From contact electrification to triboelectric nanogenerators

Area of Science:

• Physics and Engineering of Energy Harvesting
• Materials Science and Electrodynamics

Background:

• The scientific mechanism of contact electrification (CE), also known as triboelectrification, remains debated despite its long history.
• Renewed interest in CE is driven by triboelectric nanogenerators (TENGs) for converting mechanical energy into electrical power.

Purpose of the Study:

• To provide a comprehensive review of CE mechanisms, from fundamental physics to TENG applications.
• To expand Maxwell's equations to incorporate CE-induced polarization for a first-principles derivation of TENG behavior.
• To systematically analyze the electromagnetic behavior and energy conversion of TENGs.

Main Methods:

• Review and analysis of various physics models explaining CE across different phases (solid, liquid, gas).
• Extension of Maxwell's equations with a time-dependent polarization term to model TENGs.
• First-principles derivation of TENG output power, electromagnetic behavior, and current transport.
• Presentation of general and analytical solutions for modified Maxwell's equations.

Main Results:

• Electron transfer is identified as the dominant CE mechanism for solid-solid, liquid-solid, and liquid-liquid interfaces.
• An electron-cloud overlap model is proposed for general CE explanation.
• Modified Maxwell's equations yield insights into TENG energy generation and electromagnetic wave behavior.
• The term ∂P_s/∂t is identified as crucial for energy harvesting and sensor applications.

Conclusions:

• This work establishes a standard theory for quantifying TENG performance and electromagnetic behavior.
• CE mechanisms are clarified, particularly at liquid-solid interfaces, revising the electric double-layer formation.
• TENGs offer a versatile platform for harvesting diverse mechanical energies for various applications.