Polymeric Frameworks as Organic Semiconductors with Controlled Electronic Properties

The rational assembly of monomers, in principle, enables the design of a specific periodicity of polymeric frameworks, leading to a tailored set of electronic structure properties in these solid-state materials. The further development of these emerging systems requires a combination of both experimental and theoretical studies. Here, we investigated the electronic structures of two-dimensional polymeric frameworks based on triazine and benzene rings, by means of electrochemical techniques. The experimental density of states was obtained from quasi-open-circuit voltage measurements through galvanostatic intermittent titration technique, which we show to be in excellent agreement with first principles calculations performed for two and three-dimensional structures of these polymeric frameworks. These findings suggest that the electronic properties do not only depend on the number of stacked layers but also on the ratio of the different aromatic rings

Electric field gradients and bipolar electrochemistry effects on neural growth : A finite element study on immersed electroactive conducting electrode materials

Acknowledgments This work was funded by the European Commission FP6 NEST Program (Contract 028473), RTI2018-097753, MAT2011-24363 and MAT2015-65192-R from the Spanish Science Ministry, La Marató de TV3 Foundation (Identification Number 110131), and Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). LI. Abad thanks MINECO for a Ramón y Cajal Contract (RYC-2013-12640). The authors also thank A. Beardo (NanoTransport group from UAB) for useful discussions.Peer reviewedPostprin

A bioinspired optoelectronically engineered artificial neurorobotics device with sensorimotor functionalities

Development of the next generation of bio- and nano-electronics is inseparably connected to the innovative concept of emulation and reproduction of biological sensorimotor systems and artificial neurobotics. Here, we report for the first time principally new artificial bioinspired optoelectronic sensorimotor system for the controlable immitation of opto-genetically engineered neurons in the biological motor system. The device is based on inorganic optical synapse (In-doped TiO2 nanofilm) assembled into a liquid metal (galinstan) actuator. The optoelectronic synapse generates polarised excitatory and inhibitory postsynaptic potentials to trigger the liquid metal droplet to vibrate and then mimic the expansion and contraction of biological fibre muscle. The low-energy consumption and precise modulation of electrical and mechanical outputs are the distinguished characteristics of fabricated sensorimotor system. This work is the underlying significant step towards the development of next generation of low-energy the internet of things for bioinspired neurorobotic and bioelectronic system

Wireless control of nerve growth using bipolar electrodes : a new paradigm in electrostimulation

Acknowledgements The authors want to thank financial contribution from Grants from Fundacion MARATO TV3 2011 (110131), AEI (ref MAT2015-65192-R, RTI2018-097753-B-I00, PID2021-123276OB-I00, CEX2019-000917-S).Peer reviewe

Lightweight polymer-carbon composite current collector for lithium-ion batteries

A hermetic dense polymer-carbon composite-based current collector foil (PCCF) for lithium-ion battery applications was developed and evaluated in comparison to state-of-the-art aluminum (Al) foil collector. Water-processed LiNi0.5Mn1.5O4 (LMNO) cathode and Li4Ti5O12 (LTO) anode coatings with the integration of a thin carbon primer at the interface to the collector were prepared. Despite the fact that the laboratory manufactured PCCF shows a much higher film thickness of 55 µm compared to Al foil of 19 µm, the electrode resistance was measured to be by a factor of 5 lower compared to the Al collector, which was attributed to the low contact resistance between PCCF, carbon primer and electrode microstructure. The PCCF-C-primer collector shows a sufficient voltage stability up to 5 V vs. Li/Li+ and a negligible Li-intercalation loss into the carbon primer. Electrochemical cell tests demonstrate the applicability of the developed PCCF for LMNO and LTO electrodes, with no disadvantage compared to state-of-the-art Al collector. Due to a 50% lower material density, the lightweight and hermetic dense PCCF polymer collector offers the possibility to significantly decrease the mass loading of the collector in battery cells, which can be of special interest for bipolar battery architectures. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

A survey of advanced battery systems for space applications

The results of a survey on advanced secondary battery systems for space applications are presented. Fifty-five battery experts from government, industry and universities participated in the survey by providing their opinions on the use of several battery types for six space missions, and their predictions of likely technological advances that would impact the development of these batteries. The results of the survey predict that only four battery types are likely to exceed a specific energy of 150 Wh/kg and meet the safety and reliability requirements for space applications within the next 15 years

Nonequilibrium Thermodynamics of Porous Electrodes

We reformulate and extend porous electrode theory for non-ideal active materials, including those capable of phase transformations. Using principles of non-equilibrium thermodynamics, we relate the cell voltage, ionic fluxes, and Faradaic charge-transfer kinetics to the variational electrochemical potentials of ions and electrons. The Butler-Volmer exchange current is consistently expressed in terms of the activities of the reduced, oxidized and transition states, and the activation overpotential is defined relative to the local Nernst potential. We also apply mathematical bounds on effective diffusivity to estimate porosity and tortuosity corrections. The theory is illustrated for a Li-ion battery with active solid particles described by a Cahn-Hilliard phase-field model. Depending on the applied current and porous electrode properties, the dynamics can be limited by electrolyte transport, solid diffusion and phase separation, or intercalation kinetics. In phase-separating porous electrodes, the model predicts narrow reaction fronts, mosaic instabilities and voltage fluctuations at low current, consistent with recent experiments, which could not be described by existing porous electrode models

Induced Dipoles and Possible Modulation of Wireless Effects in Implanted Electrodes. Effects of Implanting Insulated Electrodes on an Animal Test to Screen Antidepressant Activity

There is evidence that Deep Brain Stimulation (DBS) produces health benefits in patients even before initiating stimulation. Furthermore, DBS electrode insertion in rat infralimbic cortex (ILC) provokes antidepressant-like effects before stimulation, due to local inflammation and astrogliosis. Consequently, a significant effect of implanting electrodes is suspected. External fields, similar in magnitude to the brain's endogenous fields, induce electric dipoles in conducting materials, in turn influencing neural cell growth through wireless effects. To elucidate if such dipoles influence depressive-like behavior, without external stimulation, the comparative effect of conducting and insulated electrodes along with the glial response is studied in unstressed rats. Naive and implanted rats with electrically insulated or uninsulated steel electrodes were evaluated in the modified forced swimming test and expression of ILC-glial markers was assessed. An antidepressant-like effect was observed with conducting but not with insulated electrodes. Gliosis was detected in both groups, but astroglial reactivity was larger near uninsulated electrodes. Thus, induced dipoles and antidepressant-like effects were only observed with conducting implants. Such correlation suggests that dipoles induced in electrodes by endogenous fields in turn induce neuron stimulation in a feedback loop between electrodes and neural system. Further research of the effects of unwired conducting implants could open new approaches to regulating neuronal function, and possibly treat neurological disorders.This study was also supported by grants co-financed by the "Fondo Europeo de Desarrollo Regional" (FEDER)-UE "A way to build Europe" from the "Ministerio de Economia y Competitividad" (MINECO: RTI2018-099778-B-I00 (to E.B.), RTI2018-098269-B-I00 (to J.N.) and RTI2018-097753-B-I00 (to N.C.P.) and "Juan de la Cierva Formacion" postdoctoral grant FJC2018-037958-I (to L.P.C.)) and PID2019-108562GB-I00 (to V.T.M); the "Consejeria de Economia, Innovacion, Ciencia y Empleo de la Junta de Andalucia" (CTS-510, to E.B.); the Severo Ochoa Program CEX2019-000917-S (to N.C.P.) and the "Centro de Investigacion Biomedica en Red de Salud Mental-CIBERSAM" (CB/07/09/0033 and CB/07/09/0006

Investigation of Bipolar Electrochemically Exfoliated Graphene for Supercapacitor Applications

Developing a reliable, simple, cost-efficient and eco-friendly method for scale-up production of high-quality graphene-based materials is essential for the broad applications of graphene. Up to now, various manufacturing methods have been employed for synthesizing high quality graphene, however aggregation and restacking has been a major issue and the majority of commercially available graphene products are actually graphite microplates. In this study, bipolar electrochemistry techniques have been used to exfoliate and deposit graphene nanosheets in a single-step process to enable high performance device application. In the first part of this study, bipolar electrochemistry concept is utilized to design a single-step and controllable process for simultaneously exfoliating a graphite source and depositing both graphene oxide (GO) and reduced graphene oxide (rGO) layers on conductive substrates. The electrochemical performance of the fabricated graphene-based materials as the electrode for supercapacitors has been investigated. Areal capacitance of 1.932 mF cm-2 for the rGO, and 0.404 mF cm-2 for GO at a scan rate of 2 mV s-1 were achieved. Moreover, a cut-off frequency of 1820 Hz was obtained, which is a promising characteristic for AC filtering applications. Although the physicochemical characteristics of produced graphene have been evaluated in the first part, the exfoliation and deposition mechanisms were still unclear. In the second part of this dissertation, a novel modified BPE system with an electrically connected graphite-platinum couple acting as the bipolar electrode has been designed in order to decouple and investigate the contribution of anodic/cathodic exfoliation and deposition of graphene in the BPE process. Electron microscopy and infrared spectroscopy results indicate that both anodic and cathodic exfoliation of graphene could take place regardless of the type of polarization; however, the morphology and deposition rate highly depend on the polarization. Furthermore, the graphene fabricated by anodic exfoliation was found to show higher levels of oxidation compared to the graphene produced by cathodic exfoliation. In the last part of this study, for the first time, a vertically aligned graphene layer was deposited on a micro-sized interdigitated gold current collector by a modified bipolar electrochemistry method. Both time domain and frequency domain electrochemical performance of on-chip micro-supercapacitors (MSCs) were evaluated. An areal capacity of 640.9 μF cm-2 at a scan rate of 2 mV s-1 and 239.31 μF cm-2 at discharge current density of 25 μA cm-2 was delivered with an excellent cyclability. Most importantly, the MSC exhibited a very fast response (cut-off frequency of 3486 Hz) and very close to ideal performance (phase angle reached -83.2°) at low frequencies. For the first time, this dissertation reported the modified BPE method as a novel approach for three in one exfoliation, deposition and reduction of high-quality graphene with vertically aligned and porous structure. The unique design of the BPE cell enabled the author to study the BPE mechanisms and measure the bipolar current for the first time. The method could successfully be employed to fabricate fast response microsupercapacitors based on vertically aligned graphene nanosheets

Bipolar anodic electrochemical exfoliation of graphite powders

The electrochemical exfoliation of graphite has attracted considerable attention as a method for large-scale, rapid production of graphene and graphene oxide (GO). As exfoliation typically requires direct electrical contact, and is limited by the shape and/or size of the starting graphite, treatment of small graphite particles and powders, the typical form available commercially, is extremely difficult. In this study, GO nanosheets were successfully prepared from small graphite particles and powders by a bipolar electrochemical process. Graphite samples were placed between two platinum feeder electrodes, and a constant current was applied between the feeder electrodes using dilute sulfuric acid as the electrolyte. Optical microscopy, atomic force microscopy, X-ray diffractometry, Raman spectroscopy, and X-ray photoelectron spectroscopy were employed to examine the samples obtained after electrolysis. The results obtained from these analyses confirmed that anodic electrochemical exfoliation occurs in the graphite samples, and the exfoliated samples are basically highly crystalline GO nanosheets with a low degree of oxidation (C/O = 3.6–5.3). This simple electrochemical method is extremely useful for preparing large amounts of graphene and GO from small particles of graphite