•LiCoO2 thin-film electrodes with different preferred orientations have been prepared by magnetron sputtering method.•Electrodes with {101¯1} orientation deliver better performance than that of ...(0003).•In-situ CASAFM combined with XPS were used to understand the microscopic fundamentals behind the macroscopic electrochemicalperformance.
Surface properties of cathode materials play important roles in the transport of lithium-ions/electrons and the formation of surface passivation layer. Optimizing the exposed crystal facets of cathode materials can promote the diffusion of lithium-ions and enhance cathode surface stability, which may ultimately dominate cathode’s performance and stability in lithium-ion batteries. Here, polycrystalline LiCoO2 (LCO) thin films with (0003) and {101-1} preferred orientations were prepared as the well-defined model electrodes. In situ Current-Sensing Atomic Force Microscopy (CSAFM) was employed to investigate the lithium de-intercalation and electronic conductivity evolution of the (0003) and {101-1} facts in organic electrolyte at the nanoscale. It was found that the lithium deintercalation following a “Li-rich core model” in the LCO grains, and the LCO grains with (0003) crystal face show less conductivity than those with {101-1} faces. Moreover, X-ray Photoelectron Spectroscopy characterization of the charged electrode surface indicates that a denser surface passivation layer is formed on {101-1} than that on (0003) crystal faces. This is caused by the lower adsorption energy of decomposition molecule on {101-1} crystal faces and higher work function (due to the surface atomic structure) for {101-1} crystal faces, as confirmed by Density Functional Theory (DFT) and Kelvin probe force microscopy (KPFM) results. In addition, electrochemical measurements confirm that the thin film electrodes with {101-1} preferred orientation not only show smaller electrode polarization, but also more readily form a stable surface passivation layer compared with the (0003) preferred orientation. This work highlights the importance of cathode conductivity, and suggests that the LCO {101-1} facet atomic structure may thermodynamically promote the physical/chemical adsorption and decomposition of electrolyte.
Screen printing of graphene‐based ink shows promise for the integration of graphene within supercapacitor electrodes. A series of graphene/polyaniline inks are formulated, and screen printing is used ...to produce thin‐film electrodes from these inks. Using these electrodes, supercapacitors are fabricated that exhibit high capacity, flexibility, and stability. These results provide an important step towards the industrial development of printable supercapacitors.
Determination of plasma uracil was reported as a method for evaluation of Dihydropyrimidine dehydrogenase (DPD) activity that is highly demanded to ensure the safe administration of 5-fluorouracil ...(5-FU)-based therapies to cancer patients. This work reports the development of a simple electroanalytical method based on adsorptive stripping square wave voltammetry (AdSWV) at mercury film-coated glassy carbon electrode (MF/GCE) for the highly sensitive determination of uracil in biological fluids that can be used for diagnosis of decreased DPD activity. Due to the formation of the HgII–Uracil complex at the electrode surface, the accuracy of the measurement was not affected by the complicated matrices in biological fluids including human serum, plasma, and urine. The high sensitivity of the developed method results in a low limit of detection (≈1.3 nM) in human plasma samples, falling below the practical cut-off level of 15 ng mL−1 (≈0.14 μM). This threshold concentration is crucial for predicting 5-FU toxicity, as reported in buffer, and ≤1.15% in biological samples), and accuracy (recovery percentage close to 100%).
Highly Reversible Lithiation
Batteries that last for millions of charge cycles could drive humanity thousands of times around the earth and on into the future. Towards this end, in article number ...2312839, Morgan Stefik, Sean Cade Wechsler, and Alexander Greg elucidate the conditions under which T‐Nb2O5 maintains ∼90% capacity after 0.25 million (de)lithiation cycles. Enhanced durability directly improves the lifetime economics of energy storage technologies. Original oil painting by Julia Stefik.
Fast energy storage via intercalation requires quick ionic diffusion and often results in pseudocapacitive behavior. The cycling stability of such energy storage materials remains understudied ...despite the relevance to lifetime cost. Orthorhombic niobium oxide (T‐Nb2O5) is a rapid ion intercalation material with a theoretical capacity of 201.7 mAh g−1 (Li2Nb2O5) and good cycling stability due to the minimal unit cell strain during (de)intercalation. Prior reports of T‐Nb2O5 cycling between 1.3–3.1 V versus Li/Li+ noted a 50% loss in capacity after 10 000 cycles. Here, cyclic voltammetry is used to identify the role of the voltage window, state of charge, and potentiostatic holds on the cycling stability of mesoporous T‐Nb2O5 thin films. Films cycled between 1.2–3.0 V versus Li/Li+ without voltage holds (Li1.1Nb2O5) exhibited extreme cycling stability with 90.8% capacity retention after 0.25 million cycles without detectable morphological/crystallographic changes. In contrast, the inclusion of 60 s voltage holds (Li2.18Nb2O5) led to rapid capacity loss with 61.6% retention after 10 000 cycles with corresponding X‐ray diffraction evidence of amorphization. Cycling with other limited voltage windows identifies that most crystallographic degradation occurs at higher extents of lithiation. These results reveal remarkable stability over limited conditions and suggest that T‐Nb2O5 amorphization is associated with high extents of lithiation.
Typical electrode materials can cycle for a few hundred to thousand cycles before an appreciable capacity loss occurs. Improving this cycling stability leads to proportionally reduced costs of energy storage. Using kinetically limited lithiation (see picture), T‐Nb2O5 thin films are cycled at high rates for 0.25 million cycles and retain an impressive 90.8% of the initial capacity. This improvement enabled a 25× increase in the number of report cycles as compared to similar electrodes.
Understanding the fundamentals of surface decoration effects in phase‐separation materials, such as lithium titanate (LTO), is important for optimizing the lithium‐ion battery (LIB) performance. LTO ...polycrystalline thin‐film electrodes with and without doped Al–ZnO (AZO) surface coating decoration are used as ideal models to gain insights into the mechanisms involved. Operando shear force modulation spectroscopy is used to observe for the first time the nanoscale dynamics of solid‐electrolyte‐interphase (SEI) formation on the electrode surfaces, confirming that the AZO coating is electrochemically converted into a stiff, homogenous SEI layer that protects the surface from the electrolyte‐induced decomposition. This AZO layer and its resultant artificial SEI‐layer have higher Li‐ion transport rates than the unmodified surface. These layers can reduce barriers to surface nucleation and facilitate rapid redistribution of lithium‐ions during the Li4Ti5O12 ⇄ Li7Ti5O12 phase separation, significantly inhabiting the orderly collective phase‐separation behavior (electrochemical oscillation) in the LTO electrode. The suppressed voltage oscillations indicate more homogeneous local exchange current density and de/intercalation states with the decorated electrodes, thereby extending their battery efficiency and long‐term cycling stability. This work highlights the ultimate importance of surface treatment for LIB materials for determining their interfacial chemistry and phase transition during the intercalation/deintercalation.
To study the fundamentals of surface‐decoration effects in a phase‐separation electrochemical system, operando atomic force microscopy spectroscopy is used to observe the dynamics of solid‐electrolyte‐interphase formation on the electrode–electrolyte interfaces of lithium‐titanate‐oxide thin‐film electrodes with/without nanocoating layers; electrochemical measurements confirm that the surface‐decoration can modulate the interface‐reductive‐capability, and improve phase transition kinetics by inhibiting electrochemical oscillations.
For incompletely reduced graphene oxides (RGOs), an effect of oxygen functional groups such as carboxyl, phenol, carbonyl, and quinone on electrochemical capacitive behavior was studied. To prepare ...RGO thin-film electrodes, a simple fabrication process by (i) dropping and evaporating the graphene oxide (GO) solution, (ii) irradiating pulsed light, and (iii) heat-treating at 200 ∼ 360°C was applied. It was notable that the pulsed light irradiation was effective to prevent the disfiguring of deposited GO thin-film during the thermal reduction. From XRD analyses, interlayer distances of the RGOs were gradually decreased from 0.379 to 0.354nm. As increasing the thermal reduction temperature from 200 to 360°C, XPS O 1s spectra analyses showed that the atomic percentages of carboxyl and phenol of the RGOs were sustained as 5.40±0.36 and 4.77±0.41 at% respectively. Meanwhile, those of carbonyl and quinone of the RGOs were gradually declined from 3.10 to 1.81 and from 1.32 to 0.65 at% with different thermal reduction temperature respectively. For all RGO thin-film electrodes, the specific capacitance from the CV measurement in 6M KOH was sustained as ca. 220 F g−1 at the scan of 5mV s−1. However, in 1M H2SO4, the specific capacitance was gradually decreased from 171 to 136 F g−1. After 100,000 cycles in 6M KOH, 1M H2SO4, and 0.5M Na2SO4, the RGO (200°C) electrodes showed ca. 92, 54, and 104% of the initial capacitances respectively. The atomic percentages of the oxygen functional groups involved in the pseudocapacitive Faradaic reaction were decreased after the cycle test. Especially in 1M H2SO4, quinone group was decreased to ca. 48% of initial atomic percentage, which seems to be a main reason for the drastic reduction of capacitance. The specific pseudocapacitance per unit atomic percentage for either carboxyl or phenol group in 6M KOH was obtained as 12.59 F g−1 at%−1. For carbonyl group in 1M H2SO4, it was a slightly deviated value as 13.55 F g−1 at%−1. For quinone group in 1M H2SO4, it was 27.09 F g−1at%−1.
CuFeO2/CuO thin film electrodes are fabricated by electrodeposition method in dimethyl sulfoxide. With the increase of deposition potential and annealing temperature, the peak intensity of both ...CuO(111) and CuFeO2(101) becomes stronger. The resulted thin film electrodes exhibit high absorbance in visible light range. The photoelectrocatalytic performance of CuFeO2/CuO thin film electrodes for CO2 reduction is examined. At the applied potential between -0.50 to -0.80 V (vs. saturated calomel electrode), CO2 can be reduced to methanol and ethanol. The highest concentration of ethanol occurs at the applied potential of -0.63 V, whereas that of methanol occurs at -0.70 V. There is a strong relationship between Cu/Fe molar ratio on the thin film electrode surface and ethanol concentration, and ethanol concentration increases with the decrease of the Cu/Fe molar ratio of the thin film surface.
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•Nanostructured electrodes were prepared from surfactant-free gold nanoparticles.•Nanostructure changed the quasi-reversible reaction of cyt c to a reversible one.•Clear voltammetric ...signal of cyt c was also obtained without surface modification.
Electrochemical manipulation of enzymes is expected to enable the rapid detection of marker molecules and the efficient production of valuable materials. We have fabricated an Au nanoparticle (AuNP) thin film electrode in our previous study, which enables more enhanced heterogeneous electron transfer reactions than a conventional planner Au electrode. In this study, electrochemical evaluation of cytochrome c was performed using the AuNP thin film electrodes with and without self-assembled monolayer (SAM) modification to assess its practicality for protein electrochemistry. The 4-pyridinethiol- and 7-carboxy-1-heptanethiol-modified AuNP thin film electrodes showed much larger faradaic current values attributed to redox reactions compared to those of the Au electrodes. The results indicate that the nanostructural effects of the AuNP thin film electrode are beneficial. Importantly, even when the non-modified (bare) AuNP thin film electrode was applied, it exhibited the clear electrochemical response of cyt c, while the bare Au electrode showed no such a response. This study provides evidence that the AuNP thin film electrode functions as a potent bioelectrocatalysts due to the nanostructure-specific properties.
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