Figure 4 (a) Stress−strain curve of the hydrogel. The tests
were carried out with a stretching rate of 20 mm min−1. Insets show
pictures of the TG hydrogel in its original and stretched state. The
scale bar is 1 cm. (b) Thermogravimetric characterization of
thermogalvanic hydrogel. Reprinted with permission from Pu et al.
Copyright 2020, American Chemical Society. (c) The double-network
thermocell with a thickness of 3 mm and a width of 5 mm lifts a bag of
oranges with a weight of 1.5 kg. The red circle indicates the location
of the thermocell. (d) The nominal stress-strain curve of the
double-network thermocell (un-notched). The yellow dashed line indicates
the strain-at-break of a notched sample. Reproduced with permission from
Lei et al. Copyright 2021, Elsevier. (e) Stress-strain curves of the
PAAm and PAAm/Alg hydrogels. Inset shows the stretching process of the
PAAm/Alg hydrogel, which can be easily stretched over 700%. (f) The
elastic modulus, breaking stress, and elongation data of the PAAm and
PAAm/Alg hydrogels.[22]Copyright 2022, Springer
Nature.
Meanwhile, the thermoelectric properties of these hydrogels are the
biggest concern. Hu’s TG hydrogel exhibits favorable physical and
electrochemical properties.Figure 5a depicts the thermoelectric
properties of the hydrogel, including the\(S\) is 1.2 mV
K-1, theeffective conductivity of approximately 100
mS/cm, and the thermal conductivity ranging from 0.30 to 0.39 W
(mK)-1 , and the power generation factor of 6.5-12
μW(m K2)-1. Chen et al. observed a
remarkably significant \(S\)value of up to 1.43 mV K-1for the PAMM/ALg hydrogel, while simultaneously retaining high
stretchability. Previously, Wu et al. achieved a remarkably
high\(S\)value of 1.5 mV K-1 for their double-network
thermocell, influenced by the concentration of NaCl. Despite the
satisfactory thermoelectric performance of hydrogels, there is ample
opportunity for improvement.