Moisture-enabled self-charging and voltage stabilizing supercapacitor

Abstract

Supercapacitor is highly demanded in emerging portable electronics, however, which faces frequent charging and inevitable rapid self-discharging of huge inconvenient. Here, we present a flexible moisture-powered supercapacitor (mp-SC) that capable of spontaneously moisture-enabled self-charging and persistently voltage stabilizing. Based on the synergy effect of moisture-induced ions diffusion of inner polyelectrolyte-based moist-electric generator and charges storage ability of inner graphene electrochemical capacitor, this mp-SC demonstrates the self-charged high areal capacitance of 138.3 mF cm⁻² and ~96.6% voltage maintenance for 120 h. In addition, a large-scale flexible device of 72 mp-SC units connected in series achieves a self-charged 60 V voltage in air, efficiently powering various commercial electronics in practical applications. This work will provide insight into the design self-powered and ultra-long term stable supercapacitors and other energy storage devices.

Full text

Article https://doi.org/10.1038/s41467-024-49393-9
Moisture-enabled self-charging and voltage
stabilizing supercapacitor
Lifeng Wang
1,2,3,4
, Haiyan Wang
2
, Chunxiao Wu
1,2
,JiaxinBai
4
, Tiancheng He
4
,
Yan Li
1
, Huhu Cheng
2,4,5
&LiangtiQu
2,4,5
Supercapacitor is highly demanded in emerging portable electronics, how-
ever, which faces frequent charging and inevitable rapid self-discharging of
huge inconvenient. Here, we present a flexible moisture-powered super-
capacitor (mp-SC) that capable of spontaneously moisture-enabled self-char-
ging and persistently voltage stabilizing. Based on the synergy effect of
moisture-induced ions diffusion of inner polyelectrolyte-based moist-electric
generator and charges storage ability of inner graphene electrochemical
capacitor, this mp-SC demonstrates the self-charged high areal capacitance of
138.3mFcm
−2and ~96.6% voltage maintenance for 120 h. In addition, a large-
scale flexible device of 72 mp-SC units connected in series achieves a self-
charged 60 V voltage in air, efficiently powering various commercial electro-
nics in practical applications. This work will provide insight into the design self-
powered and ultra-long term stable supercapacitors and other energy storage
devices.
Flexible and miniaturized supercapacitors with high power density,
long cycling life, and excellent safety are highly demanded in emerging
portable electronics of micro aerialvehicles, intelligent robots, human-
computer interaction, and the Internet of Things sensing1–5.Thefre-
quent charging process and inevitable self-discharging of current
supercapacitors are dramatically inhibiting the practical convenience
of power source devices6.
Harvesting power from the ambient environment in the highly
integrated energy conversion and storage system has become a pro-
mising strategy to solve the shortcoming of supercapacitors above
mentioned, which can be continuously self-charging, avoiding
frequent power source replacement or bulky external charging
dependence7–9. Ambient solar energy, mechanical movements,
and thermal difference have been employed to achieve the
electricity generation and storage system by integrating solar cells,
piezo/tribo-electric generators, and thermoelectric devices with
supercapacitors7,9–11. The development of self-charging integrated
devices across one-dimensional fibers12,13, two-dimensional films9,
three-dimensional bulk structures14, and textile forms15,16 has emerged
for various applications including health monitoring bioelectronics17,
sensors18, and wearable electronics7, which always require external
mechanical stimuli or specific geographic and climatic conditions. A
recently developed moist-electric generator (MEG) is able to produce
electricity by utilizing atmosphere water within the stereoscopic space
around us, which could provide a sustainable self-powered strategy in
an all-weather and 24-h way19–24. It becomes possible to develop the
highly integrated energy conversion and storage system without
intermittent environmental conditions limitations.
In this regard, the flexible moisture-powered supercapacitor (mp-
SC) has been developed, which can be spontaneously self-charging
and voltage self-stabilizing when absorbing water from the air.
Through layer-by-layer highly-integrating polyelectrolyte-based MEG
for electricity generation and graphene electrochemical capacitor (EC)
for energy storage, this mp-SC delivers a voltage output of ~0.9 V in
90% relative humidity (RH) air. Especially, the electricity generation
provides the constant moist-electric potential that counteracts the
Received: 27 October 2023
Accepted: 29 May 2024
Check for updates
1
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, PR China.
2
Key Laboratory of Organic Optoelectronics &
Molecular Engineering, Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China.
3
State Key Laboratory of Transient Optics
and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an, PR China.
4
State Key Laboratory of Tribology in
Advanced Equipment (SKLT), Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
5
Laboratory of Flexible Electronics
Technology, Tsinghua University, Beijing 100084, PR China. e-mail: liyan2011@ustb.edu.cn;huhucheng@tsinghua.edu.cn;lqu@mail.tsinghua.edu.cn
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effect of self-discharge for the electrochemical energy storage,
achieving 96.6% voltage maintenance for 120 h without obvious dis-
charge and a high areal capacitance of 138.3 mF cm−2at the current
density of 10 μAcm
−2of mp-SC. Meanwhile, the power output
(49.4 μWcm
−2) is greatly enhanced by the synergistic effect of elec-
tricity generation and stored energy supply that is beyond the indivi-
dual energy production or storage part. Besides, this mp-SC exhibits
remarkable mechanical flexibility and demonstrates ~100% voltage
retention under 180° bending for 1000 cycles. The large-scale flexible
device array with 72 mp-SC units connected in series reaches 60V
voltage in the air, which powers various electronics such as electronic
watches, temperature and humidity meters, and calculators. This study
presents a strategy for designing self-powered and ultra-long term
stable supercapacitors and paves the way for development of spon-
taneous energy harvest devices.
Results
The configuration and fabrication of mp-SC
The schematic illustration of mp-SC is shown in Fig. 1a. The mp-SC has
a multi-layer structure that can be divided into two parts, including
graphene-based interdigitated EC and polyelectrolyte-based MEG with
rationally designed electrodes. First, a graphene oxide (GO) suspen-
sion was blade-coated on a flexible polyethylene terephthalate (PET)
substrate. Direct-laser writing approach was then conducted to con-
struct the pair of interdigitated reduced GO (rGO) microelectrodes on
the dried GO film (Fig. 1b). After being coated by the PVA/LiCl elec-
trolyte and the epoxy resin in sequence, the bottom graphene-based
interdigitated EC part was constructed (Fig. 1c). Afterward, a con-
ductive carbon paste was coated on top of the epoxy resin and was
connected with one rGO microelectrode of EC by the screen-printing
process (Fig. 1d). A polyelectrolytes film was adopted and coated on
the carbon electrode to harvest energy from moisture (Fig. 1e). Finally,
carbon tape is adhered to the polyelectrolytes film and connected to
another rGO microelectrode of EC (Fig. 1f), achieving the integration of
graphene-based interdigitated EC and polyelectrolyte-based MEG for
mp-SC fabrication.
Characterization and electrochemical performance of the EC
part of mp-SC
Figure 2a–c showthe black interdigitated rGO microelectrodes and GO
intervals of the EC part in mp-SC. The rGO microelectrodes are con-
verted from GO film after laser treatment (355 nm, ~2.2W) as above
mentioned25. Due to the photothermal effect, the compact GO film in
the interdigitatedregions changes into three-dimensional porous rGO
microelectrodes (Fig. 2b, c and Supplementary Fig. 1) attached to the
GO film22,26. Compared with GO, the lower Dband in 1350 cm–1of rGO
Carbon slurry
Carbon tape Self-charging
Carbon electrode
Polyelectrolytes
Carbon electrode
Epoxy resin separator
Gel electrolyte
rGO microelectrodes
PET substrate
MEG
EC
Laser scribing Spraying electrolyte
mp-SC
rGO
PVA/LiCl
GO
Coating separator
and carbon electrodes
Coating polyelectrolytes
and top electrode
a
b
d
cf
e
Electrode of EC
Counter
electrode of EC
Bottom electrode
of MEG
Top electrode of
MEG
Fig. 1 | Schematic of the mp-SC. a Photos of the bilayer polyelectrolytes film and
the rGO microelectrodes array obtained by direct-laser writing as well as the
scheme of the mp-SC. The mp-SC consists of a polyelectrolyte-based MEG and a
graphene EC. b–eSchematic illustration of the fabrication process of mp-SC. fThe
schematic diagram of connection between between SC and MEG of the mp-SC.
Article https://doi.org/10.1038/s41467-024-49393-9
Nature Communications | (2024) 15:4929 2
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microelectrodes in Raman spectroscopy (Supplementary Fig. 2a)
result indicates the oxygen functional groups and other defects are
significantly decreased. X-ray photoelectron spectroscopy (XPS)
spectra (Supplementary Fig. 2b, c) reveal the O atom ratio in rGO
microelectrodes is about 14.79% that is much lower than that of GO
(~31.29%), further resulting in a drastic increase in electrical con-
ductivity from 5.09 × 10-3Sm
–1(GO) to 2.73 × 103Sm
–1of rGO micro-
electrodes (Supplementary Fig. 2d). The porous structure and the high
electrical conductivity will facilitate the electrolyte diffusion and
electron transport in the microelectrodes27, endowing them with
promising energy storage capabilities.
Cyclic voltammetry (CV) and galvanostatic charge−discharge
profiles were recorded at the potential window between 0 and 1 V to
evaluate the electrochemical performance ofthe EC part in mp-SC. The
nearly rectangular CV curves (Fig. 2d) indicate the typical double-layer
capacitive behavior of the rGO microelectrodes28,29. The area-specific
capacitance of the EC part according to the CV profiles is shown in
Fig. 2e, which shows the areal capacitance of 2.21 mF cm–2at a current
density of 10 mA cm–2, comparable to values of the state-of-the-art
carbon-based supercapacitors28. Figure 2f displays nearly symmetric
triangular galvanostatic charge and discharge profiles with fast charge-
discharge characteristics and high Coulombic efficiencies close to
100%. Besides, epoxy encapsulation shows negligible influence on the
capacitance performance of the EC (Supplementary Fig. 3). For
instance, by connecting ECs in series or in parallel, the devices
achieved a further expanded voltage window or boosted capacitance
(Supplementary Fig. 4). The nearly vertical slope in the low-frequency
region shown in Nyquist plots (Fig. 2g) further confirms their ideal
double-layer capacitive behavior30. The short45° line inserted in Fig. 2g
proves that the interconnection of the porous structures exists in the
rGO filmbythedeLeviemodel
31. Furthermore, the EC part is highly
robust and flexibleshowninFig.2h. According to the CV curves,
almost 100% of initial capacitance is maintained even under a bending
angle of 180°. Besides, the EC demonstrates an impressive capacitance
retention of 92.5% and a high Coulombic efficiency of 99% after more
than 120,000 charge-discharge cycles (Fig. 2i).
The power generation performance of the MEG part of mp-SC
For the MEG part of mp-SC, polydiallyl dimethyl ammonium chloride
(PDDA) and polystyrene sulfonic acid (PSS) bilayer polyelectrolytes
film are adopted (Fig. 3a). Figure 3b shows the cross-section scanning
electron microscopy (SEM) image of this bilayer polyelectrolytes film,
020406080100
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Current density (mA cm-2)
Current density (mA cm-2)
Areal C (mF cm-2)
Voltage (V)
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0.02 mV s-1
0.05 mV s-1
0.1 mV s-1
50 μA cm-2
75 μA cm-2
100 μA cm-2
150 μA cm-2
200 μA cm-2
Voltage (V)
Time (s) Scan rate (V s-1)
Z’ (kΩ cm-2)
Z’ (Ω cm-2)
Cycle number
Voltage (V)
-Z’’ (KΩ cm-2)
-Z’’ (Ω cm-2)
Capacitance retention (%)
Coulombic efficiency (%)
0.0 0.1 0.2 0.3 0.4 0.5
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40
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80
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300
600
900
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c
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i
0 3000 6000 9000 12000
0
20
40
60
80
100
120
90
92
94
96
98
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Fig. 2 | Electrochemical energy storage properties of the EC part of mp-SC.
Photomicrograph (a) and SEM images (b,c) of the laser-reduced rGO microelec-
trodes. dCV curves of the EC part of mp-SC at scan rates of 10mV s–1,20mVs
–1,
50 mV s–1,and100mVs
–1.eAreal capacitance versus scan rate of the EC at scan
rates between 10 and 500 mV s–1.fGalvanostatic charg e/discharge curves at
different current densities. gElectrochemical impedance spectroscopy analysis of
the EC part of mp-SC, the inset shows the high-frequency region of the EC. hCV
curves of the EC part of mp-SC under normal and bent conditions, inserted optical
images show the EC at different bending angles. iCycling stability and Coulombic
efficiency of the EC after 12,000 charge-discharge cycles.
Article https://doi.org/10.1038/s41467-024-49393-9
Nature Communications | (2024) 15:4929 3
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demonstrating the PDDA layer and PSS layer clearly. Cl and S elements
mapping via energy dispersive spectroscopy (EDS) (Fig. 3b) further
confirm the successful fabrication of bilayer structure because the Cl
element is mainly distributed at the PDDA layer and the S element is
mainly distributed at the PSS layer. In the PSS layer, PVA is incorpo-
rated into the polyelectrol ytes film with a mass ratio of 14.5% that could
improve the mechanical properties and flexibility (Fig. 3c). Simulta-
neously, the PVA has contributed a fraction of dissociable hydrogen
ions. The failure strain of the composite film is 4.5 times higher than
pure PSS film as shown in Fig. 3c. Owing to the abundant -SO
3
H, -OH,
and -NCl functional groups content (Supplementary Fig. 5), the poly-
electrolytes film could spontaneously absorb or desorb water when
the ambient humidity changes and a high water absorption capacity of
78.3% is achieved at 95% RH and 25 °C (Fig. 3d). After sandwiching the
bilayer polyelectrolytes film between the blade-coated carbon bottom
electrode (Supplementary Fig. 6) and carbon tape top electrode, the
MEG part in mp-SC is obtained.
The power generation mechanisms are investigated by simula-
tions and experimental studies (Supplementary Figs. 7 and 8). After
exposure to moisture, polyelectrolytes film harvests water molecules
from the ambient environment and dissociates movable H+and Cl–.
The unevenly distributed ions will create an electric potential differ-
ence between the two electrodes driven by a concentration gradient
(Fig. 3e). The surface potential values of –0.87V for PSS and 0.92 V for
PDDA have been conclusively confirmed via Kelvin probe force
microscopy tests. These potential disparities arise from the gradient
distribution of mobile H+and Cl–ions. The electric power generation
process is demonstrated using Poisson and Nernst–Planck (PNP) the-
ory (Supplementary Fig. 7). A 1.07 V open-circuit voltage is attained
through the gradual diffusion of H+and Cl-ions within the bilayer
polyelectrolytes film, closely aligning with the experimental test
results.
The power generation performance of the MEG is then tested as
shown in Supplementary Fig. 9. After adsorbing water from the air
PDDA
Strain (%)
Time (s)
Time (s)
5 14 20 33 45 60 75 90
Time (min)
PSS+PVA film
PSS film
RH (%) Bending angle (degree)
Bending
angle
Stress (MPa)
Change in mass (%)
Target RH (%)
Voltage (V)
Voltage (V)
Voltage (V)
Current density (µA cm-2)
Current density (µA cm
-2
)
PSS+PVA
30 μm
Cl S
d
gh i
ab c
fe
V
Cl-
Cl-
Cl-
Cl-
H+
H+
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+ + +
+
- - -
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5
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20
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20
40
60
80
0
20
40
60
80
100
0 1000 2000 3000
0.0
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0.6
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0 2500 5000 7500
0
2
4
6
8
10
0.0
0.3
0.6
0.9
1.2
1.5
0
1
2
3
-180 -90 0 90 180
0.0
0.5
1.0
1.5
SOO
OH
n
Cl
-
N
+
n
CH
3
H
3
C
Fig. 3 | Moisture energy-harvesting properties. a Chemical structures of the PSS
and PDDA. bCross-section SEM image of the polyelectrolytes film and corre-
sponding energy-dispersive X-ray spectroscopy (EDS) mappings of Cl and S. cThe
stress-strain curve of the polyelectrolytes film. dThe mass change of the
polyelectrolytes filmat different RH. eSchematic illustration of the polyelectrolyte-
based MEG.The output voltage(f) and currentdensity (g)oftheMEG.hThe output
voltage and current density of the MEG under different RH from ~5 to ~95%.
iVoltage retention of the generator under different bending angles.
Article https://doi.org/10.1038/s41467-024-49393-9
Nature Communications | (2024) 15:4929 4
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(90% RH and 25 °C), a sustained voltage of 1.27 V and a current density
of 2.7 µAcm
–2are generated as shown in Fig. 3f, g. Figure 3h displays
the electricity generation of the MEG part in mp-SC at different
humidity air. Even at very low humidity of 15%, this MEG part has a
favorable voltage of 0.65 V, revealing excellent environmental suit-
ability. With the rise in RH, the produced voltage and current increases
because of the enhanced ion dissociation ratio and ion migration rate
of polyelectrolytes related to the higher water content ratio32–34.
Meanwhile, the MEG part in mp-SC exhibits a stable voltage output
under the bending state, indicating excellent mechanical flexible
properties (Fig. 3i).
Moisture-powered energy storage performance of mp-SC
By integrating the energy generation part and energy storage part with
well-designed electrodes as indicated in Fig. 4a and Supplementary
Fig. S10, this mp-SC can absorb water from the air and gradually dis-
sociates and releases moveable H+and Cl–at the MEG part. Then, the
asymmetrically distributed migratable ions (H+and Cl–) in the bilayer
polyelectrolytes film will diffuse to the opposite side driven by the
concentration difference above mentioned and produce electrical
power. The voltage generated by the polyelectrolytes film is applied
the carbon electrodes and then actson the rGO microelectrodes of the
EC through the internally connected electrodes. Under the applied
voltage bias, the electrolyte within the EC selectively adsorbs onto the
surface of the porous electrodes, facilitating the conversion of
electrical energy into chemical energy. Based on this method,
the power energy produced by the MEG is storaged in the EC via the
electric double-layer mechanism2. Furthermore, the mp-SC is capable
to harvest energy in a wide RH or temperature range (Fig. 4b, c; Sup-
plementary Fig. S11, Video S1, and Video S2) indicating its robustness
toward harsh environmental conditions. As shown in Fig. 4d, the vol-
tage of mp-SC can spontaneously self-charged to ~0.9 V after 380 s
when absorbing water in 90% RH air and the stored electricity can be
discharged at constant current density for power output. As a new-
type moisture-powered energy storage device, this mp-SC represents
distinctive moisture-induced self-charging and electricity-discharging
curves. The moisture-induced self-charging voltage curve experiences
a rapid initial increase, followed by a gradual stabilization, which is
determined by the moisture-enabled energy generation process.
Besides, the mp-SC represents a typical galvanostatic discharge
behavior at different current densities. Notably, the discharge time is
about 12,985 s at a current density of 10 µAcm
–2, which is much longer
than that of individual EC parts (459 s) because of the synergistic effect
of electricity generation and stored energy release. As a result, the mp-
SC exhibits an ultra-high areal capacitance of 138.3 mF cm–2. The areal
capacitance is one or two orders of magnitude greater than previously
reported graphene supercapacitors and some pseudocapacitors
(Fig. 4e, f)26,28,35–37.
Meanwhile, the output voltage increases and the output current
decreases as the electric load varied from 10Ωto 1 GΩ(Fig. 4g),
Power generating
RH (%) Temperature (°C) Time (s)
Time (s)
Voltage (V)
Voltage (V)
Voltage (V)
Voltage (V)
Voltage (V)
Voltage (V)
Areal C (mF cm-2)
Current density (mA cm-2)
Power density (µW cm-2)
Current density (µA cm-2)Areal C (mF cm-2)Resistance (Ω) Resistance (Ω)
Power density (µW cm-2)Bending angel (degree)
MEG
mp-SC
Energy storing
MEG
EC
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0.0
0.3
0.6
0.9
1.2
20 40 60 80 100
10
0
10
1
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0 20 40 60 80 100 -18 0 25 60
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100 μA cm-2
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50 μA cm-2
25 μA cm-2
20 μA cm-2
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Fig. 4 | The performance of themp-SC. a Schematicof the charging processof the
mp-SC. bThe voltage output of the mp-SCat different RH. cThe voltage output of
the mp-SC at different temperature. dGalvanostatic charge-discharge profiles of
the mp-SC at different current densities. eThe areal capacitance of the mp-SC at
different current densities. fComparison of the capacitance of the mp-SC with the
recently reported ECs. Output voltage and current (g)aswellasthepowerdensity
(h) of the mp-SCwith differentelectric resistors. iComparisonof the power density
of the mp-SCand the recently reported moisturepower generators.jThe mo isture-
charging/discharging cycling stability of the mp-SC at 90% RH. kOptical images of
the mp-SC at the bending state. lThe voltage output of the device at different
bending states. The voltage retention rate of the mp-SC after cyclic bending and
flat test.
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Nature Communications | (2024) 15:4929 5
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achieving a maximum value of ~49.4 µWcm
–2at an optimal resistance
of about 500 Ω.Generally,highpowerdensityisdifficult to achieve for
MEG due to its relatively high internal resistance. In combination with
high energy density EC, the maximum power density is 1500 times
higher than the polyelectrolyte-based generator and outperforms the
state-of-the-art moisture electric power generators as shown in Sup-
plementary Table 1 and Fig. 4h, i21,22,38–46.Figure4j represents the
moisture-charging/discharging cycling performance with the same
discharge current density (50 µAcm
–2) under high RH (~90% RH at
25 °C). The mp-SC maintains durable moisture-charging/discharging
output performance more than 15 cycles. Moreover, the integrated
device demonstrates a good voltage retention rate of ~100% under
bending and flat states after 1000 bending cycles, showing the
remarkable mechanical durability (Fig. 4k, l, Supplementary Fig. 12).
Compared with individual supercapacitor energy storage (Fig. 5a),
this mp-SC self-powered energy storage deviceprevents the significant
voltage drop. Figure 5b represents that mp-SC has an ultra-long open-
circuit voltage maintenance time of up to 120 h. While the self-
discharge curves of individual EC show the open-circuit voltage drops
to 0.45 V sharply within 10 min due to the intrinsic self-discharge
effect of supercapacitors47. This can be contributed to that the
polyelectrolyte-based generator continuously charges the energy
storage part in mp-SC, making the unique voltage retention behavior.
The voltage retention rate of the mp-SC is up to 96.6% after 120 h,
which is superior to those of supercapacitors by suppressing the self-
discharging processes (Fig. 5c) through modifying the electrode,
introducing additives or ion-exchange membranes and chemically
active separation materials48–55.
Thelarge-scaleintegrationofthedeviceiscriticaltosupplysuffi-
cient power for electronics. Herein, the laser processing, screen printing,
and spraying processes are easy to scale up to obtain the integration of
mp-SC units as shown in Fig. 5d. By connecting in series, the voltage
increases linearly with the number of the mp-SCs, allowing for a max-
imum output voltage of ~60 V with 72 units just putting them in the air
(90% RH and 25 °C). Four mp-SCs are connected in series to harvest and
store energy from the ambient environment. Subsequently, these devi-
ces can be utilized to power a commercial temperature-humidity
monitor (~60% RH at 25 °C). To demonstrate stability, the temperature-
humidity monitor can be driven again by the mp-SCs five days later due
to its robust and stable output performance. Furthermore, the flexibility
of the mp-SC enable it to be seamlessly integrated into the wristband of a
conventional electronic watch and powering the watch for minutes after
self-charging even under bending or twisting conditions (Fig. 5gand
Video S3). In addition, four mp-SCs connect in series are able to directly
power an electronic calculator in ambient conditions (Supplementary
Fig. 13 and Video S4) without requiring supplementary power manage-
ment circuits. This impressive capability highlights the potential of mp-
SC as a promising long-term self-powered source for wearable and
flexible electronics. Moreover, the integrated mp-SCs (Fig. 5h) can
directly power a Bluetooth-enabled sensor and transmit the data to a
smartphone through Bluetooth, demonstrating their immense potential
for powering distributed Internet of Things (IoT) sensors.
Discussion
To summarize, this study has developed a flexible, durable, and ultra-
stable flexible mp-SC. By combining polyelectrolyte-based MEG for
0 18365472
0
10
20
30
40
50
60
Time (h) Time (h)
rGO@VO
Battery-capacitor
VN/MnO
Graphene film
Carbon fabric
TiC/α-MnO
PEDOT-Cl
Activated carbon
AG carbon
Activated carbon
AC fiber
This work
Series number
Time (h)
Laser scribing EC Integration device Laser cutting polyelectrolyte
Charging
Day 1 Day 5 Integrated mp-SC
Smartphone receiver
Bluetooth sensor
Voltage (V)
Voltage (V)
Voltage (V)
Voltage retention (%)
a
fgh
bc
ed
0 1 2 2021222324
0.0
0.2
0.4
0.6
0.8
1.0
02040
60
80 100 120
0.0
0.2
0.4
0.6
0.8
1.0
020406080100120
0
20
40
60
80
100
Fig. 5 | Applications of the mp-SC. a The self-disc harge curve of the individual EC.
bThe continuous voltage output of the mp-SC for over 120 h at 90% RH and 25 °C.
cComparison of voltage retention rate of the mp-SC and the reported ECs.
dSchematic diagram of large-scale fabrication of mp-SC.eA plot of voltage output
with different serial numbers of mp-SC. fThe self-charging process of the mp-SCs
and a demonstration of a commercial temperature-humidity monitor are directly
driven by four mp-SCs connected in serial as well as the monitor is driving again 5
days later.gDemonstration ofthree mp-SCs coherent in the wristband andserving
as the power supply for an electronic watch.hDemonstrationof applying thelarge-
scale integrated mp-SCs for powering a commercial thermohygrometer and
transmitting the data to a smartphone through Bluetooth.
Article https://doi.org/10.1038/s41467-024-49393-9
Nature Communications | (2024) 15:4929 6
Content courtesy of Springer Nature, terms of use apply. Rights reserved

electricity generation with graphene EC for energy storage, the mp-SC
can harvest energy directly from atmospheric moisture, generate
electric power, and store it simultaneously. This mp-SC delivers a
voltage output of ~0.9 V in 90% RH air 96.6% and has excellent voltage
maintenance for 120h. The high areal capacitance of 138.3 mF cm–2at
the current density of 10 μAcm
–2and the power output (49.4 μWcm
–2)
of mp-SC is achieved based on the synergistic effect of electricity
generation and stored energy supply. The large-scale flexible mp-SC
units connected in series can power various electronics such as elec-
tronic watches, temperature and humidity meters, and calculators,
which delivers great potential for the development of self-powered
and ultra-long term stable supercapacitors for future applications.
Methods
Materials
GO dispersion was prepared by using a modified Hummers’
method2,55–57. PSS (with weight-averaged molecular weight,
M
w
= 75,000, 30 wt% in water), PVA (M
w
= 15,000), PDDA
(M
w
= 100,000, 35 wt% in water) were purchased from Shanghai
Aladdin Biochemical Technology Co., Ltd and were used as received
without further purification. Conductive carbon paste (CH-8) was
purchased from Jelcon Corp., Japan. Conductive carbon tape (No.
7321) was purchased from Nisshin EM Co.
Preparation of bilayer polyelectrolytes film
40 g PVA was added into 360 g of deionized water, and the mixture was
stired at 90 °C in a water bath until the PVA is completely dissolved,
resulting in a 10 wt% PVA solution. 2 g PVA solution was added in 3.92 g
of 30 wt% PSS solution and 4 g deionized water, and was stirred at room
temperature to obtain a homogeneous solution. Adding the resulting
solution to a laboratory dish with a diameter of 9 cm, and drying 35 °C
and 50% RH to obtain a PVA + PSS composite film. Next, 1.5 mL of PDDA
was sprayed onto the bilayer film using a pressure of 50 Psi. Hot air is
used to dry the sprayed PDDA during the spraying process to prevent it
from dissolving into the film. SEM tests indicate the thickness of the
bilayer film was ~100 μmandtheratioofPDDA:PSS+PVAwas3:7.After
the preparation process, the film was cut into small pieces
(6.6 × 6.6) mm using a 355 nm nanosecond laser (3 W) with a pulse
repetition frequency of 20 kHz and scanning speed of 20 mm s−1.
The fabrication process of the mp-SC
The integrated device was prepared by layer-by-layer stacking pro-
cessing. First, a GO (13 mg mL–1) dispersion was coated onto a PET
substrate, with a height of about 1.5 mm and dried in a 40 °C oven. The
obtained GO film with a thickness of about 8 μm tightly loaded onto
the flexible PET substrate. The rGO microelectrodes were fabricated
using direct-laser writing method (~2.2 W, 355 nm, 93 kHz), with a size
of 33.8 mm2for the electrode and the gap area. The laser scanning
speed and pulse duration were 500 mm s–1and 9.7 μs, respectively.
The PVA/LiCl gel electrolyte (5 M) was then sprayed onto the micro-
electrode area with a mask using an airbrush, with the pressure set to
50 psi2. A single-component insulating epoxy resin was used to print as
a protective layer in the electrolyte area by screen printing and then
cured at 60 °C for 6 h in an oven. In addition, a conductive carbon
paste layer (pre-doped with 1% carbon fiber to enhance the mechanical
properties of the carbon electrode) was printed to connect one of the
current collectors of the EC as serve as the bottom electrode of
the MEG. A bilayer polyelectrolytes film was coated on the bottom
electrode. Finally, a conductive carbon tape adhered to the polyelec-
trolytes film serve as the top electrode of MEG and connected to the
other electrode of the EC. The mp-SC was successfully fabricated.
Characterization and measurement
Optical images were captured using the Axio Scope A1 optical
microscope by Zeiss (Germany). SEM images were taken with a
Sirion-200 field-emission scanning electron microscope made by FEI
(USA), and EDS was performed using an INCA Energy EDS system by
Oxford Instruments (UK). Raman spectra were detected using a
LabRAM HR Raman spectrometer (Horiba Jobin Yvon, Japan) equip-
ped with a 532 nm laser. XPS data were acquired using an ESCALAB
250Xi X-ray photoelectron spectrometer by Thermo Fisher Scientific
(USA). Electronic conductivity was determined by the I-V test, with
the formula σ=(I/V)×(l/A), where Ais the cross-sectional area of
the test sample, and lis the distance between the two electrodes.
Stress–strain curves were obtained using a tensile machine (Instron
5943) with a constant strain rate of 1 mm min–1. Fourier transform
infrared spectra were obtained using a Spectrum Two infrared
spectrometer by PerkinElmer (USA). Dynamic vapor sorption (DVS)
measurements were performed using a DVS-1000 dynamic vapor
sorption analyzer (Surface Measurements Systems, UK). A weight
change of less than 0.002% was considered to reach the sorption/
desorption equilibrium state. Water contact angles were measured
using an OCA 15 contact angle tester, while the surface potential was
measured with an Asylum Research Cypher ES Kelvin probe micro-
scope (Oxford Instruments, UK).
The electrochemical performance of the EC was tested by an
electrochemical workstation (CHI 760E, Shanghai Chenhua, China).
Two-electrode systems were adopted for CV, constant current charge-
discharge, and electrochemical impedance spectroscopy (EIS) testing.
The area capacity calculation was based on the sum of the area occu-
pied by the finger electrodes and the area between them. The voltage
window was set at 1 V. The frequency range for EIS testing was from
0.01 Hz to 100 kHz, and the bias voltage was set at 5 mV. The electro-
chemical energy storage tests were carried out in a sealed container at
60% RH and 25 °C.
The capacitance of the EC was calculated from theCV curves using
the formula:
C=RVf
ViIðVÞdV
ν*ΔV
ð1Þ
CA=C
Adevice
ð2Þ
Where Cis the capacitance of the EC (F), νisthescanrate(Vs
–1), Iis
the current response (A), V
i
and V
f
are the initial and final voltages (V),
and ΔV(V) is the voltage window. A
device
(cm2) is the sum of the
area occupied by the electrodes and the area between the electrodes.
C
A
(F cm–2) is the areal capacitance of the EC.
The voltage and current of MEG and mp-SC were measured
using a Keithley 2612 multimeter, which was controlled by a
LabView-based data acquisition system. The open-circuit voltage
testing mode was used with a current bias of 0 nA. For current
measurement, the short circuit current testing mode was used with
a voltage bias of 0 V.
Reporting summary
Further information on research design is available in the Nature
Portfolio Reporting Summary linked to this article.
Data availability
The raw data generated in this study are provided in the Supplemen-
tary Information. All data are available from the corresponding author
upon request. Source data are provided with this paper.
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Acknowledgements
This work was supported by the National Natural Science Foundation of
China (No.22035005, L.Q., 52350362, 52022051, 22075165, 52090032,
H.C., 52073159, L.Q., 22175019, Y.L.), Tsinghua-Foshan Innovation Spe-
cial Fund (2020THFS0501, L.Q.).
Author contributions
L.Q., H.C., and Y.L. proposed and supervised this project. L.W. and H.C.
designed the experiments and accomplished the original draft. H.W.,
C.W., J.B., and T.H. contributed to material preparation and the experi-
mental setup. All authors contributed to writing and reviewing the
manuscript.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information The online version contains
supplementary material available at
https://doi.org/10.1038/s41467-024-49393-9.
Correspondence and requests for materials should be addressed to
Yan Li, Huhu Cheng or Liangti Qu.
Peer review information Nature Communications thanks Xingbin Yan,
Weilin Chen, and the other, anonymous, reviewer for their contribution
to the peer review of this work. A peer review file is available.
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