# Electrode Kinetics of Ion Jelly and Ion Sol-Gel Redox Materials on Screen-Printed Electrodes
## 1 Introduction  
Hybrid materials have attracted much interest in research aiming for novel materials and applications. Among these are the so-called 'ionogels' that consist of an ionic liquid (IL) immobilized in a solid/gel matrix. Part of their attractiveness is that they possess the conductive properties of ILs and the physical properties of the matrix materials used, and the physicochemical properties can be tuned by choosing from an enormous array of cation-anion pairs. The ionogels described in the literature continue to grow in number and have been the subjects of various reviews [1; 2; 3; 4]. One of the most common approaches is to use polymers to entrap or chemically bind the IL. These IL-infused gels have been explored for various fields of application, from drug delivery agents to catalysts, sensors, and electrolyte membranes [5; 6; 7]. An effort is being made to replace conventional media, solvents, and materials in batteries with IL-based materials, mainly as electrolytes or electrode materials [8]. Likewise, studies on ionogels applied to fuel cells have shown they could be used as proton-exchange membranes on H\({}_{2}\)/O\({}_{2}\) fuel cells [9; 10] and that protic ionogels could result in highly conductive electrolytes with favorable properties [11]. Ionogels have also been studied as catalytic membranes by loading the material with various types of catalysts. Since some ILs work well in enhancing the activity and stability of enzymes [12; 13], some ionogels are an attractive medium for biocatalysis, namely for building electrodes for enzymatic fuel cells or as biosensors [14; 15; 16]. Ion jelly (IJ) is a macromolecular gel material that uses gelatin as the solid phase and is obtained by mixing water and hydrophilic ionic liquids [17]. Ionic and hydrogen bonds are established, creating a microenvironment appropriate for biomolecule immobilization and stabilization, with cytochrome \(c\) and some oxidoreductase having been used as model enzymes for immobilization in IJ [15; 18; 19]. Being gelatin-based, IJ can be easily molded into various shapes, such as membranes or fibers [20; 21]. The IL employed dictates the maximum conductivity of the material. Experiments with 1-buthyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) containing IJ showed that at a high IL/gelatin ratio (3:1 \(w\)/\(w\)), the density of charge carriers per volume is comparable to that of a pure IL, meaning that the ionic conductivity of IJ and ILs were about the same, reaching 10\({}^{-2}\) S/cm [22; 23]. However, studies of the swelling kinetics of IJ in water showed extensive leakage of ionic liquid from the matrix, limiting its applicability [24]. More recently, novel materials based on different types of natural biopolymers and ILs have arisen, combining, for instance, 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) or cholinium lysinate ([Ch][Lys]) and cellulose to yield new membrane materials with high porosity and conductivity [25; 26]. Colloidal ionic liquid gels based on silica structures have also garnered much interest [1; 27]. The most common method to obtain these structures is through the use of alkoxysilanes in the presence of an IL, water, alcohol, and a catalyst, forming a final material suitable for immobilizing biomolecules, depending on the IL used [28; 29; 30; 31]. Tetramethyl orthosilicate (TMOS) and tetraethyl orthosilicate (TEOS) are some of the most commonly used precursors [32], but other derivatives also have been used [30; 33]. A different method of obtaining a silica sol-gel consists of a two-component non-hydrolytic process involving formic acid and an alkoxysilane [34]. [PERSON] and co-workers created a particularly interesting family of ionic liquid sol-gels (also named ionogels by their authors), that was obtained by confining 1-buthyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][TFSI]) in a silica sol-gel through the formic acid method [35].