Effect of Sn insertion on hydrogen storage performance of Pd-modified silicon-based nanosheets

Metal modified silicon based nanosheets (SNS) are a promising type of composite material for hydrogen storage and transportation applications. The hydrogen storage capacity and hydrogen diffusion ability determined by the metal loading amount and uniform dispersion on the surface of silicon-based nanosheets are very important. Here, a series of Pd-Sn/SNS composite materials with different structures and properties were synthesized, and X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), pressure–composition–temperature (PCT), and electrochemical workstations were used to investigate the structure, morphology, electronic structure, hydrogen adsorption and desorption capacity, hydrogen diffusion ability, and cycling stability. The research results indicate that the insertion of Sn broaden the internal space of the SNS layers and increase the active sites for metal Pd deposition, raising the amount of metal deposition while ensuring the uniform distribution of metal Pd particles. This result leads to the promotion of electron transfers from the deposited metal to the substrate. The local electric field effect is enhanced, and the Kubas effect is boosted, which all improve the material’s hydrogen storage capacity. The maximum adsorption capacity is 4.91 wt% achieved by 15 wt% deposition sample at 450 K, and the diffusion coefficients of hydrogen D_H is 6.25 × 10^–6 cm²/s. At the same time, the cyclic stability of the material is also improved. The result of density functional theory (DFT) calculation showed that the insertion of Sn can promote the interaction between Pd deposited on the surface and H. Among them, the electron transfer number of 15 wt% Pd-Sn/SNS is the largest of 3.79 e, and the binding energy of metal atom Pd and the substrate is the largest. The H adsorption energy of 15 wt% Pd-Sn/SNS is the biggest of 0.52 eV.