Localized corrosion of 304 stainless steel being the significant parts of Starship rocket seriously threatens the long-term service of such aerospace equipment. Scanning electron microscopy, in situ instruments combining electrochemical workstation and Raman spectroscopy, and Density Dunctional Theory (DFT) calculations were employed. The surface morphologies, alloying elements, molecular fingerprint Raman evidence and theoretical mechanism for the localized corrosion of 304 stainless steel during the electrochemical polarization in the mixture solutions containing 0.5 mol/L H₂SO₄ and 2, 2′-bipyridine (bipy) with concentrations of 0.001, 0.010, 0.100 mol/L were discussed. In comparison, the presence of bipy up to 0.100 mol/L in such mixture solutions displayed the neglectable effect on the Fe(Ⅱ)/Fe(Ⅲ) reaction in the polarization process. Raman vibrational frequency around 1492 cm⁻¹ was the evidence of pink color appearance due to the formation of [Fe^Ⅱ(bipy)₃]²⁺. Raman and DFT indicated the yellow color emergence due to the presence of μ-O-[Fe^Ⅲ(bipy)₂(H₂O)]₂⁴⁺ due to the oxidation reaction of [Fe^Ⅱ(bipy)₃]²⁺ with H₂O₂ oxidant, and the dimerization of [Fe^Ⅲ(bipy)₃]³⁺. Furthermore, a quantitative model between [Fe^Ⅱ(bipy)₃]²⁺ concentration and Raman intensity at 1492 cm⁻¹ has been built up. Two linear functions were revealed when [Fe^Ⅱ(bipy)₃]²⁺ concentrations were at 0–0.002 mol/L and 0.002–0.004 mol/L and a concentration error of less than 5% was evidenced in comparison with that investigated by the inductively coupled plasma. The proposed passivation mechanism and quantitative concentration model of 304 stainless steel have certain significance for its corrosion protection and corrosion evaluation.

Electroplating at the micro and nano scales is an electrochemical deposition technique, regarded as one additive manufacturing process, to achieve the preparation and surface modification of nano devices. The present review mainly discussed two key inflcuing factors including microelectrode probe manufacturing (the length of tapered needle tipe and diameter of microelectrode tip) and the distance automation control in the micro and nano dimension between microelectrode and substrate. In addition, the mechanism and application of electrochemical etching for different microelectrode tips and automation control systems are focused. Finally, the challenges and prospect in electroplating at micro and nano scales were discussed.