Conducting polymers have been widely explored as coating materials for metal electrodes to improve neural signal recording and stimulation because of their mixed electronic–ionic conduction and biocompatibility. In particular, the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) is one of the best candidates for biomedical applications due to its high conductivity and good electrochemical stability. Coating metal electrodes with PEDOT has shown to enhance the electrode’s performance by decreasing the impedance and increasing the charge storage capacity. However, PEDOT-coated metal electrodes often have issues with delamination and stability, resulting in decreased device performance and lifetime. In this work, we were able to electropolymerize PEDOT coatings on sharp platinum-iridium recording and stimulating neural electrodes and demonstrated its mechanical and electrochemical stability. Electropolymerization of PEDOT:tetrafluoroborate was carried out in three different solvents: propylene carbonate, acetonitrile, and water. The stability of the coatings was assessed via ultrasonication, phosphate buffer solution soaking test, autoclave sterilization, and electrical pulsing. Coatings prepared with propylene carbonate or acetonitrile possessed excellent electrochemical stability and survived autoclave sterilization, prolonged soaking, and electrical stimulation without major changes in electrochemical properties. Stimulating microelectrodes were implanted in rats and stimulated daily, for 7 and 15 days. The electrochemical properties monitored in vivo demonstrated that the stimulation procedure for both coated and uncoated electrodes decreased the impedance.

Spontaneous grafting of 9,10-phenanthrenequinone (PQ) on Black Pearls carbon by reduction of the corresponding in situ generated diazonium cations has been successfully achieved.

We propose a simple yet very versatile method to functionalize conducting polymers by the use of a bifunctional copolymer that can act as a redox-active dopant. A copolymer composed of 4-vinylcatechol and styrenesulfonic acid moieties was used as both the source of ions and the dopant for poly(3,4-ethylenedioxythiophene) (PEDOT) electropolymerization. The composite polymer shows an improvement in capacity which originates from the catechol faradaic reaction (52 mAh g −1 vs 18 mAh g −1 ) compared to PEDOT:poly(styrenesulfonate) (PSS). The active material utilization in the composite polymer was further investigated by using HClO 4 as a secondary dopant and by increasing the ratio of neutral 4-vinylcatechol in the bifunctional copolymer to obtain a higher energy density electrode. Characterization by X-ray diffraction and atomic force microscopy hints at phase separation between PEDOT and the doping copolymer. Consequently, 4-vinylcatechol electronic connection to PEDOT is weakened at the microscale which prevents its complete utilization. These findings show the complex interaction between a conducting polymer and its dopant. The possibility to further tune the bifunctional copolymer composition, structure, and polymerization strategy should lead to improved energy storage performances and other new functional materials that explore properties imbedded in molecular units.

The trade-off between energy density and power capabilities is a challenge for Li-ion battery design as it highly depends on the complex porous structures that holds the liquid electrolyte. Specifically, mass-transport limitations lead to large concentration gradients in the solution-phase and subsequently to crippling overpotentials. The direct study of these solution-phase concentration profiles in Li-ion battery positive electrodes has been elusive, in part because they are shielded by an opaque and paramagnetic matrix. Herein we present a new methodology employing synchrotron hard X-ray fluorescence to observe the concentration gradient formation within Li-ion battery electrodes in operando. This methodology is substantiated with data collected on a model LiFePO 4 /Li cell using a 1 M LiAsF 6 in 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) electrolyte under galvanostatic and intermittent charge profiles. As such, the technique holds great promise for optimization of new composite electrodes and for numerical model validation.

Conducting polymers, specifically poly (3,4-ethylenedioxythiophene) (PEDOT), have recently been coated onto Pt/Ir electrodes intended for neural applications, such as deep brain stimulation (DBS). This modification reduces impedance, increases biocompatibility, and increases electrochemically active surface area. However, direct electropolymerization of PEDOT onto a metallic surface results in physically adsorbed films that suffer from poor adhesion, precluding their use in applications requiring in vivo functionality (i.e. DBS treatment). In this work, we propose a new attachment strategy, whereby PEDOT is covalently attached to an electrode surface through an intermediate phenylthiophene layer, deposited by electrochemical reduction of a diazonium salt. Our electrodes retain their electrochemical performance after more than 1000 redox cycles, whereas physically adsorbed films begin to delaminate after only 40 cycles. Additionally, covalently attached PEDOT maintained strong adhesion even after 10 minutes of ultrasonication (vs. 10 s for physically adsorbed films), confirming its suitability for long-term implantation in the brain. The simple two-step covalent attachment strategy proposed here is particularly useful for neural applications and could also be adapted to introduce other functionalities on the conducting surface.

Lithium ion battery performance becomes increasingly limited by ionic transport as the current demand increases. Especially detrimental is the transport within the liquid electrolyte that fills the porous electrode, yet reliable measurement of practical lithium diffusivity within this complex structure has been a longstanding challenge. In this work, we have developed a “single sided” analytical technique to determine the diffusivity in porous networks using scanning electrochemical microscopy (SECM) and a molecular redox marker. SECM surface mapping of porous films shows measurement consistency, and diffusion limited currents through a test structure with well-defined geometry matches the results of numerical modeling within 10%. Diffusivity measurement shows significant deviation from the Bruggeman model for porosities below 60%. The developed technique is applicable to all porous structures independent of their electronic conductivity. Importantly, for lithium-ion batteries the technique does not require free-standing electrodes and therefore is applicable to industrially relevant high power electrodes as a tool for optimization as well as for quality control.

The drastic distortion of potentiodynamic polarization curves measured at high potential scan rates prevents the extraction of accurate kinetic parameters. In this work, we start by measuring potentiodynamic polarization curves of AA7075 at scan rates ranging from 0.167 mV·s−1 to 100 mV·s−1, in an acidic 0.62 M NaH2PO4 solution and a near-neutral 3.5 wt% NaCl solution. Changes in potentiodynamic polarization curves are observed not only at different scan rates and electrolytes but also between replicated experiments. Contrary to what was reported in previous studies, the disturbance of charging current associated with high scan rates does not satisfactorily explain the potentiodynamic polarization shape. Instead, the high field model that incorporates the kinetics of anodic oxide growth successfully captures the features of experimental potentiodynamic polarization curves. Compared to Tafel’s theory, the high field model explains remarkably the changing kinetics with scan rates, electrolytes, and the variance between measurements performed at different sites.

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