Fig. 1: Device fabrication and characterization.

a Device-fabrication procedure. Scanning electron micrographs of (b) the carbon steel electrode after detaching PANI:PSS, c a porous area, and (d) a flat area. e X-ray diffraction data for a pristine carbon steel, the electrode shown in “b”, and reference data for β-FeOOH30. f Water uptake of PANI:PSS after the sample was left under the relative humidity for 8 h. Error bar: one standard deviation.