Hydrogen absorption isotherm on Ca/Al(OH)5 nanoparticles

The Figure presents the hydrogen storage performance of Ca/Al(OH)₅ nanoparticles, expressed as gravimetric hydrogen uptake (wt%) as a function of applied hydrogen pressure (bar) at four different temperatures: 77 K, 173 K, 223 K, and 273 K. This dataset was generated to evaluate the adsorption behavior, temperature dependence, and maximum storage capacity of the material under conditions relevant to practical hydrogen storage applications.Data Generation and Experimental BackgroundHydrogen adsorption measurements were conducted using a volumetric (Sieverts-type) hydrogen storage analyzer. Prior to measurements, the Ca/Al(OH)₅ nanoparticle sample was degassed under vacuum to remove adsorbed moisture and gases, ensuring that the recorded uptake values correspond exclusively to hydrogen adsorption. Hydrogen pressure was incrementally increased from low pressure (approximately 1 bar) to a maximum pressure of ~90–100 bar at each temperature, and equilibrium was allowed to be reached at every pressure step.The experiments were performed at four controlled temperatures—77, 173, 223, and 273 K—selected to capture both cryogenic and near-ambient adsorption behavior. At each temperature, the equilibrium hydrogen uptake was calculated based on the amount of hydrogen absorbed by the material relative to the sample mass, and reported as weight percent (wt%).Description of Data Content and StructureThe dataset underlying Figure 3 consists of four pressure–uptake isotherms, each corresponding to a specific temperature. The data can be organized into the following columns:Temperature (K): Fixed experimental temperature for each isotherm (77, 173, 223, or 273 K).Pressure (bar): Applied equilibrium hydrogen pressure at each measurement point.Hydrogen uptake (wt%): Gravimetric hydrogen storage capacity, calculated as the mass percentage of hydrogen stored relative to the dry mass of Ca/Al(OH)₅ nanoparticles.Each curve in Figure 3 represents a complete adsorption isotherm at a given temperature. The pressure range and number of data points were chosen to ensure accurate characterization of the low-pressure adsorption region, the mid-pressure transition region, and the high-pressure saturation regime.Data Trends and InterpretationAcross all temperatures, hydrogen uptake increases monotonically with pressure, exhibiting a steep rise at low pressures (0–20 bar) followed by a gradual approach to saturation above approximately 60–70 bar. This behavior is characteristic of adsorption-controlled hydrogen storage systems and indicates progressive filling of available adsorption sites.Temperature exerts a pronounced influence on hydrogen storage performance. Lower temperatures result in significantly higher hydrogen uptake due to enhanced physisorption arising from reduced molecular kinetic energy. At 77 K, the Ca/Al(OH)₅ nanoparticles exhibit the highest hydrogen storage capacity, reaching approximately 5.6 wt% at 66–68 bar, whereas at 273 K, the maximum uptake decreases to about 4.0 wt% at ~93 bar. The systematic decrease in storage capacity with increasing temperature confirms the exothermic nature of hydrogen adsorption.Data Value and Mechanistic SignificanceThe high gravimetric hydrogen storage capacity observed at 77 K demonstrates the strong adsorption affinity of Ca/Al(OH)₅ nanoparticles for hydrogen under cryogenic conditions. This performance is competitive with, and in some cases superior to, many conventional and advanced hydrogen storage materials reported under comparable experimental conditions.The observed storage behavior is attributed to a synergistic combination of nanostructural features and chemical composition. The nanoscale particle size and porous morphology (including lamellar and channel-like structures) provide a large accessible surface area and a high density of adsorption sites. Additionally, the hydroxide framework of calcium and aluminum likely facilitates both physisorption through van der Waals interactions and weak chemisorption through surface hydroxyl groups, enhancing overall hydrogen uptake.Although the operating conditions strongly favor physisorption—particularly at 77 K—the substantial hydrogen uptake suggests that the material possesses a favorable pore architecture and energetically suitable adsorption sites, enabling efficient hydrogen storage over a wide pressure range.