A Correlative Study of Polyaniline Electropolymerization and its Electrochromic Behavior

Abstract

The electrochemical polymerization of polyaniline (PANI) was studied using correlative measurements of electrochemistry and UV–vis spectroscopy, i.e., spectroelectrochemistry. The electropolymerization of PANI was performed in an acidic medium (1 M HCl) containing 0.1 M aniline with cyclic voltammetry (CV) in a potential window from −0.3 to 1 V and a 50 mV s−1 scan rate. At the same time, UV–vis absorbance spectra in the wavelength range from 200 to 900 nm were measured for every 10 mV change in the CV. The CV results show the oxidation of the monomer at a high positive potential (0.9 V vs Ag), the continuous growth of the PANI film and the transformation between the three best-known forms of PANI redox in the potential range between −0.3 V and 1 V. In parallel, the spectroscopic study confirmed the formation of PANI oxidation. The spectroscopic results showed the formation of the final conductive PANI product (emeraldine salt) due to the absorbance of the formed charge carriers (polarons, bipolarons) during the polymerization. The correlative electrochemical/spectroscopy study gave an additional dimension to the PANI polymerization mechanism, where not only was the oxidation the lead type of reaction, but the reduction was also found to play an important role.

Facile Fabrication of an Ammonia-Gas Sensor Using Electrochemically Synthesised Polyaniline on Commercial Screen-Printed Three-Electrode Systems

“…Leucoemeraldine is known to be an unstable state of PANI [ 61 ]; therefore, after exposing the electrode to air at the end of the electropolymerisation, it is oxidised in the direction of emeraldine. The same conclusion was made after a correlative study of the electrodeposition and electrochromic behaviour of PANI [ 54 ]. Due to the fact that we are performing the electropolymerisation in an HCl electrolyte [ 43 ], the final product is HCl-doped PANI.…”

“…Only the first oxidation peak of the PANIs’ CV behaviour contains information of just the PANI reaction. In all the other peaks, pure bare-electrode material oxidation or reduction is included [ 53 , 54 , 55 ]. Therefore, by controlling the equality of the anodic current of the first oxidation, the reproducibility between polymerisations can be achieved.…”

Carbon Nanomaterials Embedded in Conductive Polymers: A State of the Art

“…The polymerization occurs between 0.1 and at 0.82 V vs. Ag/AgCl electrode and it can be observed an increase in the voltammogram can be observed due to the deposition of the conductive layer and the oxidation of the conductive polymer [ 16 ]. The two peaks correspond to the first oxidation of a dimeric form and then the full oxidation to pernigraniline [ 17 , 18 , 19 ].…”

Preparation of Lithium Titanate Thin Film for Electrochromic Smart Window by Sol-Gel Spin Coating Method

“…Key words: electrochromic; Li4Ti5O12; all-solid-state inorganic device; cycle durability 电致变色是在外加电场作用下，材料内部结构 改变引起其光学性质(透过率、吸收率、反射率等) 变化的现象 [1][2] 。在过去几十年里，各国研究者们对 这一领域进行了深入研究，部分成果已经作为"智 能窗"应用于建筑物和交通运输工具 [3] 。由于电致 变色产品制造成本昂贵、功能单一，目前多为示范 性项目，难以大规模普及 [4][5] 。 现今电致变色研究仍集中在氧化钨 [6][7][8][9][10] 、氧化 镍 [11][12][13] 、普鲁士蓝 [14][15][16] 和聚苯胺 [17][18][19] 等材料上，对 于具有电致变色性能的其他功能材料却鲜有研究。 电致变色器件与电池储能器件有着相同的三明治结 构，以及相似的电化学原理，如果能够直接利用储 能领域已有的材料实现电致变色功能，就会节省大 量研究成本，加速实现当前社会对功能集成化的需 求。 钛酸锂是一种价格低廉、锂入嵌/脱嵌过程中无 应变、充放电平台适中稳定、循环可逆性高的优异 锂离子电池负极材料 [20][21][22][23][24] 。对钛酸锂储能性能的研 究不胜枚举， 但直到 2010 年其电致变色性能才被首 次报道 [25] 。因同时兼具电池储能和电致变色性能， 钛酸锂被认为可能成为这两个领域新的研究热点 [26][27] 。Mandal 和 Li 等 [28][29][30] [34] ，且在截面图上没有观察到分步 沉积可能带来的分层现象。 随着沉积层数的增加，较厚的 Li4Ti5O12 薄膜表 面开始出现一些大孔洞(图 2(d))，甚至发生聚集(图 2(e))。而这些缺陷会使薄膜脆弱易损，寿命急剧降 低 [35] ，这也在长时间循环伏安(CV)测试中得到了证 实。结合 XRD 的结果，可知随着活性物质和退火 过程的增加，晶粒也随之聚集和长大 [36][37] ，致使薄 膜表面变得粗糙。另一方面，表面均匀致密的 FTO 基底可能充当了初始沉积过程的结构诱导因子，而 多次旋涂后 FTO 层被覆盖，这种影响受到抑制 [38] ， 导致缺陷逐渐增加。此外，逐层旋涂也会在新旧膜 层间积累界面应力 [39] ，从而引起表面孔洞聚集。 图 2 不同厚度 Li4Ti5O12 薄膜的 SEM 表截面和 TEM 照片 [40] ，表现为极电流密度和氧化 还原峰之间电势差的增加，同时还可能因此降低其 电化学可逆性 [41] 。从原位透过率变化上 (图 4(d)…”