Hydrogel Ionic Diodes toward Harvesting Ultralow‐Frequency Mechanical Energy

Abstract

Energy harvesting from human motion is regarded as a promising protocol for powering portable electronics, biomedical devices, and smart objects of the Internet of things. However, state‐of‐the‐art mechanical‐energy‐harvesting devices generally operate at frequencies (>10 Hz) well beyond human activity frequencies. Here, a hydrogel ionic diode formed by the layered structures of anionic and cationic ionomers in hydrogels is presented. As confirmed by finite element analysis, the underlying mechanism of the hydrogel ionic diode involves the formation of the depletion region by mobile cations and anions and the subsequent increase of the built‐in potential across the depletion region in response to mechanical pressure. Owing to the enhanced ionic rectification ratio by the embedded carbon nanotube and silver nanowire electrodes, the hydrogel ionic diode exhibits a power density of ≈5 mW cm−2 and a charge density of ≈4 mC cm−2 at 0.01 Hz, outperforming the current energy‐harvesting devices by several orders of magnitude. The applications of the self‐powered hydrogel ionic diode to tactile sensing, pressure imaging, and touchpads are demonstrated, with sensing limitation is as low as 0.01 kPa. This work is expected to open up new opportunities for ionic‐current‐based ionotronics in electronics and energy devices.

Integrated Opposite Charge Grafting Induced Ionic-junction Fiber

“…The recti cation ratio (J+/J-, where J + and Jdenote the current density at forward and reverse bias) at ± 3.0 V is about 14 at 10 mV s − 1 (Fig. 2G), comparable to the ratio for previously reported two-dimensional counterparts (recti cation ratio ≈ 2 to 50) 34,35 . At the same time, SEBS-IM/SEBS-IM and SEBS-SN/SEBS-SN homojunction have no noticeable recti cation effect (Fig.…”

Flexible Ionic Diodes with High Rectifying Ratio and Wide Temperature Tolerance

“…This rectifying performance is superior than that of most ionic diodes reported in the previous literature, as summarized in Figure 2c where representative ionic diodes are compared. [1,20,22,[14][15][16][17][25][26][27][28][29]18,[30][31][32][33]19,[34][35][36][37][38] Note that the rectification ratios collected from these studies are the maximum values as claimed, and they were obtained under various ionic conditions and in different electric voltage ranges (detail information is listed in Table S2, Supporting Information).…”

Soft Ionics: Governing Physics and State of Technologies

“…Recently, type III diodes have been constructed from aqueous polyelectrolytes. One popular choice is to use PSS and PDAC as the polyanion and polycation respectively, with platinum foil as the electrode [171][172][173]. Carye et al and Zhang et al used these polymers directly while Wang et al embedded them in a double network.…”

“…Because the electrodes in these devices were made from platinum or silver and thus semipolarizable, the measured response of the diode was a function of the electrode interface in addition to the polyelectrolyte junction. For example, while the open circuit voltage of the system was likely in the hundreds of mV range [173], the device only conducted well in forward bias above 2 V when the platinum electrodes were able to split water efficiently [168]. Han et al made a similar type III diode with nonpolarizable electrodes and demonstrated a turn on voltage near 0 V [174].…”