r-GO/oil can form stable coating on metal of complex geometry and can be applied from underwater.
(a) An Al foil boat placed on 2 M HCl solution is damaged after just 8 minutes, indicated by the leakage of methylene blue solution, and completely dissolves away after 20 minutes. (b) Another Al boat coated with an r-GO/oil film stays intact after a day, when the dye solution has dried out, showing that the coating is stable on metal surface with complex geometry and sharp corners. (c) r-GO/oil film can be brushed onto an already immersed Al wire under water to protect it from reacting with concentrated HCl. As a control, a bare Al wire is also immersed, which immediately starts to bubble (dashed red circle) due to reaction with HCl. Also see Movie S1