These results reveal clearly that both HP-MoOC and HCP-MoOC possess a monoclinic crystalline structure. Notably, compared to HP-MoOC (Supplementary Figure ), HCP-MoOC exhibits a carbon-encapsuled crystalline structure, where the crystalline MoOxCy is covered by a thin layer of carbon with a thickness of ~ 1.7 nm, as shown in Figure . and G-band (ωG ∼ 1584 cm -1 ) peaks, indicating the formation of a carbon structure . In contrast, these peaks are absent in HP-MoOC, implying that the carbon layer forms only during the methane plasma treatment. X-ray diffraction (XRD) patterns of the PECVD-grown catalysts further confirm the incorporation of carbon into the lattice structure of HP-MoOC (Figure ). The peak of HP-MoO2 at 2𝜃𝜃 = ~36.9° , which corresponds to the monoclinic crystalline MoO2 (PDF Card No. 00-032-0671) , shows a gradual shift toward larger values of 37.1° and 37.3° for HP-MoOC and HCP-MoOC, respectively. This noticeable peak shift can be attributed to the decreased lattice spacing as more carbon atoms are introduced into the structure.