The chemical composition of HP-MoOC was determined using energy-dispersive X-ray spectroscopy (EDX) on the cross-section of the MoOxCy sheets, revealing a Mo:O:C atomic ratio of approximately 1:1:1 (Supplementary Figure ). For comparison, control samples (denoted as HP-MoO2) were fabricated under the same PECVD growth conditions but using nickel foam as the substrate. Although these samples share a similar morphology with HP-MoOC, their chemical composition is markedly different, containing only Mo and O (Supplementary Figure ). This difference is attributed to the lack of carbon resources in the growth environment, leading to the formation of molybdenum oxide rather than oxycarbide.