Extended Data Fig. 2: Comparison of anti-corrosion performance of Cu-FA with Cu foils with other corrosion inhibitors.

a, Electrochemical characterizations of Cu-FA foil and Cu foils treated with DT and BTA corrosion inhibitors. Whereas all measurements were carried out in 0.1 M NaOH, the Nyquist impedance and Bode plots were recorded at 0.1 V versus Ag/AgCl. The polarization parameters of Cu foils with different surface treatments in 0.1 M NaOH are: E_corr = −212 mV, J_corr = 5.12 μA cm⁻², corrosion rate 59.7 μm yr⁻¹, anti-corrosion factor 1.31 (Cu-BTA); E_corr = −210 mV, J_corr = 4.33 μA cm⁻², corrosion rate 50.4 μm yr⁻¹, anti-corrosion factor 1.55 (Cu-DT). For comparison, the anti-corrosion factor of Cu-FA in 0.1 M NaOH is 20.1. b, Tafel and Nyquist plots, SEM images and Raman spectra of the samples before and after the electrochemical measurements. The Nyquist plots were measured at 0.1 V versus Ag/AgCl in 1 M NaOH. The Raman bands at 297 cm⁻¹ and 623 cm⁻¹ come from CuO species⁶⁸. Owing to the concentration difference, the Tafel plot of Cu-FA in 1 NaOH displays a minimum that is different from that in 0.1 M NaOH. The polarization parameters of Cu foils before and after the formate treatment in 1.0 M NaOH are: E_corr = −281 mV, J_corr = 59.7 μA cm⁻², corrosion rate 695.8 μm yr⁻¹ (bare Cu); E_corr = −311 mV, J_corr = 5.10 μA cm⁻², corrosion rate 59.4 μm yr⁻¹ (Cu-FA), anti-corrosion factor 11.7. The anti-corrosion factor is defined as the ratio of the corrosion rate bare Cu foil to that of modified Cu in 1 NaOH. c, SEM images of bare Cu and Cu-FA (prepared by Method II) foils after exposure to 30% H₂O₂ for 0, 5 and 15 min. d, Optical images of Cu-FA (prepared by Method II) and untreated Cu foils before and after heating at 160 °C in air for 1 h and corresponding Raman spectra after thermal treatment. e, Localized corrosion of Cu-FA monitored by SRET/STM. The three-dimensional corrosion current maps were recorded on scratched Cu-FA and bare Cu foils after immersion in 0.1 M NaOH for 5, 30 and 90 min, and SEM images before and after the SRET/STM test were taken to identify the oxidized area.