Fig. 4: Schematic representation of the inorganic–organic competitive coating strategy.

A The metallorganic ferrocene was gradually hydrolyzed into iron ions and cyclopentadienes; B Iron ions were further hydrolyzed into hydrated iron oxides (inorganic nucleation), and cyclopentadienes were oxidized and polymerized into amorphous carbonaceous species (organic nucleation); C Schematic diagram for nucleation rate between iron oxides and amorphous carbonaceous species; D Model diagram of competitive coating process by solvothermal reaction temperature of 210, 200, 190, and 180 °C.