Ab Initio Study of Polytetrafluoroethylene Defluorination for Tribocharging Applications

Abstract

Polytetrafluoroetyhlene (PTFE) is one of the most efficient polymers for green energy-harvesting devices like triboelectric nanogenerators because of its high capability of acquiring and retaining negative charge. Despite its extensive use, the relation between PTFE triboelectric behavior and its electronic properties has never been analyzed. To shed light on this important feature we have studied the electronic properties of PTFE low-index surfaces in the high pressure phase by means of density functional theory. We start by showing that adding either a positive or a negative charge on pristine surfaces is energetically unfavorable. We then demonstrate the role played by surface defects. When a surface fluorine vacancy is introduced the analysis of the band structure reveals that the defect generates a trap state that enables the surface to acquire and retain negative charge.

Rational Design Strategy for Triboelectric Nanogenerators Based on Electron Back Flow and Ionic Defects: The Case of Polytetrafluoroethylene

“…A single PTFE chain was chosen to minimize the configurational complexity, as we showed in a previous study that interchain interactions do not affect PTFE electronic structure. [ 39 ] We found an Au(111) work function value of 5.15 eV, consistent with previous calculations performed [ 44,45 ] and in reasonable agreement with the experimental value of 5.35 eV. [ 46 ] First, we deposited the PTFE chain on gold and studied its more energetically favorable configurations.…”

“…In a previous study, we have shown that the large PTFE triboelectricity can only occur when it undergoes defluorination, due to its electronic structure. [ 39,40 ]…”

“…In a previous study, we have shown that the large PTFE triboelectricity can only occur when it undergoes defluorination, due to its electronic structure. [39,40] In this article, starting from this finding, we devise a theoretical model to predict how PTFE triboelectric performance can be enhanced by defluorination. After showing that PTFE triboelectric charging grows with increasing defluorination by means of first-principles calculations and corroborating this by Kelvin Probe Force Microscopy (KPFM) measurements, [41,42] we show that the macroscopic PTFE triboelectric output is governed by two competing mechanisms.…”

Prediction of the Effective Work Function of Aspirin and Paracetamol Crystals by Density Functional Theory─A First-Principles Study

“…Furthermore, a significant amount of research is being devoted to the study of Tribo-Electric Nano-Generators (TENGs) , to optimize their design and predict their performance. This has contributed to an increase in the use of DFT to study triboelectrification. − …”

Triboelectrification: Backflow and Stuck Charges Are Key

“…Based on our first-principles analysis for mechanisms, only interface potential barrier (IV) showed strong correlation with experimentally measured charge density and material-pair dependency; none of the other models successfully account for experimental observations. The detailed analysis for mechanisms (I–III) is presented in SI Note 5 and Figure S4. − The interface barrier ( W ) is defined as the difference between the maximum electrostatic potential of the interface and the Fermi level at equilibrium. Figure a schematically illustrates a planar electrostatic potential at contact (i.e., equilibrium), reflecting the change of the average potential along the axis perpendicular to the contact surface ( z -axis).…”