**3. Results and Discussion**

## *3.1. Characterization*

The XRD patterns of synthesized La(OH)3@MWCNT are shown in Figure 1A. It is clear that the sample is highly crystalline and the diffraction peaks at 15.6◦, 26.3◦, 27.9◦, 31.5◦, 36.0◦, 39.5◦, 47.1◦, 48.7◦, 49.9◦, and 55.3◦ match well with the crystal planes of (100), (110), (101), (200), (111), (201), (002), (211), (102), (112). All of the reflections can be assigned to lanthanum hydroxide having a hexagonal symmetry and P63/m space group (JCPDS #36-148128) [52]. The average crystallite size of La(OH)3 nanoparticles is (26 ± 4) nm, calculated by Scherrer's equation. The peaks from other phases occurring at 19.6◦ and 42.3◦ can be assigned to (002) and (110) reflections of graphitic MWCNT [53]. This can be proof of successful composite formation.

**Figure 1.** (**A**) XRD pattern of prepared La(OH)3@MWCNT composite, (**B**,**C**) SEM micrographs of La(OH)3@MWCNT at different magnifications.

The morphology and the shape of prepared La(OH)3, as well as the La(OH)3@MWCNT composite, are analyzed by FE-SEM. Different magnifications of the composite are displayed in Figure 1B,C. The La(OH)3 nanoparticles are scattered over long multi-walled carbon nanotubes. This makes the surface of the nanotubes significantly larger, which can potentially affect the electrochemical properties of the composite. The rice-like lanthanum hydroxide nanoparticles are partially agglomerated, with an average diameter between 100 and 200 nm, and a width ranging from 30 to 60 nm (inset of Figure 1C).
