Fig. 4: Working mechanism of moisture-electric generator (MEG).
a Homemade set-up to measure the Raman spectrum of MEG sample. A transparent quartz tube is used to load MEG with only an open side to enable unidirectional moisture invasion. The yellow dotted line is the scanning route of laser. Water gradient is defined as the difference in moisture content between the upper side exposed to air and bottom side of the MEG sample. b The water diffusion with the depth and time revolution by 2D Raman mapping. The time for Raman spectroscopy mapping from left to right is 20, 70, 120, 200 min, respectively. The arrow for H2O represents more moisture is absorbed based on Raman band ratio O-H bond/C-H bond. c The normalized Raman band ratio of O-H/C-H bond changes with the depth at 200 min. The C-H bonds of stretching vibration area are within 2800–3000 cm−1 and O-H bonds of stretching vibration area are within 3050–3650 cm−1. d In situ FTIR (Fourier Transform Infrared Spectroscopy) spectrum tracking once the sample is exposed in the air (65% RH) versus time. 2D-FTIR correlation spectra in the 3700–2900 cm−1 wavenumber region: e synchronous; f asynchronous contour maps. The red area and sky-blue area denote positive and negative correlation peaks, respectively. g Chemical component characterization of detective Ca2+ variation between the top and bottom surface of MEG in different states by EDS. Data represent the mean ± standard deviation (n = 4). h The KPFM (Kelvin probe force microscope) detecting potential change of gel. The scan range is 20 × 20 μm. Source data are provided with this paper.
