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1. A universal model of electrochemical safety limits in vivo for electrophysiological stimulation

   https://doi.org/10.3389/fnins.2022.972252  

   Vatsyayan, Ritwik ; Dayeh, Shadi A. ( October 2022 , Frontiers in Neuroscience)

   Electrophysiological stimulation has been widely adopted for clinical diagnostic and therapeutic treatments for modulation of neuronal activity. Safety is a primary concern in an interventional design leveraging the effects of electrical charge injection into tissue in the proximity of target neurons. While modalities of tissue damage during stimulation have been extensively investigated for specific electrode geometries and stimulation paradigms, a comprehensive model that can predict the electrochemical safety limits in vivo doesn’t yet exist. Here we develop a model that accounts for the electrode geometry, inter-electrode separation, material, and stimulation paradigm in predicting safe current injection limits. We performed a parametric investigation of the stimulation limits in both benchtop and in vivo setups for flexible microelectrode arrays with low impedance, high geometric surface area platinum nanorods and PEDOT:PSS, and higher impedance, planar platinum contacts. We benchmark our findings against standard clinical electrocorticography and depth electrodes. Using four, three and two contact electrochemical impedance measurements and comprehensive circuit models derived from these measurements, we developed a more accurate, clinically relevant and predictive model for the electrochemical interface potential. For each electrode configuration, we experimentally determined the geometric correction factors that dictate geometry-enforced current spreading effects. We also determined the electrolysis windowmore »from cyclic-voltammetry measurements which allowed us to calculate stimulation current safety limits from voltage transient measurements. From parametric benchtop electrochemical measurements and analyses for different electrode types, we created a predictive equation for the cathodal excitation measured at the electrode interface as a function of the electrode dimensions, geometric factor, material and stimulation paradigm. We validated the accuracy of our equation in vivo and compared the experimentally determined safety limits to clinically used stimulation protocols. Our new model overcomes the design limitations of Shannon’s equation and applies to macro- and micro-electrodes at different density or separation of contacts, captures the breakdown of charge-density based approaches at long stimulation pulse widths, and invokes appropriate power exponents to current, pulse width, and material/electrode-dependent impedance.« less
2. Characterization of Ag/AgCl Dry Electrodes for Wearable Electrophysiological Sensing

   https://doi.org/10.3389/felec.2021.700363  

   Lee, Min Suk ; Paul, Akshay ; Xu, Yuchen ; Hairston, W. David ; Cauwenberghs, Gert ( January 2022 , Frontiers in Electronics)

   With the rising need for on-body biometric sensing, the development of wearable electrophysiological sensors has been faster than ever. Surface electrodes placed on the skin need to be robust in order to measure biopotentials from the body reliably and comfortable for extended wearability. The electrical stability of nonpolarizable silver/silver chloride (Ag/AgCl) and its low-cost, commercial production have made these electrodes ubiquitous health sensors in the clinical environment, where wet gels and long wires are accommodated by patient immobility. However, smaller, dry electrodes with wireless acquisition are essential for truly wearable, continuous health sensing. Currently, techniques for the robust fabrication of custom Ag/AgCl electrodes are lacking. Here, we present three methods for the fabrication of Ag/AgCl electrodes: oxidizing Ag in a chlorine solution, electroplating Ag, and curing Ag/AgCl ink. Each of these methods is then used to create three different electrode shapes for wearable application. Bench-top and on-body evaluation of the electrode techniques was achieved by electrochemical impedance spectroscopy (EIS), calculation of variance in electrocardiogram (ECG) measurements, and analysis of auditory steady-state response (ASSR) measurement. Microstructures produced on the electrode by each fabrication technique were also investigated with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The custom Ag/AgCl electrodesmore »were found to be efficient in comparison with standard, commercial Ag/AgCl wet electrodes across all three of our presented techniques, with Ag/AgCl ink shown to be the better out of the three in bench-top and biometric recordings.« less
3. Cascade synthesis and optoelectronic applications of intermediate bandgap Cu3VSe4 nanosheets

   https://doi.org/10.1038/s41598-020-78649-9  

   Liu, Mimi ; Lai, Cheng-Yu ; Zhang, Meng ; Radu, Daniela R. ( December 2020 , Scientific Reports)

   Two-dimensional (2D) ternary materials recently generated interest in optoelectronics and energy-related applications, alongside their binary counterparts. To date, only a few naturally occurring layered 2D ternary materials have been explored. The plethora of benefits owed to reduced dimensionality prompted exploration of expanding non-layered ternary chalcogenides into the 2D realm. This work presents a templating method that uses 2D transition metal dichalcogenides as initiators to be converted into the corresponding ternary chalcogenide upon addition of copper, via a solution-phase synthesis, conducted in high boiling point solvents. The process starts with preparation of VSe₂nanosheets, which are next converted into Cu₃VSe₄sulvanite nanosheets (NSs) which retain the 2D geometry while presenting an X-ray diffraction pattern identical with the one for the bulk Cu₃VSe₄. Both the scanning electron microscopy and transmission microscopy electron microscopy show the presence of quasi-2D morphology. Recent studies of the sulfur-containing sulvanite Cu₃VS₄highlight the presence of an intermediate bandgap, associated with enhanced photovoltaic (PV) performance. The Cu₃VSe₄nanosheets reported herein exhibit multiple UV–Vis absorption peaks, related to the intermediate bandgaps similar to Cu₃VS₄and Cu₃VSe₄nanocrystals. To test the potential of Cu₃VSe₄NSs as an absorber for solar photovoltaic devices, Cu₃VSe₄NSs thin-films deposited on FTO were subjected to photoelectrochemical testing, showing p-type behavior andmore »stable photocurrents of up to ~ 0.036 mA/cm². The photocurrent shows a ninefold increase in comparison to reported performance of Cu₃VSe₄nanocrystals. This proves that quasi-2D sulvanite nanosheets are amenable to thin-film deposition and could show superior PV performance in comparison to nanocrystal thin-films. The obtained electrical impedance spectroscopy signal of the Cu₃VSe₄ NSs-FTO based electrochemical cell fits an equivalent circuit with the circuit elements of solution resistance (R_s), charge-transfer resistance (R_ct), double-layer capacitance (C_dl), and Warburg impedance (W). The estimated charge transfer resistance value of 300 Ω cm²obtained from the Nyquist plot provides an insight into the rate of charge transfer on the electrode/electrolyte interface.

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4. (Digital Presentation) Activating the Ion Transmission at the Cathode-Electrolyte Interface in All-Solid-State Batteries

   https://doi.org/10.1149/MA2022-012384mtgabs  

   Zhang, Yuxuan ; Kivevele, Thomas ; Song, Han Wook ; Lee, Sunghwan ( July 2022 , ECS Meeting Abstracts)

   All-solid-state batteries (ASSBs) have garnered increasing attention due to the enhanced safety, featuring nonflammable solid electrolytes as well as the potential to achieve high energy density. 1 The advancement of the ASSBs is expected to provide, arguably, the most straightforward path towards practical, high-energy, and rechargeable batteries based on metallic anodes. 1 However, the sluggish ion transmission at the cathode-electrolyte (solid/solid) interface would result in the high resistant at the contact and limit the practical implementation of these all solid-state materials in real world batteries. 2 Several methods were suggested to enhance the kinetic condition of the ion migration between the cathode and the solid electrolyte (SE). 3 A composite strategy that mixes active materials and SEs for the cathode is a general way to decrease the ion transmission barrier at the cathode-electrolyte interface. 3 The active material concentration in the cathode is reduced as much as the SE portion increases by which the energy density of the ASSB is restricted. In addition, the mixing approach generally accompanies lattice mismatches between the cathode active materials and the SE, thus providing only limited improvements, which is imputed by random contacts between the cathode active materials and the SE during the mixingmore »process. Implementing high-pressure for the electrode and electrolyte of ASSB in the assembling process has been verified is a but effective way to boost the ion transmission ability between the cathode active materials and the SE by decreasing the grain boundary impedance. Whereas the short-circuit of the battery would be induced by the mechanical deformation of the electrolyte under high pressure. 4 Herein, we demonstrate a novel way to address the ion transmission problem at the cathode-electrolyte interface in ASSBs. Starting from the cathode configuration, the finite element method (FEM) was employed to evaluate the current concentration and the distribution of the space charge layer at the cathode-electrolyte interface. Hierarchical three-dimensional (HTD) structures are found to have a higher Li + transfer number (t Li+ ), fewer free anions, and the weaker space-charge layer at the cathode-electrolyte interface in the resulting FEM simulation. To take advantage of the HTD structure, stereolithography is adopted as a manufacturing technique and single-crystalline Ni-rich (SCN) materials are selected as the active materials. Next, the manufactured HTD cathode is sintered at 600 °C in an N 2 atmosphere for the carbonization of the resin, which induces sufficient electronic conductivity for the cathode. Then, the gel-like Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) precursor is synthesized and filled into the voids of the HTD structure cathode sufficiently. And the filled HTD structure cathodes are sintered at 900 °C to achieve the crystallization of the LATP gel. Scanning transmission electron microscopy (STEM) is used to unveil the morphology of the cathode-electrolyte interface between the sintered HTD cathode and the in-situ generated electrolyte (LATP). A transient phase has been found generated at the interface and matched with both lattices of the SCN and the SE, accelerating the transmission of the Li-ions, which is further verified by density functional theory calculations. In addition, Electron Energy Loss Spectroscopy demonstrates the preserved interface between HTD cathode and SEs. Atomic force microscopy is employed to measure the potential image of the cross-sectional interface by the peak force tapping mode. The average potential of modified samples is lower than the sample that mix SCN and SEs simply in the 2D planar structure, which confirms a weakened space charge layer by the enhanced contact capability as well as the ion transmission ability. To see if the demonstrated method is universally applicable, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) is selected as the cathode active material and manufactured in the same way as the SCN. The HTD cathode based on NCM811 exhibits higher electrochemical performance compared with the reference sample based on the 2D planar mixing-type cathode. We believe such a demonstrated universal strategy provides a new guideline to engineer the cathode/electrolyte interface by revolutionizing electrode structures that can be applicable to all-solid-state batteries. Figure 1. Schematic of comparing of traditional 2D planar cathode and HTD cathode in ASSB Tikekar, M. D. , et al. , Nature Energy (2016) 1 (9), 16114 Banerjee, A. , et al. , Chem Rev (2020) 120 (14), 6878 Chen, R. , et al. , Chem Rev (2020) 120 (14), 6820 Cheng, X. , et al. , Advanced Energy Materials (2018) 8 (7) Figure 1« less
5. Tunnel structured manganese oxide nanowires as redox active electrodes for hybrid capacitive deionization

   https://doi.org/https://doi.org/10.1016/j.nanoen.2017.12.015  

   Byles, Bryan W. ; Cullen, David A. ; More, Karren L. ; Pomerantseva, Ekaterina ( January 2018 , Nano energy)

   Hybrid capacitive deionization (HCDI), which combines a capacitive carbon electrode and a redox active electrode in a single device, has emerged as a promising method for water desalination, enabling higher ion removal capacity than devices containing two carbon electrodes. However, to date, the desalination performance of few redox active materials has been reported. For the first time, we present the electrochemical behavior of manganese oxide nanowires with four different tunnel crystal structures as faradaic electrodes in HCDI cells. Two of these phases are square tunnel structured manganese oxides, α-MnO2 and todorokite-MnO2. The other two phases have novel structures that cross-sectional scanning transmission electron microscopy analysis revealed to have ordered and disordered combinations of structural tunnels with different dimensions. The ion removal performance of the nanowires was evaluated not only in NaCl solution, which is traditionally used in laboratory experiments, but also in KCl and MgCl2 solutions, providing better understanding of the behavior of these materials for desalination of brackish water that contains multiple cation species. High ion removal capacities (as large as 27.8 mg g−1, 44.4 mg g−1, and 43.1 mg g−1 in NaCl, KCl, and MgCl2 solutions, respectively) and high ion removal rates (as large as 0.112 mg g−1more »s−1, 0.165 mg g−1 s−1, and 0.164 mg g−1 s−1 in NaCl, KCl, and MgCl2 solutions, respectively) were achieved. By comparing ion removal capacity to structural tunnel size, it was found that smaller tunnels do not favor the removal of cations with larger hydrated radii, and more efficient removal of larger hydrated cations can be achieved by utilizing manganese oxides with larger structural tunnels. Extended HCDI cycling and ex situ X-ray diffraction analysis revealed the excellent stability of the manganese oxide electrodes in repeated ion removal/ion release cycles, and compositional analysis of the electrodes indicated that ion removal is achieved through both surface redox reactions and intercalation of ions into the structural tunnels. This work contributes to the understanding of the behavior of faradaic materials in electrochemical water desalination and elucidates the relationship between the electrode material crystal structure and the ion removal capacity/ion removal rate in various salt solutions.« less