Enhanced Chemical and Electrochemical Stability of Polyaniline-Based Layer-by-Layer Films

Abstract

Polyaniline (PANI) has been widely used as an electroactive material in various applications including sensors, electrochromic devices, solar cells, electroluminescence, and electrochemical energy storage, owing to PANI’s unique redox properties. However, the chemical and electrochemical stability of PANI-based materials is not sufficiently high to maintain the performance of devices under many practical applications. Herein, we report a route to enhancing the chemical and electrochemical stability of PANI through layer-by-layer (LbL) assembly. PANI was assembled with different types of polyelectrolytes, and a comparative study between three different PANI-based layer-by-layer (LbL) films is presented here. Polyacids of different acidity and molecular structure, i.e., poly(acrylic acid) (PAA), polystyrene sulfonate (PSS), and tannic acid (TA), were used. The effect of polyacids’ acidity on film growth, conductivity, and chemical and electrochemical stability of PANI was investigated. The results showed that the film growth of the LbL system depended on the acidic strength of the polyacids. All LbL films exhibited improved chemical and electrochemical stability compared to PANI films. The doping level of PANI was strongly affected by the type of dopants, resulting in different chemical and electrochemical properties; the strongest polyacid (PSS) can provide the highest conductivity and chemical stability of conductive PANI. However, the electrochemical stability of PANI/PAA was found to be better than all the other films.

Recovery of Electrochemical Properties of Polyaniline-Based Multilayer Films with Improved Electrochemical Stability

“…As depicted in Figure f, film roughness also increased with the number of bilayers. These results are consistent with our previous finding that the higher molecular weight of polyacid results in faster film growth and higher film roughness in dip-assisted and spray-assisted LbL assembly techniques …”

“…On the other hand, the weaker polyacid PAA formed much more porous and open structures due to the low density of charged carboxylic acid group in PAA. The PANI/PAA film fabricated by the SA LbL assembly technique has higher roughness and is more porous than previously reported PANI/PAA films assembled by the dip-assisted LbL technique . In SA LbL assembly, polymers have insufficient time for diffusion, adsorption, and rearrangement of chains, unlike dip-assisted LbL assembly .…”

“…EIS was performed to study the change in electrochemical properties of PANI-based films after the reactivation process. The Nyquist plot in Figure b shows that the PANI/PSS film has the highest conductivity, followed by PANI/PAA, PANI/TA, and PANI homopolymer, which is consistent with our previous study . All PANI-based films exhibited a decrement in the conductivity characteristics after electrochemical cycling, which might be caused by the dedoping and gradual conversion of ES PANI to EB during discharge (Figure c).…”

“…For instance, PANI films commonly suffer from the loss of electroactivity during the repeated electrochemical tests . Many efforts have been reported to enhance the PANI stability and durability, such as doping, structural engineering, incorporating carbon-based materials or inorganic materials, and so on. − Previously, PANI multilayer films having improved electrochemical stability were fabricated using polymer dopants, showing that poly­(acrylic acid) (PAA) can improve the PANI electrochemical stability, whereas polystyrene sulfonate (PSS) enhances the conductivity and chemical stability of PANI . Even if PANI–polyacid multilayer films possess improved electrochemical stability compared to PANI homopolymers, their electroactivity characteristics still gradually degrade .…”

1,4-Bis((9H-Carbazol-9-yl)Methyl)Benzene-Containing Electrochromic Polymers as Potential Electrodes for High-Contrast Electrochromic Devices

“…Nowadays, the most popular π–conjugated polymers (e.g., polythiophenes [ 18 ], polyaniline [ 19 , 20 ], polyindoles [ 21 ], polycarbazole [ 22 , 23 ], polyfurans [ 24 ], polypyrenes [ 25 ], and PEDOT-PSS [ 26 ]) are widely applied to organic electrochromic devices. Among the many promising π–conjugated polymers, carbazole-containing polymers have attractive optoelectronic properties due to their hole-transporting characteristics via the radical cation and dication species as well as their ease of oxidation through the nitrogen centers.…”