2.3 Comprehensive Evaluation of Photo-thermo-electric Conversion
of the PTEH-Interlocking
As shown in Figure 4a , the oxidation reaction
([Fe(CN)6]3− −
e− →
[Fe(CN)6]4−) occurs at the hot
side and the reduction reaction
([Fe(CN)6]4− +
e− →
[Fe(CN)6]3−) occurs at the cold
side in the thermoelectric hydrogel. 42, 43 We
designed a devices with hot side and cold side to estimate the voltage
output as a function of temperature difference (ΔT) in the
thermoelectric cell (Figure S6 ). The voltage of the
PTEH-Interlocking cells increases from 7.14 mV to 34.79 mV as ΔT
increased from 5°C to 25°C (Figure 4b ). While the voltages of
TEH is 6.47, 12.51, 18.80, 25.42 and 31.66 mV with ΔT of 5, 10, 15, 20
and 25°C (Figure 4c ). That Seebeck coefficient of
PTEH-Interlocking is -1.40 mV K-1, which is higher
than that of TEH (-1.26 mV K-1) (Figure 4d ).
The maximum power density of PTEH-Interlocking cells increases from
0.799 to 4.341 mW m−2 as the ΔT rises from 10°C to
30°C (Figure 4e ). We investigated the influence of different
levels of [Fe(CN)6]4− oxidation on
the voltage in the PTEH-Interlocking cell under constant simulated
sunlight illumination (100 mW cm−2). As shown inFigure 4f , the cell voltage reaches to a maximum of 6.92 mV as
the dosage of PA increases to 0.1 mol L-1. Although
the color of the PA-PEI-Fe photothermal film gradually deepens as dosage
of PA increases with an higher efficient photothermal conversion
(Figure S5 ), more dosage of PA results in a slight decrease of
cell voltage because of more consumption of
[Fe(CN)6]3−. After stretching to a
strain of 100% for ten times and continuous stretching to a strain of
400% for eight times, the voltage of PTEH-Interlocking cells maintains
at ~34.88 mV with a ΔT of 25°C (Figure 4g ),
indicating the good mechanical stability.
The combination between PA-PEI-Fe film and TEH is of importance for the
heat transfer in the photo-thermo-electric cell. The thermal
conductivity of PA-PEI-Fe film and TEH is 0.408
W·m-1K-1 (Figure S7 ) and
0.895 W·m-1K-1 (Figure 4h )
at room temperature, respectively. Whereas that of TEH cells with direct
physical adhesion of PA-PEI-Fe thermal film decreased to 0.64 W
m−1 K−1 because loose adhesion
allows air to enter the interface between the TEH and PA-PEI-Fe film
(where that thermal conductivity of air is only 0.0267 W
m−1 K−1).
Notably, that thermal conductivity
of PTEH-Interlocking is the highest at 0.99 W m−1K−1, indicating the the PA-PEI-Fe photothermal film
assembled in situ facilitates rapid heat transfer from the
photothermal film to the thermo-electric hydrogels (Figure 4h ).1, 10 The electronic conductivities of
PTEH-Interlocking (22.84 mS m−1) is similar to that of
TEH (22.94 mS m−1) (Figure 4i ), indicating
that the in situ PA-PEI-Fe film has no affect on the the overall
electron transfer in
PTEH-Interlocking cells.
The higher Seebeck cofficient of the PTEH-Interlocking cells is probably
devided into two mechnasim: (1) the increasing redox entropy via
oxidation of PA and PEI by
[Fe(CN)6]3−in the system; 42, 43 (2) high thermal conductivity at
the interface due to the interlocking structure.