Doan T. Tunga,
Hoang T. Dung
ab,
Le T. T. Tam
ab,
Bui V. Cuonga,
Ha M. Dungc,
Duong V. Datc,
Ngo T. Dung
a,
Nguyen T. Dunga,
Phan N. Minh*b and
Le T. Lu
*ab
aInstitute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam. E-mail: pnminh@vast.vn; lult@ims.vast.ac.vn
bGraduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
cVNU University of Engineering and Technology, VietNam National University, 144 Xuan Thuy Road, Cau Giay, Ha Noi, Vietnam
First published on 2nd June 2025
A humidity-resistant, antibacterial triboelectric nanogenerator (TENG) was developed using polyhexamethylene guanidine hydrochloride (PHMG) as the primary functional material. To enhance performance stability, PHMG was integrated with natural chitosan (CS) to create a positively charged triboelectric electrode. When combined with a negatively charged fluorinated ethylene propylene (FEP) membrane, the TENG demonstrated outstanding electrical output, achieving a maximum peak-to-peak voltage (Vp–p) of 1470.6 V and a peak power (Ppeak) of 12 mW at a 10 MΩ load under 40% relative humidity. Notably, the device maintained stable operation in high-humidity conditions (up to 90% HR), with a sustained Vp–p of 862.7 V and a Ppeak of 6.5 mW. In addition to its energy-harvesting capability, the TENG exhibited strong antibacterial activity as it effectively eliminated E. coli (at a concentration of 1.7 × 104) and S. aureus (at a concentration of 1.6 × 104) bacteria within just 60 seconds at 90% relative humidity. This combination of reliable triboelectric generation in humid environments and rapid antibacterial activity indicates the potential of this TENG for self-powered applications in wearable electronics and hygienic surfaces, including smart face masks and antibacterial shoe insoles.
To address the growing demand for antibacterial performance, numerous studies have explored the integration of functional nanomaterials into TENGs. These materials include inorganic nanoparticles (e.g., Ag, TiO2, ZnO, Te)13–19 and organic antibacterial agents (e.g., cationic polymers).20–24 For example, Lin et al. developed a TENG using tellurium nanowire (Te NW) coated on carbon fiber, followed by a thin gold layer to enhance electrical conductivity. The resulting system employed a dual antibacterial mechanism involved electroporation (electrical pulse-induced membrane disruption) and controlled hydrogen peroxide (H2O2) production, which effectively eliminated bacterial during TENG operation. Notably, this design achieved bactericidal efficiencies of 87% against S. aureus and 96% against E. coli at a frequency of 4 Hz after 60 minutes of operation.13,19
In another study emphasising environmental sustainability, Long Gu's research group reported the fabrication of a high-performance TENG using recycled PET combined with antibacterial polymer PHMG. The PET-PHMG nanofiber membrane, fabricated through electrospinning, served as the positive triboelectric layer, while a polyvinylidene fluoride (PVDF) membrane was employed as the negative counterpart. The device achieved a peak output voltage of 120.2 V, current of 2.9 μA, and charge density of 22.1 nC cm−2, among the highest values reported for TENGs derived from waste materials.22 Moreover, the device exhibited stable operation over 2500 test cycles and demonstrated effective antibacterial activity against S. aureus and E. coli.
Cationic polymers combined with polysaccharides have attracted increasing interest due to their intrinsic antibacterial properties, environmental friendliness, and high biocompatibility.25–27 Among these, the combination of chitosan and PHMG has been widely employed in the development of antibacterial coatings and membranes.28,29 In addition to their antimicrobial activity, both chitosan and PHMG exhibited strong positive triboelectric properties.22,24,30,31 However, reports on the integration of PHMG and chitosan specific for antibacterial TENG remain very limited.
In this study, we report the development of a novel antibacterial TENG capable of maintaining high performance under elevated humidity conditions (up to 90% RH). The device features an innovative design in which the positive electrode membrane is fabricated through integration of naturally-derived chitosan polymer (CS) with PHMG, utilising glutaraldehyde (GA) as a cross-linking agent. This composite material leverages the biocompatibility and environmental sustainability of chitosan, while harnessing the potent antibacterial activity of PHMG. The negative triboelectric electrode is constructed using a FEP membrane, creating an efficient interface for charge separation. This configuration enables dual functionality, providing both robust triboelectric output and enhanced bactericidal performance. The TENG exhibits outstanding electrical characteristics, achieving a peak-to-peak open-circuit voltage, Vp–p of 1470.6 V and a maximum power output, Ppeak of 12 mW under ambient conditions. Notably, the device maintains remarkable operational stability in high-humidity environments, generating a Vp–p of 862.7 V and Ppeak of 6.5 mW at 90% relative humidity, while preserving its antibacterial efficacy.
Copper adhesive tape, sourced from Korea, had a thickness ranging from 0.05 to 0.06 mm. Commercial transparent fluorinated ethylene propylene (FEP) film, approximately 0.1 mm thick, was obtained from materials commonly used in Anycubic MONO X 3D printers.
The CS–PHMG–GA mixture was prepared by combining the PHMG–GA solution with the chitosan solution in various mass ratios of CS:
PHMG–GA, specifically 9
:
1, 8
:
2, 7
:
3, 6
:
4, and 5
:
5. These samples were labeled C9P1, C8P2, C7P3, C6P4, and C5P5, respectively. During the preparation, 1 mL of isopropyl alcohol was first mixed with the PHMG–GA solution before being added to the CS solution, and the entire mixture was stirred thoroughly to ensure uniform blending.
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Fig. 1 Schematic illustration of the fabrication process and high bactericidal ability during operation of CS–PHMG–GA based TENG. |
To investigate the device performance under various environmental conditions, the entire TENG module was enclosed in a sealed polycarbonate (PC) chamber. This setup allowed precise control of relative humidity levels and bacterial exposure conditions for comprehensive performance evaluation.
The open-circuit voltages (OCV or VOC) and load voltages of the TENG device were characterised using Lecroy Wave Surfer 424 oscilloscope. The load currents were indirectly measured through the voltage divider resistor (shunt resistor) by Instek GDS-806S digital storage oscilloscope.
Regarding antibacterial properties, two bacterial strains, Escherichia coli ATCC 25922 (E. coli) and Staphylococcus aureus ATCC 6538 (S. aureus), were cultured on tryptic soy agar (TSA) plates for 32 hours. Bacterial cells were harvested using sterile 0.9% NaCl solution and adjusted to a final concentration of 107 CFU mL−1, standardised according to the McFarland method. A 0.2 mL aliquot of each suspension was evenly spread onto the surface of electrode samples (bare Cu and Cu coated with CS–PHMG–GA of 4 × 4 cm) using sterile cotton swabs. The inoculated samples were then air-dried under aseptic conditions in a laminar flow cabinet for 60 minutes prior to pulsed electric treatment.
The inoculated electrode samples were employed as the positive electrode in the TENG setup operating in contact–separation mode for various time intervals. Following triboelectric pulse exposure, antibacterial activity was assessed using two methods: (i) quantitative colony-forming unit (CFU mL−1) analysis based on ISO 7218:2024 guidelines, and (ii) the direct agar imprint method (the dried inoculated samples were pressed onto agar plates for 15 min and then removed). All treated and control samples were incubated at 30 °C for 24 hours. Control samples, which were inoculated identically but not subjected to triboelectric pulses, served as negative controls for comparison of bactericidal efficiency.
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Fig. 2 (a) Appearance photo, (b) SEM, (c) EDX and (d) EDX mapping of the CS–PHMG–GA electrode prepared at CS![]() ![]() ![]() ![]() |
EDX analysis confirms the presence of C, O, N, and Cl elements, corresponding to the major components of CS, PHMG, and GA, along with a small amount of copper (Cu) from the substrate was also detected (Fig. 2c and d). The elemental composition was approximately 51.8% C, 22% O, 17% N, 4.9% Cl, and 4.2% Cu. The relatively high nitrogen content is attributed to contributions from both CS and PHMG, which is favorable for enhancing the positive triboelectric performance of the electrode. Moreover, EDX elemental mapping reveals a uniform distribution of C, N, O, and Cl across the membrane surface, indicating homogeneous dispersion of PHMG and GA within the chitosan matrix.
Fig. 3 shows the FTIR spectra of pure CS, PHMG–GA, and CS–PHMG–GA composite membranes prepared at varying mass ratio of CS to PHMG–GA. The spectrum of pure CS exhibited typical features, including a broad absorption band in the region of 3300–3100 cm−1 corresponding to the stretching vibrations of –OH and –NH2 groups. A peak at approximately 2900 cm−1 is attributed to C–H stretching vibrations. Additional prominent peaks are observed at 1635 cm−1 (CO stretching, amide I), 1539 cm−1 (–NH2 bending), and in the region of 1000–1100 cm−1, which corresponds to the saccharide backbone vibrations.
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Fig. 3 FTIR spectra of pure CS, PHMG–GA, and CS–PHMG–GA composite membranes at varying CS![]() ![]() |
For the PHMG–GA sample, distinctive peaks appear at 1500–1700 cm−1, assignable to the CN stretching vibration within the guanidine group, and at 2800–2900 cm−1, corresponding to C–H stretching of the methylene units. As the PHMG–GA content increased from a CS
:
PHMG–GA mass ratio of 9
:
1 to 5
:
5, several notable spectral changes were observed. These include a gradual reduction in the relative intensity of the broad –OH/–NH2 absorption band, and an increase and slight shift in the peak near 1650–1700 cm−1, and a noticeable shift in the region around 1550 cm−1. These spectral modifications indicate molecular interactions between the guanidine moieties of PHMG–GA and the carboxyl or amino groups of chitosan, most likely via ionic bonding.
Furthermore, the emergence or enhancement of the band at ∼1650 cm−1 suggests the formation of imine bonds (CN), arising from reactions between aldehyde groups of glutaraldehyde (GA) and amine groups in either CS or PHMG. However, due to the overlap of amide I and C
N stretching regions, unambiguous assignment of this peak remains challenging.
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Fig. 4 (a) Open-circuit voltage VOC output and (b) the VOC profiles of TENG devices with CS–PHMG–GA electrodes prepared at various PHMG–GA/CS mass ratios under 70% RH. |
Samples (CS![]() ![]() |
Vmax (V) | Vmin (V) | Vp–p (V) |
---|---|---|---|
5![]() ![]() |
407.8 | −643,2 | 1051.0 |
6![]() ![]() |
400.0 | −541.2 | 941.2 |
7![]() ![]() |
329.4 | −415.7 | 745.1 |
8![]() ![]() |
329.4 | −298.0 | 627.4 |
9![]() ![]() |
313.7 | −282.3 | 596.0 |
Fig. 5a presents the VOC output of the CS–PHMG–GA based TENG under varying humidity conditions from 40 to 90%. The voltage pulses recorded from left to right correspond to increasing humidity levels. It can be seen that the negative voltage exhibits a higher absolute magnitude compared to the positive voltage; however, both components demonstrate a decreasing trend as humidity increases. Notably, the positive voltage remains relatively stable, whereas the negative voltage undergoes a more pronounced attenuation. At low humidity levels (40% and 50%), the TENG generates strong oscillatory signals with high amplitude, achieving a peak-to-peak open-circuit voltage of up to 1470.6 V (Table 2). This demonstrates the excellent triboelectric performance of the CS–PHMG–GA membrane. As humidity increases, the amplitude of the output voltages significantly declines, reflecting the substantial influence of humidity on the surface charge density and dielectric properties of the membrane. Nevertheless, even at a high relative humidity of 90%, the device maintains a considerable peak-to-peak VOC of 862.7 V (Table 2), indicating its ability to sustain a high electrical potential output under humid conditions.
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Fig. 5 (a and b) Open-circuit voltage according to operating humidity and (c and d) volt–ampere–power vs. resistance load characteristics at 40% and 90% humidity of C5P5-based TENG. |
Humidity (%) | C5P5 vs. FEP | ||
---|---|---|---|
Vmax (V) | Vmin (V) | Vp–p (V) | |
40 | 509.8 | −960.8 | 1470.6 |
50 | 454.9 | −1003.9 | 1458.8 |
60 | 454.9 | −721.6 | 1176.5 |
70 | 407.8 | −643.1 | 1050.9 |
80 | 400.1 | −541.2 | 941.3 |
90 | 400.0 | −462.7 | 862.7 |
Fig. 5b and Table 2 illustrate the detailed variation of the Vmax, Vmin, and Vp–p under different humidity conditions. The declining trend of these parameters indicates a reduction in TENG output as humidity increases. This behavior is likely attributed to enhanced electrical conductivity of the material in humid environments, which accelerates charge dissipation. Notably, humidity predominantly influences the negative voltage component, whereas the device maintains a relatively high positive output even under high humidity (up to 90% RH).
Fig. 5c and d further investigate the power output characteristics, based on the positive pulse peak, under varying resistive loads (R) at 40% and 90% relative humidity, respectively. The voltage–current–power profiles display conventional behavior: output voltage increases with load resistance and approaches the open-circuit voltage, while output current decreases accordingly. At 40% RH (Fig. 5c), maximum power output reaches approximately 12 mW at 327 V and 38 μA with a 10 MΩ load. In contrast, at 90% RH (Fig. 5d), the peak power drops to 6.5 mW with 274.5 V and 23.5 μA at the same load. These results indicate the detrimental effect of high humidity on triboelectric performance, with reductions in output power, voltage, and current.
The underlying mechanism of this phenomenon is attributed to the increased surface conductivity under humid conditions, which hinders the accumulation and retention of triboelectric charges. Additionally, moisture may alter surface morphology and dielectric properties, thereby reducing the charge transfer efficiency during contact–separation cycles. Despite its humidity sensitivity, the CS–PHMG–GA-based TENG exhibits robust performance in high humidity environments, demonstrating its potential for practical applications.
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Fig. 6 Antibacterial test results of (a) Cu-based TENG and (b) C5P5-based TENG at different operation times: 0, 30, 60 and 120 seconds. |
Bacteria | Count (CFU mL−1) | |||||||
---|---|---|---|---|---|---|---|---|
Cu-FEP | 30 s | 60 s | 120 s | Cu/C5P5-FEP | 30 s | 60 s | 120 s | |
E. coli | 5.6 × 106 | 5.4 × 104 | 3.4 × 103 | 1.7 × 102 | 1.6 × 104 | 2.1 × 102 | 0 | 0 |
S. aureus | 5.2 × 106 | 6.7 × 103 | 2.1 × 103 | 1.6 × 102 | 1.7 × 104 | 1.7 × 102 | 0 | 0 |
The enhanced antibacterial activity of the C5P5-based TENG can be attributed to two synergistic factors. First, the integration of the CS–PHMG–GA electrode facilitates the generation of stronger electrical pulses via the triboelectric effect, contributing to membrane disruption through electrostatic stimulation. Second, PHMG, a well-known broad-spectrum antimicrobial polymer,32 can partly eliminate bacteria upon direct contact with the electrode surface. Consequently, the material exhibits a dual mode antibacterial mechanism, combining inherent biocidal activity with triboelectrically induced physical disruption.
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