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Page 20 of 32 Zhao et al. Soft Sci 2024;4:18 https://dx.doi.org/10.20517/ss.2024.04

Table 5. The summarization of sweat-based SABs and their performance
Electrode
Anode Cathode OCP (V) Power density Ref.
Mg LIGA@MnO 2 1.5 6.31 mW·cm -2 [150]
-2
Mg Ag O 1.8 122 mW·cm [149]
2
Mg Ni/graphene foam 1.41 16.3 mW·cm -2 [148]
-2
Mg Graphene 1.54 3.17 mW·cm [69]
-2
Zn foil-wrapped yarn Carbon-black-modified yarn 1 33.1 μW·cm [151]
Zn-wire Carbon 1 1.72 mW·cm -2 [146]
-2
Zn Ag O ~1 3.47 mW·cm [152]
2
Zn CuSO 4 0.93 7.46 mW·cm -2 [147]
SABs: Sweat-activated batteries; OCP: open-circuit potential; LIGA@MnO2: laser-induced PI/gelatin based graphene anchored with manganese
dioxide.

Sweat-activated supercapacitor
Supercapacitors offer advantages over batteries, such as high power density, fast charge-discharge rates, and
long cycling life. Traditional supercapacitors use toxic electrolytes, requiring special packaging for safety. In
contrast, SASs utilize biocompatible biological fluids such as sweat as electrolytes. This section explores the
emerging field of SASs and their potential for energy storage. Luo et al. devised an on-skin supercapacitor
[153]
integrated into garments that harvests energy from sweat during sports . It utilizes a NaCl electrolyte and
a polyaniline (PANI)/CNT electrode, offering an extended potential window of 0.8 to 1.4 V, with the energy
density at 112.1 mF·cm (3.0 M NaCl) and 110.5 mF·cm (1.0 M NaCl). A sweat-charging watchband
-2
-2
integrates four supercapacitors for effective charging up to 3.2 V [Figure 10A]. Manjakkal et al. introduced a
flexible supercapacitor based on sweat for applications in wearables and smart textiles. Sweat serves as the
electrolyte, and the active electrode is polypyrrole/poly (3,4-ethylenedioxythiophene):poly
(styrenesulfonate) (PEDOT:PSS). Because of the redox reactions of PEDOT:PSS and electrochemical
double-layer capacitance, the supercapacitor covered with PEDOT:PSS on cellulose/polyester cloth exhibits
high capacitance. It attains a weight-specific capacitance of 8.94 F·g and area-specific capacitance of
-1
10 mF·cm at 1 mV·s in sweat equivalent solution. Tested with real human sweat, the supercapacitor shows
-2
-1
an energy density of 0.25 Wh·kg and a power density of 30.62 W·kg , providing a safe and sustainable
-1
-1
power solution for wearables [Figure 10B] . The sweat-based yarn biosupercapacitor (SYBSC) utilizes
[154]
hydrophilic cotton fibers wrapped around stainless steel yarns modified with PEDOT:PSS, forming
symmetrical electrodes. It attains a high areal capacitance of 343.1 mF·cm at a current density of
-2
0.5 mA·cm . The device maintains its capacitance at 68% after 10,000 charge-discharge cycles and 73% after
-2
25 cycles of machine washing. When integrated with yarn-based self-charging power units and pH sensing
fibers, it creates a comprehensive sensing textile triggered by sweat, allowing for real-time monitoring of pH
levels in sweat generated during physical activity [Figure 10C] .
[37]
The power requirements of a complete sweat-based platform typically fall within the range of nanowatts
(nW) to milliwatts (mW). The existing sweat-based energy generators, such as BFCs and SABs, can generate
maximum voltages of 1.8 V and 122 mW·cm , respectively. This voltage and power output are adequate to
-2
power certain sensors and related devices for a few minutes. Here, we summarize the recent advancements
in sweat-based BFCs and SABs and the typical power requirements for wearable devices [Figure 11A and B].
Additionally, Figure 11C demonstrates the significant power density consumption of bioelectronics systems,
thereby confirming the viability and effectiveness of sweat-based energy harvesters . However,
[155]
multifunctional sensing capabilities and additional components such as iontophoresis electrodes and
wireless transmission modules may require higher energy levels to operate effectively. Furthermore, the
performance of the BFCs, SABs, and SASs can indeed vary due to differences in sweat composition and pH