Abstract
<title>Abstract</title> <p> The design of advanced adsorbents for hydrogen storage and isotope separation requires a reliable methodology for pore-structure characterization. Due to its smallest size and relatively weak adsorption strength, hydrogen preferentially adsorbs in the smallest ultramicropores, which are insufficiently resolved using standard nitrogen adsorption measurements. Here, we demonstrate, using a representative example of ACC-ILL microporous carbon, the advantages of employing hydrogen as a molecular probe for adsorption characterization. The kernels of reference H <sub>2</sub> and D <sub>2</sub> isotherms at 77.4 K in cylindrical carbon pores ranging from 0.35 to 20 nm in diameter are generated with a classical density functional theory (DFT), which accounts for the fluid-solid interactions via statistical associating fluid theory (SAFT) with quantum-corrected Mie potentials (SAFT-VRQ Mie). We found that the isotope-specific differences in adsorption behavior are consistently captured by this quantum-corrected DFT model. The constructed kernels are used to derive the pore-size distributions from the experimental H <sub>2</sub> and D <sub>2</sub> isotherms. Furthermore, we show that the experimental D <sub>2</sub> isotherm can be predicted by convolving the pore-size distribution determined from the experimental H <sub>2</sub> isotherm with the D <sub>2</sub> adsorption kernel. Reliable prediction of D <sub>2</sub> adsorption behavior from relatively inexpensive H <sub>2</sub> experiments greatly expands the practicality of nanoporous material screening for isotope separation applications, where distinguishing candidate materials often depends on subtle differences in confinement behavior that are costly to measure directly. The proposed H <sub>2</sub> adsorption methodology is recommended for testing nanoporous carbons for hydrogen-based applications. </p>