Fig. 2: Characterizations of hydrogel diodes.
a The current response of hydrogel diodes with H+, K+, Mg2+, or Al3+ after a fixed time (t0 = 80 s) of ion migrations until the current reached a plateau, showing the decreased values of backward currents and enhanced rectification performances of diodes with high-valence cations. b The rectification ratios and backward currents of hydrogel ionic diodes with different cations including H+, Na+, K+, Mg2+, Ca2+, Al3+, and In3+, showing the enhanced rectification ratios and decreased backward currents for diodes high-valence cations. c The rectification ratios and backward currents of hydrogel ionic diodes with different amounts of added Ca(OH)2 and d Al(OH)3. The Ca2+ and Al3+ were incorporated through Ca(OH)2 and Al(OH)3. e The rectification ratios of hydrogel diodes made with AlCl3 and Al(OH)3, respectively. f The rectification ratios and backward currents of hydrogel ionic diodes with different amounts of added InCl3. The In3+ was incorporated through InCl3. g The Nyquist plot of hydrogel ionic diodes with different cations, measured under a negative voltage bias of −5 V and sweeping frequency from 106 to 10−1 Hz, showing increased impedances of diodes with cations having higher valence. Here, Cl−–Cl− represents a control sample made by two attached N-type hydrogel layers. h The rectification ratio of hydrogel ionic diodes with Al3+ under different stretching strains. The two insets show the rectification performance of diodes under the strain of 0% and 100%, respectively. i The Ashby plot of previously reported ionic diodes and our hydrogel ionic diodes comparing their rectification ratio and stretchability. Data points are from references labeled in Fig. S10 and Table S3
