Soft‐ionic materials with biocompatibility and 3D printability are needed to develop next‐generation devices to interface between electronic and biological signals. Herein, thermoreversible and biocompatible ionic liquid gels or iongels, which can be processed by direct ink writing are reported. The iongels are designed by taking advantage of polyvinyl alcohol/phenol interactions to gelify biocompatible cholinium carboxylate ionic liquids. The obtained iongels are stable, soft, and flexible materials (Young modulus between 14 and 70 kPa) with high ionic conductivity (1.8 × 10–2 S cm–1). Interestingly, they presented thermoreversible properties with gel–sol transitions ranging from 85 and 110 °C, which allows the iongel processing via direct ink writing 3D printing by material extrusion at temperatures over its transition. These 3D printable iongels are integrated into a variety of body sensors applications, namely pressure sensors, motion sensors and electrodes for electrophysiological recordings. The iongels are used as pressure sensors with a sensitivity of 0.1 kPa–1, ten times higher than that of others similar materials reported so far; showing its ability to detect human motion. Furthermore, the iongels showed excellent performance in electrodes for electrocardiography (ECG) recording, presenting good stability over time with electrocardiographic waves maintained their typical shape even after weeks.

The formic acid oxidation (FAO) reaction is studied on platinum in acid solutions using a specially designed flow cell and different experimental techniques, such as open circuit potential decay, chronoamperometry, voltammetric stripping, HCOOH concentration pulses and rotating disc electrode. It allows for the first time the evaluation of the surface coverage of irreversibly adsorbed reaction intermediates on steady state conditions. It is found that the unique species adsorbed irreversibly is CO (E < 0.5 V). It is demonstrated that at higher potentials the adsorption of the intermediate species involved in the FAO is highly reversible and their decomposition is the rate determining step. From the analysis of the results and taken into account available spectroscopic measurements, a new reaction mechanism is proposed, which is compatible with all the known experimental evidences and allows the interpretations of previous unexplained results. The formic acid oxidation (FAO) on metallic electrodes has been intensely studied, particularly because among several candidate fuels for low temperature fuel cells, HCOOH is considered one of the most promising.1,2 However, in spite of the attention paid to this reaction on platinum, its kinetic mechanism remains uncertain. The different authors only agree in that the reaction mechanism involves basically two parallel pathways, direct and indirect respectively.2-12 The direct path starts from the HCOOH electroadsorption step giving an active intermediate, which is then oxidized to CO 2 . Meanwhile, the adsorbed carbon monoxide intermediate is formed in the indirect pathway. In this context, it should be taken into account that at room temperature formic acid is thermodynamically unstable, as its decomposition through both dehydrogenation and dehydration processes has negative values of the reaction Gibbs free energies, although the corresponding reaction rates are negligible. [13][14][15] However, in contact with metals such as those usually employed as electrocatalysts, the spontaneous decomposition is strongly catalyzed, involving adsorbed species. [13][14][15] In electrochemistry this situation corresponds to the open circuit potential (OCP). Consequently, the kinetic studies of the formic acid electrooxidation should consider the simultaneous occurrence of both processes, catalytic (dehydrogenation and/or dehydration) and electrocatalytic (direct and/or indirect), which are coupled by reaction intermediates that are common to both.On the other hand, the revision of the literature indicates that the kinetic study of the FAO was preferably carried out on the basis of the voltammetric response in a solution of HCOOH with H 2 SO 4 or HClO 4 as supporting electrolyte. [2][3][4][5][6][7][8][9][10][11][12] There are some studies that have also used chronoamperometric measurements, 7-11,16 dynamic electrochemical impedance spectroscopy 17,18 and hydrodynamic impedance spectroscopy. 19 In the latter case, a no significant mass transfer effect was reported in the voltammetric an...

The pursuit of sustainable and environmentally friendly materials has been powered by environmental concerns and the decline in oil reserves. Among the different routes toward this end, the replacement of oil-based materials by renewable materials stands out. In this way, protein based materials have gained interest. This review article summarizes the progress achieved in the synthesis of hybrid protein/synthetic polymer nanoparticles which have the potential to be used in industrial applications. Although technical achievements and efficacy proofs concerning the increased compatibility of polymer/protein are already available, practical implementation in industry still represents an additional challenge and should be the focus of interest in future research. The available literature supports the potential of hybrid protein/polymer nanoparticles in the production of ecofriendly alternatives for large scale applications as coatings, paints, adhesives and films.

A kinetic mechanism recently proposed for the formic acid oxidation (FAO) on platinum in acid solutions was analytically solved in order to verify its capability to correlate experimental measurements in steady state conditions. It involves three adsorbed reaction intermediates (COad, HCOOad, OHad) and two reaction pathways. The derived kinetic equations enabled the fitting of the experimental current‐potential curves at three different formic acid concentrations, as well as the evaluation of the corresponding kinetic constants of the elementary steps involved in the mechanism. An expression for the variation of the COad surface coverage on potential was included in the calculations, obtained from measurements of the oxidation charges by voltammetric stripping. Finally, the dependences of the surface coverages of OHad and HCOOad on potential could be simulated, which are consistent with results obtained by other authors through spectroscopic techniques.

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Iongels have attracted much attention over the years as ion-conducting soft materials for applications in several technologies including stimuli-responsive drug release and flexible (bio)electronics. Nowadays, iongels with additional functionalities such as electronic conductivity, self-healing, thermo-responsiveness or biocompatibility are actively being searched for high demanding applications. In this work, we present a simple and rapid synthetic pathway to prepare hyperelastic and thermoreversible iongels. These iongels were prepared by supramolecular crosslinking between polyphenols biomolecules with a hydroxyl-rich biocompatible polymer such as poly(vinyl alcohol) (PVA) in the presence of ionic liquids. Using this strategy, a variety of iongels were obtained by combining different plant-derived polyphenol compounds such as gallic acid, pyrogallol, and tannic acid with imidazolium-based ionic liquids, namely [C 2 mim][N(CN) 2 ] and [C 2 mim][Br]. A suite of characterization tools was used to study the structural, morphological, mechanical, rheological and thermal properties of the supramolecular iongels. These iongels can withstand large deformations (40 % under compression) with full recovery, revealing reversible transitions from solid to liquid state between 87 to 125 °C. Finally, the polyphenol-based thermoreversible iongels shows appropriated properties for their potential application as printable electrolytes for bioelectronics.

Iongels are soft ionic conducting materials, usually composed of polymer networks swollen with ionic liquids (ILs), which are being investigated for applications ranging from energy to bioelectronics. The employment of iongels in bioelectronic devices such as bioelectrodes or body sensors has been limited by the lack of biocompatibility of the ILs and/or polymer matrices. In this work, we present iongels prepared from solely biocompatible materials: (i) a biobased polymer network containing tannic acid as a cross-linker in a gelatin matrix and (ii) three different biocompatible cholinium carboxylate ionic liquids. The resulting iongels are flexible and elastic with Young‘s modulus between 11.3 and 28.9 kPa. The morphology of the iongels is based on a dual polymer network system formed by both chemical bonding due to the reaction of the gelatin’s amines with the polyphenol units and physical interactions between the tannic acid and the gelatin. These biocompatible iongels presented high ionic conductivity values, from 0.003 and up to 0.015 S·cm–1 at room temperature. Furthermore, they showed excellent performance as a conducting gel in electrodes for electromyography and electrocardiogram recording as well as muscle stimulation.