Preparation of natural polymer-based
highly conductive hydrogels
with tunable mechanical properties for applications in flexible electronics
is still challenging. Herein, we report a facile method to prepare
lignin-based Fe3+-rich, high-conductivity hydrogels via
the following two-step process: (1) lignin hydrogels are prepared
by cross-linking sulfonated lignin with poly(ethylene glycol) diglycidyl
ether (PEGDGE) and (2) Fe3+ ions are impregnated into the
lignin hydrogel by simply soaking in FeCl3. Benefiting
from Fe3+ ion complexation with catechol groups and other
functional groups in lignin, the resultant hydrogels exhibit unique
properties, such as high conductivity (as high as 6.69 S·m–1) and excellent mechanical and hydrophobic properties.
As a strain sensor, the as-prepared lignin hydrogel shows high sensitivity
when detecting various human motions. With the flow of moist air,
the Fe3+-rich lignin hydrogel generates an output voltage
of 162.8 mV. The assembled supercapacitor of the hydrogel electrolyte
demonstrates a high specific capacitance of 301.8 F·g–1, with a maximum energy density of 26.73 Wh·kg–1, a power density of 2.38 kW·kg–1, and a capacitance
retention of 94.1% after 10 000 consecutive charge–discharge
cycles. These results support the conclusion that lignin-based Fe3+-rich, high-conductivity hydrogels have promising applications
in different fields, including sensors and supercapacitors, rendering
a new platform for the value-added utilization of lignin.
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