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. 2021 Oct 8;14(19):5901.
doi: 10.3390/ma14195901.

Electrochromism of Viologen/Polymer Composite: From Gel to Insulating Bulk for High-Voltage Applications

Yongjie Nie  1 , Meng Zhang  2 , Yuanwei Zhu  2 , Yu Jing  3 , Wenli Shi  4 , Guoping Li  2 , Haopeng Chen  2 , Yihang Jiang  2 , Xianping Zhao  1 , Tengfei Zhao  1 , Guanghao Lu  2 , Shengtao Li  2
Affiliations

Electrochromism of Viologen/Polymer Composite: From Gel to Insulating Bulk for High-Voltage Applications

Yongjie Nie et al. Materials (Basel). .

Abstract

Power equipment operates under high voltages, inducing space charge accumulation on the surface of key insulating structures, which increases the risk of discharge/breakdown and the possibility of maintenance workers experiencing electric shock accidents. Hence, a visualized non-equipment space charge detection method is of great demand in the power industry. Typical electrochromic phenomenon is based on redox of the material, triggered by a voltage smaller than 5 V with a continuous current in μA~mA level, which is not applicable to high electric fields above 106 V/m with pA~nA operation current in power equipment. Until now, no naked-eye observation technique has been realized for space charge detection to ensure the operation of power systems as well as the safety of maintenance workers. In this work, a viologen/poly(vinylidene fluoride-co-hexafluoropropylene)(P(VDF-HFP)) composite is investigated from gel to insulating bulk configurations to achieve high-voltage electrical-insulating electrochromism. The results show that viologen/P(VDF-HFP) composite bulk can withstand high electric fields at the 107 V/m level, and its electrochromism is triggered by space charges. This electrochromism phenomenon can be visually extended by increasing viologen content towards 5 wt.% and shows a positive response to voltage amplitude and application duration. As viologen/P(VDF-HFP) composite bulk exhibits a typical electrical insulating performance, it could be attached to the surface of insulating structures or clamped between metal and insulating materials as a space charge accumulation indicator in high-voltage power equipment.

Keywords: electrochromism; high voltage; insulation; polymer; space charge.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Molecular structures of OTf–MVOTF and/P(VDF–HFP); and (b) electrochromic redox process of viologen (OTf–MVOTF).
Figure 2
Figure 2
Structure and preparation of the viologen/P(VDF–HFP) electrochromic device.
Figure 3
Figure 3
(a) The cyclic voltammogram of viologen at different scan rates in DMF solution; (b) the UV–Vis absorption of viologen in DMF solution, c = 10−4 mol/L.
Figure 4
Figure 4
UV–Vis absorption characteristics of viologen (2 wt%)/P(VDF–HFP) gel with 3 V voltage ON (a) and OFF (b); UV–Vis absorption characteristics of viologen (5 wt%)/P(VDF–HFP) gel with 3 V voltage ON (c) and OFF (d).
Figure 5
Figure 5
UV-Vis absorption characteristics of viologen (2 wt%)/P(VDF–HFP) gel with 5 V voltage ON (a,b) and OFF (c,d).
Figure 6
Figure 6
UV–vis absorption characteristics of viologen (5 wt%)/P(VDF–HFP) gel with 5 V voltage ON (a,b) and OFF (c,d).
Figure 7
Figure 7
Electrochromism of 2 wt% and 5 wt% viologen/P(VDF–HFP)-insulating bulks under 6 kV voltages in up to 1 h.
Figure 8
Figure 8
Dielectric spectra of 2 wt% (a) and 5 wt% (b) viologen/P(VDF–HFP) bulks in frequency of 10−1~106 Hz, temperature of −100~100 °C.
Figure 9
Figure 9
Volume resistivity spectra of 2 wt% (a) and 5 wt% (b) viologen/P(VDF–HFP) bulks in frequency of 10−1~106 Hz, temperature of −100~100 °C.
Figure 10
Figure 10
Variations in volume resistivity with 1 wt%~5 wt% viologen content in viologen/P(VDF–HFP) bulks.
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