Hydrogen storage capacity -HSC- of multilayer graphitic carbon nitride, d-g-C3N4 -d is interlayer spacing-, and its palladium nanocomposite, d-Pd@g-C3N4, were investigated using multiscale computational techniques including quantum mechanics calculations and grand canonical Monte Carlo -GCMC- simulation. According to the results, the volumetric HSC of 8-g-C3N4 and 8-Pd@g-C3N4 can reach to DOE target of 30 gH2/L at 177 K, 5.7 MPa, and 177 K, 4.0 MPa, respectively. The gravimetric HSC of 10-g-C3N4 and 12-Pd@gC3N4 meet the DOE target of 4.5 wt% at 150 K, 3.5 MPa, and 125 K, 4.0 MPa, respectively. The incorporation of Pd atoms enhances the delivery volumetric HSC of 6-, 8-, 10-, and 12-gC3N4 by 49, 55, 129, and 146%, respectively at 177 K and 0.5 MPa. On the other hand, the incorporation of Pd atoms has a negative effect on the delivery gravimetric HSC of 6- and 8-g-C3N4 and positive effect for 10- and 12-g-C3N4. The estimated isostric heat, Qst, of adsorption is 5.5e8.5 kJ/mol. The maximum value of Qst for both nanoadsorbents belong to those with d ¼ 8 A. The structure of adsorbates and possibility of multilayer adsorption occurrence were also investigated using pair correlation functions and density profiles.

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