Frequency-engineered MXene supercapacitors enable efficient pulse charging in TENG–SC hybrid systems

A team of researchers from Yonsei University and Pohang University of Science and Technology, led by Professors Sang-Young Lee, Sang-Woo Kim, and Changshin Jo, has unveiled a groundbreaking strategy to overcome the long-standing challenge of efficient energy storage in triboelectric nanogenerator (TENG) systems. Published in Nano-Micro Letters, this work introduces a system-level solution that leverages frequency modulation to significantly enhance the compatibility and charging efficiency between TENGs and supercapacitors (SCs), presenting a major step forward for self-powered electronics and energy-autonomous devices.

Why This Research Matters

• Frequency-Matched Energy Storage: For the first time, the study establishes a quantitative link between the frequency response of SCs (f_SC) and the output pulse duration of TENGs (Δt_TENG), identifying the product f_SC·Δt_TENG as a critical design parameter to maximize charging efficiency.
• Twofold Charging Efficiency: By introducing a hollow-structured MXene/carbon (h-MXene/C) electrode material, the researchers fabricated a high-frequency SC that achieved up to twice the charging efficiency of conventional carbon-based SCs.
• No Circuit Matching Required: This performance was attained without any impedance matching or power management circuits, simplifying system integration for practical applications.

Core Innovation: Frequency-Responsive Supercapacitors with h-MXene/C Electrodes

The research addresses a major hurdle in TENG-SC hybrid systems: the mismatch between high-frequency, short-pulse AC outputs from TENGs and the low-frequency, DC-biased nature of traditional supercapacitors. To solve this, the team developed a high-frequency SC using a three-dimensional hollow-structured MXene-carbon composite (h-MXene/C).

• Structural Advantages: The h-MXene/C electrode features a percolated porous architecture derived from polystyrene templating and thermal annealing, leading to:
  • Faster ion transport
  • Enhanced conductivity
  • Increased accessible surface area
• Superior Frequency Response: The h-MXene/C SC exhibited a characteristic frequency (f_SC) of 3548 Hz, compared to just 39 Hz for the control SC.
• Short Relaxation Time: The relaxation time (τ₀) of the h-MXene/C SC was reduced to 0.38 ms, enabling rapid charge/discharge cycles essential for pulse-based energy harvesting.

Performance Highlights

• TENG–SC Charging Efficiency:
  • At vibration frequencies of 3–7 Hz, the effective Coulombic efficiency (η) of the h-MXene/C SC reached up to 78.1%, outperforming the control by a factor of nearly 2.
  • The hybrid system successfully powered an LED in half the time required by the control SC.
• Versatility and Stability:
  • High charging efficiency was maintained across a wide temperature range (25–70 °C).
  • The h-MXene/C SC was also tested with high-output rotational TENGs, reducing charging time by 13.6% compared to control systems.

Fundamental Insights: f_SC·Δt_TENG as a Design Rule

To validate the universal applicability of this concept, the team fabricated a series of model SCs with varying frequency responses (High-SC, Mid-SC, Low-SC). They observed:

• Linear Relationship: The effective Coulombic efficiency increased linearly with f_SC·Δt_TENG, confirming this metric as a key figure-of-merit for hybrid system design.
• Optimization Strategy:
  • Higher f_SC values were achieved via thin-film electrodes, higher conductivity, and optimized porosity.
  • Longer Δt_TENG values were tuned by adjusting TENG vibration frequencies.

This mechanistic understanding not only highlights the role of electrode design in SCs, but also positions pulse-duration control of TENGs as a powerful and underutilized strategy for improving energy storage.

Additional Functionality: AC Line Filtering

Beyond energy storage, the h-MXene/C SC was shown to function effectively in AC line-filtering, smoothing 60 Hz AC signals with high fidelity, underscoring its potential for broader applications in power conditioning and smart electronics.

Future Outlook

This study marks a pivotal advancement in the development of high-performance, self-powered systems by offering a frequency-matched solution for TENG energy harvesting. The h-MXene/C-based supercapacitors serve as a new class of high-frequency energy storage materials, capable of efficient pulse energy absorption and release. With further optimization, this platform could be extended to:

• Wearable and biomedical electronics
• Wireless sensor networks
• Next-generation power systems for IoT

The researchers propose that frequency-response engineering—centered around the f_SC·Δt_TENG parameter—can guide the design of future TENG–SC hybrid systems and self-powered devices.

Stay tuned for more pioneering contributions from Professors Lee, Kim, and Jo’s teams as they lead the charge toward scalable, high-efficiency energy storage solutions for the era of self-powered electronics!