**1. Introduction**

Conducting polymers (CPs) are a fascinating family of organic materials that can be easily synthesized with a large diversity of chemical structures and a wide variety of micro- and nano-morphologies, in order to ge<sup>t</sup> tailored macroscopic physical and chemical properties [1]. Further, facile and reversible doping enables a set of unique and tunable optical, electronic and redox properties, particularly an electrical conductivity ranging from insulating to metallic. For these reasons, CPs have found promising application as flexible and lightweight functional materials in opto-electronic devices (e.g., light-emitting diodes, thin-film transistors, electrochromic displays, etc.), energy conversion and storage systems (rechargeable batteries, supercapacitors, solar cells or thermoelectric devices), as well as sensor and actuator devices [1–4]. Owing to the ease of synthesis, low cost, good environmental and chemical stability, high electrical conductivity and capacitance, together with its electrochromic character and ion-exchange properties [5], polyaniline (PAni) has emerged as one of the most industrially important CPs today. These virtues have made PAni an attractive material for a broad spectrum of technologically important applications, such as Li-ion batteries, supercapacitors, electromagnetic interference shielding, electrochemical sensors, and anti-corrosion coatings [1,6]. Also, it is worth mentioning the advent of recent new applications in solid-phase micro-extraction [7] or as (electro)adsorbent/ion-exchange materials for environmental issues [8–10], where the affinity of target pollutants for PAni active groups (charged and neutral amine and imine groups) is exploited to an advantage.

However, PAni has the main shortcomings of a relatively low porosity, specific surface area, slow degradation, and poor mechanical stability because of volume changes produced upon repeated charge/discharge process [2,4,11,12]. Composites of PAni with carbon materials, metal oxides, natural and modified clay minerals, zeolites or mesoporous silica [2,4,9,10], have been extensively investigated with the goal of overcoming these disadvantages and further improving existing properties via synergistic effects. Carbons are outstanding versatile materials with regards to their use as composite supports because of the wide availability of allotropes, microtextures, 0 to 3D dimensionality, and macroscopic forms. In addition, their excellent chemical and thermal stability, good electrical conductivity, large specific surface area, wide range of pore structures, and mechanical strength [11, 12] make them particularly suitable as composite constituents for electrochemical applications or environmental adsorbents. To date, much work has been undertaken on PAni composites with carbon nanotubes [13,14], graphene/reduced graphene oxide nanosheets [4,13], porous carbon foams or rods [15,16] and activated carbon fibers [11,17] or powders [18,19]. Only recently, activated carbon fiber cloths (ACC) have gained popularity as inexpensive, highly porous and flexible mechanical supports for conducting polymers in electrode materials for wearable power microelectronics or roll-up electrochemical systems [8,20–25]. Furthermore, the highly porous 3D conductive framework of the carbon fabric allowed PAni-ACC composites to be directly used as electrodes without the use of insulating binders and conductive additives. Thus, the unique combination of wide accessibility of the fabric pore nanoarchitecture [24]; the binderless CP–carbon interface [25]; and simple, fast and reversible surface redox reactions in PAni [24] has shown to provide the composite with shortened path lengths for direct electron transfer and fast ion transport [20,22,24,25].

PAni-carbon composites have been synthesized by conventional in situ chemical, emulsion/interfacial, vapor chemical or electrochemical polymerization, just to cite a few [6,26,27]. Electrochemical methods have proven to be simple and powerful tools to produce uniform, adherent thin PAni films over a number of different conductive substrates [6], including porous carbon materials, which have served as hard templates capable of transcribing their nanostructure to the growing polymer. However, it is often claimed that electrochemical routes for the preparation of PAni are limited in terms of mass production [23]. In fact, the vast majority of examples of electrosynthesized carbon-PAni composites deal with small size (typically 1 to 2 cm2) samples, while research treating significantly larger areas is scarce [8,28] and generally does not focus on a systematic study of the effect of synthesis variables on the structure and properties of the resulting composites.

In this work, we show the feasibility of producing flexible PAni-ACC composites of large size (~20 cm2) by simple galvanostatic (i.e., constant current) electrolpolymerization in a filter-press electrolyzer, a type of cell design advantageous for industrial scaling-up [29]. The polymer loading density was controlled by changing the electropolymerization time (i.e., the amount of passed charge), and the surface microstructure, chemical composition, porous texture, and thermal stability of the fabricated composites were studied by Scanning Electron microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), N2/CO2 adsorption experiments, and thermogravimetric analysis (TGA). Some important properties for practical application as electrodes in supercapacitors, secondary batteries or as adsorbent materials in dyestuff effluent treatment were examined and correlated with their structural and chemical features. For this purpose, the capacitance and electrical conductivity were derived from cyclic voltammetry (CV) and four-strip probe conductance experiments, and the liquid-phase

adsorptive capability was studied by using aqueous solutions of Acid Red 27, a model dye of anionic azo dyes used in the food and textile industries.

### **2. Materials and Methods**
