Bulk Reaction Research Articles

Accelerated reactions in field desorption mass spectrometry.

Field desorption mass spectrometry under ambient conditions is used to study solution-phase organic reactions in micro-volumes. Reagent solution is transferred onto the microdendrites of the field emitter, and reaction products are examined online by mass spectrometry. Three reactions, hydrazone formation by phenyl hydrazine and indoline-2,3-dione, the Katritzky reaction between a pyrylium salt and anisidine, and the Hantzsch synthesis of 1,4-dihydropyridine, were investigated, and reaction acceleration was observed to different extents. The increase in rate relative to the corresponding bulk reactions is attributed to solvent evaporation (simple concentration effect) and to the increase of surface-to-volume ratio (enhanced interfacial reactions). A distinguishing feature of this method of reaction acceleration, relative to that based on nano electrospray ionization, is the observation of radical cations and the formation of radical cation products. The study also breaks new ground in using field emitters at atmospheric pressure.

In situ fabrication of cellular architecture on silver metals using methane/oxygen gas mixture and its application for energy storage

Cellular metals with a large surface-to-volume ratio and excellent electrical conductivity have attracted great attention due to their wide application. However, the existing processes for fabrication of cellular metallic structures are generally complex and dependent on the sacrificial materials or templates, and therefore, it is highly desirable to develop a facile process. Herein, we propose a novel gas-assisted reconstruction strategy for in situ fabrication of micron-porous architectures on Ag precursor metal using a CH4/O2 gas mixture at 750 °C. The obtained results indicate that large-area and clean, porous Ag architectures are successfully created through the treatment in CH4/O2 gas. The formation of cellular structure is mainly due to the simultaneous diffusion of H2, CO and O2 into Ag bulk and fast reaction at elevated temperatures. The process is clean and applicable to creation of porous architectures (from surface texturing to 3-D cellular structure) on Ag metal, avoiding the use of sacrificial materials or templates. Furthermore, we have demonstrated that the formed micron-porous Ag sheet with large effective area, high electrical conductivity can be directly used as a free-standing electrode for electrochemical supercapacitors with a high capacitance.

Immobilized cutinases: Preparation, solvent tolerance and thermal stability

Developing active immobilized enzymes and characterization of their use conditions is critically important prior to initiating studies of enzyme selectivity and substrate specificity in organic media. To this end, physical immobilization by hydrophobic interactions was performed with three well-characterized cutinases (Aspergillus oryzae Cutinase (AoC), Humicola insolens Cutinase (HiC), and Thielavia terrestris Cutinase (TtC)) using Lewatit VP OC 1600 as the macroporous support. We found that immobilization yields >98% were achieved for all three cutinases under the following immobilization conditions: 100 mg/g loading ratio, immobilization buffers of 100 mM phosphate pH 8 (AoC and HiC) and 100 mM acetate pH 5 (TtC), mixing at 150 rpm and 30 °C for 24 h. Among the three cutinases, HiC has the highest tolerance towards solvents of increased polarity while TtC has the highest thermal stability (up to 80 °C) in a bulk reaction system that consists of the reactants butanol and lauric acid. In nonane, these cutinases retain >64% of their activity at 90 °C. Furthermore, kinetic stability (residual activity as a function of time) analysis reveals that the cutinases retain >75% residual activity at 70 °C in 3 h. Moreover, at 80 °C, the kinetic stability of TtC is higher than that of HiC and AoC. Collectively, the results herein set the stage for the in-depth evaluation of these catalysts for selective transformations in organic media.

Classification of Similarity Criteria in Combustion Theory and the Problem of Autoignition of a Combustible Mixture by Compression

The dynamic problems of the theory of combustion and explosion are classified from the point of view of competition of the characteristic times of bulk chemical reaction, frontal combustion, heat transfer, gas flow from the vessel, compression (motion of the piston), and heating (cooling) rate. We consider dynamic similarity criteria such as the ratio of the characteristic times in problems of classical thermal explosion, dynamic thermal explosion, flammability limits, combustion in communicating vessels, competition of frontal and volumetric combustion, autoignition by adiabatic compression, competition of frontal combustion and piston motion, as well as compound similarity criteria (such as functions of simple dynamic similarity criteria). The problem of autoignition of a mixture by compression is considered, and a method for obtaining an analytical solution of the problem and an algorithm for the approximate solution based on a special differential criterion are proposed.

Pair Interaction of Catalytical Sphere Dimers in Chemically Active Media.

We study the pair dynamics of two self-propelled sphere dimers in the chemically active medium in which a cubic autocatalytic chemical reaction takes place. Concentration gradient around the dimer, created by reactions occurring on the catalytic sphere surface and responsible for the self-propulsion, is greatly influenced by the chemical activities of the environment. Consequently, the pair dynamics of two dimers mediated by the concentration field are affected. In the particle-based mesoscopic simulation, we combine molecular dynamics (MD) for potential interactions and reactive multiparticle collision dynamics (RMPC) for solvent flow and bulk reactions. Our results indicate three different configurations between a pair of dimers after the collision, i.e., two possible scenarios of bound dimer pairs and one unbound dimer pair. A phase diagram is sketched as a function of the rate coefficients of the environment reactions. Since the pair interactions are the basic elements of larger scale systems, we believe the results may shed light on the understanding of the collective dynamics.

Efficient metoprolol degradation by heterogeneous copper ferrite/sulfite reaction

Metal/sulfite systems are currently used for SO 4 •− generation and oxidative removal of organic contaminants. However, homogeneous metal/sulfite systems are limited because their working pHs must be acidic and metal ions cannot be separated from the bulk reaction solution. As a consequence, these drawbacks have severely limited the application of metal/sulfite systems in real conditions. To address these issues, we tested the use of copper ferrite (CuFe2O4), a ferromagnetic nanoparticle, to catalyze sulfite oxidation for the degradation of the metoprolol drug. The reaction mechanism was investigated by electron spin resonance, X-ray photoelectron spectroscopy, and radical quenching assay. The effects of pH, CuFe2O4, and sulfite dosages were also assessed. Results show that SO 4 •− was the primary radical responsible for metoprolol degradation. Higher pHs induced more metoprolol degradation using CuFe2O4/sulfite. Moreover, CuFe2O4 remained morphologically intact and catalytically active after four batches of recycling. Overall, our findings show that CuFe2O4/sulfite can effectively degrade water contaminants in alkali pH and withhold catalyst activity after multiple reuses, therefore addressing the issues associated with homogeneous metal/sulfite systems.

Simultaneous monitoring of transcription and translation in mammalian cell-free expression in bulk and in cell-sized droplets.

Transcription and translation are two critical processes during eukaryotic gene expression that regulate cellular activities. The development of mammalian cell-free expression (CFE) systems provides a platform for studying these two critical processes in vitro for bottom-up synthetic biology applications such as construction of an artificial cell. Moreover, real-time monitoring of the dynamics of synthesized mRNA and protein is key to characterize and optimize gene circuits before implementing in living cells or in artificial cells. However, there are few tools for measurement of mRNA and protein dynamics in mammalian CFE systems. Here, we developed a locked nucleic acid (LNA) probe for monitoring transcription in a HeLa-based CFE system in real-time. By using this LNA probe in conjunction with a fluorescent reporter protein, we were able to simultaneously monitor mRNA and protein dynamics in bulk reactions and cell-sized single-emulsion droplets. We found rapid production of mRNA transcripts that decreased over time as protein production ensued in bulk reactions. Our results also showed that transcription in cell-sized droplets has different dynamics compared to the transcription in bulk reactions. The use of this LNA probe in conjunction with fluorescent proteins in HeLa-based mammalian CFE system provides a versatile in vitro platform for studying mRNA dynamics for bottom-up synthetic biology applications.

A revisit of the interaction of gaseous ozone with aqueous iodide. Estimating the contributions of the surface and bulk reactions

The main source of atmospheric iodine is the heterogeneous reaction of aqueous iodide (I-) with ozone (O3), which takes place in surface seawater and probably in sea-salt aerosols. However, there are seemingly contradictory conclusions about whether this heterogeneous reaction occurs in the bulk of the aqueous phase, via O3 dissolution, or at the aqueous surface, via O3 adsorption. In this work, the ozone uptake coefficient has been calculated as a function of the concentration of aqueous iodide ([I-]aq) and gaseous ozone near the aqueous surface ([O3]gs) by estimating parameters of the resistor model using results of previous studies. The calculated uptake coefficients suggest that the aqueous-phase reaction dominates at low I- concentrations (about <10-4 mol L-1), regardless of [O3]gs, and also at sufficiently high [O3]gs (about >80 ppm), regardless of [I-]aq. In contrast, the surface reaction dominates at high [I-]aq (about >10-4 mol L-1) as long as [O3]gs is low enough (about <80 ppm). This trend is able to reconcile previous studies of this reaction, and is a consequence of several factors, including the high surface excess of both reactants ozone and iodide. Given the typical O3 concentrations in the troposphere and the possible I- concentrations and O3 solubilities in sea-salt aerosols, the surface reaction may compete with the aqueous-phase reaction in accumulation-mode aerosols, unlike in surface seawater, where the aqueous-phase reaction probably prevails. The rate constant of the surface reaction has been estimated as (3-40) × 10-13 cm2 molecule-1 s-1.

A 'Fluid' Nickel-Based Ferrite as an Efficient Redox Material for Thermochemical Two-Step CO &lt;sub&gt;2&lt;/sub&gt; Splitting

The solar-driven, thermochemical two-step CO2 splitting reaction is essentially hindered by sintering of the redox material, and thermostable supports are often employed to alleviate this issue, although they usually play a limited role due to the harsh thermal condition. Herein, we demonstrate a distinct strategy, by engineering a “fluid” nickel-based ferrite material without using any support. It maintains a steady-state CO yield over 20 cycles, which is up to three times higher than that of the traditional NiFe2O4/ZrO2 material. Characterizations and first principles calculations suggest that its superiority can be attributed to the significantly enhanced flow of Fe cations, dramatically different from the NiFe2O4/ZrO2, where the oxygen ion undertakes the major transport. Such cation diffusion mode in our novel ferrite material provides a more accessible path to the bulk reaction, leading to a fast bulk reaction kinetics in the ferrite. Thus, we developed a new approach to overcome the sintering problem of ferrite materials.

The Performance of Syngas-Fueled SOFCs Predicted by a Reduced Order Model (ROM): Temperature and Fuel Composition Effects

An electrochemical reduced order model (ROM) has been developed in this study to simulate the performance of syngas-fueled anode-supported SOFCs with coupled bulk chemical reactions and multi-species gas diffusion in the electrodes. Experimental V-I curves with syngas fuel were used to validate the model to ensure its high fidelity. The model was used to investigate the effects of fuel composition and temperature on the electrochemical performance of the cell, chemical reaction rate and concentration distributions of gaseous species across the anode. The results show that H2 electro-oxidation dominates the overall cell performance, and that CO contributes to the performance indirectly via water gas shift (WGS) reaction, especially at low CO:H2 ratio and low current densities. Increasing the temperature enhances the performance of syngas-fueled SOFCs by increasing the rates of total electrochemical oxidation and the WGS reaction. The present work provides fundamental knowledge and framework for future performance simulations of large-scale and more complex syngas-fueled SOFC systems.

High yield accelerated reactions in nonvolatile microthin films: chemical derivatization for analysis of single-cell intracellular fluid.

The identification of trace components from biological media can require derivatization under mild conditions for successful analysis by mass spectrometry (MS). When aqueous droplets (ca. 500 nL) containing a sugar and an amine as reagents are allowed to evaporate they may form long-lasting microthin films in which derivatization reactions can occur fast relative to reaction rates in bulk solution. Evidence is presented that these reactions are heterogeneous in nature and comparisons are made with reactions in pastes and in neat reagent mixtures. Moreover, these thin film reactors can be made stable for the long periods of time that may be necessary to give high product yields. The situation is typified by imine formation from reducing sugars which have reaction times of much more than 1 hour provided that small concentrations (e.g. 20 ppm) of nonvolatile solvents are included. After evaporation of almost all the water, the reaction occurs at an approximately constant rate for the first hour. The rate is two orders of magnitude faster than the reaction in the corresponding homogeneous saturated bulk solution. Conversion of the reagent to the Schiff base product is 67% to 96% efficient in these long-lasting thin films, in sharp contrast to the corresponding derivatization efficiencies in the bulk of less than 1%. This method was used to chemically derivatize and thus to identify, using tandem mass spectrometry, 29 reducing sugars in ca. 1 nL of intracellular fluid from a single onion epidermis cell. A formal description of the kinetics of reversible and irreversible second order reactions in thin films is provided. The effects of thermodynamic and kinetic factors are separated and the measured apparent acceleration factor is shown to represent the ratio of intrinsic rate constants for the microthin film reactor relative to the bulk reaction.

Chemotactic and hydrodynamic effects on collective dynamics of self-diffusiophoretic Janus motors

Collective motion in nonequilibrium steady state suspensions of self-propelled Janus motors driven by chemical reactions can arise due to interactions coming from direct intermolecular forces, hydrodynamic flow effects, or chemotactic effects mediated by chemical gradients. The relative importance of these interactions depends on the reactive characteristics of the motors, the way in which the system is maintained in a steady state, and properties of the suspension, such as the volume fraction. From simulations of a microscopic hard collision model for the interaction of fluid particles with the Janus motor we show that dynamic cluster states exist and determine the interaction mechanisms that are responsible for their formation. The relative importance of chemotactic and hydrodynamic effects is identified by considering a microscopic model in which chemotactic effects are turned off while the full hydrodynamic interactions are retained. The system is maintained in a steady state by means of a bulk reaction in which product particles are reconverted into fuel particles. The influence of the bulk reaction rate on the collective dynamics is also studied.

A Nuclear Jet at Chernobyl Around 21:23:45 UTC on April 25, 1986

The nature of two explosions that were witnessed within 3 s at the Chernobyl-4 reactor less than a minute after 21:23:00 UTC on April 25, 1986, have since then been the subject of sprawling interpretations. This paper renders the following hypothesis. The first explosion consisted of thermal neutron mediated nuclear explosions in one or rather a few fuel channels, which caused a jet of debris that reached an altitude of some 2500 to 3000 m. The second explosion would then have been the steam explosion most experts believe was the first one. The solid support for this new scenario rests on two pillars and three pieces of corroborating evidence. The first pillar is that a group at the V. G. Khlopin Radium Institute in then Leningrad on April 29, 1986, detected newly produced, or fresh, xenon fission products at Cherepovets, 370 km north of Moscow and far away from the major track of Chernobyl debris ejected by the steam explosion and subsequent fires. The second pillar is built on state-of-the-art meteorological dispersion calculations, which show that the fresh xenon signature observed at Cherepovets was only possible if the injection altitude of the fresh debris was considerably higher than that of the bulk reactor core releases that turned toward Scandinavia and central Europe. These two strong pieces of evidence are corroborated by what were manifest physical effects of a downward jet in the southeastern part of the reactor, by seismic measurements some 100 km west of the reactor, and by observations of a blue flash above the reactor a few seconds after the first explosion.

Colliding-Droplet Microreactor: Rapid On-Demand Inertial Mixing and Metal-Catalyzed Aqueous Phase Oxidation Processes.

In-depth investigations of the kinetics of aqueous chemistry occurring in microdroplet environments require experimental techniques that allow a reaction to be initiated at a well-defined point in time and space. Merging microdroplets of different reactants is one such approach. The mixing dynamics of unconfined (airborne) microdroplets have yet to be studied in detail, which is an essential step toward widespread use and application of merged droplet microreactors for monitoring chemical reactions. Here, we present an on-demand experimental approach for initiating chemical reactions in and characterizing the mixing dynamics of colliding airborne microdroplets (40 ± 5 μm diameter) using a streak-based fluorescence microscopy technique. The advantages of this approach include the ability to generate two well-controlled monodisperse microdroplet streams and collide (and thus mix) the microdroplets with high spatial and temporal control while consuming small amounts of sample (<0.1 μL/s). Mixing times are influenced not only by the velocity at which microdroplets collide but also the geometry of the collision (i.e., head-on vs off-center collision). For head-on collisions, we achieve submillisecond mixing times ranging from ∼900 μs at a collision velocity of 0.1 m/s to <200 μs at ∼6 m/s. For low-velocity (<1 m/s) off-center collisions, mixing times were consistent with the head-on cases. For high-velocity (i.e., > 1 m/s) off-center collisions, mixing times increased by as much as a factor of 6 (e.g., at ∼6 m/s, mixing times increased from <200 μs for head-on collisions to ∼1200 μs for highly off-center collisions). At collision velocities >7 m/s, droplet separation and fragmentation occurred, resulting in incomplete mixing. These results suggest a limited range of collision velocities over which complete and rapid mixing can be achieved when using airborne merged microdroplets to, e.g., study reaction kinetics when reaction times are short relative to typical bulk reactor mixing times. We benchmark our reactor using an aqueous-phase oxidation reaction: iron-catalyzed hydroxyl radical production from hydrogen peroxide (Fenton's reaction) and subsequent aqueous-phase oxidation of organic species in solution. Kinetic simulations of our measurements show that quantitative agreement can be obtained using known bulk-phase kinetics for bimolecular reactions in our colliding-droplet microreactor.

Cu2O nanocrystals/TiO2 microspheres film on a rotating disk containing long-afterglow phosphor for enhanced round-the-clock photocatalysis

A Cu2O nanocrystals/TiO2 microspheres (Cu2O NCs/M-TiO2) rotating disk reactor assisted by long-afterglow phosphor was successfully designed and fabricated in order to achieve enhanced round-the-clock photocatalysis. The Cu2O NCs/M-TiO2 composite exhibited good photocatalytic activity owing to enlarged light absorption and efficient quantum yield by integrating Cu2O NCs with core-shell M-TiO2. Through rotating the catalyst disk, a thin aqueous film was formed on its upper part as well as continuously refreshed. Compared with bulk reaction, the photon propagation distance within this film was greatly shortened, and the possibility of light absorption by solution was correspondingly reduced, increasing the light utilization yield of photocatalytic system. Additionally, the continuous update of pollutants and their intermediates on catalyst was beneficial to photocatalysis. The long-afterglow phosphor in reactor could absorb excessive light energy and give out persistent fluorescence, exciting Cu2O NCs/M-TiO2 composite and realizing round-the-clock photocatalysis. As a result, the Cu2O NCs/M-TiO2 rotating disk reactor containing long-afterglow phosphor presented high reactivity in the photocatalytic degradation of rhodamine B and bisphenol A. The recycle experiments confirmed the stability and reliability of prepared reactor.

Carbide-metal assemblages in a sample returned from asteroid 25143 Itokawa: Evidence for methane-rich fluids during metamorphism

We found that the particle RA-QD02-0115 returned by the Hayabusa spacecraft from near-Earth asteroid 25143 Itokawa contains the iron carbide haxonite (Fe21.9-22.7Co0.2-0.3Ni0.2-0.8)C6 and several Fe,Ni alloys, including multi-domain tetrataenite and spinodally decomposed taenite. Ellipsoidal to nearly spherical voids occur throughout the particle and suggest the presence of a fluid phase during textural and chemical equilibration of the host rock within the parent asteroid of 25143 Itokawa. The calculated solubility of carbon in Fe,Ni metal indicates that the carbide formed at temperatures larger than 600 °C during thermal metamorphism of the LL-chondritic mineral assemblage. Haxonite formed metastably with respect to graphite and cohenite, probably due to its high degree of lattice match with neighboring taenite, a low cooling rate at peak metamorphic temperatures, and the hindered nucleation of graphite. Thermodynamic equilibrium calculations indicate that the fluid present was dry (H2O-poor) and dominated by methane. The reactive fluid most plausibly had an atomic H/C ratio of 4–5 and was derived from the reduction of macromolecular, insoluble organic matter (IOM) that initially co-accreted with water ice. The initial presence of water is a necessary assumption to provide sufficient hydrogen for the formation of methane from hydrolyzed IOM. Metallic iron was in turn partially oxidized and incorporated into the ferromagnesian silicates during the high-temperature stage of metamorphism. An exemplary bulk reaction from unequilibrated material on the left to an equilibrated assemblage on the right may be written as:330 CH0.8O0.2(IOM) + 500 H2O(ice/g) + 681 Fe(in alloy) + 566 FeSiO3(in Opx) → 300 CH4(g) + 32 H2(g) + 5 Fe23C6(in Hx) + 566 Fe2SiO4(in Ol)(Opx = orthopyroxene, Hx = haxonite, Ol = olivine, g = fluid species).The best estimate of the fluid/rock ratio in the region of the LL parent body where RA-QD02-0115 formed is about 3 × 10−3 and corresponds to an initial ice/rock ratio of about 7 × 10−3 (both by mass).

Hetero-multivalent binding of cholera toxin subunit B with glycolipid mixtures

GM1 has generally been considered as the major receptor that binds to cholera toxin subunit B (CTB) due to its low dissociation constant. However, using a unique nanocube sensor technology, we have shown that CTB can also bind to other glycolipid receptors, fucosyl-GM1 and GD1b. Additionally, we have demonstrated that GM2 can contribute to CTB binding if present in a glycolipid mixture with a strongly binding receptor (GM1/fucosyl-GM1/GD1b). This hetero-multivalent binding result was unintuitive because the interaction between CTB and pure GM2 is negligible. We hypothesized that the reduced dimensionality of CTB-GM2 binding events is a major cause of the observed CTB binding enhancement. Once CTB has attached to a strong receptor, subsequent binding events are confined to a 2D membrane surface. Therefore, even a weak GM2 receptor could now participate in second or higher binding events because its surface reaction rate can be up to 104 times higher than the bulk reaction rate. To test this hypothesis, we altered the surface reaction rate by modulating the fluidity and heterogeneity of the model membrane. Decreasing membrane fluidity reduced the binding cooperativity between GM2 and a strong receptor. Our findings indicated a new protein-receptor binding assay, that can mimic complex cell membrane environment more accurately, is required to explore the inherent hetero-multivalency of the cell membrane. We have thus developed a new membrane perturbation protocol to efficiently screen receptor candidates involved in hetero-multivalent protein binding.

Comparison of exciplex generation under optical and X-ray excitation.

Exciplex generation under optical and X-ray excitation in identical conditions is experimentally compared using a specially chosen model donor-acceptor system, anthracene (electron acceptor) and N,N-dimethylaniline (electron donor) in non-polar solution, and the results are analyzed and interpreted based on analytically calculated luminescence quantum yields. Calculations are performed on the basis of kinetic equations for multistage schemes of bulk exciplex production reaction under optical excitation and combination of bulk and geminate reactions of radical ion pairs under X-ray excitation. These results explain the earlier experimentally found difference in the ratio of the quantum yields of exciplexes and excited electron acceptors (exciplex generation efficiency) and the corresponding change in the exciplex generation efficiency under X-irradiation as compared to the reaction under optical excitation.

Control of serpentinisation rate by reaction-induced cracking

Serpentinisation of mantle rocks requires the generation and maintenance of transport pathways for water. The solid volume increase during serpentinisation can lead to stress build-up and trigger cracking, which ease fluid penetration into the rock. The quantitative effect of this reaction-induced cracking mechanism on reactive surface generation is poorly constrained, thus hampering our ability to predict serpentinisation rate in geological environments. Here we use a combined approach with numerical modelling and observations in natural samples to provide estimates of serpentinisation rate at mid-ocean ridges. We develop a micromechanical model to quantify the propagation of serpentinisation-induced cracks in olivine. The maximum crystallisation pressure deduced from thermodynamic calculations reaches several hundreds of megapascals but does not necessary lead to crack propagation if the olivine grain is subjected to high compressive stresses. The micromechanical model is then coupled to a simple geometrical model to predict reactive surface area formation during grain splitting, and thus bulk reaction rate. Our model reproduces quantitatively experimental kinetic data and the typical mesh texture formed during serpentinisation. We also compare the model results with olivine grain size distribution data obtained on natural serpentinised peridotites from the Marum ophiolite and the Papuan ultramafic belt (Papua New Guinea). The natural serpentinised peridotites show an increase of the number of olivine grains for a decrease of the mean grain size by one order of magnitude as reaction progresses from 5 to 40%. These results are in agreement with our model predictions, suggesting that reaction-induced cracking controls the serpentinisation rate. We use our model to estimate that, at mid-ocean ridges, serpentinisation occurs up to 12 km depth and reaction-induced cracking reduces the characteristic time of serpentinisation by one order of magnitude, down to values comprised between 10 and 1000 yr. The increase of effective pressure with depth also prevents cracking, which positions the peak in serpentinisation rate at shallower depths, 4 km above previous predictions.

Reaction Heterogeneity in LiNi0.8Co0.15Al0.05O2 Induced by Surface Layer

Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact versus an eroded Li2CO3 surf...