TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: In the process (P2), the poly-imide based coating is produced onto the layer of CNT/CNF by: applying a polyamic acid (PAA) layer followed by imidization and/or by adding manganese (Mn), silver (Ag), silicon (Si), titanium (Ti), aluminum (Al) and/or magnesium (Mg) while synthesizing PAA followed by imidization and/or by applying a liquid polyether imide (PEI) solution, preferably by roll coating and/or spraying and/or where the poly-imide is produced from poly-ether imides. In the process (P1), the CNT/CNF are subsequently treated with a suitable compound such as magnesium oxide (MgO) or calcium oxide (CaO) to produce a catalytic support for storing carbon dioxide (CO2) in the form of carboneous compounds, or with a photocatalyst such as titania or organic photo initiators to produce a catalytic converter to convert carbon dioxide into carboxylic acid such as formic acid (HCOOH) and/or alcohols such as ethanol (C2H5OH). In the process (P1) or (P2), a continuous process involves providing a coil of cold-rolled steel, subjecting the coil to continuous annealing, optionally for recrystallization of the cold-rolled coil, reducing the surface of the steel, providing a layer of CNT/CNF onto the steel at 600-750 degrees C and cooling the steel, optionally followed by providing the coated steel with a poly-imide based coating. Preferred Components: The carbon source gas comprises at least one of acetylene, ethylene, methane, carbon-monoxide, carbon dioxide or low molecular weight fatty oil. The carbon source gas consists of hydrogen, carbon monoxide and carbon dioxide, preferably in a ratio of 30:60:10. The steel substrate is high strength steel (HSS), advanced HSS, ultra HSS or complex phases steel, preferably comprising carbon (0.01-1%), manganese (0.15-2%), silicon (0.005-2%), aluminum (0.01-1.5%), nitrogen (10-200 parts per million (ppm)), phosphorus (at most 0.015%), sulfur (at most 0.15%), optionally at least one niobium (0.01-0.1%), titanium (0.002-0.15), vanadium (0.02-0.2%), boron (10-60 ppm), and iron (balance) and inevitable impurities. The steel substrate is provided with a nickel, nickel-chromium or chromium plating layer or a zinc alloy layer prior to growing CNT/CNF onto one or both surfaces of the substrate. EXAMPLE - No suitable example given.