The reported material composition and mass recovery appear to require clarification. Each Fe2 batch received approximately 2 mg of added Fe from two 1 mL additions of a 1000 ppm Fe standard, yet Table 2 reports 7.46 wt% Fe for RP + cg + Fe2-CVD, while another Fe2 sample reportedly produced 6.7 wt% oxide residue by TGA and contained local EDX regions with up to 26% Fe. Could the authors provide the initial and final sample masses, a quantitative Fe mass balance, bulk elemental analysis, the complete TGA method and raw thermograms, and the original EDX spectra and sampling locations?
Several related inconsistencies also merit clarification. Table 2 reports some CNT growth in RP + c + Fe2-CVD, whereas the text states that nanotubes were not observed in this sample. In addition, the Raman discussion assigns the 1.06 ratio to RP + cg + Fe-CVD, while Table 3 assigns it to RP + cg + Fe2-CVD. Original analytical data and confirmed sample identifiers would help determine whether these are reporting errors or whether they affect the proposed relationship among iron loading, CNT formation, and HER activity.