Fig. 3: Characterization and performance of the ion-engine hydrogel.
A Photographs (left) and corresponding SEM images (right) of the PVA/Cu(TFSI)2-GdmCl hydrogel and CNT layer, with scale bars of 5 cm and 5 μm, respectively. B High-resolution O 1 s spectra of Cu(TFSI)2, PVA/Cu(TFSI)2, and PVA/Cu(TFSI)2-GdmCl, showing a redshift in binding energy upon the incorporation of Cu2+. C 1H-NMR spectra showing the chemical shift for Gdm+, with an inset showing the locally magnified spectrum. D Zeta potential of the PVA, PVA/Cu(TFSI)2, and PVA/Cu(TFSI)2-GdmCl hydrogels. E Nyquist diagram of the PVA, PVA/Cu(TFSI)2, and PVA/Cu(TFSI)2-GdmCl hydrogels, with an inset showing an enlarged view for PVA/Cu(TFSI)2, and PVA/Cu(TFSI)2-GdmCl hydrogels. F Ionic electrical conductivity of PVA/x Cu(TFSI)2 (bottom) and PVA/60 wt% Cu(TFSI)2-y GdmCl (top) hydrogels. G Schematic diagram (top left), photograph (top right), evaporation flux and corresponding salinity changes (bottom) in the residual solution over time using an ion-engine hydrogel under 3.5 wt% NaCl and 1 kW m−2 solar illumination. H IC reveals changes in Na+ and Cl− concentrations in residual solution. I Transference numbers of Na+ and Cl− determined by Hittorf method in an H-type electrolytic cell, confirming the high anion selectivity of the ion-engine mechanism, with an inset showing the schematic of the Hittorf method test. All the error bar represents the standard deviation of three-time measurements.
