Unveiling the synergistic mechanism of C-F and C-Cl bonds in enhancing the triboelectric performance of fluorinated polymers

Domain: neuroscience
Published: 2026-04-07
Editorial outcome: major_revision

Abstract
Achieving superior tribo-negative performance beyond traditional fluorinated polymers (TFPs) is
crucial for advancing triboelectric devices. In this work, we identified an approach to enhance the tribo-
negative properties of TFPs via synergistic effects of C-F and C-Cl bonds, based on the significant tribo-
differences observed in polyvinylidene fluoride (PVDF) based copolymers. Our findings indicate that the
-CTFE unit, particularly its C-Cl bond, significantly lowers the LUMO of the copolymer system, resulting
in PVDF-CTFE (PC) exhibiting the strongest tribo-negative properties. By controlling the surface Cl/F
ratio via chlorine plasma treatment, it was demonstrated that a higher C-Cl content enhances electron
acquisition, whereas a higher C-F content improves charge retention. The synergistic effect optimally
balances triboelectric charge capture and losses, enabling PC-Cl to achieve the highest triboelectric charge
density (310 µC cm-2) among PVDF copolymers. Our results will provide a versatile strategy for
enhancing a wide range of tribo-negative materials.

Introduction
In the 21st century, the challenges of energy consumption and climate change have prompted
significant attention toward the development of renewable energy sources.1 Among these, the ubiquitous
mechanical energies, such as biomechanical motions, wind and water waves, present considerable
potential as reliable power sources for the numerous electronics distributed worldwide, particularly in
light of the rapid evolution of the Internet of Things.2 To achieve efficient utilization of mechanical
energies, triboelectric nanogenerators (TENGs) that harvest mechanical energies through the coupling of
triboelectrification and electrostatic induction have immediately garnered considerable interest since their
invention.3 Through decades of development, TENGs have shown significant potential for a wide range
of applications, from powering small electronic devices in self-powered systems4 to serving as active
sensors for medical,5,6 human-machine interaction,7,8 environmental monitoring, and security purposes.9
However, TENG still faces a significant gap as a power source compared to traditional energy solutions.
Therefore, continually improving its output performance has always been one of the important goals of
its ongoing development.

Up to date, researchers have achieved notable advancements in improving the output performance
of TENGs by focusing on several key areas. These approaches involve material selection,10 surface
modification,11 composite materials,12 artificial prior-charge injection,13 device structure design (such as
charge excitation,14,15 charge migration,16 quick discharge,17,18 side-discharge restriction,19 and charge
space accumulation,20 etc.), and the regulation of environmental factors (such as vacuum21 and
temperature22). In addition, energy management (EM) strategies23-26 (such as transformers,24 switched
capacitors,25 buck converters,26 etc.) have also been employed to achieve a significant improvement in
energy utilization efficiency. Across these studies, whether focusing on materials or structural designs, the
energy conversion process in TENGs fundamentally hinges on the movement of bound tribo-charges on
the surfaces of dielectric materials, and thereby materials with high triboelectric charge density are crucial
for achieving high-performance TENGs. The material selection strategy, being the most fundamental
approach, currently primarily follows the triboelectric series.27 It is generally accepted that higher fluorine
content leads to a greater triboelectric charge density. Consequently, fluorine-containing polymers such
as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and polyvinylidene fluoride
(PVDF) are commonly chosen for high-performance TENG designs.27-30 However, the selection of
negative polarity materials has seen little advancement since the introduction of TENGs over a decade
ago. Although chemical modifications can modulate the triboelectric polarity of some materials, no reports
have demonstrated materials exceeding the triboelectric charge density of traditional fluorine-containing
polymers. This stagnation highlights a need for further exploration and innovation in material
development for TENGs.

It is well-known that the chemical composition of materials, functional groups, and the interactions
between these functional groups determine their inherent triboelectric properties.31 Specifically, for
fluorine-containing polymers such as PTFE and PVDF, the strong electrophilicity of the fluorine
functional groups leads to their exceptional negative triboelectric polarity. Given that fluorine groups are
the most electrophilic, it becomes crucial to explore the interactions between other functional groups and
fluorine groups. This exploration will be a key approach to developing and designing materials with higher
triboelectric charge density. In our previous research, we created a PVDF/PS composite triboelectric layer
that increased charge density eightfold compared to pure PVDF.16 This enhancement was the result of
optimizing the balance between charge acquisition and losses, driven by the synergistic effects of the
functional groups in both materials. This finding suggests that designing new materials at the molecular
level to interact synergistically with fluorine groups is possible to achieve higher charge densities than
common fluorine-containing polymers. To investigate the interaction effects between different functional
groups and fluorine groups, PVDF and its diverse copolymer varieties (PVDF-TrFE (PT), PVDF-HFP
(PH), PVDF-CTFE (PC), PVDF-TrFE-CFE (PT-CFE), and PVDF-TrFE-CTFE (PT-CTFE)) provide us
with an ideal platform for study. It is regret that current researchers are uncertain about which one has the
strongest tribo-negative properties, leading them to simply choose one at random for TENG
development.32 Therefore, understanding the interactions between functional groups in different
copolymer units and their impact on the triboelectric properties of PVDF copolymers, is crucial for
advancing the development of new high-performance tribo-negative materials.

In this work, we systematically explored the triboelectric properties of PVDF and its copolymers
using density functional theory (DFT) and scanning kelvin probe force microscopy (SKPFM) techniques,
and accurately ranked their electronic capturing capabilities. The results showed that the -CTFE unit
especially its C-Cl groups significantly lower the LUMO energy level of the copolymer system, making
PC exhibit the strongest negative triboelectric polarity. In addition, by controlling the surface Cl/F atomic
ratio on PC through chlorine plasma treatment, we found that C-Cl exhibits a stronger capability for
electron acquisition when tribo-positive materials such as copper was used as a reference, while C-F
demonstrates a greater ability for triboelectric charge retention. The synergistic effect of these two
properties effectively facilitates the capture of triboelectric charge while minimizing loss, allowing PC-
Cl to achieve the highest triboelectric charge density (310 µC cm-2) within the PVDF copolymers. The
new developed chlorinated PC-Cl fibrous membrane was further used to construct an air-permeable smart
insole. By incorporating an AI predictive model, this smart insole can accurately identify individual users,
generate personalized information, and evaluate exercise states. This finding can not only guide the
development of next-generation PVDF copolymers with enhanced negative triboelectric properties but
also hold potential as a universal method to enhance the negative triboelectric polarity of other materials.

Results
Theoretical analysis of the triboelectric properties of PVDF based polymers.

In PVDF based copolymers, macromolecule chains are synthesized from various monomers. Each
type of monomer possesses unique structural characteristics, resulting in different tribo-properties. To
date, commercially available PVDF based copolymers include PVDF, PT, PC, PH, PT-CFE, and PT-CTFE.
From a chemical perspective, the structural unit of PVDF consists of repeating VDF units (-CH
2
-CF
2
-).
Each unit features two hydrogen (H) atoms and two fluorine (F) atoms connected to the same carbon atom,
respectively. In PT, the distinguishing feature of TrFE units (-CHF-CF -) is the presence of three F atoms.
2
In PC, the CTFE units (-CFCl-CF -) include a chlorine (Cl) atom in addition to three F atoms, resulting
2
in a larger molecular volume compared to TrFE. In PT-CFE, the structural unit of CFE (-CH -CFCl-)
2
comprises two H atoms, one F and one Cl. In PH, the unique characteristic of the HFP units (-CF -
2
CF(CF )-) is the presence of three F atoms and a -CF group connected to the main carbon chains, which
3 3
gives the highest F content among the above copolymers’ units. To systematically investigate the impact
of different copolymer units on the electron trapping abilities of PVDF, density functional theory (DFT)
calculations were first performed on six simplified molecular models of the aforementioned PVDF based
polymers.33-35 This analysis aimed to evaluate their tribo-properties at the molecular level. In this study,
each model consists of 10 monomeric units, with the following ratios of -VDF to copolymer units: PVDF
(10:0), PT (8:2), PC (8:2), PH (8:2), PT-CFE (8:1:1), PT-CTFE (8:1:1).

The electrostatic potential distributions for the six molecular models are depicted in Fig. 1a, where
the color gradient from blue to red represents the transition from positive (electron-deficient) to negative
(electron-rich) potential. Due to the strong electronegativity of halogens, the electron-rich areas capable
of accepting electrons are predominantly centered on the F and Cl atoms. In contrast, the electron-deficient
blue regions observed on the carbon skeleton (-C-C-) and methylene (-CH2-) groups confirm their role as
electron-donating components. It can be clearly found that the introduction of different copolymer units
into PVDF chains significantly influences its electrostatic potential values and their distribution,
ultimately leading to distinct triboelectric properties. To elucidate the triboelectric disparities among
PVDF and its copolymers, we investigated their key electron-accepting characteristics, specifically the
lowest unoccupied molecular orbital (LUMO) distributions and vertical electron affinity (VEA). Here,
VEA is defined as the energy difference between the neutral and anionic states, i.e., VEA=E(N)–E(N+1),
where N is the electron count of the neutral system. Fig. 1b depicts the LUMO of the six PVDF based
polymers, respectively, for their optimized geometry. It is evident that the LUMO of the PVDF-based
copolymers is significantly influenced by the introduced copolymer units, leading to a lower LUMO level
compared to pure PVDF. This suggests that the introduced copolymer units enhance the electron-
electron-accepting ability of PVDF, resulting in stronger tribo-negative properties (Fig. 1c). The calculated VEA
presented in Fig. 1d further supports this conclusion. In addition, it is also important to note that, among
these PVDF based copolymers, PC exhibits the lowest LUMO energy level, making it the most effective
at acquiring electrons. This finding suggests that the introduction of C-Cl structures, in contrast to C-F
and C-CF , significantly lowers the LUMO in these polymers. Subsequently, we employed charge
3
decomposition analysis (CDA) to analyze the impact of different molecular fragment structures on the
frontier orbitals, particularly the LUMO, to explain how the introduction of C-Cl enhances the electron-
accepting ability of these polymers. As shown in the Supplementary Fig. 1, the LUMO of PC is primarily
contributed by the -CTFE fragment, while the -VDF fragment is associated with higher-energy
unoccupied orbitals. Among these fragments, the LUMO of -CTFE is significantly lower than that of -
VDF, which can be attributed to the σ* bond formed by the p orbitals of carbon (p (C)) and chlorine
z z
(p (Cl)). Similarly, the LUMO of PT-CTFE and PT-CFE is also much lower than that of PVDF, PT, and
z
PH for the same reason. Based on these theoretical results, the electron acquisition ability of the PVDF-
based polymers, listed from weakest to strongest, is as follows: PVDF, PT, PH, PT-CFE, PT-CTFE, and
PC.

Tribo-differences among PVDF based polymers in membrane form.

To experimentally verify the above simulation results, scanning kelvin probe force microscopy
(SKPFM) was employed to analyze the effect of introducing copolymer units on the surface potential of
PVDF. In the experiment, commercially available PVDF-based copolymers were initially processed into
films on a conductive substrate using the spin-coating method. Each polymer with the following ratios of
-VDF to copolymer units: PVDF (10:0), PT (7:3), PC (7:3), PH (8.5:1.5), PT-CFE (6:3:1), PT-CTFE (6:3:1).
The morphology of these films is characterized and presented in Supplementary Fig. 2.
Subsequently, contact mode was employed to engage a Pt-coated probe with the sample surface through
friction, after which the surface potential was measured using the SKPFM mode. Since PVDF based
polymers are more tribo-negative than Pt, electrons transfer from the Pt tip to the surfaces of the polymers
occurs when they come into contacted, as schematically illustrated in Fig. 2a. It can be observed that
PVDF and PC exhibit the lowest and highest surface potentials, respectively, with values of approximately
-224.8 mV and -538.4 mV (Fig. 2b, and Supplementary Fig. 3). The error bars represent the standard
deviation based on five independent replicates (Supplementary Table 1). In addition, TENGs composed
of PVDF based copolymers (with area of 4 cm × 4 cm) were constructed to verify the differences in their
tribo-properties. The thickness of these films was maintained at approximately 30 μm (Supplementary
Fig. 4). As shown in Fig. 2c, the output voltages, list from lowest to highest, are PVDF, PH, PT, PT-CFE,
PT-CTFE, and PC, which aligns with the variation trend observed in the surface potential. However, it is
important to note that the experimental results show some discrepancies compared to the theoretical
predictions regarding the tribo-properties of PT and PH. Since there is no significant difference in their
surface roughness (Supplementary Fig. 5-11), the main reasons for this difference may conclude as
follows: (1) the presence of the -CF group, which introduces significant steric resistance, resulting in
3
lower crystallinity and polar phase (β and γ) content compared to other polymers (Supplementary Fig.
12); (2) a lower dielectric constant (Supplementary Fig. 13); (3) a lower HFP ratio in commercially
available PH compared to other copolymers, making its tribo-property more similar to that of PVDF. All
of the above factors contribute to the observed experimental tribo-negative property of PH being weaker
than that of PT. Based on these results, the triboelectric series of PVDF-based copolymers in membrane
can be ranked from weakest to strongest as follows: PVDF, PH, PT, PT-CFE, PT-CTFE, and PC (Fig. 2d).

Tribo-differences among PVDF based polymers in electrospun nanofiber form.

Electrospinning is a vital technique for producing high-performance tribo-materials, particularly for
ferroelectric polymers. During the electrospinning process, PVDF-based polymers undergo uniaxial
stretching and high-voltage electric field polarization, leading to the formation of a nanofiber-based rough
film (Fig. 3a). Importantly, this process also enhances their crystallinity and significantly increases the
content of the β-phase, which subsequently modifies their triboelectric properties. To further investigate
the effect of different copolymer units on the triboelectric properties of PVDF in electrospun nanofiber
form, six types of PVDF-based polymers were prepared, as shown in Fig. 3b. All these polymers formed
well-defined nanofibers with no preferred orientation, with diameters ranging from hundreds of
nanometers to several micrometers. The diameter distribution histograms for each sample are shown in
Supplementary Fig. 14. The average diameters of 0.99± 0.33 μm (PVDF), 1.38 ± 0.55 μm (PT), 1.37 ±
0.40 μm (PT-CFE), 1.15 ± 0.36 μm (PT-CTFE), 1.45 ± 0.37 μm (PH), 1.11 ± 0.22 μm (PC) for each
sample can be yielded. By comparing the XRD patterns of PVDF-based polymers in both electrospun
nanofiber (Fig. 3c) and film (Supplementary Fig. 12a) forms, variations in the intensity of characteristic
peaks corresponding to the α-phase and β-phase were clearly observed after electrospinning. Notably, the
relative intensity of the α-phase diffraction peak was substantially reduced following the electrospinning
process. The crystallinity and the content of the polarized phase were further calculated and analyzed
based on their XRD and FTIR spectra. The results presented in Supplementary Fig. 15 indicate that both
crystallinity and β-phase content in all polymers have significantly increased, and the differences among
the six samples have become minimal. Subsequently, single nanofiber SKPM tests were conducted on
each sample (Supplementary Fig. 16), with the results displayed in Fig. 3d, and Supplementary Fig. 17.
The inset shows the 3D morphology of a PVDF nanofiber. The error bars represent the standard deviation
based on five independent replicates (Supplementary Table 2). Since the polar phase modulates the surface
potential, a higher content of polar phases generally shifts the surface potential toward more negative
values, reflecting enhanced electron affinity. Meanwhile, higher crystallinity usually corresponds to a
larger dielectric constant, which amplifies the electrostatic induction effect. Consequently, the surface
potential of the PVDF-based electrospun nanofibers is significantly increased, as shown in Fig. 3d. It
should be noted that PC still demonstrates the most negative triboelectric behavior even though neither
its crystallinity nor its polar phase content is the highest. This further highlights the important role of the
chemical composition of PC in achieving superior triboelectric performance. In addition, PH nanofiber
exhibits a significant enhancement in negative tribo-property compared to PH in solid membrane form,
surpassing even those of PT and PT-CFE. This improvement can be attributed to the markedly increased
crystallinity and polar phase content of PH (membrane form: crystallinity 65.6% and polar phase 43.3%,
nanofiber form: crystallinity 74.5% and polar phase 84.1%, Supplementary Fig. 12 and 15). As a result,
the triboelectric series of PVDF-based copolymers in electrospun nanofiber form can be ranked from
weakest to strongest as follows: PVDF, PT, PT- CFE, PH, PT-CTFE, and PC (Fig. 3e).

Role of C-F and C-Cl bonds in enhancing the tribo-negative properties of PC.

According to the theoretical and experimental results we discussed above, the notable tribo-negative
property of PC underscores the significant role of the C-Cl structure in enhancing this characteristic. More
importantly, this finding challenges the conventional understanding that a higher fluorine content leads to
stronger tribo-negative properties. In contrast, a combination of C-F and C-Cl in PC show us a possible
approach to further enhance the tribo-negative properties of fluorine-contained polymers. Building on this
hypothesis, we sought to introduce additional C-Cl groups on the PC surface using chlorine plasma
treatment (Fig. 4a) to investigate the synergistic mechanism between the C-Cl and C-F functional groups.
Due to the high-energy Cl plasma randomly bombarding the PC surface (PC-Cl), it may replace H or F in
the molecular chain of PC. Taking the introduction of a Cl substitution as an example, we can identify
four different scenarios based on the chemical environment of the substituted atom: replacing the H in the
-VDF unit (PC-Cl-Ⅰ), replacing the F in the -VDF unit (PC-Cl-Ⅱ), replacing the F in the -CF - of the -
2
CTFE unit (PC-Cl-Ⅲ), and replacing the F in the -C(FCl)- of the -CTFE unit (PC-Cl-Ⅳ), as schematically
shown in Fig. 4b. We still employed CDA to analyze the impact of different Cl-substitution molecular
fragment structures on the frontier orbitals of the PC, particularly the LUMO, to elucidate how the extra
introduction of C-Cl bonds enhances the electron-accepting ability of PC. As illustrated in Fig. 4c and
Supplementary Fig. 18, the effects of Cl substitution on the molecular orbital energy levels vary depending
on the sites of substitution. However, all substituted structures demonstrate a reduction in the LUMO
energy level compared to the original structure. This reduction is primarily due to the σ anti-bonding
orbital contributed by the p orbitals of carbon (pz(C)) and chlorine (p (Cl)). Notably, the significant
z z
decrease in the LUMO energy of PC-Cl-I can also be attributed to Cl’s higher electronegativity compared
to H. Therefore, the strategic introduction of Cl atoms theoretically enhances the electron affinity of the
PC.

Influence of surface Cl:F atomic ratio on the tribo-negative properties of PC.

To verify the impact of Cl content on the triboelectric properties of the PC-Cl, we subjected the PC
to Cl plasma treatment for varying durations (0, 1, 3, and 5 min). X-ray photoelectron spectroscopy (XPS)
analysis clearly shows that the intensity of the characteristic Cl peaks (Cl 1s and Cl 2p) gradually increases
with longer treatment times (Fig. 4d and 4e). The high-resolution Cl 2p spectrum of the plasma-treated
sample reveals a characteristic doublet at binding energies of approximately 200.8 eV (Cl 2p ) and 202.4
3/2
eV (Cl 2p
1/2
), as shown in Supplementary Fig. 19. This spectral feature is a definitive signature of
covalently bonded organic chlorine (C-Cl bonds). Meanwhile, the roughness of PC-Cl increases from 29.7
nm to 46.5 nm (Supplementary Fig. 20). Based on the XPS data, we calculated the atomic ratio of Cl to F
(Cl:F) in the surface layer of PC-Cl, which is presented in the Fig. 4f and Supplementary Table 3. The
results indicate that Cl plasma treatment significantly enhances the Cl content on the PC-Cl surface, with
the Cl:F ratio increasing from 0.6 for PC-Cl (0 min) to 2.4 for PC-Cl (5 min). With copper as a reference,
the output charge density of PC-Cl samples was measured. It can be observed that the output charge
density of PC-Cl does not increase concurrently with the rising Cl:F ratio and surface roughness. Instead,
it reaches a maximum value of 25 nC/cm² when the Cl:F ratio is 1.8 (Fig. 4g), with a corresponding
roughness is 38.4 nm. This result suggests that only an optimal Cl:F ratio can maximize the negative
triboelectric performance of PC-Cl. To better understand the reason for this phenomenon, we further
investigate the tribo-charge retention capacity of C-F and C-Cl structures, as the output charge density is
ultimately determined by a balance between tribo-charge acquisition and loss processes. After the PC-Cl
has accumulated tribo-charges to a stable level, its charge keeping rate was evaluated through single-cycle
intermittent testing with a time interval of 10 min. The corresponding working curve of the linear motor
is shown in Supplementary Fig. 21. The triboelectric charge retention rate versus time curves for PC films
with different surface C-Cl bond contents are shown in Supplementary Fig. 22. It can be observed that the
tribo-charge retention rate of the PC-Cl significantly decreases as the increase of Cl:F ratio (Fig. 4h). This
result demonstrates that C-Cl and C-F exhibit distinct performances in withdrawing tribo-charges. The
weaker charge retention ability of PC-Cl, which contains more C-Cl structures compared to those with
higher proportion of C-F structures, can be explained by the lower atomic electronegativity of Cl relative
to F. This observation is further supported by the triboelectric performance of commercial PTFE
(thickness of ~50 μm), PCTFE (thickness of ~50 μm), and chlorine plasma-treated PCTFE (thickness of
~50 μm), as shown in Supplementary Fig. 23-25. Based on these results, we can conclude that a higher
concentration of C-Cl structures in the polymer facilitate easier charge acquisition and faster charge loss
processes, whereas C-F structures demonstrate the opposite behavior. Therefore, only an appropriate ratio
of C-F and C-Cl can achieve a balance in the acquisition and loss of tribo-charges, resulting in optimal
triboelectric performance. This is also why the best triboelectric performance was observed in the
experiment when the Cl:F ratio was 1.8 in PC-Cl. To verify the general applicability of our findings, we
extended the conclusion to non-fluorinated polymer materials, such as polyethylene (PE). Commercially
available PE films (thickness of ~25 μm) were treated using fluorine, chlorine, and fluorine/chlorine
composite plasmas, respectively. The surface roughness of the four PE films is shown in Supplementary
Fig. 26. XPS analysis confirmed that after plasma treatment, corresponding F and/or Cl elements were
successfully introduced onto the PE film surfaces, forming C-F and C-Cl bonds (Supplementary Fig. 27).
Tests on their triboelectric output performance (Supplementary Fig. 28a) revealed that all plasma-treated
PE films exhibited a significant increase in output voltage compared to the pristine PE film. This is
because both fluorine and chlorine possess higher electronegativity than the original C-H/C-C backbone,
thereby enhancing the electron-accepting ability of the material. It is particularly noteworthy that among
all treatments, the sample treated with the fluorine/chlorine composite plasma showed the highest output
voltage. The triboelectric charge retention capability of different films (Supplementary Fig. 28b and 29)
also indicated that although the introduction of C-Cl bonds can improve the output, compared to the
introduction of C-F bonds alone, it also accelerates the decay of triboelectric charges (weaker charge
retention capability). This observation is entirely consistent with our earlier discussion on the roles of C-
F and C-Cl bonds in PVDF-based copolymers, strongly supporting that our key finding.

High-performance TENG based on PC-Cl nanofibers.

By utilizing the synergistic effect of C-F and C-Cl, we developed a high performance TENG based
on PC-Cl and nylon nanofibers. The working mechanism of this TENG relies on the coupling effects of
triboelectrification and electrostatic induction. As shown in Fig. 5a, when PC-Cl and nylon nanofibers
come into contact and then separate, they exchange electrons due to their differing electron affinities,
resulting in a charge imbalance. This imbalance creates a potential difference between the electrodes on
their backside. When connected to an external circuit, this potential difference drives the flow of electrons,
generating electrical energy. The optical image of the fabricated TENG with an active area of 16 cm2 is
shown in Fig. 5b. The thickness of PC-Cl nanofiber membrane is about 19.3 μm in this device
(Supplementary Fig. 30). According to Maxwell’s displacement current theory, the output performance
of the TENG is very sensitive to the external stimuli. With the applied force increasing, more sites of the
frictional layer come into contact, resulting in an increase in output voltage and current from 468 V and
23 μA to 643 V and 35 μA, respectively (Supplementary Fig. 31). Additionally, as the driving frequency
increases, the peak value of the output voltage and current rise due to the rapid charge transfer process in
the external circuit (Supplementary Fig. 32). When we simulate external environmental stimuli by rapidly
striking the TENG with our hand, the maximum output voltage and current can reach 957 V and 388 µA,
respectively (Fig. 5c and 5d). The corresponding charge density can reach 310 µC cm-2 (Supplementary
Fig. 33), which represents the highest intrinsic charge density of PVDF-based polymer materials reported
among previous studies (Fig. 5e).36-41 Its excellent output performance enables it to directly power a
thermohygrometer without the need for an energy storage process (see inset in Fig. 5d and Supplementary
Movie 1). The generated electrical energy can also be stored in capacitors for use in high-energy
consumption devices, as illustrated in Fig. 5f. Given that the external load significantly affects the output
power of the TENG, the relationships between output current and external load resistance of the TENG
was also recorded and plotted in Fig. 4g. According to Ohm’s law of P = I2R, where P, I, and R are the
output power, current, and external load resistance, respectively, the maximum output power density of
the TENG is approximately 43 W m-2 at a loading resistance of 50 MΩ. In addition, a longevity test of
the TENG is likewise carried out, and the output voltage keeps stable in ~4500 working cycles without
any degradation (Fig. 5h), which shows its excellent durability and stability.

Application of the PC-Cl nanofibers based TENG.

PVDF based polymers not only exhibit excellent negative triboelectric properties but also are the
most easily processed among fluoropolymers. They can be effortlessly transformed into breathable
nanofiber nonwoven fabrics, making them perfectly suited for applications in wearable self-powered
electronic devices, such as electronic skin and motion monitoring. To ensure optimal breathability of the
TENG device, PC-Cl nanofiber membranes are applied to both sides of a breathability carbon nanofiber
cloth (Supplementary Fig. 34a), which serves as the electrode in the TENG. This configuration allows for
the fabrication of a single-electrode TENG, with its physical diagram presented in Supplementary Fig.
34b. The prepared TENG features a three-layer structure, which can be clearly observed from its cross-
sectional image (Supplementary Fig. 35), and exhibits excellent breathability (Supplementary Fig. 36).
When the TENG is activated by human motion, the PC-Cl nanofiber will rub against the skin or clothing,
and thereby transforming biomechanical energy into electric energy. Since the movement states of
different body parts vary significantly in terms of amplitude and frequency, the output signals exhibit
distinct waveforms and amplitudes. As a result, this variation enables the TENG to be used effectively for
monitoring human motions (Supplementary Fig. 37).

To move beyond traditional data analysis methods, we further integrated artificial intelligence (AI),
including machine learning and deep learning, with TENG technology to achieve efficient and accurate
data analysis in monitoring and interpreting biomechanical signals. In the experiment, the breathable PC-
Cl nanofiber based TENG was remodeled as a smart insole as an example. By incorporating AI predictive
models, the TENG-based insole can identify individual users, generate personalized information, and
evaluate exercise states. The fundamental layout and workflow of the smart insole are depicted in Fig. 6a.
Deep learning models (1D-CNN and Transformer, as shown in Fig. 6b and Supplementary Fig. 38) and
machine learning models (Random Forest Classifier, Gradient Boosting Classifier, and Extra Trees
Classifier, illustrated in Supplementary Fig. 38) were selected to evaluate the applicability and advantages
of various algorithms for individual identification and human motion recognition. During the experiment,
six participants weighing between 45 and 90 kg were invited to perform identical stepping motions while
wearing shoes equipped with the smart insole. Each participant records over 70 sensing signals, with the
typical sensor outputs from different participants presented in Fig. 6c. According to these data, a machine
learning dataset is constructed by extracting features from time series data and a deep learning dataset is
constructed by reducing the dimensionality of the original data. We then build five prediction models to
identify and analyze gait data. Among the deep learning models, the 1D-CNN model demonstrated
superior performance compared to the Transformer, achieving a remarkable classification accuracy of
99.2% in the people identification task (Fig. 6d and Supplementary Fig. 39). This indicates that the 1D-
CNN model can effectively capture local features of time series data, providing robust support for
distinguishing complex motion patterns. In contrast, the Transformer model attained a classification
accuracy of 87.1%, showing slightly lower accuracy and recall (Fig. 6d and Supplementary Fig. 39). This
discrepancy may stem from the Transformer's limited ability to capture local data features, highlighting
the need for further optimization in multi-categoric complex tasks. As for the three machine learning
models (Random Forest Classifier, Gradient Boosting Classifier), all of them achieved a classification
accuracy of 100%, highlighting the powerful classification capabilities of traditional machine learning
techniques when combined with effective feature extraction (Fig. 6d and Supplementary Fig. 39).
Building on the smart insole's capabilities for person recognition, we applied the same algorithmic models
to assess the motion types of two volunteers (walk, jump, and run). The typical sensor outputs from
various participants across these different activities are illustrated in Fig. 6e. The three types of movements
performed by the two participators can be categorized as six distinct motion states, which were classified
using machine learning and deep learning models. According to the confusion matrices (Fig. 6f and
Supplementary Fig. 40), the classification accuracy for the 1D-CNN model was 99.8%, while the
Transformer model achieved 99.5%. Additionally, the Random Forest, Gradient Boosting, and Extra Trees
model all attained a classification accuracy of 100% (Fig. 6f and Supplementary Fig. 40). The results from
these five models not only confirm the successful identification of individuals but also accurately classify
their corresponding motion states. Notably, the recognition of identical motion states among different
individuals occurred without interference. Consequently, these findings substantiate that the PC-Cl
nanofiber based TENG demonstrates exceptional precision and sensitivity in the recognition of multiple
motion states across diverse individuals.

Methods
Chemicals and reagents
Nylon powder (from BASF SE), formic acid solution (85% purity, from Shanghai McLean
Biochemical Science and Technology Co., Ltd.), N, N-dimethylformamide (DMF, purity ≥99.5%, from
Tianjin Fuyu Fine Chemical Co., Ltd.), anhydrous ethanol (purity ≥99.7%, Sinopharm Chemical Reagent
Co.), PVDF and its copolymers were purchased from Shanghai Claman Reagent Co. Ltd, and Shanghai
Jadel Chemical Technology Co., Ltd.

Preparation of PVDF and its copolymers films
0.5 g of polymer was weighed and added into 6 g of DMF, and the polymer was completely dissolved
by stirring at 60 ℃, then the solution was spin-coated on the glass substrate by using a spin-coater, and
then put into an oven to be heated at 110 ℃ for 2 h. The films were then peeled off from the substrate for
subsequent experiments. The films used for testing AFM and SKPM were prepared using platinum-plated
silicon wafers as the substrate.

Preparation of PVDF and its copolymers nanofibers
0.5 g of polymer was weighed and added into a beaker, then 1.5 g of acetone was added, and then
4.5 g of DMF was added, and the polymer was completely dissolved by stirring at 60℃, and then the
fiber membrane was prepared by electrostatic spinning (the applied voltage of 17 kV, liquid propulsion
speed of 1.8 mL h-1) the sample prepared by electrostatic spinning is dried in a ventilated oven at 60 ℃
for 1 h. In the production of the samples required for SKPM, the fibers will be spun to platinum-plated
silicon wafers, and then the samples are placed in the oven to be dried at 60 ℃ for 12 h to eliminate the
static influence of the high-voltage field, and after that the samples are subjected to the SKPM to test their
surface potential.

Preparation of nylon fibers
0.5 g of nylon powder was weighed and added to 2 g of formic acid solution (85%), and stirred at
60°C until the polymer was completely dissolved, after which the nylon solution was electrostatically
spun (applied voltage of 16 kV, liquid propulsion rate of 1.5 mL h-1). The samples were then dried in an
oven at 60 °C for 1 h.

Fabrication of the arch TENG device
Kapton is used as the substrate material. Ag layer, i.e. electrode layer, is deposited on Kapton by
magnetron sputtering with magnetron sputtering stage. Nylon fiber membrane is prepared on the electrode
layer as positive triboelectric material by electrostatic spinning, and negative triboelectric fiber membrane
is prepared by the same method. After that, the two parts are connected and fixed by Kapton tape. Cu wire
is used as the conductive wire.

Fabrication method of breathable TENG device
First, the PC electrospinning precursor liquid was loaded into the liquid pushing device. The working
voltage of the electrospinning machine was set to 17 kV, with a liquid flow rate of 1.8 mL h-1 and a
distance of 15 cm from the needle to the sample. The carbon fiber membrane was then fixed onto the
receiving plate to allow for the deposition of PC nanofibers on the carbon fiber membrane. At the end of
the electrospinning process, the carbon fiber covered with PC nanofibers was removed, and copper wires
were attached to the carbon fiber for connection to the electrometer. Medical breathable tape was used to
secure the device at each joint of the human body during energy harvesting tests.

Plasma treatment of polymers
The PC sample was placed in the inductively coupled plasma etcher (ICP) (etching gas: CCl /Ar (5%
vol), etching gas pressure: 3 Pa, etching power:100 W), the etching time is adjusted according to the
experiment. For the PE film, etching gas: CCl /Ar (5% vol) or CF /Ar (5% vol), etching gas pressure: 3
Pa, etching power:100 W, the etching time is adjusted according to the experiment.

Electric measurement
A low-noise voltage preamplifier (SR560 ) and a current preamplifier (SR570) (Stanford Research
Systems) were used to amplify the voltage and current outputs, respectively. The amplified signals were
subsequently acquired by a data acquisition card (PCI-6259, National Instruments) and processed using a
custom LabVIEW program.

Water vapor transmission rate (WVTR) test
Performed at 20.9 °C with a humidity of 47.7 %. 2 ml of deionized water was placed in a glass vial
and sealed completely by the sample. The mass of water lost is tested at regular intervals. The WVTR is
calculated by dividing the mass of water lost by the area of the opening and the duration.

Density functional theory calculation
All computations were conducted using the Gaussian 16 software package.33 Geometry
optimizations were carried out at the M06-2X/6-31G(d) level of theory.34,35 The vertical electron affinity
(VEA) was calculated as the energy difference between the neutral and anionic species, i.e., VEA=E(N)–
E(N+1), where N and N+1 denote the electron counts of the system before and after electron attachment,
respectively.

Written informed consent of volunteers
Written informed consent was received from all volunteers.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In the manuscript titled “Unveiling the Synergistic Mechanism of C-F and C-Cl Bonds in Enhancing the Triboelectric Performance of Fluorinated Polymers,” the authors proposed a novel strategy to improve the triboelectric properties of fluorinated polymers by exploiting the synergistic effects between C–F and C–Cl bonds. Through a combination of experimental characterizations, theoretical calculations, and device demonstrations, the study highlights how vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) co-polymers exhibit enhanced charge transfer ability and triboelectric output relative to conventional PVDF-based materials. The work further integrates the modified materials into a wearable triboelectric nanogenerator (TENG) for energy harvesting and human motion sensing applications, showing strongly improved electrical and mechanical performance. While the manuscript offers valuable insights, the following concerns should be satisfactorily addressed before recommending the work for publication.\n1.Could the authors revise the caption for Figure 2 to be arranged alphabetically and clearly formatted for better readability?\n2.The authors have added standard deviation to their data; please specify the number of replicates.\n3.For the electrospun nanofiber membranes, the authors should provide quantitative data on the uniformity of fiber orientation and thickness across the device area. Inclusion of SEM mapping and statistical analysis of fiber diameter and membrane thickness is recommended.\n4.Would the authors consider including polarization–electric field (P–E) hysteresis loops or polarization charge density versus time graphs to better visualize the dipole behavior, charge retention, and fatigue characteristics of the materials?\n5.The authors are encouraged to include measurements of air permeability or specific surface area of the electrospun membranes using Brunauer–Emmett–Teller (BET) analysis or equivalent techniques, to elucidate the relationship between membrane microstructure and triboelectric performance.\n6.Can the authors conduct a more detailed analysis on how variations in crystallinity and phase content (such as α, β, γ phases in PVDF) caused by electrospinning influence the triboelectric output?\n7.Does the work provide sufficient multi-technique characterization (e.g., confirming composition, structure, and surface chemistry)? The authors mention XPS, FTIR, XRD, AFM, SKPFM, but figures could more explicitly compare C-F and C-Cl bonds and quantify their ratios after plasma treatment.\n8.How do environmental factors such as sweat, temperature fluctuations, and mechanical abrasion encountered during daily wear or application impact the durability, triboelectric stability, and overall performance of the device? Could testing under these realistic conditions provide more practical insights?", "reviewer_2": "The authors claim that synergistic effects between C–F and C–Cl bonds in PVDF-based copolymers lead to very high triboelectric charge density. The authors also present an electrospun, plasma-treated TENG insole with AI-based gait recognition as an application example. The topic is interesting and potentially relevant. However, the experimental evidence provided in the manuscript does not convincingly support the proposed mechanism.\nThe first major issue is that the manuscript does not clearly separate chemical effects from processing effects. The authors compare spin-coated films, electrospun nanofibers, and plasma-treated nanofibers. These samples are structurally very different: they have different morphology, different chain packing, different β-phase content, different surface roughness, and different effective contact area. PVDF-based polymers are also known to rearrange differently depending on the solvent used for casting or dissolution, and such solvent-dependent rearrangement can change both crystallinity and surface potential. In the manuscript, these factors are not controlled or normalized. As a result, it is not possible to conclude that the improved performance mainly comes from the proposed “C–F / C–Cl synergy.” The performance could instead be dominated by differences in morphology, phase content, roughness, or solvent history.\nThe second issue is that the effect of chlorine plasma treatment on the polymer is not sufficiently characterized. The manuscript assumes that plasma treatment simply adjusts the Cl:F ratio and creates an optimal balance between C–Cl (for charge capture) and C–F (for charge retention. However, the manuscript does not provide direct evidence of what the plasma is actually doing to the polymer. For example, it is not clear whether new C–Cl bonds are truly formed, how deeply chlorine is incorporated, whether the polymer backbone is damaged, or whether the dielectric behavior is altered. Without this information, the proposed mechanism behind the improved triboelectric performance remains unproven.\nThe third issue is that the triboelectric performance data are compared across samples that were not fabricated or tested under the same conditions. Because the device structures, surface states, and even test conditions are not clearly kept constant, the reported performance differences cannot be independently evaluated or fairly compared.\nThe manuscript does not yet demonstrate that the claimed chemical mechanism is responsible for the reported performance. The chemical effects are not isolated from morphology and solvent-driven rearrangement, the plasma-induced chemistry is not verified, the device comparisons are not normalized, and the definition and evaluation of the key performance metrics are not clearly established. For this reason, the reviewer cannot recommend publication in this journal.", "reviewer_3": "This manuscript, titled “Unveiling the Synergistic Mechanism of C–F and C–Cl Bonds in Enhancing the Triboelectric Performance of Fluorinated Polymers” by Liu et al., proposes a novel approach to enhance the contact electrification of PVDF and its copolymers, including P(VDF-TrFE), P(VDF-HFP), P(VDF-TrFE-CFE), P(VDF-TrFE-CTFE), and P(VDF-CTFE), through the synergistic effects of C–F and C–Cl bonds. The results suggest that PVDF-CTFE (PC) exhibits the strongest tribo-negative properties. Additionally, it was found that the surface Cl/F atomic ratio in PC influences the output performance of TENG. An increase in C–Cl content enhances electron acquisition in contact with tribo-positive materials, while a higher C–F content improves charge retention. Finally, PC-Cl was developed for an air-permeable smart insole that incorporates AI predictive models for accurate user identification and exercise-state evaluation.\nThe findings and the proposed strategy for enhancing the tribo-negative property are interesting. However, the manuscript lacks a systematic examination of the theory supported by sufficient experimental data. The effects of certain variables on the output performance of TENGs during the comparison of PVDF copolymers such as the roughness and thickness of the dielectric layers have been neglected. Additionally, the possibility of extending this strategy to a wider range of materials has not been demonstrated. Hence, at its current stage, the work cannot be accepted in Nature Communications. The following specific questions and issues must be addressed before the manuscript can be considered for further review.\n1. Thickness plays a critical role in TENG results. Therefore, the authors should provide detailed information on the thickness of all samples, as variations in this parameter can significantly influence the triboelectric performance.\n• What was the thickness of the samples used for TENG measurements in Figure 2C? Did the authors measure and control the thickness in this case?\n• Similar to the films, did the authors check and control the thickness of electrospun mats?\n• What was the thickness of the commercial PTFE and PCTFE films discussed in Figures S11 and S12?\n2. Line 227–232: “PH nanofiber shows a significant enhancement in negative tribo-property, surpassing that of PT and PT-CFE. This improvement may be attributed to its markedly increased crystallinity and polar phase content (Figure S7c).” This explanation does not appear to support the reported results. As shown in Figure S7, the crystallinity of PH is lower than that of PT and PT-CFE. Similarly, the polar phase content of PH is not the highest among these samples. Please provide a more consistent discussion of these findings and support your explanation with relevant references.\n3. Although AFM is a powerful tool for measuring the roughness of samples, its measurement area is very small, whereas the TENG contact surfaces are relatively large (4 × 4 cm²). Could the authors investigate the large-scale roughness of the samples both lab-prepared and commercial in order to provide a more representative assessment?\n4. Could the authors expand their findings to other materials by chemical modification under controlled conditions? For example, imparting Cl and F groups to chemically modified substances such as cellulose paper or non-fluorinated polymers would help demonstrate whether their findings are applicable to a wider range of materials.\n5. All abbreviations in the abstract and the main text should be defined at their first occurrence. For example PVDF, PTFE, FEP, etc."}, "author_response": "Thank you very much for your valuable comments, which are very helpful for revising and improving our manuscript. We have revised the manuscript carefully in accordance with your comments point-by-point. And all changes are indicated in highlights in the marked copy of the revised manuscript. The responses to all comments are listed as follows. We hope that the responses and revisions could meet with your approval.\n1. Could the authors revise the caption for Figure 2 to be arranged alphabetically and clearly formatted for better readability?\nResponse: Thank you very much for your careful review of this paper and insightful questions. We have reorganized Figure 2 in alphabetical order to improve clarity and ensure visual consistency throughout, as shown in Revised Figure 2.\nRevised Figure 2 Experimental analysis of the triboelectric properties of PVDF based polymers in membrane form. (a) Schematic of the triboelectrification effect. (b) Surface potential differences when various copolymer units are introduced into PVDF. Inset is a SEM image of the PC film. (c) The TENG based electric output differences when various copolymer units are introduced into PVDF, with PVDF used as a reference. (d) Triboelectric series of the PVDF based polymers in membrane form.\n2. The authors have added standard deviation to their data; please specify the number of replicates.\nResponse: Thank you very much for your valuable comments. The error bars represent the standard deviation based on five independent replicates in Figure 2b and Figure 3d. We have now clarified this in the revised manuscript. The detailed data is shown in Table R1 and R2 (corresponding to Table S1 and Table S2 in the Supporting Information) as below:\nTable R1 Surface potential of various PVDF copolymer in membrane form. Materials Surface potential/mV Average/mV Error/mV PVDF -190.64 -191.75 -223.13 -267.57 -250.88 -224.79 34.54 PT -405.31 -314.47 -363.65 -304.61 -328.09 -343.23 41.29 PT-CFE -522.51 -445.33 -403.69 -424.19 -372.68 -433.68 56.43 PT-CTFE -522.23 -403.49 -443.95 -540.42 -509.33 -483.88 57.82 PH -520.59 -527.45 -536.83 -518.72 -499.37 -520.59 13.82 PC -637.57 -549.20 -510.25 -500.02 -494.69 -538.35 59.43\nTable R2 Surface potential of various PVDF copolymer in nanofiber form. Materials Surface potential/mV Average/mV Error/mV PVDF -576.11 -574.26 -560.85 -571.28 -558.48 -568.19 32.07 PT -594.42 -598.46 -596.21 -594.02 -592.19 -595.06 9.51 PT-CFE -671.27 -686.43 -689.91 -682.38 -691.86 -684.37 32.66 PH -713.66 -711.05 -712.55 -718.95 -718.74 -714.99 14.56 PT-CTFE -822.18 -804.65 -796.97 -804.54 -814.26 -808.52 39.18 PC -883.29 -882.15 -878.54 -880.04 -882.30 -881.26 7.72\n3. For the electrospun nanofiber membranes, the authors should provide quantitative data on the uniformity of fiber orientation and thickness across the device area. Inclusion of SEM mapping and statistical analysis of fiber diameter and membrane thickness is recommended.\nResponse: Thank you very much for your careful review and valuable suggestion regarding the quantitative characterization of our electrospun nanofibers. We fully agree that statistical data are crucial for evaluating material uniformity. According to your comment, we have supplemented the manuscript with the following quantitative analyses:\n1. Assessment of nanofiber orientation. The nanofibers in this study (e.g., in Figures 3, 5 and S33) were fabricated using a static electrospinning setup as shown in Figure R1. In this configuration, electrospinning nanofibers are deposited randomly on the collector, resulting in nanofibers without a preferred orientation. A representative large-area SEM images of PC and PT (Figure R2) visually confirms this isotropic, random network structure.\n2. Quantitative statistical analysis of nanofiber diameter. As suggested, we have performed statistical analysis on the SEM images presented in the original Figures 3b. The diameter distribution histograms for each sample are shown in Figure R3, which are now provided as Figure S14 in the Supporting Information. The average diameters of 0.99± 0.33 μm (PVDF), 1.38 ± 0.55 μm (PT), 1.37 ± 0.40 μm (PT-CFE), 1.15 ± 0.36 μm (PT-CTFE), 1.45 ± 0.37 μm (PH), 1.11 ± 0.22 μm (PC) for each sample can be yielded. It should be noted that the PC nanofiber membrane used in Figure 5 and Figure S33 were prepared under the same electrospinning conditions as those in Figure 3b. Therefore, their average diameter is likewise 1.11 ± 0.22 μm.\n3. Thickness of the nanofiber membranes. The samples shown in Figure 3b were prepared primarily to characterize the morphology of different PVDF based copolymer nanofibers, enabling fundamental property screening via single nanofiber SKPFM. A representative image of isolated nanofibers on a Pt-coated Si substrate, used for SKPFM analysis, is provided in Figure R4. This nanoscale measurement probes the surface potential directly on individual nanofibers, thereby eliminating interference from macroscopic membrane properties, such as thickness and porosity, which are inherently difficult to control consistently across different samples in the electrospinning process. Consequently, these samples were not integrated into macroscopic TENG devices for intrinsic tribo-property characterization, and their thickness was neither controlled nor optimized in this part. Therefore, thickness characterization was not performed on these samples, and we kindly ask for the reviewer’s understanding.\nTo address the core concern behind the suggestion, we wish to highlight that for all device-grade films used in functional TENG fabrication (e.g., in Figures 5, and S33), we have now added the corresponding thickness characterization. Cross-sectional SEM measurements taken from the periphery to the center (along the diagonal direction) confirm an average thickness of ~19.3 μm, as shown in Figure R5 (corresponding to Figure S29 in the Supporting Information). The thickness of the nanofiber membrane in Figure S17 is ~40 μm (Figure R6). Given the heterogeneity in both surface distribution (Figure R2) and thickness (Figure R5), we selected the surface potential variation of individual fibers to investigate the influence of different functional groups in this study (Figure R4).\n4. Would the authors consider including polarization-electric field (P-E) hysteresis loops or polarization charge density versus time graphs to better visualize the dipole behavior, charge retention, and fatigue characteristics of the materials?\nResponse: We thank the reviewer for the insightful suggestion regarding the use of P-E hysteresis loops or polarization charge vs. time measurements to characterize dipole behavior and charge retention. We have carefully considered this point and provide the following clarifications based on the focus and findings of our study:\nFirstly, our research primarily investigates the surface charge acquisition and binding mechanisms of triboelectric materials, which are mainly governed by surface chemistry, and electronic structure. In contrast, P-E loops measure bulk ferroelectric polarization resulting from the reorientation of intrinsic dipoles under a high electric field. These are fundamentally different phenomena. The core of our work is to decouple the influence of surface chemical bonds (C-Cl vs. C-F) from other factors.\nSecondly, we understand the reviewer’s suggestion, likely because the platform used in our study is based on PVDF copolymers, which are typical ferroelectric polymer materials. The influence of ferroelectric dipoles on the surface charge acquisition and binding capabilities of the materials is also a factor we aimed to minimize during our investigation. For example, in the study of PVDF copolymer film properties, we used the same preparation method to obtain different types of PVDF copolymer films and avoided high-voltage poling processes. In this case, the polar phases in the films are randomly oriented, and no macroscopic piezoelectric effect is observed. The content of polar phases (Figure S12) may influence the triboelectric properties by affecting the dielectric performance. Additionally, differences in surface roughness among the PVDF copolymer films are another important factor. Therefore, we systematically analyzed the dielectric properties (Figure S13) and surface roughness (Figure S5-S11) of the prepared PVDF copolymer films. It is worth noting that the PC film does not possess advantages such as high polar phase content, high dielectric constant, or high surface roughness (for instance, PT exhibits higher values in each parameter compared to PC), yet it demonstrates the best triboelectric performance. Similarly, although the electrospinning process can in situ polarize PVDF copolymer fibers, PC nanofibers still yield the best triboelectric performance despite having the lowest polar phase content. While this evidence may not perfectly indicate the quantitative role of dipoles in this complex process, it is sufficient to infer that the chemical composition and bonding in PC play a crucial role. This conclusion can be further strengthened by DFT calculations (Figure 1), which show that introducing C-Cl bonds significantly lowers the LUMO energy and the energy barrier for electron acquisition (EVA) compared to C-F bonds. This provides a fundamental electronic-structure basis for the superior charge acquisition capability of the PC polymer, aligning perfectly with our experimental observations. Therefore, our results fully support the viewpoint presented in our work even without the analyses such as P-E loops.\nFinally, regarding tribo-charge retention, TENG researchers often employ triboelectric charge density versus time decay curves to demonstrate the binding capabilities of C-Cl and C-F bonds to triboelectric charges. This method is more directly relevant to surface charge behavior in triboelectric contexts than P-E loop or polarization charge density measurements. These curves can be obtained through intermittent output triboelectric charge density tests. The specific method is as follows: first, a rapid contact-separation working mode is used to allow the accumulation of triboelectric charges on the surface of the tested samples until stabilization; then, intermittent contact-separation tests are conducted (one working cycle tested every 10 minutes to avoid re-accumulation of charges). The schematic of the TENG output performance testing setup, and the corresponding working curve of the linear motor is shown in Figure R7 and R8 (corresponding to Figure S21 in the Supporting Information). The triboelectric charge retention rate versus time curves for PC films with different surface C-Cl bond contents are shown in Figure R9 (corresponding to Figure S22 in the Supporting Information) and Figure 4h. The results strongly confirm that the introduction of C-Cl bonds does not provide an advantage in triboelectric charge retention compared to C-F bonds.\nIn addition, we fully agree with the reviewer that the role of dipole alignment in charge retention represents a fascinating direction. Investigating the triboelectric behaviors of polarized versus non-polarized ferroelectric films could yield profound insights into systems harnessing coupled triboelectric and piezoelectric effects. We envision future work to explore this, and we sincerely appreciate the reviewe’s valuable suggestion for guiding our subsequent research.\n5. The authors are encouraged to include measurements of air permeability or specific surface area of the electrospun membranes using Brunauer–Emmett–Teller (BET) analysis or equivalent techniques, to elucidate the relationship between membrane microstructure and triboelectric performance.\nResponse: Thank you for this excellent and insightful suggestion. The electrospun fibers prepared in this study primarily consist of dense and smooth fibers with average diameter of 0.99-1.45 μm (Figure R3), resulting in a relatively low theoretical specific surface area (SSA). Based on a solid smooth cylinder model, the theoretical specific surface area range of the PVDF based fibers can be calculated to be approximately 1.55-2.25 m2/g (calculated via SSA=4/ρd, where ρ is the density of PVDF based polymers, and d is the diameter of the fibers). When measured using the nitrogen adsorption method (BET), the adsorption quantity within the effective pressure range fell below the instrument’s detection limit, preventing valid linear fitting results, as shown in Figure R10. This behavior is consistent with the typical characteristics of such non-microporous polymer fibrous materials. However, we can estimate their specific surface area based on the average fiber diameter. The order of specific surface area for different PVDF copolymers from high to low is as follows: PVDF, PC, PT-CTFE, PT-CFE, PT, PH. A comparison with the electron-accepting ability ranking of PVDF-based fibers (Figure 3d and 3e) reveals that the specific surface area of the fibers shows no correlation with their triboelectric performance. This finding further underscores the importance of the surface chemical groups.\n6. Can the authors conduct a more detailed analysis on how variations in crystallinity and phase content (such as α, β, γ phases in PVDF) caused by electrospinning influence the triboelectric output?\nResponse: Thank you for this excellent and insightful suggestion. According to the theory model of a TENG, the device can be represented by an equivalent circuit comprising three capacitors connected in series (Figure R11). The resulting triboelectric potential (V) in contact-separation mode is expressed by Equation (1): X(t) Q d d V   ( 1  2  X(t)) (1)  S   0 0 1 2 where σ denotes the surface charge density, Q is the induced charge on the electrodes, d and d are the thicknesses of the two dielectric layers, ε and ε are their respective 1 2 1 2 relative permittivity, S is the electrode area, X(t) is the separation distance, and ε is the 0 vacuum permittivity. As indicated by Equation 1, the output performance of the TENG depends critically on the surface charge density σ, the induced charge Q, and the permittivity of the dielectric materials.\nDuring the electrospinning process, PVDF-based polymers undergo uniaxial stretching and high-voltage electric field polarization, leading to the formation of nanofiber networks. This processing not only enhances the overall crystallinity but also significantly increases the content of polar phases, particularly the β-phase, which is known to improve triboelectric performance. The polar phase modifies the surface potential: a higher content of polar phases generally shifts the surface potential toward more negative values, indicating enhanced electron affinity (correlated with increased surface charge density σ) (Advanced Functional Materials, 2017, 27, 1700702, Progress in Materials Science, 2025, 148, 101376). Moreover, higher crystallinity typically leads to a higher dielectric constant. The resulting increase in permittivity strengthens the electrostatic induction effect, thereby raising the induced charge Q. According to equation (1), both elevated σ and Q contribute synergistically to improving the material’s triboelectric properties. This discussion has been incorporated into the revised manuscript on Page 9.\n7. Does the work provide sufficient multi-technique characterization (e.g., confirming composition, structure, and surface chemistry)? The authors mention XPS, FTIR, XRD, AFM, SKPFM, but figures could more explicitly compare C-F and C-Cl bonds and quantify their ratios after plasma treatment.\nResponse: We sincerely thank the reviewer for this constructive suggestion. The elemental atomic percentages were quantified from the XPS survey spectra (Figure 4d). Based on the fitted peak areas and the relative sensitivity factors (Avantage software), we calculated the atomic percentages (at.%) of C, N, O F, and Cl, as summarized in Table R3. Considering that the Cl 2p binding energy at 200.8 eV rules out the presence of inorganic chlorides (e.g., NaCl, ~198.5 eV) and confirms the formation of covalent C-Cl bonds. Similarly, the F 1s peak at 687.2 eV is exclusive to organic fluorine (C-F), distinguishing it from metal fluorides (~684-686 eV). Therefore, Thus, the F/Cl atomic ratio derived from the XPS spectra reliably represents the relative abundance of C-F to C-Cl bonds on the treated surface, as quantified in Table R3. We have added this information in the Supporting Information as Table S3.\n8. How do environmental factors such as sweat, temperature fluctuations, and mechanical abrasion encountered during daily wear or application impact the durability, triboelectric stability, and overall performance of the device? Could testing under these realistic conditions provide more practical insights?\nResponse: Thank you for this excellent and insightful suggestion. Sweating from the human body increases the humidity in the TENG device’s operating environment. In humid environments, a thin layer of water molecules adsorbs on material surfaces. This layer can provide a conductive path, leading to rapid charge leakage and therefore decrease the output performance (Figure R12).\nUnder real-world operating conditions, temperature fluctuations also frequently occur and directly impact TENG’s output. Elevated temperatures impart greater thermal energy to the system, which increases the kinetic activity of charge carriers. This enhanced mobility allows trapped charges in shallow energy states to more easily overcome their relatively low energy barriers. Such a thermally activated de-trapping process accelerates charge recombination and dissipation, leading to a reduction of the surface triboelectric charges. As a result, the output performance of the TENG device can be significantly degraded under conditions of high temperature (Figure R13).\nWe employed a linear motor to simulate the vertical driving force encountered in daily use. After approximately 4,500 cycles, the device shown in Figure 5b still maintained highly stable output performance, demonstrating its excellent durability and stability (Figure 5h). Additionally, we used manual actuation to simulate a driving force with a certain tangential component. After 1000 cycles, we re-measured its output performance using the linear motor and observed a significant decline (from ~350 V to ~200 V). This is because, under the influence of the tangential component of the driving force, the electrospun membrane is highly susceptible to damage, where fibers in certain areas are pushed and stacked together in other regions, reducing the overall effective contact area and thus leading to performance degradation (Figure R14).\nThe issue of wear and tear is a common challenge faced by TENG devices. Since the primary focus of this work is to elucidate the synergistic enhancement mechanism of C-F and C-Cl bonds on the triboelectric performance of fluorinated polymer materials, we have not conducted optimization design for the ultimate wear resistance of the device. We kindly ask for the reviewer’s understanding regarding this aspect.\nReviewer #2: The authors claim that synergistic effects between C–F and C–Cl bonds in PVDF-based copolymers lead to very high triboelectric charge density. The authors also present an electrospun, plasma-treated TENG insole with AI-based gait recognition as an application example. The topic is interesting and potentially relevant. However, the experimental evidence provided in the manuscript does not convincingly support the proposed mechanism.\nResponse: We really appreciate the reviewer’s positive and valuable comments. And we have carefully revised the manuscript accordingly.\n1. The first major issue is that the manuscript does not clearly separate chemical effects from processing effects. The authors compare spin-coated films, electrospun nanofibers, and plasma-treated nanofibers. These samples are structurally very different: they have different morphology, different chain packing, different β-phase content, different surface roughness, and different effective contact area. PVDF-based polymers are also known to rearrange differently depending on the solvent used for casting or dissolution, and such solvent-dependent rearrangement can change both crystallinity and surface potential. In the manuscript, these factors are not controlled or normalized. As a result, it is not possible to conclude that the improved performance mainly comes from the proposed “C-F/C-Cl synergy.” The performance could instead be dominated by differences in morphology, phase content, roughness, or solvent history.\nResponse: We sincerely thank the reviewer for this exceptionally insightful and critical comment. However, we believe the intention behind our experimental design may not have been fully conveyed. A detailed explanation is provided below:\nFirst of all, we did not derive the existing conclusions by directly comparing PVDF-based copolymer films, fibers, and chlorine plasma-treated films obtained through different preparation methods, as they possess distinct morphologies, roughness levels, polar phase contents, etc. (as noted by the reviewer).\nSecondly, we separately compared the triboelectric properties of PVDF based copolymers in film and fiber forms. The specific process through which the conclusions presented in this work were drawn is as follows: For PVDF based copolymer films, we used the same preparation method to obtain different types of PVDF copolymer films and avoided high-voltage poling processes. In this case, the polar phases in the films are randomly oriented, and no macroscopic piezoelectric effect is observed. The content of polar phases (Figure S12) may influence the triboelectric properties by affecting the dielectric performance. Additionally, differences in surface roughness among the PVDF copolymer films are another important factor. Therefore, we systematically analyzed the dielectric properties (Figure S13) and surface roughness (Figure S5-S11) of the prepared PVDF copolymer films. It is worth noting that the PC film does not possess advantages such as high polar phase content, high dielectric constant, or high surface roughness (for instance, PT exhibits higher values in each parameter compared to PC), yet it demonstrates the best triboelectric performance. For PVDF based copolymer fibers, similarly, although the electrospinning process can in situ polarize PVDF copolymer fibers, PC nanofibers still yield the best triboelectric performance despite having the lowest polar phase content. While this evidence may not perfectly indicate the quantitative role of dipoles in this complex process, it is sufficient to infer that the chemical composition and bonding in PC play a crucial role. This conclusion can be further strengthened by DFT calculations (Figure 1), which show that introducing C-Cl bonds significantly lowers the LUMO energy and the energy barrier for electron acquisition (EVA) compared to C-F bonds. This provides a fundamental electronic-structure basis for the superior charge acquisition capability of the PC polymer, aligning perfectly with our experimental observations. For Cl plasma-treated PC films, the base PC films were prepared identically and only differed in the duration of Cl plasma treatment. As shown in Figure R1, the thickness of the PC film is approximately 30 μm. Given that the plasma modification depth is below 50 nm (representing only about 0.17% of the total film thickness) (Figure R3, R4 and Table R2), its influence on the bulk dielectric constant and loss is negligible. This is directly confirmed by the dielectric spectra in Figure R5, which show no significant change before and after treatment across the investigated frequency range. In addition, a noticeable change that can substantially affect triboelectric performance is surface roughness. However, while the PC film treated with Cl plasma for 5 minutes exhibits the highest surface roughness, its output charge density is not the highest. This indicates that surface chemical groups play a more decisive role in enhancing triboelectric properties. Therefore, we attribute the performance improvement primarily to the proposed synergistic effect between C-F and C-Cl bonds, which can be supported by the data in Figure 4d-4h.\nFinally, we would like to express our sincere gratitude to the reviewer for raising these constructive questions. We hope that our responses have clearly addressed the reviewer’s concerns and provided a satisfactory explanation.\n2. The second issue is that the effect of chlorine plasma treatment on the polymer is not sufficiently characterized. The manuscript assumes that plasma treatment simply adjusts the Cl:F ratio and creates an optimal balance between C-Cl (for charge capture) and C-F (for charge retention. However, the manuscript does not provide direct evidence of what the plasma is actually doing to the polymer. For example, it is not clear whether new C-Cl bonds are truly formed, how deeply chlorine is incorporated, whether the polymer backbone is damaged, or whether the dielectric behavior is altered. Without this information, the proposed mechanism behind the improved triboelectric performance remains unproven.\nResponse: We sincerely thank the reviewer’s constructive comments. We have carefully considered the concerns raised and have supplemented our analysis with additional data in response. We hope our revisions meet with your approval. The detailed responses are provided below.\n1. What is the plasma actually doing to the polymer? The experimental results provide clear and complementary evidence of successful surface modification by chlorine plasma (Figure R2 and Table R1). The two key observations, increased surface chlorine content and enhanced surface roughness are directly correlated outcomes of the plasma-polymer interaction, and together they explain the enhanced triboelectric properties of the treated material. These physical and chemical processes are commonly reported in previous works (such as Chapter 4-Plasma Assisted Polymer Modifications, Non-Thermal Plasma Technology for Polymeric Materials, 2019, pp. 9-127).\n2. Whether new C-Cl bonds are truly formed? As shown in Figure R2, the high-resolution Cl 2p spectrum of the plasma-treated sample reveals a characteristic doublet at binding energies of approximately 200.8 eV (Cl 2p 3/2) and 202.4 eV (Cl 2p 1/2). This spectral feature is a definitive signature of covalently bonded organic chlorine (C-Cl bonds). Furthermore, the elemental composition was quantified from the XPS survey spectra (Figure 4d). Using the integrated peak areas and the relative sensitivity factors within the Avantage software, we calculated the atomic percentages (at.%) of C, N, O, F, and Cl, as summarized in Table R1. The significant increase in the Cl atomic percentage after treatment provides strong quantitative evidence for the formation of new C-Cl bonds on the surface.\n3. How deeply chlorine is incorporated? To quantitatively determine the depth of chlorine incorporation, we performed XPS depth profiling using alternating cycles of low-energy Ar⁺ sputtering (1 keV) and XPS analysis. The sputtering rate was calibrated by measuring the crater depth with atomic force microscopy (AFM) on a reference polymer film under identical conditions, yielding a rate of approximately 10 nm/min. High-resolution spectra of Cl and C were recorded after successive Ar⁺ etching intervals to analyze the variation in elemental content. From these spectra, the corresponding elemental ratios were calculated. As shown in Figure R3 and Table R2, the Cl/C atomic ratio on the sample surface after a cumulative etching time of 4 minutes (~0.017 according to Table R2) recovers to the level of the untreated sample (~0.052 according to Table R1). Given the calibrated sputtering rate of ~9.2 nm/min for PC-Cl film (Figure R4), this result indicates that the effective depth of chlorine plasma treatment is less than 50 nm in this work.\n4. Whether the polymer backbone is damaged? The change in surface morphology (increased roughness) is intrinsically linked to chemical damage at the molecular level, specifically the cleavage of the main carbon chains, which compromises the structural integrity of the surface layer. Therefore, localized scission of the polymer backbone occurs during the plasma treatment, as shown in Figure S20.\n5. Whether the dielectric behavior is altered? For a film approximately 30 μm thick, the impact of chlorine plasma treatment on its bulk dielectric constant and loss is negligible. This is because the modification depth (<50 nm) represents merely ~0.17% of the total thickness. This conclusion is directly confirmed by the dielectric spectra of the PC film before and after treatment, as shown in Figure R5, which exhibit no significant change within the investigated frequency range.\n3. The third issue is that the triboelectric performance data are compared across samples that were not fabricated or tested under the same conditions. Because the device structures, surface states, and even test conditions are not clearly kept constant, the reported performance differences cannot be independently evaluated or fairly compared.\nResponse: We thank the reviewer for raising this point. In this work, all films were prepared using an identical solvent system and spin-coating method, as detailed in the section of Materials and Experimental methods: 0.5 g of polymer was weighed and added into 6 g of DMF, and the polymer was completely dissolved by stirring at 60 ℃, then the solution was spin-coated on the glass substrate by using a spin-coater, and then put into an oven to be heated at 110 ℃ for 2 h. Then the films and glass substrate were put into deionized water for ion exchange, and then the films were peeled off. The films used for testing AFM and SKPM were prepared using platinum-plated silicon wafers as the substrate. The film thickness, controlled via spin-coating parameters, was consistently maintained at approximately 30 μm, as illustrated in the Figure R1. Surface potential measurements were performed under identical ambient conditions using SKPFM, and the electrical output was evaluated under the same driving conditions controlled by a linear motor.\nAll fiber samples were fabricated using the same solvent system and electrospinning process, as specified in the section of Materials and Experimental methods: 0.5 g of polymer was weighed and added into a beaker, then 1.5 g of acetone was added, and then 4.5 g of DMF was added, and the polymer was completely dissolved by stirring at 60 ℃, and then the fiber membrane was prepared by electrostatic spinning (the applied voltage was 17 kV and liquid propulsion speed of 1.8 mL/h). The sample prepared by electrospinning is dried in a ventilated oven at 60 ℃ for 1 h. In the production of the samples required for SKPM, the fibers will be spun to platinum-plated silicon wafers, and then the samples are placed in the oven to be dried at 60 ℃ for 12 h to eliminate the static influence of the high-voltage field, and after that the samples are subjected to the SKPFM to test their surface potential, as shown in Figure R6. Due to the inherent challenges in precisely controlling the surface distribution and local thickness of static electrospun fibers, the triboelectric performance of the fibers was assessed solely based on variations in surface potential, which were also measured under fully consistent testing conditions.\nWe sincerely thank the reviewer for these thoughtful questions. We believe our responses have comprehensively addressed the concerns raised and hope they now find our explanations satisfactory.\n4. The manuscript does not yet demonstrate that the claimed chemical mechanism is responsible for the reported performance. The chemical effects are not isolated from morphology and solvent-driven rearrangement, the plasma-induced chemistry is not verified, the device comparisons are not normalized, and the definition and evaluation of the key performance metrics are not clearly established. For this reason, the reviewer cannot recommend publication in this journal.\nResponse: We thank the reviewer for this valuable comment. The reviewer’s specific concerns have been systematically addressed in our detailed responses to Comments 1, 2, and 3. Through the additional data, clarifications, and expanded discussion provided in those point-by-point replies, we believe the core issue raised here has been fully resolved. We sincerely appreciate the reviewer’s rigorous and constructive critique, which has significantly strengthened the mechanistic explanation and experimental support in our work. We trust that our comprehensive revisions and explanations now satisfactorily address these fundamental concerns.\nReviewer #3: This manuscript, titled “Unveiling the Synergistic Mechanism of C-F and C-Cl Bonds in Enhancing the Triboelectric Performance of Fluorinated Polymers” by Liu et al., proposes a novel approach to enhance the contact electrification of PVDF and its copolymers, including P(VDF-TrFE), P(VDF-HFP), P(VDF-TrFE-CFE), P(VDF-TrFE-CTFE), and P(VDF-CTFE), through the synergistic effects of C-F and C-Cl bonds. The results suggest that PVDF-CTFE (PC) exhibits the strongest tribo-negative properties. Additionally, it was found that the surface Cl/F atomic ratio in PC influences the output performance of TENG. An increase in C-Cl content enhances electron acquisition in contact with tribo-positive materials, while a higher C-F content improves charge retention. Finally, PC-Cl was developed for an air-permeable smart insole that incorporates AI predictive models for accurate user identification and exercise-state evaluation. The findings and the proposed strategy for enhancing the tribo-negative property are interesting. However, the manuscript lacks a systematic examination of the theory supported by sufficient experimental data. The effects of certain variables on the output performance of TENGs during the comparison of PVDF copolymers such as the roughness and thickness of the dielectric layers have been neglected. Additionally, the possibility of extending this strategy to a wider range of materials has not been demonstrated. Hence, at its current stage, the work cannot be accepted in Nature Communications. The following specific questions and issues must be addressed before the manuscript can be considered for further review.\nResponse: Thank you very much for your valuable feedback, which has been extremely helpful in revising and improving our manuscript. We have carefully addressed each of your comments point by point. All corresponding changes have been highlighted in the revised manuscript. Our responses to each comment are provided below. We hope that the revisions and our responses meet with your approval.\n1. Thickness plays a critical role in TENG results. Therefore, the authors should provide detailed information on the thickness of all samples, as variations in this parameter can significantly influence the triboelectric performance.\nResponse: Thank you for this valuable suggestion. According to the theory model of a TENG, the device can be represented by an equivalent circuit comprising three capacitors connected in series (Figure R1). The resulting triboelectric potential (V) in contact-separation mode is expressed by Equation (1): X(t) Q d d V   ( 1  2  X(t)) (1)  S   0 0 1 2 where σ denotes the surface charge density, Q is the induced charge on the electrodes, d and d are the thicknesses of the two dielectric layers, ε and ε are their respective 1 2 1 2 relative permittivity, S is the electrode area, X(t) is the separation distance, and ε is the 0 vacuum permittivity. As indicated by Equation 1, the output performance of the TENG depends critically on the surface charge density σ, the induced charge Q, the permittivity of the dielectric materials, and the thickness of the materials d.\n• What was the thickness of the samples used for TENG measurements in Figure 2C? Did the authors measure and control the thickness in this case?\nResponse: The thickness of the PVDF-based copolymer films was maintained at approximately 30 μm for the measurements presented in Figure 2c, as shown in Figure R2. This information has been incorporated into the Revised Manuscript and Supporting Information as Figure S4.\n• Similar to the films, did the authors check and control the thickness of electrospun mats?\nResponse: The samples shown in Figure 3b were prepared primarily to characterize the morphology of different PVDF based copolymer nanofibers, enabling fundamental property screening via single nanofiber SKPFM. A representative image of isolated nanofibers on a Pt-coated Si substrate, used for SKPFM analysis, is provided in Figure R3 (corresponding to Figure S16 in the Supporting Information). This nanoscale measurement probes the surface potential directly on individual nanofibers, thereby eliminating interference from macroscopic membrane properties, such as thickness and porosity, which are inherently difficult to control consistently across different samples in the electrospinning process. Consequently, these samples were not integrated into macroscopic TENG devices for intrinsic tribo-property characterization, and their thickness was neither controlled nor optimized in this part. Therefore, thickness characterization was not performed on these samples, and we kindly ask for the reviewer’s understanding.\nTo address the core concern behind the suggestion, we wish to highlight that for all device-grade films used in functional TENG fabrication (e.g., in Figures 5, and S33), we have now added the corresponding thickness characterization. Cross-sectional SEM measurements taken from the periphery to the center (along the diagonal direction) confirm an average thickness of ~19.3 μm, as shown in Figure R4 (corresponding to Figure S29 in the Supporting Information). The thickness of the nanofiber membrane in Figure S17 is ~40 μm (Figure R5). This information has been added to the respective figure captions. Given the heterogeneity in both surface distribution and thickness, we selected the surface potential variation of individual fibers to investigate the influence of different functional groups in this study.\n• What was the thickness of the commercial PTFE and PCTFE films discussed in Figures S11 and S12?\nResponse: The thickness of the commercial PTFE and PCTFE films used in Figure S11 and S12 is about 50 μm, as shown in Figure R6. This information has been incorporated into the Revised Manuscript and Supporting Information as Figure S23.\n2. Line 227–232: “PH nanofiber shows a significant enhancement in negative tribo-property, surpassing that of PT and PT-CFE. This improvement may be attributed to its markedly increased crystallinity and polar phase content (Figure S7c).” This explanation does not appear to support the reported results. As shown in Figure S7, the crystallinity of PH is lower than that of PT and PT-CFE. Similarly, the polar phase content of PH is not the highest among these samples. Please provide a more consistent discussion of these findings and support your explanation with relevant references.\nResponse: Thank you very much for your careful review of this paper and insightful questions. The discussion here aims to explain the significant difference observed in the triboelectric series between PVDF based copolymer films and electrospun fibers, particularly regarding the position of PH. According to Figures 2d and 3e, the electron trapping ability of PH in film form is relatively weak (with PT and PT-CFE stronger than PH), whereas in fiber form, PH surpasses both PT and PT-CFE. Analysis of crystalline phase content and polar phase proportion reveals that PH in fiber form (Figure S15) exhibits a substantial increase in both crystalline and polar phase content compared to its film counterpart (Figure S12), which explains its shift in the triboelectric series. Additionally, it should be noted that while the electron-trapping ability of PH varies significantly with its form from film to fiber, PC remains the most tribo-negative material among all PVDF-based copolymers. Therefore, this particular discussion does not conflict with our overall conclusions. We have revised the explanation to clarify this point more effectively on Page 9 in the Revised Manuscript and hope this addresses the reviewer’s concern.\n3. Although AFM is a powerful tool for measuring the roughness of samples, its measurement area is very small, whereas the TENG contact surfaces are relatively large (4 × 4 cm²). Could the authors investigate the large-scale roughness of the samples both lab-prepared and commercial in order to provide a more representative assessment?\nResponse: Thank you very much for your valuable comment. The surface roughness of the PVDF based copolymer films was characterized by laser scanning confocal microscopy, as shown in Figures R7-R12. For each film, three points were measured with a sampling area of 2.5 mm² per point. The arithmetic mean roughness of the PVDF, PH, PT-CFE, PT-CTFE, PC, and PT films is 1.42, 1.08, 1.59, 1.30, 1.04, and 1.10 μm (Figure R7-R12) (corresponding to Figure S6-S11 in the Supporting Information), respectively. It can be observed that PC continues to exhibit the lowest large-scale surface roughness among these films, further supporting our findings.\nThe surface roughness of the commercial films used in this work was also characterized by laser scanning confocal microscopy, as shown in Figures R13 and R14. For each film, three points were measured with a sampling area of 2.5 mm² per point. The arithmetic means roughness of the PCTFE and PTFE films is 1.17 μm and 1.57 μm (Figure R13 and R14), respectively.\n4. Could the authors expand their findings to other materials by chemical modification under controlled conditions? For example, imparting Cl and F groups to chemically modified substances such as cellulose paper or non-fluorinated polymers would help demonstrate whether their findings are applicable to a wider range of materials.\nResponse: Thank you for this excellent and insightful suggestion. We fully agree that expanding the study to a broader range of material systems is of great significance for verifying the general applicability of our conclusions. In fact, we have already extended the research to non-fluorinated polymer materials, such as polyethylene (PE). We treated commercially available PE films using fluorine, chlorine, and fluorine/chlorine composite plasmas, respectively. XPS analysis confirmed that after plasma treatment, corresponding F and/or Cl elements were successfully introduced onto the PE film surfaces, forming C-F and C-Cl bonds. Tests on their triboelectric output performance (Figure R15) (corresponding to Figure S26 in the Supporting Information) revealed that all plasma-treated PE films exhibited a significant increase in output voltage compared to the pristine PE film. This is because both fluorine and chlorine possess higher electronegativity than the original C–H/C–C backbone, thereby enhancing the electron-accepting ability of the material. It is particularly noteworthy that among all treatments, the sample treated with the fluorine/chlorine composite plasma showed the highest output voltage. The triboelectric charge retention capability of different films (Figure R16 and R17) (corresponding to Figure S27 and S28 in the Supporting Information) also indicated that although the introduction of C-Cl bonds can improve the output, compared to the introduction of C-F bonds alone, it also accelerates the decay of triboelectric charges (weaker charge retention capability). This observation is entirely consistent with our earlier discussion on the roles of C-F and C-Cl bonds in PVDF-based copolymers, strongly supporting that our key finding. More systematic extension studies are currently underway, and we plan to report the application of these findings in future work. We appreciate the reviewer’s understanding. Thank you for your valuable guidance on our research.\n5. All abbreviations in the abstract and the main text should be defined at their first occurrence. For example, PVDF, PTFE, FEP, etc.\nResponse: Thank you very much for your suggestion. We have checked and confirmed that all abbreviations are clearly defined at their first occurrence throughout the text."}, {"round": 2, "reviewer_comments": {"reviewer_1": "[Note from the Editor: Reviewer #1 was asked to look also over the response given to Reviewer #3]\nThe authors have successfully addressed all previous concerns with convincing new data. The revised manuscript is now solid and ready for publication.\nAs requested, I have looked into the responses of the authors to the concerns from reviewer #3, and I have included this note here as well.\nOverall, the authors have made a serious effort to address the concerns, and the volume of new data is substantial.\nTherefore, I recommend a minor revision as below.\nThe authors should add the actual numerical values (crystallinity % and polar phase %) for PH to the main text.\nThe authors need to add roughness measurements for the four PE conditions to the Supporting Information.", "reviewer_2": "The authors have adequately addressed the reviewer’s comments in a point-by-point manner, and the reviewer recommends publication of the revised manuscript in the journal.", "reviewer_3": "Overall, the authors have made a serious effort to address the concerns, and the volume of new data is substantial. Therefore, I recommend a minor revision as below."}, "author_response": "Response to Referees\nReviewer #1\nThe authors have successfully addressed all previous concerns with convincing new data. The revised manuscript is now solid and ready for publication.\nResponse: We thank the reviewer for the positive feedback and appreciate the reviewer's time and constructive comments throughout the review process.\nReviewer #2\nThe authors have adequately addressed the reviewer’s comments in a point-by-point manner, and the reviewer recommends publication of the revised manuscript in the journal.\nResponse: We greatly appreciate the reviewer’s positive feedback and constructive suggestions, which have helped us improve the quality of our manuscript.\nReviewer #3\nOverall, the authors have made a serious effort to address the concerns, and the volume of new data is substantial. Therefore, I recommend a minor revision as below.\nResponse: We sincerely thank the reviewer for the positive feedback and valuable time, as well as for the constructive comments throughout the review process.\n1. The authors should add the actual numerical values (crystallinity % and polar phase %) for PH to the main text.\nResponse: Thank you for your valuable suggestion. We have added the numerical values for the crystallinity and polar phase content of PH on Page 10, as follows: “This improvement can be attributed to the markedly increased crystallinity and polar phase content of PH (membrane form: crystallinity 65.6% and polar phase 43.3%, nanofiber form: crystallinity 74.5% and polar phase 84.1%, Supplementary Fig. 12 and 15).”\n2. The authors need to add roughness measurements for the four PE conditions to the Supporting Information.\nResponse: Thank you for your valuable comment. We have added the roughness measurements for the four PE conditions, as shown in Figure R1 (corresponding to Supplementary Fig. 26)."}]

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