In this study, a simultaneously decorated graphene sheet with titanium (Ti) and palladium (Pd) atoms is proposed to improve hydrogen adsorption uptake. Density functional theory (DFT) with a DFT-D3 correction dispersion study was applied. Initially, the hydrogen adsorption energy, energy band gap, partial density of state (PDOS), thermal stability, and H-2 desorption temperature for Ti-decorated, Pd-decorated, and Ti-Pd-decorated graphene sheets were investigated. Clustering formation for the Ti-decorated graphene sheet was examined in detail. Grand canonical Monte Carlo (GCMC) simulation was applied to examine the hydrogen adsorption isotherm. Simulation results showed that the hydrogen adsorption energy and desorption temperature of the Ti-decorated graphene sheet are -0.61 eV and 765.4 K, respectively, which are significantly higher than those of the Pd-decorated graphene sheet (-0.108 eV and 135.5 K). However, Ti atoms form clusters when their distances from each other are less than 6 & Aring;. Inserting adaptable metal atoms such as Pd into the Ti-decorated graphene adjusts the hydrogen adsorption energy to -0.544 eV and the desorption temperature to 627.4 K. In addition, the values of Gibbs free energy changes (Delta G) of metal adsorption showed that the Ti-Pd graphene sheet has good stability at different temperatures. Calculated hydrogen adsorption isotherm using the GCMC method approved the suitable performance of the Ti-Pd-decorated graphene sheet for hydrogen adsorption. At the pressure of 60 bar and temperature of 298 K, the hydrogen adsorption content increases from 1.49 wt % on the Ti-decorated graphene sheet with cluster to 2.06 wt % on the Ti-Pd-decorated graphene sheet. Finally, Ti-Pd-decorated graphene sheet was proposed as a novel adsorbent in the hydrogen storage industry.
