A long debate on the charge identity and the associated mechanisms occurring in contact-electrification (CE) (or triboelectrification) has persisted for many decades, while a conclusive model has not yet been reached for explaining this phenomenon known for more than 2600 years! Here, a new method is reported to quantitatively investigate real-time charge transfer in CE via triboelectric nanogenerator as a function of temperature, which reveals that electron transfer is the dominant process for CE between two inorganic solids. A study on the surface charge density evolution with time at various high temperatures is consistent with the electron thermionic emission theory for triboelectric pairs composed of Ti-SiO and Ti-Al O . Moreover, it is found that a potential barrier exists at the surface that prevents the charges generated by CE from flowing back to the solid where they are escaping from the surface after the contacting. This pinpoints the main reason why the charges generated in CE are readily retained by the material as electrostatic charges for hours at room temperature. Furthermore, an electron-cloud-potential-well model is proposed based on the electron-emission-dominatedcharge-transfer mechanism, which can be generally applied to explain all types of CE in conventional materials.
As previously demonstrated, contact-electrification (CE) is strongly dependent on temperature, however the highest temperature in which a triboelectric nanogenerator (TENG) can still function is unknown. Here, by designing and preparing a rotating free-standing mode Ti/SiO TENG, the relationship between CE and temperature is revealed. It is found that the dominant deterring factor of CE at high temperatures is the electron thermionic emission. Although it is normally difficult for CE to occur at temperatures higher than 583 K, the working temperature of the rotating TENG can be raised to 673 K when thermionic emission is prevented by direct physical contact of the two materials via preannealing. The surface states model is proposed for explaining the experimental phenomenon. Moreover, the developed electron cloud-potential well model accounts for the CE mechanism with temperature effects for all types of materials. The model indicates that besides thermionic emission of electrons, the atomic thermal vibration also influences CE. This study is fundamentally important for understanding triboelectrification, which will impact the design and improve the TENG for practical applications in a high temperature environment.
It is known that contact-electrification
(or triboelectrification) usually occurs between two different materials,
which could be explained by several models for different materials
systems (Adv. Mater. 2018, 30, 1706790; Adv. Mater. 2018, 30, 1803968). But contact between two pieces of the chemically
same material could also result in electrostatic charges, although
the charge density is rather low, which is hard to understand from
a physics point of view. In this paper, by preparing a contact-separation
mode triboelectric nanogenerator using two pieces of an identical
material, the direction of charge transfer during contact-electrification
is studied regarding its dependence on curvatures of the sample surfaces.
For materials such as polytetrafluoroethylene, fluorinated ethylene
propylene, Kapton, polyester, and nylon, the positive curvature surfaces
are net negatively charged, while the negative curvature surfaces
tend to be net positively charged. Further verification of the above-mentioned
trends was obtained under vacuum (∼1 Pa) and higher temperature
(≤358
K) conditions. Based on the received data acquired for gentle contacting
cases, we propose a curvature-dependent charge transfer model by introducing
curvature-induced energy shifts of the surface states. However, this
model is subject to be revised if the mutual contact mode turns into
a sliding mode or more complicated hard-pressed contact mode, in which
a rigorous contact between the two pieces of the same material could
result in nanoscale damage/fracture and possible species transfer.
Our study provides a primitive step toward understanding the basics
of contact-electrification.
A charge-transfer model considering
the mixed conductivities of proton, oxygen ion, and free electron
in interface-modified La2Ce2O7 (LCO)
electrolyte is designed to analyze the characteristics of proton ceramics
fuel cell in the field of the open-circuit voltage, internal short-circuit
current, proton-transfer number, discharging curves, oxygen/hydrogen
partial pressure, and cell efficiencies. The properties of anode-supported
single cells with the modified anode–electrolyte interface
containing an in situ formed doped BaCeO3 reaction layer
are compared to those of unmodified cells at various temperatures T and H2O partial pressures. Besides, the electrochemical
impedance spectroscopies of both cells were investigated by the relaxation
time distribution to distinguish different polarization processes.
The results indicated that the reaction interface layer can effectively
reduce the internal short-circuit current density and increase the
proton-transfer number of electrolytes. Importantly, the NiO–BaZr0.1Ce0.7Y0.2O3‑δ anode
can also make more protons transfer from anode to cathode and participate
in the cathodic reaction for LCO-based proton ceramics fuel cell.
The polarization of the cell decreases with the increase of water
partial pressure, which leads to the increase of open-circuit voltage
and cell efficiency.
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