An In Situ Multiscale Study of Ion and Electron Motion in a Lithium‐Ion Battery Composite Electrode

This work reveals the great potential of in situ dielectric spectroscopy for deciphering the motion of ions and electrons on different scales in lithium‐ion battery electrodes. One of the main bottlenecks limiting composite electrode kinetics and energy density, is a critical lack of fundamental understanding with respect to the electronic and the ionic transport within the electrode architecture. The latter is a granular material made up of clusters of particles, in which the particles are separated by boundaries that limit the electronic transport. The ionic transport is also severely restricted due to its tortuous porosity. Here, in situ dielectric spectroscopy is used to study the lithium‐ion battery LiNi_1/3Co_1/3Mn_1/3O₂ composite electrodes. Short‐ and long‐range motions of ions are evident in the low‐frequency region. At higher frequencies, the influence of the adsorbed electrolyte ions on the electronic transfer at the micrometer scale is shown.     

Higher,Stronger, Better…︁ A Review of 5 Volt Cathode Materials for Advanced Lithium‐Ion Batteries

The ever‐increasing demand for high‐performing, economical, and safe power storage for portable electronics and electric vehicles stimulates R&D in the field of chemical power sources. In the past two decades, lithium‐ion technology has proven itself a most robust technology, which delivers high energy and power capabilities. At the same time, current technology requires that the energy and power capabilities of Li‐ion batteries be ‘beefed up’ beyond the existing state of the art. Increasing the battery voltage is one of the ways to improve battery energy density; in Li‐ion cells, the objective of current research is to develop a 5‐volt cell, and at the same time to maintain high specific charge capacity, excellent cycling, and safety. Since current anode materials possess working potentials fairly close to the potential of a lithium metal, the focus is on the development of cathode materials. This work reviews and analyzes the current state of the art, achievements, and challenges in the field of high‐voltage cathode materials for Li‐ion cells. Some suggestions regarding possible approaches for future development in the field are also presented.     

Dislocation Network-Boosted PtNi Nanocatalysts Welded on Nickel Foam for Efficient and Durable Hydrogen Evolution at Ultrahigh Current Densities

Large-scale application of alkaline water electrolysis for high-rate hydrogen production is severely hindered by high electricity cost, mainly due to difficulties to acquire cost-effective catalytic electrodes with both extremely low overpotential and long-term durability at ultrahigh current densities (≥1 A cm⁻²). Here it is demonstrated that by adopting a synthetic method of laser direct writing in liquid nitrogen via a commercial laser welding machine, a remarkably efficient and durable electrode with large area and low platinum content is obtained, where PtNi nanocatalysts with dislocation network are firmly welded on a nickel foam (NF). The dense dislocation network not only improves intrinsic activity of a majority of surface-active sites induced by coupled compressive-tensile strains synergistically promoting both Volmer and Tafel steps of alkaline hydrogen evolution reaction (HER), but also well stabilizes surface dislocations for HER at ultrahigh current densities. Such a robust electrode achieves record-low overpotentials of 5 and 63 mV at 10 and 1000 mA cm⁻² in alkaline medium, respectively, exhibiting negligible activity decay after 300 h chronoamperometric test at 1 A cm⁻². It displays a high Pt mass activity 16 times higher than 20 wt% Pt/C loaded on NF, surpassing most of the recently reported efficient Pt-based catalysts.     

A Layered Inorganic–Organic Open Framework Material as a 4 V Positive Electrode with High‐Rate Performance for K‐Ion Batteries

K‐ion batteries (KIBs) are promising for large‐scale energy storage owing to various advantages like the high abundance of potassium resources in the Earth's crust, high operational potentials, and high power due to fast diffusion of K⁺ ions. However, to realize the practical application of KIBs, electrode materials are needed with high operational voltage, good capacity, long cycle life, and low‐cost. This work reports a layered open framework material, K₂[(VOHPO₄)₂(C₂O₄)], composited with reduced graphene oxide (rGO) as a 4 V positive electrode material for KIBs. The material is prepared by a simple precipitation reaction at room temperature. The material demonstrates reversible K‐extraction/insertion with conventional carbonate ester KPF₆ solutions; however, with low specific capacity and low Coulombic efficiency. A high discharge capacity of >100 mAh g^?1 with good cycling stability and higher Coulombic efficiency is achieved in a highly concentrated electrolyte, 7 mol kg^?1 of potassium bis(fluorosulfonyl)amide (KFSA) in dimethoxyethane (DME) at 0.1 C rate. Due to the facile migration of K⁺ ions in the framework, the material exhibits excellent rate capability with a discharge capacity of 80 mAh g^?1 at 10 C rate, and a good capacity retention of 67% after 500 cycles at 2 C rate.     

Low-threshold,high-resolution,chronically stable intracortical microstimulation by ultraflexible electrodes

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Conductive,Solution‐Processed Dioxythiophene Copolymers for Thermoelectric and Transparent Electrode Applications

Conjugated polymers with high electrical conductivities are attractive for applications in capacitors, biosensors, organic thermoelectrics, and transparent electrodes. Here, a series of solution processable dioxythiophene copolymers based on 3,4‐propylenedioxythiophene (ProDOT) and 3,4‐ethylenedioxythiophene (EDOT) is investigated as thermoelectric and transparent electrode materials. Through structural manipulation of the polymer repeat unit, the conductivity of the polymers upon oxidative solution doping is tuned from 1 × 10^?3 to 3 S cm^?1, with a polymer consisting of a solubilizing alkylated ProDOT unit and an electron‐rich biEDOT unit (referred to as PE₂) showing the highest electrical conductivity. Optimization of the film casting method and screening of dopants result in AgPF₆‐doped PE₂ achieving a high electrical conductivity of over 250 S cm^?1 and a thermoelectric power factor of 7 μW m^?1 K^?2. Oxidized spray cast films of PE₂ are also assessed as a transparent electrode material for use with another electrochromic polymer. This bilayer shows reversible electrochemical switching from a colored charge‐neutral state to a highly transmissive color‐neutral, oxidized state. These results demonstrate that dioxythiophene‐based copolymers are a promising class of materials, with ProDOT–biEDOT serving as a soluble analog to the well‐studied PEDOT as a p‐type thermoelectric and electrode material.     

Manganese Oxide/Carbon Aerogel Composite: an Outstanding Supercapacitor Electrode Material

Manganese oxide/carbon aerogel composite electrodes are prepared by a self‐limiting anodic‐electrochemical deposition of manganese oxide into a binder‐enriched carbon aerogel layer, drop‐cast on a graphite substrate, using 0.1 M Mn(CH₃COO)₂·4H₂O as the electrolyte. Manganese oxide grows in the form of thin nanofibers along the backbone of the carbon aerogel, leaving adequate working space for the electrolyte and enabling a fuller extent of the utilization of the manganese oxide to make the composite an outstanding supercapacitor electrode material. The manganese oxide is determined to be Mn₃O₄ with the Raman spectroscopy and high‐resolution transmission electron microscopy. The rectangularity of the cyclic‐voltammogram loops of the composite electrode is excellent and remains that way for scan rates up to a very‐high value of 500 mV s^?1, indicating extremely good redox reversibility and cycle efficiency. At a scan rate of 25 mV s^?1, the specific capacitance, as measured in 0.5 M Na₂SO₄ for a potential window of 0.1–0.9 V vs. Ag/AgCl, reaches a maximum value of 503 F g^?1 and experiences only a negligible decay of less than 1% at the 6000th cycle, implying an extraordinary cycling stability. The cycling efficiency is as high as 98% at a current density of 8 A g^?1 cm^?2, showing an almost‐ideal capacitive behavior. The power density reaches 48.5 kW kg^?1 and the energy density 21.6 W h kg^?1 at a scan rate of 500 mV s^?1, well above the specifications of current state‐of‐the‐art supercapacitors.     

Photoelectric effects in bacterial chromatophores. Comparison of spectral and direct electrometric methods

Generation of photoelectric potential in chromatophores of Rhodopseudomonas sphaeroides has been measured (i) spectrophotometrically, using electrochromic shift of carotenoid absorption band or (ii) electrometrically, by means of two electrodes separated by a collodion film covered on one side with chromatophores. A 15 ns laser flash was used to induce a single turnover of photosynthetic reaction centers. It was found that results obtained by both methods are similar in (i) direction of electric vector (the chromatophore interior positive) and (ii) redox titration curves (E_m = 10mV). The magnitudes of the photopotential were about 60 and 25 mV, when monitored with spectral and electrometric techniques, respectively. In both cases, the rise times of the photopotentials were faster than time resolution of the techniques used. Decay of the response of carotenoids was found to be slower than that in the collodion film system. The addition of ubiquinone Q₁₀ into the decane solution of asolectin used to impregnate the collodion film led to slowing down of the decay. The carotenoid response decay could be accelerated by FCCP or o-phenanthroline. In the latter case, the shape of the decay curve coincides with decay of the photopotential measured in the collodion film system. It is suggested that decane extracts secondary ubiquinone from chromatophores attached to the collodion film. Such an unfavorable effect can be strongly decreased by added ubiquinone     

Inhibited enzyme electrodes. Part 1: Theoretical model

A theoretical model is developed for an electrochemical sensor for toxic substances which works by measuring the inhibition of the enzyme activity. The enzyme is assumed to follow Michaelis-Menten kinetics and the diffusion kinetic equation describing the concentration profile of the enzyme's substrate in the electrolyte layer between the electrode and the membrane covering the electrode is solved. A complete set of analytical solutions is found which corresponds to a number of different rate limiting processes. The set of solutions is described in a case diagram. The use of cytochrome oxidase in particular is discussed.