(a) Absorption spectrum of the RGO-GeNPs dispersed in aqueous solution. (b) FTIR spectra of the RGO-GeNPs and PSS-RGO-GeNPs. (c) XRD spectra of the RGO-GeNPs. (d) EDS analysis of the RGO-GeNPs. Stability test Stability is an important issue for the nanomaterials’ future Regorafenib application. We measured the zeta potential of the nanocomposites to examine the surface properties and stability of the RGO-GeNPs. Zeta potential is a measurement for electrostatic, Nec-1s charge repulsion or attraction strength between the particles [27]. The American Society of Testing Materials (ASTM) has confirmed that the zeta potential has a close relationship with the degree of dispersion
and stability of materials, and the zeta potential can be used as an effective evaluative measure for material stability. Generally, when
the zeta potential value of the material is close to ±40 mV, the stability of the material is considered relatively good. As shown in Figure 4, the zeta potential of RGO-GeNPs was -38.7 mV, which just decreased to -36.4 mV after 30 days, explaining a good stability of the RGO-GeNPs. However, the zeta potential of the RGO-GeNPs decreased to -23.3 mV after 60 days, which meant that RGO-GeNPs began to become unstable. Figure 4 Stability of RGO-GeNPs in aqueous solutions. Electrical properties testing The theoretical researches showed that Ge exhibits a huge theoretical SU5402 capacity (1,600 mAhg-1) and faster diffusivity of Li compared with Si [22]. Ge can be expected to exhibit excellent electrical properties as anode material for LBIs. Graphene also was a good candidate for Li ion batteries because of its high electrical conductivity, specific wrinkled structures, and flexibility, which made graphene suppress local stress and large volume expansions/shrinkages during a lithiation/delithiation process and alleviate the aggregation Astemizole or pulverization problems [22]. Therefore, by combining with Ge nanomaterials, the RGO-GeNPs could have enhanced electrical properties, which would be promising materials for various kinds of market-demanded LIBs. The electrochemical performance of the PSS-RGO-GeNPs was tested
by galvanostatic discharge/charge technique. Figure 5a showed the discharge/charge voltage profiles cycled under a current density of 50 mAg-1 over the voltage range from 0 to 1.5 V vs. Li+/Li. The initial discharge and charge specific capacities were 764 and 517 mAhg-1, respectively, based on the total mass of the PSS-RGO-GeNPs. The large initial discharge capacity of the nanocomposite could be attributed to the formation of a solid electrolyte interface (SEI) layer. Figure 5 The electrochemical performance of Ge nanomaterials. (a) The initial discharge–charge curve of the PSS-RGO-GeNPs cycled between 0 and 1.5 V under a current density of 50 mAg-1. (b) Cycling behaviors of the PSS-RGO-GeNPs, RGO-GeNPs, and RGO-Ge under a current density of 50 mAg-1.