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JPhys energy 5(2), 021501 (2023). doi:10.1088/2515-7655/acaa57, Published by IOP Publishing, Bristol

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling performance, which is exacerbated by increased cell voltage. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 (LiNi0.8Mn0.1Co0.1O2) is charged above 4.4 V vs. Li/Li+ – the onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes – compared to EC-free – and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. In contrast, NMC111 (LiNi0.33Mn0.33Co0.33O2), which does not release oxygen up to 4.6 V, shows similar extents of degradation irrespective of the electrolyte. This work highlights the incompatibility between conventional EC-based electrolytes and Ni-rich cathodes (more generally, cathodes that release lattice oxygen such as Li-/Mn-rich and disordered rocksalt cathodes), and motivates further work on wider classes of electrolytes and additives., The present research has been supported by the Faraday Institution degradation project (FIRG001) and EPSRC (EP/S003053/1). W. M. D., M. F. L. D., and C. P. G. acknowledge funding from Cambridge Royce facilities grant EP/P024947/1 and Sir Henry Royce Institute grant EP/R00661X/1. The authors are grateful to A. Jansen, S.E. Trask, B.J. Polzin, and A.R. Dunlop at the U.S. Department of Energy’s CAMP (Cell Analysis, Modeling, and Prototyping) Facility, Argonne National Laboratory, for producing and supplying the electrodes in this work. We thank Nigel Howard for assistance with the ICP-OES measurements, and Bernardine Rinkel and Jennifer Allen for useful discussions.

A new bismuth metal–organic framework (MOF), bismuth-NU-901 (Bi-NU-901), featuring the scu topology and a pore with a diameter of ∼11 A, was solvothermally synthesized, and its use as an X-ray comp...

The chemical and electrochemical reactions at the positive electrode–electrolyte interface in Li-ion batteries are hugely influential on cycle life and safety. Ni-rich layered transition metal oxides exhibit higher interfacial reactivity than their lower Ni-content analogues, reacting via mechanisms that are poorly understood. Here, we study the pivotal role of the electrolyte solvent, specifically cyclic ethylene carbonate (EC) and linear ethyl methyl carbonate (EMC), in determining the interfacial reactivity at charged LiNi0.33Mn0.33Co0.33O2(NMC111) and LiNi0.8Mn0.1Co0.1O2(NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells. While NMC111 exhibits similar parasitic currents with EC-containing and EC-free electrolytes during high voltage holds in NMC/Li4Ti5O12(LTO) cells, this is not the case for NMC811. Online gas analysis reveals that the solvent-dependent reactivity for Ni-rich cathodes is related to the extent of lattice oxygen release and accompanying electrolyte decomposition, which is higher for EC-containing than EC-free electrolytes. Combined findings from electrochemical impedance spectroscopy (EIS), TEM, solution NMR, ICP, and XPS reveal that the electrolyte solvent has a profound impact on the degradation of the Ni-rich cathode and the electrolyte. Higher lattice oxygen release with EC-containing electrolytes is coupled with higher cathode interfacial impedance, a thicker oxygen-deficient rock-salt surface reconstruction layer, more electrolyte solvent and salt breakdown, and higher amounts of transition metal dissolution. These processes are suppressed in the EC-free electrolyte, highlighting the incompatibility between Ni-rich cathodes and conventional electrolyte solvents. Finally, new mechanistic insights into the chemical oxidation pathways of electrolyte solvents and, critically, the knock-on chemical and electrochemical reactions that further degrade the electrolyte and electrodes curtailing battery lifetime are provided.

When high-energy electrons from a scanning transmission electron microscope (STEM) are incident on a liquid, the vast majority of the chemical reactions that are observed are induced by the radiolysis breakdown of the liquid molecules. In the study of liquids, the radiolysis products of pure water are well known, and their rate of formation for a given flux of high-energy electrons has been studied intensively over the last few years for uniform TEM illumination. In this paper, we demonstrate that the temporal and spatial distribution of the electron illumination can significantly affect the final density of radiolysis products in water and even change the type of reaction taking place. We simulate the complex array of possible spatial/temporal distributions of electrons that are accessible experimentally by controlling the size, the scan rate and the hopping distance of the electron probe in STEM mode and then compare the results to the uniformly illuminated TEM mode of imaging. By distributing the electron dose both spatially and temporally in the STEM through a randomised “spot-scan” mode of imaging, the diffusion overlap of the radiolysis products can be reduced, and the resulting reactions can be more readily controlled. This control allows the resolution of the images to be separated from the speed of the induced reaction (which is based on beam current alone) and this facet of the experiment will allow a wide range of chemical reactions to be uniquely tailored and observed in all liquid cell STEM experiments.

A major challenge for lithium-ion batteries based on nickel-rich layered oxide cathodes is capacity fading. While chemo-mechanical degradation and/or structural transformation are widely considered responsible for degradation, a comprehensive understanding of this process is still not complete. For the stable performance of these cathode materials, aluminium (Al) plays a crucial role, not only as a current collector but also as substitutional element for the transition metals in the cathodes and a protective oxide coating (as Al2O3). However, excess Al can be detrimental due to both its redox inactive nature in the cathode and the insulating nature of Al2O3. In this work, we report an analysis of the Al content in two different types of nickel-rich manganese cobalt oxide cathode materials after battery cycling. Our results indicate a significant thickening of Al-containing phases on the surface of the NMC811 electrode. Similar results are observed from commercial batteries (a mixture of NMC532 and LiMn2O4) that were analysed before use and at the end of life, where Al-containing phases were found to increase significantly at surfaces and grain boundaries. Considering the detrimental effects of the excess Al in the nickel-rich cathodes, our observation of increased Al content via battery cycling is believed to bring a new perspective to the ongoing discussions regarding the capacity fading phenomenon of nickel-rich layered oxide materials as part of their complex degradation mechanisms.

In recent years, extensive research has been performed on high energy cathode materials for lithium ion batteries being used in electric vehicles to reduce carbon emissions. Compared to the commercial layered cathode materials, the absence of cobalt in the spinel LiMn1.5Ni0.5O4 (LMNO) makes this material more environmentally friendly and cheaper.1 Spinel LMNO cathodes also reveal attractive gravimetric and volumetric energy densities of 635Whkg−1 and 2820WhL−1, respectively.2 According to the distribution of transition metals (TM) within the cubic crystal structure, spinel LMNO can be categorized into either ordered or disordered. Normally, disordered LMNO materials are produced at temperatures higher than the theoretical oxygen release temperature of spinel LMNO (715 °C).3 The formation of O vacancies is accompanied by some Mn4+ atoms being reduced to Mn3+ to maintain the electroneutrality of spinel LMNO. Ordered LMNO can be obtained through calcination at temperatures lower than 715 °C or post-annealing disordered LMNO materials at 700 °C.4 The reversible extraction and insertion of O atoms accompanied with different distribution of TM during spinel LMNO preparation drive up a hypothesis that the oxygen activity during cycling of spinel LMNO may be affected by the distribution of TM atoms, especially since the operating voltage of spinel LMNO (> 4.7 V) is high enough to trigger oxygen redox in other lithium transition metal oxides.5 To explore the feasibility of oxygen activity during cycling of spinel LMNO, the normal, core-shell and sandwich designed synthesis are performed using special Mn0.75Ni0.25(OH)2 precursors to arrange different distributions of TM atoms in the obtained N-, CS- and SW-LMNO. As shown in Figure 1(a) – (c), the three materials show similar XRD patterns in the pristine state, yet different reflection peaks are observed in the three materials after charging to 4.9 V. The unclear phase transition of SW-LMNO indicates it show stable structure. The three materials also show different CV curves, see Figure 1(d). This indicates the extraction and insertion of Li atoms lead to different redox reactions in the three materials. Besides, differential electrochemical mass spectrometry (DEMS), in-situ transmission electron microscope (TEM) as well as hard and soft X-ray absorption spectroscopy (XAS) measurements are utilized to further investigate the oxygen activity during cycling of spinel LMNO. Reference 1. Li, M. & Lu, J. Cobalt in lithium-ion batteries. Science 367, 979-980 (2020). 2. Hagh, N. M. & Amatucci, G. G. A new solid-state process for synthesis of LiMn1. 5Ni0. 5O4−δ spinel. Journal of Power Sources 195, 5005-5012 (2010). 3. Manthiram, A., Chemelewski, K. & Lee, E.-S. A perspective on the high-voltage LiMn1.5Ni0.5O4 spinel cathode for lithium-ion batteries. Energy & Environmental Science 7, 1339-1350 (2014). 4. Chemelewski, K. R., Shin, D. W., Li, W. & Manthiram, A. Octahedral and truncated high-voltage spinel cathodes: the role of morphology and surface planes in electrochemical properties. Journal of Materials Chemistry A 1, 3347-3354 (2013). 5. Seo, D.-H. et al. The structural and chemical origin of the oxygen redox activity in layered and cation-disordered Li-excess cathode materials. Nature chemistry 8, 692-697 (2016). Figure 1. Operando X-ray diffraction patterns of N- (a), CS- (b) and SW- (c) LiMn1.5Ni0.5O4 in the pristine states and at the charge states of 4.9 V and the corresponding cyclic voltammetry curves of the three materials (d) Figure 1

Beam damage caused during acquisition of the highest resolution images is the current limitation in the vast majority of experiments performed in a scanning transmission electron microscope (STEM). While the principles behind the processes of knock-on and radiolysis damage are well-known (as are other contributing effects, such as heat and electric fields), understanding how and especially when beam damage is distributed across the entire sample volume during an experiment has not been examined in detail. Here we use standard models for damage and diffusion to elucidate how beam damage spreads across the sample as a function of the microscope conditions to determine an "optimum" sampling approach that maximises the high-resolution information in any image acquisition. We find that the standard STEM approach of scanning an image sequentially accelerates damage because of increased overlap of diffusion processes. These regions of accelerated damage can be significantly decelerated by increasing the distance between the acquired pixels in the scan, forming a "spotscan" mode of acquisition. The optimum distance between these pixels can be broadly defined by the fundamental properties of each material, allowing experiments to be designed for specific beam sensitive materials. As an added bonus, if we use inpainting to reconstruct the sparse distribution of pixels in the image we can significantly increase the speed of the STEM process, allowing dynamic phenomena, and the onset of damage, to be studied directly.

Insights into the dynamics of electrochemical processes are critically needed to improve our fundamental understanding of electron, charge, and mass transfer mechanisms and reaction kinetics that influence a broad range of applications, from the functionality of electrical energy-storage and conversion devices (e.g., batteries, fuel cells, and supercapacitors), to materials degradation issues (e.g., corrosion and oxidation), and materials synthesis (e.g., electrodeposition). To unravel these processes, in situ electrochemical scanning/transmission electron microscopy (ec-S/TEM) was developed to permit detailed site-specific characterization of evolving electrochemical processes that occur at electrode–electrolyte interfaces in their native electrolyte environment, in real time and at high-spatial resolution. This approach utilizes “closed-form” microfabricated electrochemical cells that couple the capability for quantitative electrochemical measurements with high spatial and temporal resolution imaging, spectroscopy, and diffraction. In this article, we review the state-of-the-art instrumentation for in situ ec-S/TEM and how this approach has resulted in new observations of electrochemical processes.

Electrodeposition is widely used to fabricate tunable nanostructured materials in applications ranging from biosensing to energy conversion. A model based on 3D island growth is widely accepted in the explanation of the initial stages of nucleation and growth in electrodeposition. However, there are regions in the electrodeposition parameter space where this model becomes inapplicable. We use liquid cell transmission electron microscopy along with post situ scanning electron microscopy to investigate electrodeposition in this parameter space, focusing on the effect of the supporting electrolyte, and to shed light on the nucleation and growth of palladium. Using a collection of electron microscopy images and current time transients recorded during electrodeposition, we discover that electrochemical aggregative growth, rather than 3D island growth, best describes the electrodeposition process. We then use this model to explain the change in the morphology of palladium electrodeposits from spherical to open clusters with nonspherical morphology when HCl is added to the electrolyte solution. The enhanced understanding of the early stages of palladium nucleation and growth and the role of electrolyte in this process provides a systematic route toward the electrochemical fabrication of nanostructured materials.

Electrolyte-filled subnanometre pores exhibit exciting physics and play an increasingly important role in science and technology. In supercapacitors, for instance, ultranarrow pores provide excellent capacitive characteristics. However, ions experience difficulties in entering and leaving such pores, which slows down charging and discharging processes. In an earlier work we showed for a simple model that a slow voltage sweep charges ultranarrow pores quicker than an abrupt voltage step. A slowly applied voltage avoids ionic clogging and co-ion trapping - a problem known to occur when the applied potential is varied too quickly - causing sluggish dynamics. Herein, we verify this finding experimentally. Guided by theoretical considerations, we also develop a non-linear voltage sweep and demonstrate, with molecular dynamics simulations, that it can charge a nanopore even faster than the corresponding optimized linear sweep. For discharging we find, with simulations and in experiments, that if we reverse the applied potential and then sweep it to zero, the pores lose their charge much quicker than they do for a short-circuited discharge over their internal resistance. Our findings open up opportunities to greatly accelerate charging and discharging of subnanometre pores without compromising the capacitive characteristics, improving their importance for energy storage, capacitive deionization, and electrochemical heat harvesting., Deutsche Forschungsgemeinschaft (German Research Foundation), Projekt DEAL

Ni-rich layered cathode materials are among the most promising candidates for high-energy-density Li-ion batteries, yet their degradation mechanisms are still poorly understood. We report a structure-driven degradation mechanism for NMC811 (LiNi0.8Mn0.1Co0.1O2), in which a proportion of the material exhibits a lowered accessible state of charge at the end of charging after repetitive cycling and becomes fatigued. Operando synchrotron long-duration X-ray diffraction enabled by a laser-thinned coin cell shows the emergence and growth in the concentration of this fatigued phase with cycle number. This degradation is structure driven and is not solely due to kinetic limitations or intergranular cracking: no bulk phase transformations, no increase in Li/Ni antisite mixing and no notable changes in the local structure or Li-ion mobility of the bulk are seen in aged NMCs. Instead, we propose that this degradation stems from the high interfacial lattice strain between the reconstructed surface and the bulk layered structure that develops when the latter is at states of charge above a distinct threshold of approximately 75%. This mechanism is expected to be universal in Ni-rich layered cathodes. Our findings provide fundamental insights into strategies to help mitigate this degradation process. Ni-rich layered cathode materials are promising for high-energy-density Li-ion batteries, but their degradation mechanisms are still poorly understood. A structure-driven mechanism with a lowered accessible state of charge after repetitive cycling is proposed for a typical NMC811 cathode.

Ni-rich layered cathode materials are among the most promising candidates for high energy density Li-ion batteries. However, the low cobalt containing materials suffer from rapid degradation, the underlying mechanism of which is still poorly understood. We herein report a novel structure-drive degradation mechanism for the NMC811(LiNi0.8Mn0.1Co0.1O2) cathode, in which a proportion of the material exhibits a lowered accessible state-of-charge (SoC) at the end of charge after repetitive cycling, i.e. becomes fatigued. Ex-situ and operando long- duration high-resolution X-ray diffraction enabled by a laser-thinned coin cell design clearly shows the emergence of the fatigued phase and the increase in its population as the cycling progresses. We show that the fatigue degradation is a structure-driven process rather than originating solely due to kinetic limitations or inter-granular cracking. No bulk phase transformations or increase in Li/Ni antisite mixing were observed by diffraction; no significant change in the local structure or Li-ion mobility of the bulk were observed by 7Li solid-state NMR spectroscopy. Instead, we propose that the fatigue process is a result of the high interfacial lattice strain between the reconstructed surface and the bulk layered structure when the latter is at SoCs above a distinct threshold of ~75 %. This mechanism is expected to be universal to Ni-rich layer cathodes, and our findings provide a fundamental guide for designing effective approaches to mitigate such deleterious processes.

Developing the ability to synthesize compositionally and morphologically well-defined gibbsite particles with high yield is an ongoing need that has not yet achieved the required level of rational design. Here we report optimization of a clean inorganic synthesis route based on statistical experimental design examining the influence of Al(OH)3 gel precursor concentration, pH, and aging time at temperature. At 80 °C, the optimum synthesis conditions of gel concentration at 0.5 M, pH at 9.2, and time at 72 h maximized the reaction yield up to ∼88%. The resulting gibbsite product is composed of highly uniform euhedral hexagonal nanoplates within a basal plane diameter range of 200–400 nm. The independent roles of key system variables in the growth mechanism are considered. On the basis of these optimized experimental conditions, the synthesis procedure, which is both cost-effective and environmentally friendly, has the potential for mass production scale-up of high quality gibbsite material for various funda...

Metal–organic frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for preparing well-defined nanostructures wherein functionality such as catalysis can be incorporated. Notably, atomic layer deposition (ALD) in MOFs has recently emerged as a versatile approach to functionalize MOF surfaces with a wide variety of catalytic metal-oxo species. Understanding the structure of newly deposited species and how they are tethered within the MOF is critical to understanding how these components couple to govern the active material properties. By combining local and long-range structure probes, including X-ray absorption spectroscopy, pair distribution function analysis, and difference envelope density analysis, with electron microscopy imaging and computational modeling, we resolve the precise atomic structure of metal-oxo species deposited in the MOF NU-1000 through ALD. These analyses demonstrate that deposition of NiOxHy clusters occurs selectively ...

A Keggin-type polyoxometalate (H3PW12O40) was incorporated into a mesoporous Zr-based MOF (NU-1000) via an impregnation method in aqueous media, resulting in the hybrid material, PW12@NU-1000. The POM@MOF composite was characterized by a suite of physical methods, indicating the retention of crystallinity and high porosity of the parent MOF. The hybrid material was also stable to leaching in aqueous media at varying pH. Finally, the material was tested as a heterogeneous catalyst for the oxidation of 2-chloroethyl ethyl sulfide using hydrogen peroxide as the oxidant. PW12@NU-1000 was shown to have a higher catalytic activity than either of the individual constituents alone.

In recent years, a wealth of new desalination technologies based on reversible electrochemical redox reactions has emerged. Among them, the use of redox-active electrolytes is highly attractive due...

Mononuclear and dinuclear copper species were synthesized at the nodes of an NU-1000 metal-organic framework (MOF) via cation exchange and subsequent oxidation at 200 °C in oxygen. Copper-exchanged MOFs are active for selectively converting methane to methanol at 150-200 °C. At 150 °C and 1 bar methane, approximately a third of the copper centers are involved in converting methane to methanol. Methanol productivity increased by 3-4-fold and selectivity increased from 70% to 90% by increasing the methane pressure from 1 to 40 bar. Density functional theory showed that reaction pathways on various copper sites are able to convert methane to methanol, the copper oxyl sites with much lower free energies of activation. Combining studies of the stoichiometric activity with characterization by in situ X-ray absorption spectroscopy and density functional theory, we conclude that dehydrated dinuclear copper oxyl sites formed after activation at 200 °C are responsible for the activity.

Polyoxometalates (POM) have been deposited onto carbon nanotube (CNT) electrodes using benchtop ion soft landing (SL) enabled by a vortex-confined electrohydrodynamic desolvation process. The device is based on the dry ion localization and locomotion (DRILL) mass spectrometry interface of Fedorov and co-workers. By adding electrospray emitters, heating the desolvation gas, and operating at high gas flow rates, it is possible to obtain stable ion currents up to -15 nA that are ideal for deposition. Coupled with ambient ion optics, this interface enables desolvated ions to be delivered to surfaces while excluding solvent and counterions. Electron microscopy of surfaces prepared using the device reveal discrete POM and no aggregation that degrades electrode performance. Characterization of POM-coated CNT electrodes in a supercapacitor showed an energy storage capacity similar to that achieved with SL in vacuum. For solutions that produce primarily a single ion by electrospray ionization, benchtop SL offers a simpler and less costly approach for surface modification with applications in catalysis, energy storage, and beyond.

We demonstrate that silanization can control the adhesion of nanostructures to the SiN windows compatible with liquid-cell transmission electron microscopy (LC-TEM). Formation of an (3-aminopropyl)triethoxysilane (APTES) self-assembled monolayer on a SiN window, producing a surface decorated with amino groups, permits strong adhesion of Au nanoparticles to the window. Many of these nanoparticles remain static, undergoing minimal translation or rotation during LC-TEM up to high electron beam current densities due to the strong interaction between the APTES amino group and Au. We then use this technique to perform a direct comparative LC-TEM study on the behavior of ligand and nonligand-coated Au nanoparticles in a Au growth solution. While the ligand coated nanoparticles remain consistent even under high electron beam current densities, the naked nanoparticles acted as sites for secondary Au nucleation. These nucleated particles decorated the parent nanoparticle surface, forming consecutive monolayer assemblies of ∼2 nm diameter nanoparticles, which sinter into the parent particle when the electron beam was shut off. This method for facile immobilization of nanostructures for LC-TEM study will permit more sophisticated and controlled in situ experiments into the properties of solid-liquid interfaces in the future.

Summary Highly efficient cell-free enzymatic systems are typically difficult to achieve in traditional immobilized enzyme systems because of the lack of optimal spatial control of enzyme localization, substrate and product diffusion, and enzyme and coenzyme accessibility. Here, we report a strategy for expanding the pore apertures (from 3.3 to 6.7 nm) of a series of Zr-based metallic-organic frameworks (MOFs) (termed NU-100x , x = 3, 4, 5, 6, 7) with interconnected hierarchical pores by maintaining precise control of torsional angles associated with the linkers. As a proof of concept, we use the expanded NU-100x MOF structures to encapsulate lactate dehydrogenase (LDH) and demonstrate the use of the captured protein in a cell-free biosynthetic catalytic system. Remarkably, LDH immobilized in the large pores of the MOF is accessible to nicotinamide adenine dinucleotide coenzymes (NAD and NADH), allowing for in situ coenzyme regeneration leading to higher activity than that of the free enzyme.

Intricacy anchored by uranium Metal-organic frameworks generally have one level of assembly complexity: Organic linkers join inorganic nodes in a repeating lattice. Li et al. created a structure composed of cuboctahedra, assembled from uranium cations and organic linkers, that shared triangular faces to form prisms. These structures formed cages, which in turn joined to make tetrahedra that assembled with a diamond-lattice topology. This hierarchical open structure generated a huge unit cell with more than 800 nodes and linkers, containing internal cavities with diameters of 5 and 6 nm. Science , this issue p. 624

One of the most promising means to increase the energy density of state-of-the-art lithium Li-ion batteries is to replace the graphite anode with a Li metal anode. While the direct use of Li metal may be highly advantageous, at present its practical application is limited by issues related to dendrite growth and low Coulombic efficiency, CE. Here operando electrochemical scanning transmission electron microscopy (STEM) is used to directly image the deposition/stripping of Li at the anode-electrolyte interface in a Li-based battery. A non-aqueous electrolyte containing small amounts of H2O as an additive results in remarkably different deposition/stripping properties as compared to the “dry” electrolyte when operated under identical electrochemical conditions. The electrolyte with the additive deposits more Li during the first cycle, with the grain sizes of the Li deposits being significantly larger and more variable. The stripping of the Li upon discharge is also more complete, i.e., there is a higher cycling CE. This suggests that larger grain sizes are indicative of better performance by leading to more uniform Li deposition and an overall decrease in the formation of Li dendrites and side reactions with electrolyte components, thus potentially paving the way for the direct use of Li metal in battery technologies.

The rational design of improved electrode–electrolyte interfaces (EEI) for energy storage is critically dependent on a molecular-level understanding of ionic interactions and nanoscale phenomena. The presence of non-redox active species at EEI has been shown to strongly influence Faradaic efficiency and long-term operational stability during energy storage processes. Herein, we achieve substantially higher performance and long-term stability of EEI prepared with highly dispersed discrete redox-active cluster anions (50 ng of pure ∼0.75 nm size molybdenum polyoxometalate (POM) anions on 25 μg (∼0.2 wt%) carbon nanotube (CNT) electrodes) by complete elimination of strongly coordinating non-redox species through ion soft landing (SL). Electron microscopy provides atomically resolved images of a uniform distribution of individual POM species soft landed directly on complex technologically relevant CNT electrodes. In this context, SL is established as a versatile approach for the controlled design of novel surfaces for both fundamental and applied research in energy storage., The design and understanding of electrode–electrolyte interfaces is important for the development of improved energy storage devices. Here, the authors study the controlled deposition of molybdenum polyoxometalate anions onto carbon nanotube electrodes, and show this can result in increased specific capacitance.

The recent development of in-situ liquid stages for (scanning) transmission electron microscopes now makes it possible for us to study the details of electrochemical processes under operando conditions. As electrochemical processes are complex, care must be taken to calibrate the system before any in-situ/operando observations. In addition, as the electron beam can cause effects that look similar to electrochemical processes at the electrolyte/electrode interface, an understanding of the role of the electron beam in modifying the operando observations must also be understood. In this paper we describe the design, assembly, and operation of an in-situ electrochemical cell, paying particular attention to the method for controlling and quantifying the experimental parameters. The use of this system is then demonstrated for the lithiation/delithiation of silicon nanowires.

Electrochemical deposition of crosslinked oxo-cyanoruthenate, Ru-O/CN-O, from a mixture of RuCl 3 and K 4 Ru(CN) 6 is known to yield a film on glassy carbon that promotes oxidations by a combination of electron and oxygen transfer. Layer-by-layer (LbL) deposition of this species at a film formed by cycling of the electrode potential in a ZrO 2 solution systematically increases the number of catalytically active sites of the Ru-O/CN-O on the electrode. The evaluation of the electrocatalytic activity was by cyclic voltammetric oxidation of cysteine at pH 2. Plots of the anodic peak current vs. the square root of scan rate were indicative of linear diffusion control of this oxidation, even in the absence of ZrO 2 , but the slopes of these linear plots increased with bilayer number, n , of (ZrO 2 | Ru-O/CN-O) n . The latter observation is hypothesized to be due to an increased number of active sites for a given geometric electrode area, but proof requires further study. To optimize utilization of the catalyst and to provide a size-exclusion characteristic to the electrode, the study was extended to LbL deposition of the composite in 50-nm pores of an organically modified silica film deposited by electrochemically assisted sol-gel processing using surface-bound poly(styrene sulfonate) nanospheres as a templating agent.

Precise analysis of both (S)TEM images and video are time and labor intensive processes. As an example, determining when crystal growth and shrinkage occurs during the dynamic process of Li dendrite deposition and stripping involves manually scanning through each frame in the video to extract a specific set of frames/images. For large numbers of images, this process can be very time consuming, so a fast and accurate automated method is desirable. Given this need, we developed software that uses analysis of video compression statistics for detecting and characterizing events in large data sets. This software works by converting the data into a series of images which it compresses into an MPEG-2 video using the open source “avconv” utility [1]. The software does not use the video itself, but rather analyzes the video statistics from the first pass of the video encoding that avconv records in the log file. This file contains statistics for each frame of the video including the frame quality, intra-texture and predicted texture bits, forward and backward motion vector resolution, among others. In all, avconv records 15 statistics for each frame. By combining different statistics, we have been able to detect events in various types of data.more » We have developed an interactive tool for exploring the data and the statistics that aids the analyst in selecting useful statistics for each analysis. Going forward, an algorithm for detecting and possibly describing events automatically can be written based on statistic(s) for each data type.« less

Modification of electrodes with nanometer-scale organically modified silica films with pore diameters controlled at 10- and 50-nm is described. An oxidation catalyst, mixed-valence ruthenium oxide with cyano cross-links or gold nanoparticles protected by dirhodium-substituted phosphomolybdate (AuNP-Rh2PMo11), was immobilized in the pores. These systems comprise size-exclusion films at which the biological compounds, phosphatidylcholine and cardiolipin, were electrocatalytically oxidized without interference from surface-active concomitants such as bovine serum albumin. Ten-nanometer pores were obtained by adding generation-4 poly(amidoamine) dendrimer, G4-PAMAM, to a (CH3)3SiOCH3 sol. Fifty-nanometer pores were obtained by modifying a glassy carbon electrode (GC) with a sub-monolayer film of aminopropyltriethoxylsilane, attaching 50-nm diameter poly(styrene sulfonate), PSS, spheres to the protonated amine, transferring this electrode to a (CH3)3SiOCH3 sol, and electrochemically generating hydronium at uncoated GC sites, which catalyzed ormosil growth around the PSS. Voltammetry of Fe(CN)6 3− and Ru(NH3)6 3+ demonstrated the absence of residual charge after removal of the templating agents. With the 50-nm system, the pore structure was sufficiently defined to use layer-by-layer electrostatic assembly of AuNP-Rh2PMo11 therein. Flow injection amperometry of phosphatidylcholine and cardiolipin demonstrated analytical utility of these electrodes.