Unexpected Improved Performance of ALD Coated LiCoO2/Graphite Li‐Ion Batteries

The performance of Al₂O₃ atomic layer deposition (ALD) coatings for LiCoO₂/natural graphite (LCO/NG) batteries is investigated, where various permutations of the electrodes are coated in a full battery. Coating both electrodes with ～1 nm of alumina as well as coating only the LCO (positive electrode) enables improved performance when cycling at high voltage, where the LCO is known to degrade. However, we found that coating only the NG (negative electrode) also improves the performance of the whole battery when cycling at high voltage. Under these conditions, the uncoated LCO (positive electrode) should degrade quickly, and the NG should be unaffected. A variety of characterization techniques show the surface reactions that occur on the negative electrode and positive electrode are related, resulting in the enhanced performance of the uncoated LCO.     

Interaction of nucleic acids with electrically charged surfaces. VI. A comparative study on the electrochemical behaviour of native and denatured DNAs at graphite electrodes.

Adsorption and electrochemical oxidation of deoxyribonucleic acid (DNA) at a pyrolytic graphite electrode (PGE) and a paraffin wax-impregnated spectroscopic graphite electrode (WISGE) were studied using differential pulse voltammetry. DNA is adsorbed at the surface of the graphite electrodes in a broad range of potentials including the potentials of electrochemical oxidation of DNA. Both native and denatured DNAs yield two single, well-defined and separated peaks, G and A, on the differential pulse voltammograms at the PGE and WISGE. The more negative peak, G, corresponds to electrochemical oxidation of adenine residues. Peaks G and A of native DNA occur at the same potentials as peaks G and A of denatured DNA. However, electrochemical oxidation of adenine and guanine residues at graphite electrodes is markedly suppressed in native DNA. The heights of the peaks G and A represent a sensitive indicator of the helix-coil transition of DNA. An analysis of the product of interaction of a sample of native DNA with a large pyrolytic graphite electrode in the presence of formaldehyde at approximately neutral pH did not prove changes in the secondary structure of native DNA due to its interaction with the graphite electrode. It is suggested that the decreased differential pulse-voltammetric activity of native DNA is connected with its decreased flexibility.     

Electrode materials for nitric oxide detection.

Nitric oxide oxidation signals were compared for uniform test electrodes of platinum, iridium, palladium, rhodium, ruthenium, gold, graphite, and a nickel-porphyrin on graphite in deaerated phosphate-buffered saline (pH 7.0) at 35 degrees C. All tested materials detected NO(*) amperometrically. Current densities (A/M/cm(2) +/- S.D.) were Ir (0.021 +/- 0.002), Rh (0.088 +/- 0.012), graphite (0.117 +/- 0.018), Pd (0.118 +/- 0.033), Au (0.149 +/- 0. 039), Pt (0.237 +/- 0.117), Ni (II)-tetra(3-methoxy-4-hydroxyphenyl) porphyrin on graphite (0.239 +/- 0.009), and Ru (0.680 +/- 0.058). NO(*) oxidation current on ruthenium was maximal at 675 mV (vs Ag/AgCl), nearly three times that on the next-best materials, platinum and Ni-porphyrin on graphite poised at 800 mV. The measured limit of detection for NO(*) on Ru was below 3 nM. Enhanced NO(*) oxidation current on ruthenium is apparently due to formation of nitrosyl- or chloronitrosyl-ruthenium complexes at the electrode surface. At fixed potentials above 675 mV, ruthenium exhibited an even larger NO(*) response, characterized by current flow opposite in polarity to an oxidation, which we hypothesize reflects suppression of the oxidative background current (presumably due to chloride oxidation or to the electrolysis of water) by a film consisting of nitrosyl- or chloronitrosyl-ruthenium complexes. The sensitive response of the ruthenium electrode to the direct oxidation of NO(*) may be useful in sensors for biomedical applications.     

Interaction of nucleic acids with electrically charged surfaces. VI. A comparative study on the electrochemical behaviour of native and denatured DNAs at graphite electrodes

Adsorption and electrochemical oxidation of deoxyribonucleic acid (DNA) at a pyrolytic graphite electrode (PGE) and a paraffin wax-impregnated spectroscopic graphite electrode (WISGE) were studied using differential pulse voltammetry. DNA is adsorbed at the surface of the graphite electrodes in a broad range of potentials including the potentials of electrochemical oxidation of DNA. Both native and denatured DNAs yield two single, well-defined and separated peaks, G and A, on the differential pulse voltammograms at the PGE and WISGE. The more negative peak, G, corresponds to electrochemical oxidation of guanine residues, whereas the more positive peak, A, corresponds to electrochemical oxidation of adenine residues. Peaks G and A of native DNA occur at the same potentials as peaks G and A of denatured DNA. However, electrochemical oxidation of adenine and guanine residues at graphite electrodes is markedly suppressed in native DNA. The heights of the peaks G and A represent a sensitive indicator of the helix-coil transition of DNA. An analysis of the product of interaction of a sample of native DNA with a large pyrolytic graphite electrode in the presence of formaldehyde at approximately neutral pH did not prove changes in the secondary structure of native DNA due to its interaction with the graphite electrode. It is suggested that the decreased differential pulse-voltammetric activity of native DNA is connected with its decreased flexibility.     

The Use of Cyclic Voltammetry to Detect Biofilms formed by Pseudomonas fluorescens on Platinum Electrodes

The development of an electrochemical detector to monitor the in situ formation of biofilms is described. The detector consisted of an electrochemical cell containing three electrodes, whose response to the application of a potential profile to the working electrode was sensitive to the amount of biofilm present on the surface. The electrochemical technique used was repetitive cyclic voltammetry. Differences between the response of the uncolonised electrode and after Pseudomonas fluorescens biofilms of different ages were grown on its surface were determined. The results show that cyclic voltammetry applied to platinum electrodes can be used to detect young biofilms. The development of the shape of the voltammogram as the potential is cycled may constitute a means of providing information on the coverage of the surface. Observation of the platinum electrodes before and after the electrochemical measurements showed that even after 30 min of recycling, most of the cells were still adhered to the surface, although some may have lost viability.     

The use of cyclic voltammetry to detect biofilms formed by Pseudomonas fluorescens on platinum electrodes

The development of an electrochemical detector to monitor the in situ formation of biofilms is described. The detector consisted of an electrochemical cell containing three electrodes, whose response to the application of a potential profile to the working electrode was sensitive to the amount of biofilm present on the surface. The electrochemical technique used was repetitive cyclic voltammetry. Differences between the response of the uncolonised electrode and after Pseudomonas fluorescens biofilms of different ages were grown on its surface were determined. The results show that cyclic voltammetry applied to platinum electrodes can be used to detect young biofilms. The development of the shape of the voltammogram as the potential is cycled may constitute a means of providing information on the coverage of the surface. Observation of the platinum electrodes before and after the electrochemical measurements showed that even after 30 min of recycling, most of the cells were still adhered to the surface, although some may have lost viability.     

Enhanced electron-transfer reactivity of horseradish peroxidase in phosphatidylcholine films and its catalysis to nitric oxide

Direct electrochemistry of horseradish peroxidase (HRP) embedded in film of phosphatidylcholine (PC) is investigated at a pyrolytic graphite electrode by voltammetric methods. The electron-transfer reactivity between incorporated HRP and the electrode is found to be greatly enhanced by phosphatidylcholine film. Cyclic voltammetry (CV) of this incorporated peroxidase shows a pair of well-defined and nearly reversible peaks, and the cathodic and anodic peak potentials are located at about -0.261 and -0.180 V, respectively versus saturated calomel electrode at pH 5.5. Ultraviolet-visible absorption spectra indicate that the heme microenvironment of HRP in phosphatidylcholine film is similar to that of its native status. It is also observed that HRP modified electrode is able to catalyze the electrochemical reduction of nitric oxide. Experimental results reveal that the peak current related to nitric oxide reduction is linearly proportional to its concentration in the ranges of 2.0 x 10(-7) -5.0 x 10(-6) mol (-1) and 2.0 x 10(-5) -1.0 x 10(-4) mol(-1), based on which an unmediated biosensor for nitric oxide is developed.     

All Pseudocapacitive MXene‐RuO2 Asymmetric Supercapacitors

2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high‐rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti₃C₂T_x) can operate at negative potentials in acidic electrolyte is exploited, to design an all‐pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO₂) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene‐based supercapacitors. The complementary working potential windows of MXene and RuO₂, along with proton‐induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm^?2 at a power density of 40 mW cm^?2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon‐based materials in asymmetric electrochemical capacitors, leading to an increased energy density.     

Exploring Advanced Sandwiched Arrays by Vertical Graphene and N‐Doped Carbon for Enhanced Sodium Storage

Smart hybridization of active materials into tailored electrode structure is highly important for developing advanced electrochemical energy storage devices. With the help of sandwiched design, herein a powerful strategy is developed to fabricate three‐layer sandwiched composite core/shell arrays via combined hydrothermal and polymerization approaches. In such a unique architecture, wrinkled MoSe₂ nanosheets are sandwiched by vertical graphene (VG) core and N‐doped carbon (N‐C) shell forming sandwiched core/shell arrays. Interesting advantages including high electrical conductivity, strong mechanical stability, and large porosity are combined in the self‐supported VG/MoSe₂/N‐C sandwiched arrays. As a preliminary test, the sodium ion storage properties of VG/MoSe₂/N‐C sandwiched arrays are characterized and demonstrated with high capacity (540 mA h g^?1), enhanced high rate capability, and long‐term cycling stability (298 mA h g^?1 at 2.0 A g^?1 after 1000 cycles). The sandwiched core/shell structure plays positive roles in the enhancement of electrochemical performances due to dual conductive carbon networks, good volume accommodation, and highly porous structure with fast ion diffusion. The directional electrode design protocol provides a general method for synthesis of high‐performance ternary core/shell electrodes.     

Electrochemically induced oxidative damage to double-stranded calf thymus DNA adsorbed on gold electrodes

Electrochemically induced oxidative damage to DNA was studied with double-stranded calf thymus DNA immobilized directly on a gold electrode surface. Pre-polarization of the DNA-modified electrodes at +0.5 V versus Ag/AgCl reference electrode, in a free from DNA blank buffer solution, pH 7.4, allowed for subsequent detection of direct electrochemical oxidation of adsorbed on gold DNA, in the potential range from +0.7 to +0.8 V. The redox potential of the process corresponded to the potentials of the oxidation of guanine bases in DNA. It is shown that with increasing potential scan rate, v, the mechanism of electrochemical oxidation of DNA changes from the irreversible 4e^– oxidative damage of DNA at low v to reversible 1e^– oxidation at high v, keeping the electrochemical activity of the adsorbed DNA layer virtually the same.     

3D Hierarchical Porous α‐Fe2O3 Nanosheets for High‐Performance Lithium‐Ion Batteries

To develop a long cycle life and good rate capability electrode, 3D hierarchical porous α‐Fe₂O₃ nanosheets are fabricated on copper foil and directly used as binder‐free anode for lithium‐ion batteries. This electrode exhibits a high reversible capacity and excellent rate capability. A reversible capacity up to 877.7 mAh g^?1 is maintained at 2 C (2.01 A g^?1) after 1000 cycles, and even when the current is increased to 20 C (20.1 A g^?1), a capacity of 433 mA h g^?1 is retained. The unique porous 3D hierarchical nanostructure improves electronic–ionic transport, mitigates the internal mechanical stress induced by the volume variations of the electrode upon cycling, and forms a 3D conductive network during cycling. No addition of any electrochemically inactive conductive agents or polymer binders is required. Therefore, binder‐free electrodes further avoid the uneven distribution of conductive carbon on the current collector due to physical mixing and the addition of an insulator (binder), which has benefits leading to outstanding electrochemical performance.     

聚3，4乙烯二氧噻吩修饰的新型碳纳米管纤维电极及其电化学性能评价

目的 植入式脑机接口在神经疾病的治疗方面已经得到了广泛应用，治疗的效果依赖于与神经组织接触的电极。与刚性材料制作的电极相比，碳基微纤维电极尺度小、生物兼容性好、组织炎症反应小，可以减少植入后的异物反应，改善神经记录信号的信噪比，可以长期保持稳定的电极特性。方法 本文设计了一种柔性碳纳米管（carbon nanotubes，CNTs）纤维电极的修饰方法，该方法采用电化学聚合的方式可以将聚3,4-乙烯二氧噻吩（poly（3,4-ethylenedioxythiophene），PEDOT）薄膜沉积到CNTs纤维电极上，作为微电极涂层。为了证明修饰涂层在电极表面具有良好的机械稳定性，对修饰电极进行了超声处理。此外，本文将PEDOT薄膜沉积到ITO玻璃上，评价了PEDOT薄膜的生物相容性。结果 恒电流方式在CNTs纤维电极表面沉积的PEDOT涂层降低了电极的电化学阻抗，提高了电极的电化学性能，且PEDOT沉积的时间越长阻抗减少的幅度越明显。对电极进行超声处理后，电极的电化学阻抗没有产生显著变化，说明超声处理后PEDOT涂层剥离较少，证明了修饰涂层在电极表面具有良好的机械稳定性。最后，细胞实验表明，PEDOT薄膜具有与ITO导电玻璃相当的细胞相容性。结论 PEDOT薄膜可以提高CNTs纤维电极的稳定性，有望提高脑机接口系统的寿命和可靠性，具有应用于长时间记录神经电信号的前景。     

Nano nickel oxide/nickel incorporated nickel composite coating for sensing and estimation of acetylcholine

Pure nickel electrodes can be used as biosensors especially for sensing and estimating acetylcholine neurotransmitter. In the present work, a good electrochemical sensor was developed by electroplating nano nickel oxide reinforced nickel on graphite substrate. The morphology of the working electrode surface was studied by using a scanning electron microscope (SEM). The electrochemical and biological performance of the modified electrode was characterized by polarization studies in different media. The present modified electrode showed good sensing performance with a response time as low as 8s during sensing and estimation of acetylcholine. The sensitivity of the modified electrode was 34.88 microA/(microM cm(2)).     

Improvement of Transparent Metal Top Electrodes for Organic Solar Cells by Introducing a High Surface Energy Seed Layer

We present highly transparent and conductive silver thin films in a thermally evaporated dielectric/metal/dielectric (DMD) multilayer architecture as top electrode for efficient small molecule organic solar cells. DMD electrodes are frequently used for optoelectronic devices and exhibit excellent optical and electrical properties. Here, we show that ultrathin seed layers such as calcium, aluminum, and gold of only 1 nm thickness strongly influence the morphology of the subsequently deposited silver layer used as electrode. The wetting of silver on the substrate is significantly improved with increasing surface energy of the seed material resulting in enhanced optical and electrical properties. Typically thermally evaporated silver on a dielectric material forms rough and granular layers which are not closed and not conductive below thicknesses of 10 nm. With gold acting as seed layer, the silver electrode forms a continuous, smooth, conductive layer down to a silver thickness of 3 nm. At 7 nm silver thickness such an electrode exhibits a sheet resistance of 19 Ω/□ and a peak transmittance of 83% at 580 nm wavelength, both superior compared to silver electrodes without seed layer and even to indium tin oxide (ITO). Top‐illuminated solar cells using gold/silver double layer electrodes achieve power conversion efficiencies of 4.7%, which is equal to 4.6% observed in bottom‐illuminated reference devices employing conventional ITO. The top electrodes investigated here exhibit promising properties for semitransparent solar cells or devices fabricated on opaque substrates.     

Multifunctional Manganese Ions Trapping and Hydrofluoric Acid Scavenging Separator for Lithium Ion Batteries Based on Poly(ethylene‐alternate‐maleic acid) Dilithium Salt

Manganese dissolution from positive electrodes seriously reduces the life of Li‐ion batteries, due to its detrimental impact on the passivation of negative electrodes. A novel multifunctional separator incorporating inexpensive mass‐produced polymeric materials may dramatically increases the durability of Li‐ion batteries. The separator is made by embedding the poly(ethylene‐alternate‐maleic acid) dilithium salt polymer into a poly(vinylidene fluoride‐hexafluoropropylene) copolymer matrix. LiMn₂O₄‐graphite cells comprising a 1 m LiPF₆ solution in ethylene carbonate plus dimethyl carbonate (1:1 v/v) and the functional separator retain 31% and 100% more capacity than baseline cells with plain commercial separators after 100 cycles at C/5 rate, respectively, at 30 and 55 °C. Analyses of cycled cells indicate greatly reduced Mn contamination of the graphite negative electrodes and almost no irreversible structural change in the LiMn₂O₄ positive electrodes from cells containing the functional separator. The Mn amount in the graphite electrodes from cycled cells with functional separators is ≈80% lower than in the graphite electrodes from cycled baseline cells. Mn ions are found in the functional separators but not in baseline (plain) separators from cycled cells. Finally, it is shown that the reported performance improvements stem from the ability of the novel separator to chelate Mn ions and to scavenge trace HF.     

MnPO4‐Coated Li(Ni0.4Co0.2Mn0.4)O2 for Lithium(‐Ion) Batteries with Outstanding Cycling Stability and Enhanced Lithiation Kinetics

Herein, the successful synthesis of MnPO₄‐coated LiNi_0.4Co_0.2Mn_0.4O₂ (MP‐NCM) as a lithium battery cathode material is reported. The MnPO₄ coating acts as an ideal protective layer, physically preventing the contact between the NCM active material and the electrolyte and, thus, stabilizing the electrode/electrolyte interface and preventing detrimental side reactions. Additionally, the coating enhances the lithium de‐/intercalation kinetics in terms of the apparent lithium‐ion diffusion coefficient. As a result, MP‐NCM‐based electrodes reveal greatly enhanced C‐rate capability and cycling stability—even under exertive conditions like extended operational potential windows, elevated temperature, and higher active material mass loadings. This superior electrochemical behavior of MP‐NCM compared to as‐synthesized NCM is attributed to the superior stability of the electrode/electrolyte interface and structural integrity when applying a MnPO₄ coating. Employing an ionic liquid as an alternative, intrinsically safer electrolyte system allows for outstanding cycling stabilities in a lithium‐metal battery configuration with a capacity retention of well above 85% after 2000 cycles. Similarly, the implementation in a lithium‐ion cell including a graphite anode provides stable cycling for more than 2000 cycles and an energy and power density of, respectively, 376 Wh kg^?1 and 1841 W kg^?1 on the active material level.     

Electrochemical optical waveguide lightmode spectroscopy (EC-OWLS): a pilot study using evanescent-field optical sensing under voltage control to monitor polycationic polymer adsorption onto indium tin oxide (ITO)-coated waveguide chips

A new technique has been developed that combines evanescent-field optical sensing with electrochemical control of surface adsorption processes. This new technique, termed "electrochemical optical waveguide lightmode spectroscopy" (EC-OWLS), proved efficient in monitoring molecular surface adsorption and layer thickness changes of an adsorbed polymer layer examined in situ as a function of potential applied to a waveguide in a pilot study. For optical sensing, a layer of indium tin oxide (ITO) served as both a high-refractive-index waveguide and a conductive electrode. In addition, an electrochemical flow-through fluid cell was provided, which incorporated working, reference, and counter electrodes, and was compatible with the constraints of optical sensing. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) served as a model, polycation adsorbate. Adsorption of PLL-g-PEG from aqueous buffer solution increased from 125 to 475 ng/cm(2 )along a sigmoidal path as a function of increasing potential between 0 and 1.5 V versus the Ag reference electrode. Upon buffer rinse, adsorption was partially reversible when a potential of >/=0.93 V was maintained on the ITO waveguide. However, reducing the applied potential back to 0 V before rinsing resulted in irreversible polymer adsorption. PLL-g-PEG modified with biotin demonstrated similar adsorption characteristics, but subsequent streptavidin binding was independent of biotin concentration. Applying positive potentials resulted in increased adsorbed mass, presumably due to polymer chain extension and reorganization in the molecular adlayer.     

A High Areal Capacity Flexible Lithium‐Ion Battery with a Strain‐Compliant Design

Early demonstrations of wearable devices have driven interest in flexible lithium‐ion batteries. Previous demonstrations of flexible lithium‐ion batteries trade off between low areal capacity, poor mechanical flexibility and/or high thickness of inactive components. Here, a reinforced electrode design is used to support the active layers of the battery and a freestanding carbon nanotube (CNT) layer is used as the current collector. The supported architecture helps to increase the areal capacity (mAh cm^‐2) of the battery and improve the tensile strength and mechanical flexibility of the electrodes. Batteries based on lithium cobalt oxide and lithium titanate oxide shows excellent electrochemical and mechanical performance. The battery has an areal capacity of ≈1 mAh cm^‐2 and a capacity retention of around 94% after cycling the battery for 450 cycles at a C/2 rate. The reinforced electrode has a tensile strength of ≈5.5–7.0 MPa and shows excellent capacity retention after repeatedly flexing to a bending radius ranging from 45 to 10 mm. The relationships between mechanical flexing, electrochemical performance, and mechanical integrity of the battery are studied using electrochemical cycling, electron microscopy, and electrochemical impedance spectroscopy (EIS).     

An Effective Lithium Sulfide Encapsulation Strategy for Stable Lithium–Sulfur Batteries

With a high theoretical capacity of 1162 mA h g^?1, Li₂S is a promising cathode that can couple with silicon, tin, or graphite anodes for next‐generation energy storage devices. Unfortunately, Li₂S is highly insulating, exhibits large charge overpotential, and suffers from active‐material loss as soluble polysulfides during battery cycling. To date, low‐cost, scalable synthesis of an electrochemically active Li₂S cathode remains a challenge. This work demonstrates that the low conductivity and material loss issues associated with Li₂S cathodes can be overcome by forming a stable, conductive encapsulation layer at the surface of the Li₂S bulk particles through in situ surface reactions between Li₂S and electrolyte additives containing transition‐metal salts. It is identified that the electronic band structure in the valence band region of the thus‐generated encapsulation layers, consisting largely of transition‐metal sulfides, determines the initial charging resistance of Li₂S. Furthermore, among the transition metals tested, the encapsulation layer formed with an addition of 10 wt% manganese (II) acetylacetonate salt proved to be robust within the cycling window, which is attributed to the chemically generated MnS surface species. This work provides an effective strategy to use micrometer‐sized Li₂S directly as a cathode material and opens up new prospects to tune the surface properties of electrode materials for energy‐storage applications.     

Concurrently Approaching Volumetric and Specific Capacity Limits of Lithium Battery Cathodes via Conformal Pickering Emulsion Graphene Coatings

To achieve the high energy densities demanded by emerging technologies, lithium battery electrodes need to approach the volumetric and specific capacity limits of their electrochemically active constituents, which requires minimization of the inactive components of the electrode. However, a reduction in the percentage of inactive conductive additives limits charge transport within the battery electrode, which results in compromised electrochemical performance. Here, an electrode design that achieves efficient electron and lithium‐ion transport kinetics at exceptionally low conductive additive levels and industrially relevant active material areal loadings is introduced. Using a scalable Pickering emulsion approach, Ni‐rich LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cathode powders are conformally coated using only 0.5 wt% of solution‐processed graphene, resulting in an electrical conductivity that is comparable to 5 wt% carbon black. Moreover, the conformal graphene coating mitigates degradation at the cathode surface, thus providing improved electrochemical cycle life. The morphology of the electrodes also facilitates rapid lithium‐ion transport kinetics, which provides superlative rate capability. Overall, this electrode design concurrently approaches theoretical volumetric and specific capacity limits without tradeoffs in cycle life, rate capability, or active material areal loading.