. According to this rule, the property values are determined by the weighted contribution of each parent material. This approach makes it possible to assess whether the observed values are within the expected range, or whether they show a deviation relative to the predicted value.

### 2.3. Physicochemical characterization

The detailed experimental procedures for the physicochemical characterization of the materials, including X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), optical and scanning electron microscopy (SEM), textural characterization, water affinity measurements, thermal conductivity, and skeletal and tapped density determination are provided in the Supplementary Information in the section entitled Physicochemical characterization.
<figure><img src="image_4.png" /><figcaption>Fig. 1. Scheme of the preparation of HKUST-1@AC hybrids.</figcaption></figure>

## 2.4. High-pressure hydrogen isotherms

Hydrogen adsorption isotherms were determined up to 140 bars at 77 K using an HPVA II high-pressure manometric adsorption equipment coupled with a single-stage closed-cycle cryogenic refrigerator (both from Micromeritics). Prior to measurement, the sample (around 1 g) was degassed in a vacuum oven at 398 K overnight. The excess amount of stored hydrogen ($n_{exc}$) was calculated using the Leachman equation of state (recommended by NIST) applied to H$_{2}$ isotherms. From $n_{exc}$, the total hydrogen uptake ($n_{tot}$) was determined using Eq. 2:

$$n_{tot} = n_{exc} + \left( \frac{1}{\rho_{tap}} - \frac{1}{\rho_{skel}} \right) \rho_{H_2} \quad (2)$$

where $n_{exc}$ is the measured excess hydrogen uptake, $\rho_{tap}$ is the tapped density of the adsorbent, $\rho_{skel}$ is the skeletal density of the solid, obtained by helium pycnometry, and $\rho_{H_2}$ is the hydrogen density of the gas phase under the same conditions [38]. The total amount of hydrogen stored

($n_{tot}$) is a crucial reference point when comparing physisorption in porous materials with other hydrogen storage methods. This value accounts for both the hydrogen adsorbed in the pores and the gas phase stored in the dead space, providing a more accurate representation of the material's storage capacity [38].

The efficiency adsorption systems for H$_{2}$ storage can be more realistically evaluated by their hydrogen charge and discharge cycles. Their performance depends on the ability to store hydrogen, by adsorption and compression, and the efficiency of its release under given operating conditions [39–41]. This efficiency is evaluated by the release capacity (also called usable or delivery capacity), which quantifies the amount of hydrogen discharged. It is calculated using Eq. 3:

$$Release \ capacity = (n_{tot})_{storage} - (n_{tot})_{release} \quad (3)$$

where $(n_{tot})_{storage}$ is the total H$_{2}$ uptake under charging conditions and $(n_{tot})_{release}$ is the total H$_{2}$ uptake under discharging conditions. Herein, the release capacity was calculated considering two release

<figure><img src="image_5.png" /><figcaption>Fig. 2. a) X-ray diffraction patterns of pure HKUST-1 before and after submitting it to RAM for 15 min; b) X-ray diffraction patterns of HKUST-1 and its hybrids with different fractions of AC; c) FTIR spectra of HKUST-1 and its hybrids; d) thermogravimetric profiles for pure HKUST-1 and its hybrids measured under argon; e) theoretical slope (open symbols) vs experimental slope (closed symbols) of mass loss calculated by the rule of mixtures (Eq. (1)); f) Thermal conductivity of the samples measured in powder form (298 K and 25 % relative humidity). The dashed line represents the thermal conductivity calculated by the rule of mixtures (Eq. (1)).</figcaption></figure>
temperatures, i.e., 77 and 160 K. Hydrogen adsorption isotherms up to 140 bar at 160 K were also obtained for all materials.

## 3. Results

### 3.1. Materials characterization

Fig. 2 shows the powder XRD patterns of pure HKUST-1 and its hybrids with AC. To assess the impact of RAM on MOF crystallinity, the XRD pattern of HKUST-1 subjected to 15 min of mixing was compared with that of pristine HKUST-1. The nearly identical XRD patterns, shown in Fig. 2-a, confirm that RAM has no significant effect on the final crystallinity of the material, ensuring that the structural integrity of HKUST-1 remains intact during the mixing process.

Fig. 2-b compares the XRD patterns of hybrids and pure HKUST-1. The characteristic diffraction peaks observed at 9.51°, 11.71° and 13.51°, corresponding to the (220), (222) and (400) reflections, are readily attributable to the crystal structure of HKUST-1 and correspond well to previously reported data [29,42,43]. In the hybrids, the intensity of these peaks decreases progressively with increasing AC content, reflecting the contribution of the amorphous nature of AC. Importantly, no additional peaks indicating the presence of impurities were detected in the XRD patterns. The strong correlation between the diffraction patterns of commercial HKUST-1 before and after RAM, as well as those of hybrids, confirms that neither RAM nor AC incorporation compromises the crystallinity of the resulting materials.

The FTIR spectra of all samples are shown in Fig. 2-c. The bands observed in the HKUST-1 spectrum originate mainly from the BTC ligand [44]. Bands appearing at wavenumbers above 3000 $cm^{-1}$ correspond to -OH functional groups with a characteristic peak at 3668 $cm^{-1}$ [45,46]. In the lower wavenumber region, peaks at 2988 $cm^{-1}$ and 2899 $cm^{-1}$ are assigned to the aliphatic C—H stretching vibration present in the BTC linker [47–49]. In the middle part of the spectra, bands within the range of 1300–1700 $cm^{-1}$ are associated with the carboxylate linker. Among these, the peak at 1646 $cm^{-1}$ corresponds to asymmetric stretching vibrations of C=C groups, while the peak at 1451 $cm^{-1}$ is attributed to C=O stretching. Additionally, peaks at 1373 $cm^{-1}$ and 1109 $cm^{-1}$ are assigned to C—O interactions, further emphasizing the contributions of the linker structure [50–53]. In the low-frequency region, the peak at 759 $cm^{-1}$ is characteristic of the inorganic framework, reflecting the single-bond between Cu and oxygen atoms (Cu—O) [54]. Finally, the appearance of a peak at 729 $cm^{-1}$ is associated with C—H bending vibrations [45].

The TGA results for pure HKUST-1 and its hybrids are shown in Fig. 2-d, and the corresponding derivative thermogravimetry (DTG) curves are shown in Fig. S2. Despite degassing the samples prior to measurement, a minor weight loss (around 2 wt%) is observed between 373 and 423 K, attributed to residual hydration from ambient humidity during sample preparation. The next weight loss, occurring between 423 and 573 K, corresponds to the loss of water coordinated to Cu, which acts as a node in the HKUST-1 structure [55]. The collapse of the framework due to the degradation of the organic linker (BTC) occurs between 619 and 621 K (Fig. 2-d and Fig. S2) [56,57]. The consistent degradation temperatures across all hybrids and the pure MOF suggest the absence of chemical bonding between HKUST-1 and AC, suggesting that the materials form a physical mixture.

Between 700 and 800 K, a change in the behavior of the TGA curve is observed, which could be associated with the degradation of the organic ligand. Finally, at 1173 K the remaining mass includes solid decomposition products such as metallic Cu, Cu oxides [43,58,59] and residual carbon, which increases with AC content. The inset in Fig. 2-d highlights that, as the percentage of AC rises, the final mass (wt%) at 1173 K also increases, as carbon remains stable and negligibly degrades at this temperature (Fig. S3). Fig. 2-e compares the theoretical mass loss (calculated using Eq. (1)) with the experimentally observed mass loss from TGA measurements. As evident from the plot, the hybrid materials

exhibit a lower mass loss than their theoretical counterparts, suggesting a protective effect of the AC on the HKUST-1 framework.

Fig. 2-f presents the thermal conductivity of the hybrids and their parent materials, which increases with the wt% of AC. For AC, the value measured in this study, 0.23 $W·m^{-1}·K^{-1}$, falls within the range reported in the literature, which indicates that activated carbon has a thermal conductivity of between 0.17 and 0.28 $W·m^{-1}·K^{-1}$ [60]. In the case of MOFs, the thermal conductivity values reported in the literature vary considerably depending on the measurement conditions, ranging from 0.07 to 0.21 $W·m^{-1}·K^{-1}$ for powders [61–63]. In our study, pure HKUST-1 has a thermal conductivity of 0.16 $W·m^{-1}·K^{-1}$, within the range reported in the literature. Due to the combination of the two materials HKUST-1 and AC, the hybrids exhibit an increase in thermal conductivity compared to pure HKUST-1. However, here again and even if the effect is moderate, this increase clearly does not follow the rule of mixtures but gives values higher than the calculation using Eq. 1 (dashed line in Fig. 2-f). By bringing the elementary constituents AC and MOF into closer contact than would be possible simply by conventional mixing of their individual grains, hybrid grains may contribute to improved powder bed conductivity. Each experiment was repeated six times to ensure statistical reliability. The values reported correspond to the average of these measurements, with a maximum standard deviation of ±0.0168 $W·m^{-1}·K^{-1}$ across all samples.

Optical microscope images are presented in Fig. 3a-c. The first image, Fig. 3-a, displays well-defined crystals of pure HKUST-1. When activated carbon (AC) is incorporated, Fig. 3-b and 3-c, the MOF undergoes noticeable agglomeration, forming irregular clusters of material around the carbon particles. Notably, no free or loose carbon particles are visible in the samples, suggesting a uniform and effective combination of materials.

A magnification corresponding to a scale bar of 300 µm was selected in order to adequately capture the overall morphology of the sample. Given the relatively large particle sizes (~15 µm for HKUST-1 and ~100 µm for AC), using a higher magnification would have significantly reduced the field of view, limiting the visualization of particle distribution. This limitation is clearly illustrated in Fig. S4, where higher-magnification images fail to provide a representative view of the sample morphology due to the narrow field of view. Fig. 3-d presents the SEM image of sample HK-AC 5, while Fig. 3-e and 3-f show the elemental mappings for C and Cu, respectively, Cu being a key component of HKUST-1. Similarly, Fig. 3-g, 3-h and 3-i display the SEM image and corresponding elemental mappings for sample HK-AC 50. Comparing the two hybrid samples, HK-AC 5 shows a more uniform dispersion of activated carbon within the MOF than HK-AC 50, where larger AC clusters and a less homogeneous distribution are observed. This difference is likely due to the higher AC content in HK-AC 50, which promotes agglomeration and reduces effective contact between components (Fig. 3). Unlike optical microscopy, SEM mapping allows a clear distinction between AC and HKUST-1 frameworks. In the Cu mapping, AC-containing regions are identified by completely black areas, indicating the absence of MOF in those zones. Conversely, C mapping reveals areas of higher intensity corresponding to AC, although carbon is also uniformly distributed throughout the sample due to its presence in the MOF’s organic linker. This uniformity, but also contiguity between the phases present, is further corroborated by the oxygen mapping (Fig. S5), which reflects the contribution of the oxygen atoms from the organic linker, appearing consistently across the surface. In contrast to the observations made under optical microscope observations, no agglomeration of the MOF around AC particles was observed in the SEM images and their corresponding mapping images (where each component is seen separately). This can be attributed to the preparation method for SEM analysis, which involved dispersing the sample in ethanol. This process may have disrupted the interactions present in the original sample.

$N_2$ adsorption-desorption isotherms are shown in Fig. 4-a for all samples. All isotherms are type I shape according to the IUPAC
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 3.** Optical microscope images of a) pure HKUST-1, b) HK-AC 5 and c) HK-AC 50. d) SEM image of HK-AC 5, alongside its e) carbon and f) copper mapping images. g) SEM image of HK-AC 50, alongside its h) carbon and i) copper mapping images.</figcaption></figure>

classification [64], which is typical of microporous materials. The N₂ isotherm of pure HKUST-1 is type I (a), while the isotherm of AC (MSC 30) is type I (b), indicating the presence of wide micropores and narrow mesopores. Consequently, with the addition of AC, the hybrid materials gradually transition from a type I (a) to a type I (b) isotherm, with this trend becoming more pronounced as the wt% of AC increases. The N₂ isotherms presented in logarithmic scale in Fig. 4-b indicate that the uptake at low relative pressures (up to ~10⁻³) is lower for the hybrids compared to the pure MOF. However, at higher relative pressures, the uptake increases for the hybrids. This increase is related to the addition of AC, which gradually reduces the contribution of ultramicropores, the majority of which are found in the MOF, while introducing more supermicropores, so that overall micropore volume increases with the amount of AC.

Argon isotherms at 87 K were also performed, as they provide a more accurate analytical method for characterizing porous materials such as MOFs since the orientation of the N₂ molecule, which depends on the surface chemistry of the material due to its quadrupole moment, can lead to uncertainties [65]. Fig. S6 confirms that pure HKUST-1 and AC (MSC30), as well as their hybrids, exhibit the same type of isotherms as those observed for N₂ adsorption. The A<sub>BET</sub> values calculated from Ar

and N₂ isotherms, compared in Fig. 4-c, reveal an increase with the addition of AC. However, the relative differences between these values remain within a narrow range (2–11 %), supporting the reliability of using 2D-NLDFT with N₂ and H₂ as a representative method for assessing the materials textural properties. Selected N₂, H₂ and Ar adsorption isotherms were repeated three times, and the measurement error was found to be lower than 3 %, confirming the reliability and reproducibility of the data.

Textural properties calculated from the PSDs of hybrid and pristine materials, including surface areas (S<sub>2D-NLDFT</sub> and A<sub>BET</sub>), total pore volumes (V<sub>tot</sub>) and pore volumes in different pore size ranges, are summarized in Table S1. The most striking and visible trend is the contribution of narrow mesoporosity, which comes exclusively from the AC and shows a clear increase, as evidenced by the cumulative pore volume, V<sub>cum</sub> (Fig. 4-d). This increase in narrow mesoporosity is also evident in the pore size distribution of the samples (Fig. 4-e), where a peak near 3 nm appears and becomes more pronounced with increasing AC content. Fig. 4-f presents the total pore volume (V<sub>tot</sub>, cm³ g⁻¹) of each range of pore size, distinguishing between microporosity and mesoporosity (V<sub>μ</sub> and V<sub>meso</sub>, respectively). HKUST-1 is predominantly microporous, whereas AC exhibits both a microporous fraction and a portion of
<figure><img src="image_9.png" /><figcaption>Fig. 4. Textural characteristics of pure HKUST-1, AC (MSC 30) and hybrids: N₂ adsorption (solid symbols) – desorption (empty symbols) isotherms at 77 K in a) linear and b) logarithmic scale; c) comparison of BET areas calculated from N₂ and Ar isotherms; d) cumulative pore volume (V~cum~) as function of the pore width; e) pore size distributions; f) BET area (A~BET~) and pore volumes in the micropore (V~μ~ (<2 nm)) and mesopore (V~meso~ (2–50 nm)) ranges.</figcaption></figure>

mesoporosity. In the hybrid materials, microporosity increases slightly with the wt% of AC, due to the incorporation of supermicropores (as observed in the pore size distribution) leading to only a small overall change in micropore volume.

Turning now to the affinity of MOFs for water, this aspect is recognized as one of their most important characteristics, as it can compromise their performance in gas adsorption applications [25,26,66]. In HKUST-1, the presence of water in the sample is readily evidenced by a color change, shifting from dark blue in the dry state to turquoise upon adsorption of moisture (Fig. S7).

According to the model proposed by Dubinin and Serpinski, water adsorption occurs at primary sites of carbon materials, mostly involving

carboxyl groups where clusters are formed [67]. These clusters serve as nucleation sites for water, which subsequently interacts with the carbon surface and, at higher relative pressure (p/p°), water interacts with the pores of the material [68,69]. The study of water affinity in MOFs differs from what has been observed in carbons due to the substantial variability in inorganic clusters, chemical functionality, pore size and pore structure [70]. Some MOFs demonstrate a distinctive rapid increase in water adsorption, often resembling a high step function, occurring at p/p° well below 0.4 [71].

Fig. 5-a and 5-b show water isotherms at 293 K for MOF, AC and hybrids. HKUST-1 and hybrids exhibit a strong affinity for water, as evidenced by the rapid uptake of water at low relative pressures (p/p° <

<figure><img src="image_10.png" /><figcaption>Fig. 5. Water affinity: a) water adsorption isotherms at 293 K for pure HKUST-1, AC and hybrids; b) Zoom on the water affinity region; c) theoretical slope (open symbols) vs experimental slope (closed symbols) of water isotherms up to a relative pressure of 0.02.</figcaption></figure>
0.1) due to the abundance of preferred adsorption sites [26]. However, this increase is more pronounced for pure HKUST-1 and decreases as the wt% of AC increases. In contrast, AC has no affinity for water, as shown by its flat isotherm and negligible adsorption for $p/p° < 0.4$ [72].

To compare water affinity in a quantifiable way, the slopes of the water isotherms up to 0.02 were calculated, bearing in mind that a higher slope indicates greater affinity for water [73,74]. Fig. 5-c shows the calculated slopes as a function of the wt% of AC incorporated; the decreasing values with increasing wt% AC suggest that water affinity in hybrid materials decreases due to the highly hydrophobic nature of AC. The reduction in slope observed experimentally ranges from 12.8% for the hybrid with the lowest AC content (HK-AC 5) to 51.4% for the hybrid with the highest AC content (HK-AC 50). However, the theoretical values calculated using Eq. 1, also shown in Fig. 5-c, indicate a greater reduction in water affinity than would be expected from a simple physical combination of materials (12–50% vs. theoretical 5–33%). This finding suggests that, contrary to what has been suggested above by TGA, AC-MOF hybrid materials are not just a mixture of powders. They are composites in their original definition, i.e. their properties are not the sum of those of their constituents, but something different, since the rule of mixtures does not apply. In the present case, the MOF becomes considerably less hydrophilic when it is one of the phases of a hybrid material in which AC is present at a level of a few wt%.

## 3.2. Determination of hydrogen storage and release capacities

Fig. 6-a shows the excess H₂ uptake ($n_{exc}$, wt%) for all samples. Pure HKUST-1 exhibits the lowest $n_{exc}$, which increases with the AC content. However, all hybrid materials demonstrate lower uptake than pure AC. At 77 K, the maximum $n_{exc}$ value, found at pressures in the range 20–40 bar, lies between 3.8 and 4.8 wt% for hybrids and 5.8 wt% for AC, see

Fig. 6-a and Table S2. The introduction of narrow mesoporosity increases the total pore volume and, as these pores are filled by compression, this leads to enhanced hydrogen adsorption capacity (wt %) at higher pressures.

In general, $n_{exc}$ at 77 K increases by 1 wt% for every 500 m² g⁻¹ increase in $A_{BET}$, a heuristic relation referred to as “Chahine’s rule” [75]. The $n_{exc}$ at 77 K is presented as a function of $A_{BET}$ in Fig. 6-b for the materials of this study. The behavior of pure HKUST-1 and hybrids deviates slightly from Chahine’s rule, showing higher values than predicted. For pure AC, $n_{exc}$ is lower than expected, due to the well-known overestimation of $A_{BET}$ for microporous materials. If Chahine’s rule worked, the BET area of the AC extrapolated from the dotted line in Fig. 6-b would be around 2800 m² g⁻¹, which is a more reasonable value and close to what can be calculated assuming all the carbon layers are separated from each other in the AC. This also applies to hybrid materials, whose actual specific surface area is lower than the BET area shown in Fig. 6-b, indicating that these hybrids have a hydrogen storage capacity even higher than those suggested by the dotted line.

$n_{exc}$ was also plotted as a function of the NLDFT surface area ($S_{2D}$, NLDFT, Fig. S8-a), revealing that the results do not align well with Chahine’s rule when surface area is calculated using a DFT model. For all hybrids materials, the observed values exceed the predictions by Chahine’s rule, whereas for the pure MOF, $n_{exc}$ falls below the expected value. Although, these discrepancies may stem from the absence of 2D-NLDFT kernel models specifically developed for MOF structures, the hydrogen uptake in AC also increases by approximately 1.25 wt% for every 500 m² g⁻¹ of $S_{2D}$-NLDFT surface area (Fig. S8-b), suggesting a potential alternative to the Chahine rule [75–77].

The deviations observed from Chahine’s rule can be attributed to the limitations of the BET method for determining the real surface area, as reported elsewhere [78]. In ACs, this problem can be addressed by using

<figure><img src="image_11.png" /><figcaption>Fig. 6. Hydrogen adsorption measurements at high pressure: a) excess H₂ uptake ($n_{exc}$) at 77 K in gravimetric capacity and b) Chahine's rule (dotted line) for pure HKUST-1, AC (MSC30) and hybrids as a function of their $A_{BET}$; c) total H₂ uptake ($n_{tot}$) at 77 K in volumetric capacity; d) cycles of $n_{exc}$ at 77 K in gravimetric capacity for the sample HK-AC 50; e) H₂ storage capacity (kg m⁻³) showing compression and adsorption contributions. f) Release capacities or usable H₂ (kg m⁻³) under different conditions: charge at 77 K and 100 bar; discharge at 5 bar and 77 or 160 K.</figcaption></figure>
NLDFT models [76], but their application to MOFs or hybrids is not yet fully validated [79]. This can lead to an overestimation or underestimation of the real accessible surface area, affecting the correlation with H₂ uptake, which in turn explains deviations from the expected Chahine behavior.

Total H₂ uptakes ($n_{tot}$, wt%), obtained with Eq. 2 and presented in Fig. S9, show higher values for AC (MSC-30) than those for hybrids, following the same trend as reported for excess H₂ uptake. However, when the total H₂ storage capacity ($n_{tot}$ in kg m⁻³) is calculated, this difference vanishes (see Fig. 6-c), with some hybrids outperforming AC, namely HK-AC 35 and HK-AC 50. This is due to the combined effect of the increased adsorption capacity provided by the AC and the higher $ρ_{tap}$ of the HKUST-1, 372 kg m⁻³ versus 240 kg m⁻³ for the AC, see Fig. S10. The increase in $ρ_{tap}$ is a critical factor, enabling the amount of porous material per unit volume to be increased and thereby improving H₂ storage in terms of volumetric capacity. Despite the decrease in $ρ_{tap}$ values with increasing AC content (Fig. S10), the HK-AC 50 sample still has a significantly higher $ρ_{tap}$ than pure AC (325 kg m⁻³), which could explain its superior volumetric storage capacity. The enhanced H₂ storage capacity observed in the HKUST-1@AC hybrids results from the synergistic combination of two components. The AC's high specific surface area facilitates H₂ adsorption, while HKUST-1's higher intrinsic density contributes to a more efficient packing of the material. This combination improves both the availability of adsorption sites and the overall density of the material, thereby enhancing volumetric H₂ storage performance.

To evaluate hybrid stability, H₂ adsorption isotherms were repeated over five cycles for the best-performing sample, i.e., HK-AC 50, see Fig. 6-d. A slight difference in desorption (open symbols) can be observed, which may be due to the fact that the sample was not degassed between cycles. The comparative results of the five cycles displayed consistent behavior, with a standard deviation below 2%, confirming the stability of the hybrid material.

As shown in Fig. 6-e, the total H₂ storage capacity for all the materials studied exceeds that of an empty tank. When a tank containing a specific adsorbent is used for gas storage, hydrogen is retained in two distinct forms: (1) as a phase adsorbed on the material's surface and (2) as a free gas phase in the remaining voids (inter- and intra-particle free space). The amount of H₂ adsorbed corresponds to the quantity stored in the porous material and is defined by the excess adsorption factor, $n_{exc}$, as expressed in Eq. 2. Meanwhile, compressed H₂ corresponds to the second term in Eq. 2, representing the quantity of gas stored in the free space. The results indicate that incorporating AC enhances the total H₂ storage capacity, even exceeding the storage capacity of pure MOF and pure AC. This effect results from the combined contributions of MOF and AC to the hybrid's properties, with AC enhancing gravimetric hydrogen adsorption capacity by increasing its surface area, and MOF improving volumetric capacity by increasing its tapped density.

The release capacity was determined under charging conditions of 77 K and 100 bar, consistent with the maximum refueling pressure for type I metal tanks [39]. According to the Hydrogen Storage Engineering Center of Excellence [80], a release pressure of 5 bar is considered the minimum pressure at which H₂ can flow effectively from a tank to an engine or a fuel cell [81,82]; discharge conditions were therefore set at this pressure. A comparison was made between two scenarios: discharging at the same temperature as the charging process at 77 K (Release 77K→77K) and using a temperature swing from 77 K during loading to 160 K (Fig. S11) during discharge (Release 77K→160K) (see Eq. 3). Under discharge conditions of 77 K and 5 bar (Table S3), the empty tank delivers a higher H₂ discharge than the tank containing the porous materials, with release values of 29.5 kg m⁻³ for the empty tank versus 25.3 kg m⁻³ for the best materials, HK-AC 50 and the AC.

Nevertheless, when the discharge temperature is increased to 160 K, this result is reversed: the release capacity of the porous materials exceeds that of the empty tank (Fig. 6-f). In this case, the maximum release capacity of 37.4 kg m⁻³ is found for HK-AC 50, surpassing that of pure

AC (35.0 kg m⁻³). These results highlight that the discharge temperature is a critical factor in determining the amount of usable H₂. Additionally, H₂ release (at 160 and 77 K) requires controlled thermal management, as the temperature decreases during discharge due to the endothermic nature of H₂ desorption and/or the Joule-Thomson (JT) effect caused by gas expansion. Since the discharge temperatures evaluated are below 200 K, which is the JT inversion temperature of H₂, the released H₂ undergoes further cooling, which may affect the efficiency of the desorption process and the overall hydrogen delivery performance if not properly managed [7].

## 4. Conclusion

A novel preparation route towards HKUST-1@AC hybrid materials was demonstrated using resonant acoustic mixing (RAM). These hybrids exhibit improved properties compared to HKUST-1 arising from the hybridization of the two parent materials. The addition of AC develops the textural properties of the materials by increasing the BET area ($A_{BET}$) and providing additional narrow mesoporosity, which contributes to an increase in total pore volume, while HKUST-1 contributes to the development of ultramicroporosity and higher tapped density in the hybrids. Moreover, the presence of AC leads to a significant reduction in water affinity, 51.4% for the HK-AC 50 hybrid, compared to that of pure HKUST-1; this reduction in its hydrophilic behavior could prevent pore blockage and degradation of the hybrids when exposed to water, ultimately extending their lifespan. In addition, the presence of AC in the hybrids contributes to achieving higher excess H₂ uptake (wt%) values compared to the pure MOF, while the higher packing (or tapped) density of HKUST-1, 380 kg m⁻³, compared to AC, 240 kg m⁻³, enhances the H₂ storage capacity of the hybrids at 77 K and 100 bars: 39.4 kg m⁻³ for the HK-AC 50 hybrid versus 35.5, and 37.0 kg m⁻³ for the MOF and the AC, respectively. At 160 K and 5 bar, the release capacity reached a maximum value of 37.4 kg m⁻³ for HK-AC 50, exceeding that of the pure AC, 35.0 kg m⁻³. This study thus demonstrates the potential of RAM-derived MOF@AC hybrids for increasing hydrogen storage and release capacities, with enhanced performance due to their higher surface area and packing density. The finding of a synergy between these base materials, with hybrids whose properties are significantly better than the simple linear combination of the properties of the phases present, suggests a composite effect. The feasibility of large-scale application is supported by the use of commercially available precursors and the simplicity of the RAM synthesis method, which is well suited for scale-up. However, for real-world implementation, further studies should focus on the densification of the hybrid materials to enhance their volumetric H₂ storage capacity and to facilitate their integration into practical systems.

## Abbreviations

(n_{tot})_{release} Total H₂ uptake at discharging conditions

(n_{tot})_{storage} Total H₂ uptake at charging conditions

2D-NLDFT Two-dimensional non-local density functional theory

A_{BET} Brunauer-Emmett-Teller area

AC Activated carbon

BTC 1,3,5-benzenetricarboxylate

DOE U.S. Department of Energy

DTG Thermogravimetric derivative

FTIR Fourier-transform infrared spectroscopy

HKUST-1 Hong Kong University of Science and Technology-1

IUPAC International Union of Pure and Applied Chemistry

JT Joule-Thomson

MOF Metal organic framework

n_{exc} Measured excess hydrogen uptake

n_{tot} Calculated total hydrogen uptake = compressed H₂ + adsorbed H₂

PSDs Pore size distributions
<table><tr><td>RAM</td><td>Resonant acoustic mixing</td></tr><tr><td>S<sub>2D-NLDF</sub></td><td>2D-NLDFT based surface area</td></tr><tr><td>SEM</td><td>Scanning electron microscope</td></tr><tr><td>TGA</td><td>Thermogravimetric analysis</td></tr><tr><td>V<sub>meso</sub></td><td>Mesopore volume</td></tr><tr><td>V<sub>μ</sub></td><td>Supermicropore volume</td></tr><tr><td>V<sub>tot</sub></td><td>Total pore volume</td></tr><tr><td>V<sub>μ</sub></td><td>Micropore volume</td></tr><tr><td>V<sub>μμ</sub></td><td>Ultramicropore volume</td></tr><tr><td>wt%<sub>AC</sub></td><td>Weight percentages of the AC present in the hybrid</td></tr><tr><td>wt%<sub>HKUST-1</sub></td><td>Weight percentages of the HKUST-1 present in the hybrid</td></tr><tr><td>X<sub>AC</sub></td><td>Measured parameter for the AC</td></tr><tr><td>X<sub>HKUST-1</sub></td><td>Measured parameter for the HKUST-1</td></tr><tr><td>X<sub>n</sub></td><td>Theoretical parameter for a specific hybrid</td></tr><tr><td>XRD</td><td>X-ray diffraction</td></tr><tr><td>ρ<sub>cry</sub></td><td>Crystal density</td></tr><tr><td>ρ<sub>H2</sub></td><td>H<sub>2</sub> density</td></tr><tr><td>ρ<sub>skel</sub></td><td>Skeletal density</td></tr><tr><td>ρ<sub>tap</sub></td><td>Tapped density</td></tr></table>

CRediT authorship contribution statement

**Laura Jimenez-Lopez:** Writing – original draft, Investigation, Formal analysis. **Rafael Morales-Ospino:** Writing – review & editing, Validation, Supervision, Formal analysis. **Jimena Castro-Gutiérrez:** Writing – original draft, Formal analysis. **Alain Celzard:** Writing – review & editing, Supervision. **Vanessa Fierro:** Writing – review & editing, Supervision, Project administration, Formal analysis.

Declaration of competing 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.

Acknowledgements

This work was made possible thanks to (i) SOLHYD project (ANR-22-PEHY-0007) funded by the Agence Nationale de la Recherche (ANR, France), (ii) FRCR HyPE project funded by Région Grand-Est, and (iii) TALiSMAN and TALiSMAN2 projects funded by FEDER.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cej.2025.165834.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

[1] E. Iliса, Microporous materials for hydrogen liquefiers and storage vessels, J. Mater. Sci. Lett. 3 (2022) 1–10.

[2] M. Ball, M. Wietschel, The hydrogen economy: opportunities and challenges, Cambridge University Press, 2009.

[3] D.J. Durbin, C. Malardier-Jugroot, Review of hydrogen storage techniques for on board vehicle applications, Int. J. Hydrog. Energy 38 (2013) 14595–14617, https://doi.org/10.1016/j.ijhydene.2013.07.058.

[4] L. Cheng, L. Qi, X. Tang, X. Li, L. Chen, W. Min, Z. Mei, R. Gao, M. Sun, J. Xiao, Q. Guan, M. Yu, Z. Sun, Effects of hydrogen cycling on the performance of 70 MPa high-pressure hydrogen storage tank liners formed by different processes, Int. J. Hydrog. Energy 83 (2024) 499–511, https://doi.org/10.1016/j.ijhydene.2024.07.345.

[5] X. Li, C. Zhu, C. Liu, Y. Liu, J. Song, X. Liu, J. Li, Research on protection methods for 70 MPa on-board type IV hydrogen storage cylinders under localized fire

conditions, Int. J. Hydrog. Energy 50 (2024) 992–1005, https://doi.org/10.1016/j.ijhydene.2023.08.130.

[6] G. AlZohbi, A. Almoaimel, L. AlShuhail, An overview on the technologies used to store hydrogen, Energy Rep. 9 (2023) 28–34, https://doi.org/10.1016/j.egyr.2023.08.072.

[7] R. Morales-Ospino, A. Celzard, V. Fierro, Strategies to recover and minimize boil-off losses during liquid hydrogen storage, Renew. Sust. Energ. Rev. 182 (2023) 113360, https://doi.org/10.1016/j.rser.2023.113360.

[8] K.M. Thomas, Hydrogen adsorption and storage on porous materials, Catal. Today 120 (2007) 389–398, https://doi.org/10.1016/j.cattod.2006.09.015.

[9] J.L. Belof, A.C. Stern, M. Eddaoudi, B. Space, On the mechanism of hydrogen storage in a metal–organic framework material, J. Am. Chem. Soc. 129 (2007) 15202–15210, https://doi.org/10.1021/ja0737164.

[10] M. Hirscher, M. Becher, M. Haluska, A. Quintel, V. Skakalova, Y.-M. Choi, U. Dettlaff-Weglikowska, S. Roth, I. Stepanek, P. Bernier, A. Leonhardt, J. Fink, Hydrogen storage in carbon nanostructures, J. Alloys Compd. 330–332 (2002) 654–658, https://doi.org/10.1016/S0925-8388(01)01643-7.

[11] V.N. Popov, Carbon nanotubes: properties and application, Mater. Sci. Eng. R. Rep. 43 (2004) 61–102, https://doi.org/10.1016/j.mser.2003.10.001.

[12] K. Shindo, T. Kondo, Y. Sakurai, Hydrogen physisorption capacities of mechanically milled activated carbon powders in a H2 atmosphere using a gravimetric method, J. Alloys Compd. 379 (2004) 252–255, https://doi.org/10.1016/j.jallcom.2004.02.019.

[13] T. Kiyobayashi, H.T. Takeshita, H. Tanaka, N. Takeichi, A. Züttel, L. Schlapbach, N. Kuriyama, Hydrogen adsorption in carbonaceous materials: how to determine the storage capacity accurately, J. Alloys Compd. (2002) 666–669, https://doi.org/10.1016/S0925-8388(01)01436-0, 330–332.

[14] J. Weitkamp, M. Fritz, S. Ernst, Zeolites as media for hydrogen storage, Int. J. Hydrog. Energy 20 (1995) 967–970, https://doi.org/10.1016/0360-3199(95)00058-L.

[15] K.P. Prasanth, R.S. Pillai, H.C. Bajaj, R.V. Jasra, H.D. Chung, T.H. Kim, S.D. Song, Adsorption of hydrogen in nickel and rhodium exchanged zeolite X, Int. J. Hydrog. Energy 33 (2008) 735–745, https://doi.org/10.1016/j.ijhydene.2007.10.047.

[16] E. Rojas-García, A.A. Castañeda-Ramírez, D. Angeles-Beltrán, R. López-Medina, A. M. Maubert-Franco, Enhancing in the hydrogen storage by SWCNT/HKUST-1 composites: effect of SWCNT amount, Catal. Today 394 (2022) 357–364, https://doi.org/10.1016/j.cattod.2021.08.004.

[17] S. Liu, L. Sun, F. Xu, J. Zhang, C. Jiao, F. Li, Z. Li, S. Wang, W. Ziqiang, X. Jiang, H. Zhou, L. Yang, C. Schick, Nanosized cu-MOFs induced by graphene oxide and enhanced gas storage capacity, Energy Environ. Sci. 6 (2013) 818–823, https://doi.org/10.1039/C3EE23421E.

[18] P. Dubey, V. Shrivastav, S. Sundriyal, P.H. Maheshwari, Sustainable nanoporous metal–organic framework/conducting polymer composites for supercapacitor applications, ACS Appl. Nano Mater. 7 (2024) 18554–18565, https://doi.org/10.1021/acsanm.4c01697.

[19] A. Vishnyakov, P.I. Ravikovitch, A.V. Neimark, M. Bülow, Q.M. Wang, Nanopore structure and sorption properties of Cu–BTC metal–organic framework, Nano Lett. 3 (2003) 713–718, https://doi.org/10.1021/nl0341281.

[20] C. Li, H. Wei, R. Hua, X. He, J. Lu, Q. Chen, B. Liu, X. Li, J. Wu, 3D cu-BTC anchored on 2D MXene nanosheets using surface control approach for urea adsorption to achieve the regeneration of dialysate, Sep. Purif. Technol. 373 (2025) 133594, https://doi.org/10.1016/j.seppur.2025.133594.

[21] N.C. Jeong, B. Samanta, C.Y. Lee, O.K. Farha, J.T. Hupp, Coordination-chemistry control of proton conductivity in the iconic metal–organic framework material HKUST-1, J. Am. Chem. Soc. 134 (2012) 51–54, https://doi.org/10.1021/ja2110152.

[22] C. Prestipino, L. Regli, J.G. Vitillo, F. Bonino, A. Damin, C. Lamberti, A. Zecchina, P.L. Solari, K.O. Kongshaug, S. Bordiga, Local structure of framework cu(II) in HKUST-1 Metallorganic framework: spectroscopic characterization upon activation and interaction with adsorbates, Chem. Mater. 18 (2006) 1337–1346, https://doi.org/10.1021/cm052191g.

[23] X. Mu, Y. Chen, E. Lester, T. Wu, Optimized synthesis of nano-scale high quality HKUST-1 under mild conditions and its application in CO2 capture, Microporous Mesoporous Mater. 270 (2018) 249–257, https://doi.org/10.1016/j.micromeso.2018.05.027.

[24] M. Singh, A. Gupta, P. Saharan, C. Kumar, S. Sundriyal, R. Padhye, T. Daeneke, N. R. Choudhary, S.R. Dhakate, Rational designed cu-MOF@1D carbon nanofibers as free-standing and flexible electrode for robust electrochemical energy storage, J. Energy Storage 67 (2023) 107617, https://doi.org/10.1016/j.est.2023.107617.

[25] M. Ding, H.-L. Jiang, Improving water stability of metal–organic frameworks by a general surface hydrophobic polymerization, CCS Chem. C 3 (2020) 2740–2748, https://doi.org/10.31635/ccschem.020.202000515.

[26] N.C. Burtch, H. Jasiua, K.S. Walton, Water stability and adsorption in metal–organic frameworks, Chem. Rev. 114 (2014) 10575–10612, https://doi.org/10.1021/cr5002589.

[27] P.K. Prabhakaran, J. Deschamps, Doping activated carbon incorporated composite MIL-101 using lithium: impact on hydrogen uptake, J. Mater. Chem. A 3 (2015) 7014–7021, https://doi.org/10.1039/C4TA07197B.

[28] K. Kamal, D.I. Grekov, A.M. Shariff, M.A. Bustam, P. Pré, Improving textural properties of magnesium-based metal-organic framework for gas adsorption by carbon doping, Microporous Mesoporous Mater. 323 (2021) 111246, https://doi.org/10.1016/j.micromeso.2021.111246.

[29] Y. Liu, P. Ghimire, M. Jaroniec, Copper benzene-1,3,5-tricarboxylate (cu-BTC) metal-organic framework (MOF) and porous carbon composites as efficient carbon dioxide adsorbents, J. Colloid Interface Sci. 535 (2019) 122–132, https://doi.org/10.1016/j.jcis.2018.09.086.
[30] Z. Yu, J. Deschamps, L. Hamon, P. Karikkethu Prabhakaran, P. Pré, Hydrogen adsorption and kinetics in MIL-101(Cr) and hybrid activated carbon-MIL-101(Cr) materials, Int. J. Hydrogen. Energy 42 (2017) 8021–8031, https://doi.org/10.1016/j.ijhydene.2017.02.192.

[31] C. Petit, J. Burress, T.J. Bandoz, The synthesis and characterization of copper-based metal-organic framework/graphene oxide composites, Carbon 49 (2011) 563–572, https://doi.org/10.1016/j.carbon.2010.09.059.

[32] J. Farrando-Pérez, M. Rodríguez-Castillo, M. Martínez-Escandell, M. Monge, J. Silvestre-Albero, Improved thermal management in HKUST-1 composites upon graphite flakes incorporation: hydrogen adsorption properties, Int. J. Hydrogen. Energy 48 (2023) 36474–36484, https://doi.org/10.1016/j.ijhydene.2023.05.357.

[33] J. Fernández-Catalá, M.E. Casco, M. Martínez-Escandell, F. Rodríguez-Reinoso, J. Silvestre-Albero, HKUST-1@ACM hybrids for adsorption applications: a systematic study of the synthesis conditions, Microporous Mesoporous Mater. 237 (2017) 74–81, https://doi.org/10.1016/j.micromeso.2016.09.020.

[34] D.K. Panchariya, R.K. Rai, E. Anil Kumar, S.K. Singh, Core–shell zeolitic imidazolate frameworks for enhanced hydrogen storage, ACS Omega 3 (2018) 167–175, https://doi.org/10.1021/acsomega.7b01693.

[35] M. Muschi, S. Devautour-Vinot, D. Aureau, N. Heymans, S. Sene, R. Emmerich, A. Ploumistos, A. Geneste, N. Steunou, G. Patriarche, G. De Weireld, C. Serre, Metal–organic framework/graphene oxide composites for CO₂ capture by microwave swing adsorption, J. Mater. Chem. A 9 (2021) 13135–13142, https://doi.org/10.1039/D9TA12215G.

[36] A. Dutta, Y. Pan, J.-Q. Liu, A. Kumar, Multicomponent isotropicular metal-organic frameworks: principles, current status and challenges, Coord. Rev. Chem. 445 (2021) 214074, https://doi.org/10.1016/j.ccr.2021.214074.

[37] R. Morales-Ospino, V. Nicolas, K. Mozet, G. Sdanghi, G. Maranzana, A. Celzard, V. Fierro, Trade-off between surface area and tap density when selecting carbon adsorbents for hydrogen compression, Chem. Eng. J. 502 (2024) 157742, https://doi.org/10.1016/j.cej.2024.157742.

[38] R. Morales-Ospino, L. Jiménez-López, A. Celzard, V. Fierro, Hydrogen – storage | physical storage, in: Reference module in chemistry, molecular sciences and chemical engineering, Elsevier, 2024, https://doi.org/10.1016/B978-0-323-96022-9-00290-5.

[39] Z. Chen, P. Li, R. Anderson, X. Wang, X. Zhang, L. Robison, L.R. Redfern, S. Moribe, T. Islamoglu, D.A. Gómez-Gualdrón, T. Yildirim, J.F. Stoddart, O.K. Farha, Balancing volumetric and gravimetric uptake in highly porous materials for clean energy, Science 368 (2020) 297–303, https://doi.org/10.1126/science.aaz8881.

[40] P. García-Holley, B. Schweitzer, T. Islamoglu, Y. Liu, L. Lin, S. Rodríguez, M. H. Weston, J.T. Hupp, D.A. Gómez-Gualdrón, T. Yildirim, O.K. Farha, Benchmark study of hydrogen storage in metal-organic frameworks under temperature and pressure swing conditions, ACS Energy Lett. 3 (2018) 748–754, https://doi.org/10.1021/acsenergylett.8b00154.

[41] M. Schlichtenmayer, M. Hirscher, The usable capacity of porous materials for hydrogen storage, Appl. Phys. A Mater. Sci. Process. 122 (2016) 379, https://doi.org/10.1007/s00339-016-9864-6.

[42] M.E. Casco, J. Fernández-Catalá, M. Martínez-Escandell, F. Rodríguez-Reinoso, E. V. Ramos-Fernández, J. Silvestre-Albero, Improved mechanical stability of HKUST-1 in confined nanospace, Chem. Commun. 51 (2015) 14191–14194, https://doi.org/10.1039/C5CC05107J.

[43] A.M. Varghese, K.S.K. Reddy, G.N. Karanikolos, An in-situ-grown Cu-BTC metal–organic framework / graphene oxide hybrid adsorbed for selective hydrogen storage at ambient temperature, Ind. Eng. Chem. Res. 61 (2022) 6200–6213, https://doi.org/10.1021/acs.iecr.1c04710.

[44] F. Xu, Y. Yu, J. Yan, Q. Xia, H. Wang, J. Li, Z. Li, Ultrafast room temperature synthesis of GrO@HKUST-1 composites with high CO₂ adsorption capacity and CO₂N2 adsorption selectivity, Chem. Eng. J. 303 (2016) 231–237, https://doi.org/10.1016/j.cej.2016.05.143.

[45] A. Yang, P. Li, J. Zhong, Facile preparation of low-cost HKUST-1 with lattice vacancies and high-efficiency adsorption for uranium, RSC Adv. 9 (2019) 10320–10325, https://doi.org/10.1039/C9RA01427F.

[46] F.S. Gentile, M. Pannico, M. Causà, G. Mensitieri, G.D. Palma, G. Scherillo, P. Musto, Metal defects in HKUST-1 MOF revealed by vibrational spectroscopy: a combined quantum mechanical and experimental study, J. Mater. Chem. A 8 (2020) 10796–10812, https://doi.org/10.1039/D9TA01760D.

[47] N.A. Gomez, R. Abonia, H. Cadavid, I.H. Vargas, Chemical and spectroscopic characterization of a vegetable oil used as dielectric coolant in distribution transformers, J. Braz. Chem. Soc. 22 (2011) 2992–2930, https://doi.org/10.1590/S0103-50532011001200009.

[48] L. Peng, J. Zhang, J. Li, B. Han, Z. Xue, B. Zhang, J. Shi, G. Yang, Hollow metal–organic framework polyhedra synthesized by a CO₂-ionic liquid interfacial templating route, J. Colloid Interface Sci. 416 (2014) 198–204, https://doi.org/10.1016/j.jcis.2013.10.041.

[49] R.S. Andriamitantsoa, W. Dong, H. Gao, G. Wang, Porous organic–inorganic hybrid xerogels for stearic acid shape-stabilized phase change materials, New J. Chem. 41 (2017) 1790–1797, https://doi.org/10.1039/C6NJ03034C.

[50] R. Lin, L. Ge, H. Diao, V. Rudolph, Z. Zhu, Ionic liquids as the MOFs/polymer interfacial binder for efficient membrane separation, ACS Appl. Mater. Interfaces 8 (2016) 32041–32049, https://doi.org/10.1021/acsami.6b11074.

[51] Y.-K. Seo, G. Hundal, I.T. Jang, Y.K. Hwang, C.-H. Jun, J.-S. Chang, Microwave synthesis of hybrid inorganic–metallic materials including porous Cu3(BTC)2 from cu(II)-trimesite mixture, Microporous Mesoporous Mater. 119 (2009) 331–337, https://doi.org/10.1016/j.micromeso.2008.10.035.

[52] K.-Y. Andrew Lin, Y.-T. Hsieh, Copper-based metal organic framework (MOF), HKUST-1, as an efficient adsorbent to remove p-nitrophenol from water, J. Taiwan Inst. Chem. Eng. 50 (2015) 223–228, https://doi.org/10.1016/j.tjice.2014.12.008.

[53] the Metropolitan Autonomous University, Azcapotzalco, Av. San Pablo 180, Col. Reynosa Tamaulipas, Azcapotzalco, Ciudad de México, 02200, Mexico, S. Loera-Serna, H. Solis, E. Ortiz, A.L. Martínez-Hernández, L. Noreña, Elimination of methylene blue and reactive black 5 from aqueous solution using HKUST-1, IJESD 17 (2021) 241–246, https://doi.org/10.18178/ijesd.2017.8.4955.

[54] M.R. Azhar, H.R. Abid, H. Sun, V. Periasamy, M.O. Tadé, S. Wang, Excellent performance of copper based metal organic framework in adsorptive removal of toxic sulfonamide antibiotics from wastewater, J. Colloid Interface Sci. 478 (2016) 344–352, https://doi.org/10.1016/j.jcis.2016.06.032.

[55] Y. Chen, X. Mu, E. Lester, T. Wu, High efficiency synthesis of HKUST-1 under mild conditions with high BET surface area and CO2 uptake capacity, Prog. Nat. Sci. Mater. Int. 28 (2018) 584–589, https://doi.org/10.1016/j.pnsc.2018.08.002.

[56] M. Alfe, A. Policicchio, L. Lisi, V. Gargiulo, Solid sorbents for CO2 and CH4 adsorption: the effect of metal organic framework hybridization with graphene-like layers on the gas sorption capacities at high pressure, Renew. Sust. Energ. Rev. 141 (2021) 110816, https://doi.org/10.1016/j.rser.2021.110816.

[57] C.T.P. da Silva, F.R. Veregue, M.P. Moisés, M.R. Guilherme, A.W. Rinaldi, Synthesis of Al2O3-nanowhisker-based HKUST1 MOF composites, Mater. Chem. Phys. 232 (2019) 446–451, https://doi.org/10.1016/j.matchemphys.2019.05.009.

[58] W.W. Lestari, M. Adreane, C. Purnawan, H. Fansuri, N. Widistiuti, S.B. Rahardjo, Solvothermal and electrochemical synthetic method of HKUST-1 and its methane storage capacity, IOP Conf. Ser.: Mater. Sci. Eng. 107 (2016) 012030, https://doi.org/10.1088/1757-899X/107/1/012030.

[59] K.-S. Lin, A.K. Adhikari, C.-N. Ku, C.-L. Chiang, H. Kuo, Synthesis and characterization of porous HKUST-1 metal organic frameworks for hydrogen storage, Int. J. Hydrogen. Energy 37 (2012) 13865–13871, https://doi.org/10.1016/j.ijhydene.2012.04.105.

[60] H. Kuwagaki, T. Meguro, J. Tatami, K. Komeya, K. Tamura, An improvement of thermal conduction of activated carbon by adding graphite, J. Mater. Sci. 38 (2003) 3279–3284, https://doi.org/10.1023/A:1025138005230.

[61] J. Zhou, M. Fang, K. Yang, K. Lu, H. Fei, P. Mu, R. He, MIL-101(Cr)-NH2/reduced graphene oxide composite carrier enhanced thermal conductivity and stability of shape-stabilized phase change materials for thermal energy management, J. Energy Storage 52 (2022) 104827, https://doi.org/10.1016/j.est.2022.104827.

[62] Y. Ming, J. Purewal, D. Liu, A. Sudik, C. Xu, J. Yang, M. Veenstra, K. Rhodes, R. Soltis, J. Warner, M. Gaab, U. Müller, D.J. Siegel, Thermophysical properties of MOF-5 powders, Microporous Mesoporous Mater. 185 (2014) 235–244, https://doi.org/10.1016/j.micromeso.2013.11.015.

[63] D. Liu, J.J. Purewal, J. Yang, A. Sudik, S. Maurer, U. Mueller, J. Ni, D.J. Siegel, MOF-5 composites exhibiting improved thermal conductivity, Int. J. Hydrogen. Energy 37 (2012) 6109–6117, https://doi.org/10.1016/j.ijhydene.2011.12.129.

[64] M. Thommes, K. Kaneko, A.V. Neimark, J.P. Olivier, F. Rodríguez-Reinoso, J. Rouquerol, K.S.W. Sing, Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC technical report), Pure Appl. Chem. 87 (2015) 1051–1069, https://doi.org/10.1515/pac-2014-1117.

[65] H.S. Cho, J. Yang, X. Gong, Y.-B. Zhang, K. Momma, B.M. Weckhuysen, H. Deng, J. K. Kang, O.M. Yaghi, O. Terasik, Isotherms of individual pores by gas adsorption crystallography, Nat. Chem. 11 (2019) 562–570, https://doi.org/10.1038/s41557-019-02527-2.

[66] A. Tóth, K. László, Water adsorption by carbons. Hydrophobicity and hydrophilicity, in: Novel carbon adsorbents, 2012, pp. 147–171, https://doi.org/10.1016/B978-0-08-097744-7.00005-3.

[67] F. Stoeckli, T. Jakubov, A. Lavanchy, Water adsorption in active carbons described by the Dubinin–Astakhov equation, J. Chem. Soc. Faraday Trans. 90 (1994) 783–786, https://doi.org/10.1039/FT9949000783.

[68] Y. Zeng, L. Prasetyo, V.T. Nguyen, T. Horikawa, D.D. Do, D. Nicholson, Characterization of oxygen functional groups on carbon surfaces with water and methanol adsorption, Carbon 81 (2015) 447–457, https://doi.org/10.1016/j.carbon.2014.09.077.

[69] V.T. Nguyen, T. Horikawa, D.D. Do, D. Nicholson, Water as a potential molecular probe for functional groups on carbon surfaces, Carbon 67 (2014) 72–78, https://doi.org/10.1016/j.carbon.2013.09.057.

[70] J. Canivet, A. Fateeva, Y. Guo, B. Coasne, D. Farrusseng, Water adsorption in MOFs: fundamentals and applications, Chem. Soc. Rev. 43 (2014) 5594–5617, https://doi.org/10.1039/C4CS00078A.

[71] X. Liu, X. Wang, F. Kapteijn, Water and metal–organic frameworks: from interaction toward utilization, Chem. Rev. 120 (2020) 8303–8377, https://doi.org/10.1021/acs.chemrev.9b00746.

[72] L. Sarkisov, A. Centineo, S. Brandani, Molecular simulation and experiments of water adsorption in a high surface area activated carbon: hysteresis, scanning curves and spatial organization of water clusters, Carbon 118 (2017) 127–138, https://doi.org/10.1016/j.carbon.2017.03.044.

[73] J. Castro-Gutiérrez, R.L.S. Canevesi, M. Emo, M.T. Izquierdo, A. Celzard, V. Fierro, CO2 outperforms KOH as an activator for high-rate supercapacitors in aqueous electrolyte, Renew. Sust. Energ. Rev. 167 (2022) 112716, https://doi.org/10.1016/j.rser.2022.112716.

[74] L. Liu, S. Tan, T. Horikawa, D.D. Do, D. Nicholson, J. Liu, Water adsorption on carbon - a review, Adv. Colloid Interf. Sci. 250 (2017) 64–78, https://doi.org/10.1016/j.jcis.2017.10.002.

[75] P. Bénard, R. Chahine, Storage of hydrogen by physisorption on carbon and nanostructured materials, Scr. Mater. 56 (2007) 803–808, https://doi.org/10.1016/j scriptamat.2007.01.008.

[76] P. Ramirez-Vidal, R.L.S. Canevesi, G. Sdanghi, S. Schaefer, G. Maranzana, A. Celzard, V. Fierro, A step forward in understanding the hydrogen adsorption and compression on activated carbons, ACS Appl. Mater. Interfaces 13 (2021) 12562–12574, https://doi.org/10.1021/acsami.0c22192.
[77] G. Sdanghi, G. Sdanghi, G. Maranzana, A. Celzard, V. Fierro, Hydrogen adsorption on nanotextured carbon materials, in: Hydrogen storage technologies, John Wiley & Sons, Ltd, 2018, pp. 263–320, https://doi.org/10.1002/9781119460572.ch9.

[78] G. Sdanghi, R.L.S. Canevesi, A. Celzard, M. Thommes, V. Fierro, Characterization of carbon materials for hydrogen storage and compression, C 6 (2020) 46, https://doi.org/10.3390/c6030046.

[79] P. Ramirez-Vidal, R.L.S. Canevesi, A. Celzard, V. Fierro, Modeling high-pressure hydrogen uptake by nanoporous metal–organic frameworks: implications for hydrogen storage and delivery, ACS Appl. Nano Mater. 5 (2022) 759–773, https://doi.org/10.1021/acsanm.1c03493.

[80] DOE Materials-Based Hydrogen Storage Summit: Defining Pathways for Onboard Automotive Applications, Energy.Gov (n.d.). https://www.energy.gov/eere/fuelce

lls/articles/doi-materials-based-hydrogen-storage-summit-defining-pathways-onboard (accessed November 12, 2024).

[81] P. García-Holley, B. Schweitzer, T. Islamoglu, Y. Liu, L. Lin, S. Rodriguez, M. H. Weston, J.T. Hupp, D.A. Gómez-Gualdrón, T. Yildirim, O.K. Farha, Benchmark study of hydrogen storage in metal–organic frameworks under temperature and pressure swing conditions, ACS Energy Lett. 3 (2018) 748–754, https://doi.org/10.1021/acsenergylett.8b00154.

[82] M.D. Allendorf, Z. Hulvey, T. Gennett, A. Ahmed, T. Autrey, J. Camp, E.S. Cho, H. Furukawa, M. Haranczyk, M. Head-Gordon, S. Jeong, A. Karkamkar, D.-J. Liu, J. R. Long, K.R. Meihaus, I.H. Nayyar, R. Nazarov, D.J. Siegel, V. Stavila, J.J. Urban, S.P. Veccham, B.C. Wood, An assessment of strategies for the development of solid-state adsorbents for vehicular hydrogen storage, Energy Environ. Sci. 11 (2018) 2784–2812, https://doi.org/10.1039/C8EE01085D.