Fig. 3: Potential change with water uptake and working principle of voltage generation.

a Experimental procedure to identify the influence of water uptake on the corrosion potential of carbon steel. b Voltage (left axis) and change of water mass (right axis) when the top electrode was left under different RH following the procedure in “a”. c ATR-FTIR spectra of PANI:PSS from the colder side as the temperature difference (∆T) was varied. The inset illustrates the in situ ATR–FTIR experiment configuration. d Evans diagram shows the cathodic-reduction reaction (black line), the anodic oxidation reaction (greenish line) under uniform temperature. The greenish line shifts toward the red (or blue) line with less (or more) water on the electrodes. e–h Illustration showing thermoelectric voltage generation and the corresponding potential changes in the hotter and colder sides. e Uniformly distributed water in PANI:PSS under ∆T = 0. f As ∆T > 0, water molecules migrate from the hotter to the colder side. g Voltage generation at steady state under ∆T > 0. h Water molecules return to their initial distributed states under ∆T→0.