**3. Experimental Section**

MoO3í*x* nanowhiskers and MoS2 nanotubes were prepared using solar ablation system [15]. The Pb and MoS2 mixture was sealed in a quartz ampoule and irradiated using solar ablation system for 30 s in the case of MoO3í*x* nanowhiskers, and for 10 min in the case of MoS2 nanotubes. Both nanostructures contain a few atomic percent of Pb. After spending a year in ambient conditions these samples were annealed at 810 °C in the presence of H2S and forming gas (5% H2 and 95% N2). The annealing time varied from 30 min to 2 h. The sample labeling can be seen in Table 2.

At each stage the samples were examined with a transmission electron microscope (TEM) operating at 120 kV, equipped with an energy-dispersive X-ray spectroscopy (EDS) detector for chemical analysis. The SEM image was generated using a scanning electron microscope (SEM), and high-resolution imaging was achieved with a field-emission gun TEM operating at 300 kV.

The calculations were performed using the SIESTA 2.0 (Madrid, Spain) implementation [23,24] within the framework of density-functional theory (DFT) [25]. The exchange-correlation potential within the local-density approximation (LDA) with the Perdew-Zunger parametrization was used [26]. The core electrons were treated within the frozen core approximation, applying norm-conserving Troullier-Martins pseudopotentials [27]. The valence electrons were taken as 3*s*<sup>2</sup> 3*p*<sup>4</sup> for S, 4*d*<sup>5</sup> 5*s*<sup>1</sup> 5*p*<sup>0</sup> for Mo, 6*s*<sup>2</sup> 6*p*<sup>2</sup> for Pb, while Pb5*d*10 electrons were included as semi-core state. The pseudopotential core radii were chosen, as suggested by Martins, and are equal to 1.70 aB for all S states, 2.45 aB for Mo4*d* and Mo5*s*, 2.65 aB for Mo5*p* states, 3.20 aB for Pb6*s* and Pb6*p*, 3.00 aB for Pb5*d* states. In all calculations double-*ȗ* basis set is used for all atoms. For *k*-point sampling, a cutoff of 10 Å was used [28]. The *k*-point mesh was generated by the method of Monkhorst and Pack [29]. The real-space grid used for the numeric integrations was set to correspond to the energy cutoff of 300 Ry. For the study of substitutional doping and intercalation of MoS2 by Pb atoms the supercell of 4 × 4 × 1 of 2H-MoS2 unit cells was considered. The energies of chemical reactions were estimated from the calculations of total energies for 2H-MoS2, bcc-Mo, fcc-Pb, fcc-PbS and molecular S8. All calculations were performed using variable-cell and atomic position relaxation, with convergence criteria set to correspond to a maximum residual stress of 0.1 GPa for each component of the stress tensor, and maximum residual force component of 0.01 eV/Å.
