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Activated carbons exhibit a high grade of porosity, which together with structural stability, regenerability and cyclability makes them capable of achieving excellent hydrogen adsorption capacity. A further advantage comes from the ease of production and the use of recyclable and biocompatible materials. A simple way to produce activated carbons from amorphous cellulose involves procedures in which a pyrolysis process is combined with physical activation in CO 2. We used this approach by optimizing the production process tuning the activation times. The aim is to evaluate the influence of this process parameter on the formation of the specific surface area, the pore volume and fraction of micropores with a typical size <2 nm. The influence of these structural parameters on the hydrogen adsorption properties was then evaluated. The textural and adsorption characteristics were investigated using a commercial volumetric apparatus (ASAP 2460, Micromeritics) at −196 °C and pressures between 0 and 1 bar, while the morphological properties were investigated using scanning electron microscopy. The results show that the nanostructured samples are characterized by a very high degree of ultra-microporosity (<0.7 nm) with an average pore size between 0.5 and 0.6 nm and a high specific surface area, reaching maximum values around 1500 m2/g and micropore volume up to 0.58 cc/g. These morphological characteristics strongly influence the hydrogen adsorption properties, where the molecules adsorbed reach values very close to the coverage of ideal monolayer. The synthesized activated carbon samples show a higher hydrogen adsorption capacity than similar commercial materials tested under the same thermodynamic conditions. [Display omitted] • Easily tuning of ultra-microporosity. • Precursor influence on storage performance. • Hierarchical porous carbons and possibility hydrogen storage at low pressure. • Fully reversible hydrogen physisorption. • Amorphous cellulose as sustainable solution. [ABSTRACT FROM AUTHOR]

The transition away from fossil fuel and ultimately to a carbon-neutral energy sector requires new storage materials for hydrogen and methane as well as new solutions for carbon capture and storage. Among the investigated adsorbents, activated carbons are considered especially promising because they have a high specific surface area, are lightweight, thermally and chemically stable, and easy to produce. Moreover, their porosity can be tuned and they can be produced from inexpensive and environmentally friendly raw materials. This study reports on the development and characterization of activated carbons synthesized starting from amorphous cellulose with and without the inclusion of copper nanoparticles. The aim was to investigate how the presence of different concentrations of metal nanoparticles affects porosity and gas storage properties. Therefore, the research work focused on synthesis and characterization of physical and chemical properties of pristine and metal-doped activated carbons materials and on further investigation to analyze their hydrogen, methane and carbon dioxide adsorption capacity. For an optimized Cu content the microporosity is improved, resulting in a specific surface area increase of 25%, which leads to a H 2 uptake (at 77 K) higher than the theoretical value predicted by the Chahine Rule. For CH 4 , the storage capacity is improved by the addition of Cu but less importantly because the size of the molecule hampers easy access of the smaller pores. For CO 2 a 26% increase in adsorption capacity compared to pure activated carbon was achieved, which translated with an absolute value of over 48 wt% at 298 K and 15 bar of pressure. [Display omitted] • Cu nanoparticles are a key factor in the development of specific surface area and porosity during the synthesis process. • Textural properties worsen using over 1% of Cu nanoparticles. • Microporosity improves H 2 adsorption (at 77 K) more than the theoretical value predicted by the Chahine Rule. • The best adsorption capacities obtained are 4 wt% for H 2 , 10.6 wt% for CH 4 and 48.2 wt% for CO 2. • High reversibility and stability of the developed material toward all gases species analyzed. [ABSTRACT FROM AUTHOR]

The hydrogen adsorption properties of commercial activated carbon (aC) samples, in particular Nuchar SA-1500, Filtercarb GCC 8x30 and Filtercarb PHA, are evaluated at different temperatures (77 K, 196 K and ambient temperature) and pressure up to 80 bar. A comprehensive characterization is carried out by means of a volumetric Sieverts-type apparatus for hydrogen adsorption measurements and helium picnometry for the skeletal density evaluation, by nitrogen adsorption measurement for the evaluation of the surface area (BET) and pore size distribution (NLDFT), by Scanning Electron Microscopy (SEM) for morphology. All the adsorption data are evaluated by Langmuir/Tóth isotherm model with a very high accuracy and the enthalpy of adsorption is calculated through the Clausius–Clapeyron equation. Comparison between the different samples is shown. The probed aC samples show interesting hydrogen storage capacity and reversible behavior up to many cycles with and without any thermal treatment in between. Our data point out the crucial role of the microporosity and ultra-microporosity in the adsorption process at low H 2 pressures. The surfaces exhibit an average adsorption enthalpy around 6.5 kJ/mol while for the ultra-microporous sites a 14 kJ/mol value is found. The observed trapping behavior at 77 K is attributed to the ultra-microporous morphology of the porous structure in GCC and PHA samples. A further result is the evaluation of the hydrogen molar density in the micropores with size below 10 Å, which is 30 mmol/cm 3 , a value very close to the liquid hydrogen one. These results could represent an interesting starting point for a real and efficient alternative method to the hydrogen storage using cheap and easy scalable materials. [ABSTRACT FROM AUTHOR]

Abstract: The methane adsorption properties of High Surface Activated Carbon (HSAC) samples were evaluated at room temperature (298K) and pressure up to 3.5MPa using a new optimized volumetric apparatus f-PcT (fast Pressure–concentration–Temperature) for accurate and reliable gas adsorption measurements. A comprehensive characterization of different activated carbon samples was carried out by means of helium picnometry for the skeletal density evaluation, by the Brunauer–Emmett–Teller (BET) method for the measurement of the surface area, by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) for topography and long-range order estimation, respectively. All the adsorption data were evaluated by Langmuir/Tóth isotherm model with a very high accuracy. Comparison with data available in the literature shows a good agreement in terms of maximum methane uptake on similar materials and an enhanced performance for the reversible adsorption at very low pressure. In fact, the probed HSAC samples show both higher methane storage values for pressure up to 1.5MPa and totally reversible methane uptake up to many cycles without any treatment in between. Furthermore, their adsorption properties are stable also after air exposure. These results represent the starting point for a real and efficient alternative method to the natural gas storage for static and/or automotive applications. [Copyright &y& Elsevier]

Pinecones, a common biomass waste, has an interesting composition in terms of cellulose and lignine content that makes them excellent precursors in various activated carbon production processes. The synthesized, nanostructured, activated carbon materials show textural properties, a high specific surface area, and a large volume of micropores, which are all features that make them suitable for various applications ranging from the purification of water to energy storage. Amongst them, a very interesting application is hydrogen storage. For this purpose, activated carbon from pinecones were prepared using chemical activation with different KOH/precursor ratios, and their hydrogen adsorption capacity was evaluated at liquid nitrogen temperatures (77 K) at pressures of up to 80 bar using a Sievert's type volumetric apparatus. Regarding the comprehensive characterization of the samples' textural properties, the measurement of the surface area was carried out using the Brunauer–Emmett–Teller method, the chemical composition was investigated using wavelength-dispersive spectrometry, and the topography and long-range order was estimated using scanning electron microscopy and X-ray diffraction, respectively. The hydrogen adsorption properties of the activated carbon samples were measured and then fitted using the Langmuir/ Töth isotherm model to estimate the adsorption capacity at higher pressures. The results showed that chemical activation induced the formation of an optimal pore size distribution for hydrogen adsorption centered at about 0.5 nm and the proportion of micropore volume was higher than 50%, which resulted in an adsorption capacity of 5.5 wt% at 77 K and 80 bar; this was an increase of as much as 150% relative to the one predicted by the Chahine rule. [ABSTRACT FROM AUTHOR]

A series of activated carbons have been produced from walnut shells by pyrolysis and physical activation in an oxidizing atmosphere. The effects of the activation time on the porosity formation and physicochemical characteristics, then hydrogen storage properties, were investigated. The synthesized samples reveal highly microporous structures with large specific surface area values that strongly influence the hydrogen adsorption capacity. The highest values of specific surface area (1163 m2/g), total pore volume (0.491 cm3/g), and micropore volume (0.450 cm3/g) were obtained with an activation time of 90 min, allowing hydrogen uptake at 77 K of 1.7 and 2.6 wt% at a pressure of 1 and 80 bar respectively. Adsorption-desorption cycles were performed to test the reversibility and reproducibility of the process. The results confirm the key role of ultra-micropores (<0.7 nm) and suggest walnut shell-derived activated carbons as promising and cost-effective materials for hydrogen storage. [Display omitted] • Walnut shells to produce cheap and ecological physically activated carbons. • Activated carbons with a high degree of microporosity. • Correlation between activation time and porosity formation. • Ultra-microporosity improves hydrogen adsorption capacity beyond Chahine's rule. [ABSTRACT FROM AUTHOR]

• Activated carbon fibers from commercial Kevlar® through an innovative pyrolysis method. • Correlation between porosity and storage capacity. • Adsorbent material with a high fraction of micropores. • CO 2 and CH 4 adsorption with maximum uptake value of 46 wt% and ≅10 wt% respectively. Carbon-based nanostructures are considered promising materials for gas storage thanks to robust structure, tunable porosity, lightweight, high thermal/chemical stability and easy production. This study reports the development of activated carbon fibers prepared from commercial Kevlar® through an innovative pyrolysis method, consisting of carbonization in inert ambient and subsequent physical activation in oxidizing atmosphere, using a unique apparatus. Varying three key parameters, time (range 60−240 min), temperature (range 1023−1123 K) and gas-flow (0.3/0.9/1.2 Nl/min of CO 2), the correlation between the activation procedure and the resulting samples structure was evaluated. The best results in terms of microporosity and gas adsorption properties have been obtained by reducing the activation times of the material. Furthermore, the purpose has been to optimize the characteristics in terms of Specific Surface Area, Total Pore Volume and optimal Pore Size Distribution. The method made it possible to develop an adsorbent material with a high fraction of micropores up to 94 % of the total pore volume, straddling the supermicroporosity (0.7−2 nm) and ultramicroporosity (<0.7 nm) region. Such textural properties have resulted in high gases storage capacities, tested at different temperatures (280, 298, 314 K), with maximum uptake of 46 wt% for CO 2 and almost 10 wt% for CH 4. All produced samples were characterized by helium picnometry to estimate skeletal density, Scanning Electron Microscopy to obtain morphological information, porosimetry to know structural properties. The adsorption behaviour was tested using a Sievert-type apparatus in the pressure range of 0−15 bar for CO 2 and 0−40 bar for CH 4. [ABSTRACT FROM AUTHOR]

The goal is to investigate the feasibility to use a local biomass (Posidonia Oceanica and Wood chips), as a raw precursor, to the production of activated carbons (AC) with a high surface area and remarkable hydrogen (H 2) adsorption properties. Biomasses (particle size of 0.3–0.4 mm) were pyrolyzed at 600 °C with a heating rate of 5 °C/min under an argon atmosphere. The biochar obtained from the carbonization step was chemically activated with KOH. The activation methodology induces a considerable improvement of the properties of the porous carbon in terms of carbon content (from 58 to 69 wt% to 93–96 wt%), surface area (from 41 to 425 m2/g to 2810–2835 m2/g) and H 2 adsorption in cryogenic condition (from 0,1 wt% to over 5 wt%). All porous carbons were characterized in terms of elemental analysis (CHNS–O), textural properties and H 2 adsorption measurements. Image 1 • High Surface Activated Carbon for hydrogen physisorption. • Fully reversible hydrogen storage. • Simple, cheap and effective synthesis process. • Suitable for static and automotive application. [ABSTRACT FROM AUTHOR]

Lemon peels, a common biomass waste, have an interesting composition in terms of cellulose and mineral salts that makes them good precursors for activated carbon production processes. From a circular economy perspective, this work highlights the possibility of turning a waste material into a new resource. The resulting nanostructures show interesting performance in terms of specific surface area and total pore volume, with excellent grade of microporosity, that make them suitable for various applications ranging from supercapacitors, sensors, gases separation and storage, etc. The last, and in particular hydrogen storage, represents the most interesting one. In this study the development of activated carbon through pyrolysis method, consisting of carbonization in inert ambient and subsequent physical activation in oxidizing atmosphere is reported. Influence of synthesis parameters on the porosity formation was investigated with the aim of textural properties optimization. All produced samples were initially characterized both morphologically and crystallographycally. Then, textural and adsorption properties were evaluated through volumetric apparatus. The experimental results show improvement of both textural and adsorption properties as function of synthesis parameters, developing adsorbent materials with high fraction of micropores (≃84 %), specific surface area (≃500 m2/g) and hydrogen uptake of 0.93 wt% at 77 K and 1 bar. [Display omitted] • Lemon peel as biomass waste for cheap and environmental friendly activated carbon production. • Tuning pyrolysis and activation process parameters for activated carbon materials optimization. • Porosity and specific surface area modification by changing activation temperature and time. • Hydrogen adsorption capacity at liquid nitrogen temperature and low pressure and its connection with textural properties. • Overcoming of the Chahine's rule already at low pressures. [ABSTRACT FROM AUTHOR]