Local Oxygen Environment Research Articles

Enhancing the Reaction Kinetics and Stability of Co-Free Li-Rich Cathode Materials via a Multifunctional Strategy.

Co-free Li-rich layered oxides (CFLLOs) with anionic redox activity are among the most promising cathode materials for high-energy-density and low-cost lithium-ion batteries (LIBs). However, irreversible oxygen release often causes severe structural deterioration, electrolyte decomposition, and the formation of unstable cathode-electrolyte interface (CEI) film with high impedance. Additionally, the elimination of cobalt elements further deteriorates the reaction kinetics, leading to reduced capacity and poor rate performance. Here, a multifunctional strategy is proposed, incorporating Li2MnO3 phase content regulation, micro-nano structure design, and heteroatom substitution. The increased content of Li2MnO3 phase enhances the capacity through oxygen redox. The smaller nanoscale primary particles induce greater tensile strain and introduce more grain boundaries, thereby improving the reaction kinetics and reactivity, while the larger micron-sized secondary particles help to reduce interfacial side reactions. Furthermore, Na⁺ doping modulates the local coordination environment of oxygen, stabilizing both the anion framework and the crystal structure. As a result, the designed cathode exhibits enhanced rate performance, delivering a capacity of 158 mAh g⁻¹ at 5.0 C and improved cyclic stability, with a high capacity retention of 99% after 400 cycles at 1.0 C. This multifunctional strategy holds great promise for advancing the practical application of CFLLOs in next-generation LIBs.

Induced Anion Redox before Full Oxidation of Ru4+/Ru5+ through Local Configuration Modulation in P2-Na0.67[Mg0.33Ru0.67]O2

The study of anionic redox in layered-oxide cathodes for Na-ion batteries (NIBs) has been extensive, aiming to attain high-energy density. The involvement of Mn4+ or Ru5+ oxidation states is known to be crucial for the anionic O2 −/O− reaction during Na+ de/intercalation. Nevertheless, our findings indicate that anionic redox can activate in Ru-based layered-oxide cathodes prior to complete Ru4+/Ru5+ oxidation. By employing first-principles calculation and experimental techniques, we disclose that additional Na+ deintercalation from P2-Na0.33[Mg0.33Ru0.67]O2 relies on anionic oxidation after extracting 0.33 mol Na+ from P2-Na0.67[Mg0.33Ru0.67]O2, concomitant with cationic oxidation of Ru4+/Ru4.5+. Specifically, only the oxygen adjacent to 2Mg/1Ru is implicated in anionic redox during Na+ de/intercalation, indicating that the Na–O–Mg arrangement in the P2-Na0.33[Mg0.33Ru0.67]O2 structure significantly reduces the thermodynamic stability of anionic redox compared to cationic redox. Through O anionic and Ru cationic reactions, P2-Na0.67[Mg0.33Ru0.67]O2 demonstrates a substantial specific capacity of ∼172 mA h g− 1 and exceptional power capability, facilitated by facile Na+ diffusion and reversible structural changes during charge/discharge. These findings propose an innovative strategy to enhance anionic redox activity by modifying the local oxygen environment, paving the way for high-energy-density cathode materials in NIBs.

High-dimensional order parameters and neural network classifiers applied to amorphous ices.

Amorphous ice phases are key constituents of water's complex structural landscape. This study investigates the polyamorphic nature of water, focusing on the complexities within low-density amorphous ice (LDA), high-density amorphous ice, and the recently discovered medium-density amorphous ice (MDA). We use rotationally invariant, high-dimensional order parameters to capture a wide spectrum of local symmetries for the characterization of local oxygen environments. We train a neural network to classify these local environments and investigate the distinctiveness of MDA within the structural landscape of amorphous ice. Our results highlight the difficulty in accurately differentiating MDA from LDA due to structural similarities. Beyond water, our methodology can be applied to investigate the structural properties and phases of disordered materials.

Formulating Local Environment of Oxygen Mitigates Voltage Hysteresis in Li-Rich Materials.

Li-rich cathode materials have emerged as one of the most prospective options for Li-ion batteries owing to their remarkable energy density (>900Wh kg-1). However, voltage hysteresis during charge and discharge process lowers the energy conversion efficiency, which hinders their application in practical devices. Herein, the fundamental reason for voltage hysteresis through investigating the O redox behavior under different (de)lithiation states is unveiled and it is successfully addressed by formulating the local environment of O2-. In Li-rich Mn-based materials, it is confirmed that there exists reaction activity of oxygen ions at low discharge voltage (<3.6V) in the presence of TM-TM-Li ordered arrangement, generating massive amount of voltage hysteresis and resulting in a decreased energy efficiency (80.95%). Moreover, in the case where Li 2b sites are numerously occupied by TM ions, the local environment of O2- evolves, the reactivity of oxygen ions at low voltage is significantly inhibited, thus giving rise to the large energy conversion efficiency (89.07%). This study reveals the structure-activity relationship between the local environment around O2- and voltage hysteresis, which provides guidance in designing next-generation high-performance cathode materials.

The Identity of Nickel Peroxide as a Nickel Superoxyhydroxide for Enhanced Electrocatalysis.

Nickel peroxides are a class of stoichiometric oxidants that can selectively oxidize various organic compounds, but their molecular level structure remained elusive until now. Herein, we utilized structural prediction using the Stochastic Surface Walking method based on a neural network potential energy surface and advanced characterization using the as-synthesized nickel peroxide to unravel its chemical identity as the bridging superoxide containing nickel hydroxide, or nickel superoxyhydroxide. Superoxide incorporation tunes the local chemical environment of nickel and oxygen beyond the conventional Bode plot, offering a 6.4-fold increase in the electrocatalytic activity of urea oxidation. A volcanic dependence of the activity on the oxygen equivalents leads to the proposed active site of the Ni(OO)(OH)Ni five-membered ring. This work not only unveils the possible structures of nickel peroxides but also emphasizes the significance of tailoring the oxygen environment for advanced catalysis.

A novel oxygen-enriched method for sentry buildings on plateaus based on an attached jet

Due to the existence of windows and the weak thermal resistance of building envelopes, the sentry building is easily affected by the low-oxygen and low-temperature environment at high-altitudes, which affects the work efficiency, cognitive ability and comfort of personnel. This study proposed a novel oxygen supply method suitable for plateau sentry buildings based on attached jet theory, which can achieve coupling control of the thermal and oxygen environment. The computational fluid dynamics (CFD) method was adopted to study the effect of air supply parameters and oxygen supply concentration on environment creation. The results showed that the environmental creation method could efficiently create the local environment. In addition, a nonuniform oxygen environment is created indoors. That is, the oxygen concentration in the head area is greater than that in the non-head area. It greatly improved the utilization rate of oxygen resources. The influence of the air supply velocity on the indoor environment creation effect is greater than that of the air supply temperature. The effect of creating a local oxygen environment is proportional to the concentration of oxygen supplied. The optimal air supply parameters are an air supply velocity (V) of 3 m/s, air supply temperature (Ts) of 30 °C, and oxygen supply concentration (C) of 90%, with the highest oxygen-enriched velocity of 1.598%/min. The research conclusions will provide new ideas for local environmental control methods in sentry buildings on the plateau and expand to actual projects to solve the problem of engineering application.

Sb@Ni6 superstructure units stabilize Li-rich layered cathode in the wide voltage window

In the practical operations of Li-ion batteries, inevitable deep charge/discharge happens locally due to the intrinsic (de)lithiation inhomogeneity at the electrode and particle level, which would damage the health of batteries and even cause the safety concern. It is essential to develop the stable cathodes operating in a wide voltage window to ensure the health and safety of Li-ion batteries. Herein, we comprehensively investigate the charge/discharge behaviors of a representative Li-rich cathode Li1.2Mn0.54Ni0.13Co0.13O2 in a wide voltage window of 1.0–4.8 V, and reveal that, deep-lithiation would drive violent TM migration and severe Li/TM mixing, thereby leading to the irreversible structural transformation from layered to spinel then to rock salt, eventually causing the fast decay in electrochemical performance. Based on these understandings, a novel Li-rich cathode Li[Li1/4Mn1/2Ni1/6Sb1/12]O2 is successfully synthesized through introducing aromatic Sb@Ni6 superstructure units in the TM layers. The introduced Sb@Ni6 superstructure units can effectively tune the local oxygen environment, suppress TM migration, and stabilize the layered framework under deep lithiation. Finally, a stable charge/discharge is achieved in 1.0–4.8 V. This work deepens the understanding into the structural stability of Li-rich cathodes in a wide voltage window, and benefits the development of high-energy-density and safe cathodes.

Structure and electronic properties of amorphous strontium titanate

Understanding the short-range structure of an amorphous material is the first step in predicting its macroscopic properties. Amorphous strontium titanate (a-STO) presents a unique challenge due to contradictory experimental findings regarding the local oxygen environment of titanium, concluded to be either tetrahedral or octahedral. To elucidate the discrepancy, 72 models of a-STO with density ranging from the crystalline value 5.12 to $3.07\phantom{\rule{4pt}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$ were prepared using ab initio molecular dynamics liquid-quench simulations and characterized by extended x-ray absorption fine structure (EXAFS) for both Ti and Sr K edge. An excellent agreement between the calculated and two independent experimental EXAFS measurements demonstrates that the discrepancy in the Ti coordination stems from differences in the material's density. Next, density-dependent structural characteristics, including Ti-O and Sr-O coordination, distances, angles, polyhedral sharing, and vibrational density of states in a-STO are thoroughly analyzed and correlated with disorder-induced changes in the electronic properties that are calculated using a hybrid density functional. The obtained increase in the band gap and broadening of Ti-$d\phantom{\rule{4pt}{0ex}}{e}_{g}$-orbital contributions in the conduction band are in excellent agreement with our x-ray absorption spectroscopy for Ti L-edge spectra and optical absorption measurements for crystalline and amorphous STO grown by pulsed laser deposition. The derived microscopic understanding of the structure-property relationship in amorphous ``perovskite'' serves as a foundation for further investigations of a-STO and related materials.

Enhancing the Reversibility of Lattice Oxygen Redox Through Modulated Transition Metal-Oxygen Covalency for Layered Battery Electrodes.

Utilizing reversible lattice oxygen redox (OR) in battery electrodes is an essential strategy to overcome the capacity limitation set by conventional transition metal redox. However, lattice OR reactions are often accompanied with irreversible oxygen oxidation, leading to local structural transformations and voltage/capacity fading. Herein, it is proposed that the reversibility of lattice OR can be remarkably improved through modulating transition metal-oxygen covalency for layered electrode of Na-ion batteries. By developing a novel layered P2-Na0.6 Mg0.15 Mn0.7 Cu0.15 O2 electrode, it is demonstrated that the highly electronegative Cu dopants can improve the lattice OR reversibility to 95% compared to 73% for Cu-free counterpart, as directly quantified through high-efficiency mapping of resonant inelastic X-ray scattering. Crucially, the large energetic overlap between Cu 3d and O 2p states dictates the rigidity of oxygen framework, which effectively mitigates the structural distortion of local oxygen environment upon (de)sodiation and leads to the enhanced lattice OR reversibility. The electrode also exhibits a completely solid-solution reaction with an ultralow volume change of only 0.45% and a reversible metal migration upon cycling, which together ensure the improved electrochemical performance. These results emphasize the critical role of transition metal-oxygen covalency for enhancing the reversibility of lattice OR toward high-capacity electrodes employing OR chemistry.

Enhanced C-H bond activation by tuning the local environment of surface lattice oxygen of MoO3.

The lattice oxygen on transition metal oxides serves as a critical active site in the dehydrogenation of alkanes, whose activity is determined by electronic properties and environmental structures. Hydrogen affinity has been used as a universal descriptor to predict C–H bond activation, while the understanding of the environmental structure is ambiguous due to its complexity. This paper describes a combined theoretical and experimental study to reveal the activity of lattice oxygen species with different local structures, taking Mo-based oxides and C–H bond activation of low-carbon alkanes as model catalytic systems. Our theoretical work suggests that oxygen species with convex curvature are more active than those with concave curvature. Theoretically, we propose an interpretative descriptor, the activation deformation energy, to quantify the surface reconstruction induced by adsorbates with various environmental structures. Experimentally, a Mo-based polyoxometalate with the convex curvature structure shows nearly five times the initial activity than single-crystal molybdenum oxide with the concave one. This work provides theoretical guidance for designing metal oxide catalysts with high activity.

Effect of Ni Content on Anionic Redox Activity in Ru-Containing Li-Rich Cathode Material

The high energy density of Li-rich layered oxides is associated with anionic redox reaction as it can deliver extra capacity. Herein, using first-principles calculations, we do a contrastive study of anionic redox mechanism in two Li-rich layered oxides, i.e., Li1.167Ni0.167Ru0.667O2 (Li7NiRu4O12) and Li1.167Ni0.333Ru0.5O2 (Li7Ni2Ru3O12), which are marked as LNR4O and LN2R3O, respectively. Our results reveal that the anionic oxidation potential is observed at around 3.95 V in LN2R3O, while, at around 4.31 V, oxygen oxidation reaction can only be achieved in LNR4O. The difference of anionic redox activity can be attributed to the different local oxygen environments between these two materials. Due to the relatively higher content of Ni in the LN2R3O, there are two additional local environments around oxygen (O-Li4NiRu and O-Li3Ni2Ru). Lattice oxygen is more easily oxidized in these two oxygen configurations, which explains the lower anionic oxidation potential in the LN2R3O. In addition, despite not containing linear Li-O-Li configuration, oxygen in the O-Li3Ni2Ru can still have anionic redox activity upon delithiation, which indicates that the anionic redox may not be only determined by linear Li-O-Li configuration. Our finding broadens the fundamental understanding of anionic redox mechanism in Li-rich oxides.

Measuring and Modeling Oxygen Transport and Consumption in 3D Hydrogels Containing Chondrocytes and Stem Cells of Different Tissue Origins.

Understanding how the local cellular environment influences cell metabolism, phenotype and matrix synthesis is crucial to engineering functional tissue grafts of a clinically relevant scale. The objective of this study was to investigate how the local oxygen environment within engineered cartilaginous tissues is influenced by factors such as cell source, environmental oxygen tension and the cell seeding density. Furthermore, the subsequent impact of such factors on both the cellular oxygen consumption rate and cartilage matrix synthesis were also examined. Bone marrow derived stem cells (BMSCs), infrapatellar fat pad derived stem cells (FPSCs) and chondrocytes (CCs) were seeded into agarose hydrogels and stimulated with transforming growth factor-β3 (TGF- β3). The local oxygen concentration was measured within the center of the constructs, and numerical modeling was employed to predict oxygen gradients and the average oxygen consumption rate within the engineered tissues. The cellular oxygen consumption rate of hydrogel encapsulated CCs remained relatively unchanged with time in culture. In contrast, stem cells were found to possess a relatively high initial oxygen consumption rate, but adopted a less oxidative, more chondrocyte-like oxygen consumption profile following chondrogenic differentiation, resulting in net increases in engineered tissue oxygenation. Furthermore, a greater reduction in oxygen uptake was observed when the oxygen concentration of the external cell culture environment was reduced. In general, cartilage matrix deposition was found to be maximal in regions of low oxygen, but collagen synthesis was inhibited in very low (less than 2%) oxygen regions. These findings suggest that promoting an oxygen consumption profile similar to that of chondrocytes might be considered a key determinant to the success of stem cell-based cartilage tissue engineering strategies.

Integrating Microfluidic Models with Hemoglobin‐Based Oxygen Carriers for Investigating Oxygen‐Mediated Endothelial Function

Inadequate oxygen delivery to tissue, or hypoxia, is caused by extensive abnormalities in the structure and function of the vascular network. Hypoxia also has a significant role in vascular diseases such as stroke, pregnancy disorders, and cancer. Despite its prevalence, there is no established method for alleviating hypoxia and its deleterious effects to vascular function. Existing experimental models are incapable of enabling cellular and intercellular microcirculatory measurements while also controlling the local oxygen environment, impeding our ability to mechanistically study these effects. Hemoglobin-based oxygen carriers (HBOCs) are a promising class of red blood cell substitute which have been well characterized for transfusion medicine applications, yet little has been done to study the effects of HBOC administration on vascular function at the cellular level. In this work, we put forth a novel integration of microfluidic vascular models with HBOCs to investigate the effects of oxygen transport in microcirculation in vitro. We hypothesize that alleviating hypoxia with HBOCs restores normal blood vessel structure and function. We fabricated fully-lumenized microvessels in vitro which mimic post-capillary venules. We assessed vessel stability by immunofluorescence staining, and permeability under environmentally-controlled normoxic and hypoxic conditions. We then synthesized polymerized hemoglobin (PolyHb), an HBOC with favorable molecular weight and oxygen-carrying properties to alleviate hypoxia while minimizing extravasation and subsequent toxicity. We validated that PolyHb may be synthesized under varying conditions to selectively control the HBOC size and oxygen affinity, demonstrating that these properties can be modified to enable favorable oxygen transport and may be varied based on the desired application. As compared to previous generation HBOCs, PolyHb can attain molecular weights which will enable intravascular circulation to minimize toxicity, making PolyHb an ideal candidate for microfluidic investigation into the physiological effects of rescuing hypoxia. In future work, we will perfuse PolyHb through the engineered microvessels at constant flow and physiological shear stress levels to assess the ability of PolyHb to relieve induced hypoxia under imposed circumferential and longitudinally oriented hypoxia gradients.

A multiwell plate-based system for toxicity screening under multiple static or cycling oxygen environments

Tumor tissue contains a continuous distribution of static and dynamically changing oxygen environments with levels ranging from physiologically normal oxygen down to anoxia. However, in vitro studies are often performed under oxygen levels that are far higher than those found in vivo. A number of devices are available to alter the oxygen environment in cell culture, including designs from our laboratory. However, in our devices and most other designs, changing the media in order to feed or dose cells remains a disruptive factor in maintaining a consistent hypoxic environment. This report presents a novel 96-well plate design that recirculates the local oxygen environment to shield cells during media changes and facilitates toxicity studies of cells cultured under varying oxygen levels. The principle behind the design is presented and the response of human pancreatic cancer PANC-1 cells treated with tirapazamine and doxorubicin under eight different static or cycling oxygen levels was measured. As expected, tirapazamine is progressively more toxic as oxygen levels decrease but retains some toxicity as oxygen is cycled between hypoxic and normoxic levels. Doxorubicin sensitivity is largely unaffected by changing oxygen levels. This technology is ideal for assessing the effects of oxygen as a variable in toxicity screens.

17 O solid-state NMR at ultrahigh magnetic field of 35.2T: Resolution of inequivalent oxygen sites in different phases of MOF MIL-53(Al).

MIL-53(Al) is a member of the most extensively studied metal-organic framework (MOF) families owing to its "flexible" framework and superior stability. 17 O solid-state NMR (SSNMR) spectroscopy is an ideal site-specific characterization tool as it probes local oxygen environments. Because oxygen local structure is often altered during phase change, 17 O SSNMR can be used to follow phase transitions. However, 17 O is a challenging nucleus to study via SSNMR due to its low sensitivity and resolution arising from the very low natural abundance of 17 O isotope and its quadrupolar nature. In this work, we describe that by using 17 O isotopic enrichment and performing 17 O SSNMR experiments at an ultrahigh magnetic field of 35.2T, all chemically and crystallographically inequivalent oxygen sites in two representative MIL-53(Al) (as-made and water adsorbed) phases can be completely resolved. The number of signals in each phase is consistent with that predicted from the space group refined from powder X-ray diffraction data. The 17 O 1D magic-angle spinning (MAS) and 2D triple-quantum MAS (3QMAS) spectra at 35.2T furnish fine information about the host-guest interactions and the structural changes associated with phase transition. The ability to completely resolve multiple chemically and crystallographically inequivalent oxygen sites in MOFs at very high magnetic field, as illustrated in this work, significantly enhances the potential for using the NMR crystallography approach to determine crystal structures of new MOFs and verify the structures of existing MOFs obtained from refining powder X-ray diffraction data.

Changes in the chemical compound and local atomic structure of ultrathin surface layers of Fe due to implantation of argon and oxygen ions

In this work, we consider the effect of irradiation in Ar+ → O+ and O+ → Ar+ sequences on changes in the chemical compound, type of chemical bond and the local atomic structure of ultrathin (~20 nm) iron surface layers. Investigation of the chemical compound and the type of chemical bond of the ion-modified surface was carried out by the XPS (X-ray photoelectron spectroscopy) and Auger electron spectroscopy. The study of changes in the local atomic structure was carried out by an XAFS-like method — electron energy loss fine structure (EELFS) spectroscopy. The parameters of the local atomic environment of oxygen and iron — partial interatomic distances, dispersion parameters, and coordination numbers — were obtained by analyzing atomic pair correlation functions. Analysis of experimental data showed that the two-stage irradiation of iron significantly changes the chemical compound and local atomic structure of the initial surface. This leads to formation of an oxide layer of greater depth than in the case of irradiation with only oxygen ions.

Oxygen Vacancies and Valence States of Iron in SrFeO3 – δ Compounds

The brownmillerite phase has been studied by X-ray diffraction and Mossbauer methods. The available data on single-phase compounds with the perovskite structure in strontium ferrite SrFeO3 – δ are analyzed. All the valence states of iron for any phase state of strontium ferrite are found to be determined by its local oxygen environment. This fact enables us to understand the regularity of transitions of iron from one valence state to another state when adding oxygen vacancies and to explain the structural states of iron in strontium ferrite, such as the single-phase and two-phase compositions. This approach is a more general case for description of all known compounds and phase combinations synthesized in SrFeO3 – δ than the formula for single-phase structures that is considered in the literature and fit well into the scheme proposed in this work.

Decoupling the Voltage Hysteresis of Li‐Rich Cathodes: Electrochemical Monitoring, Modulation Anionic Redox Chemistry and Theoretical Verifying

AbstractCathodes in lithium‐ion batteries with anionic redox can deliver extraordinarily high specific capacities but also present many issues such as oxygen release, voltage hysteresis, and sluggish kinetics. Identifying problems and developing solutions for these materials are vital for creating high‐energy lithium‐ion batteries. Herein, the electrochemical and structural monitoring is conducted on lithium‐rich cathodes to directly probe the formation processes of larger voltage hysteresis. These results indicate that the charge‐compensation properties, structural evolution, and transition metal (TM) ions migration vary from oxidation to reduction process. This leads to huge differences in charge and discharge voltage profile. Meanwhile, the anionic redox processes display a slow kinetics process with large hysteresis (≈0.5 V), compared to fast cationic redox processes without any hysteresis. More importantly, a simple yet effective strategy has been proposed where fine‐modulating local oxygen environment by the lithium/oxygen (Li/O) ratio tunes the anionic redox chemistry. This effectively improves its electrochemical properties, including the operating voltage and kinetics. This is also verified by theoretical calculations that adjusting anionic redox chemistry by the Li/O ratio shifts the TM 3d—O 2p bands and the non‐bonding O 2p band to a lower energy level, resulting in a higher redox reaction potential.

Hybridizing Li@Mn6 and Sb@Ni6 superstructure units to tune the electrochemical performance of Li-rich layered oxides

Abstract Li@Mn6 superstructure units from the model compound Li2MnO3, i.e., six MnO6 octahedra linked like a ring (Mn6) with a central LiO6 octahedron, could provide extra capacity when composited with other transition metal octahedra (TMO6) structure units in Li and Mn-rich TM layered oxides, xLi2MnO3·(1-x)LiTMO2, one of the most promising high-energy-density cathodes. Nevertheless, it suffers serious capacity and voltage fade due to the unstable local oxygen environment in the basic superstructure unit Li@Mn6. Herein, a new Li-rich layered oxide cathode, Li(Li1/6Mn1/3Ni1/3Sb1/6)O2, was designed and synthesized by compositing Li@Mn6 with a similar superstructure unit Sb@Ni6. Complementary structural/chemical analysis combining with the electronic structure calculations reveal that, the uniform mixing of these two superstructure units at the atomic level has been firstly accomplished in TM layers, which introduces a large amount of boundaries between Li@Mn6 and Sb@Ni6 super-units, thus greatly enriching the local oxygen environments, and reducing the energy barrier of Li+ diffusion. Therefore, the better electrochemical performance, especially the superb cycling stability with the larger capacity (double that of Li(Ni2/3Sb1/3)O2) is implemented. It provides another route to design new Li-rich layered oxides with the better cycling stability by modifying local oxygen environments.

Capillary Oxygen Triggers Conducted Hyperpolarization and Dilation Independent of Extracellular K+ and Endothelial KIR2.1

The matching of red blood cell (RBC) supply to oxygen demand is an intricate process which requires generation of a capillary stimulus and triggering of a transduction process that dilates upstream arterioles. The sensor’s identity, the stimulus it generates and the mechanisms that enables it are openly debated and a source of active inquiry. This study tested whether extracellular K+ is the stimulus and if capillary KIR2.1 channels enable upstream arteriolar dilation via conduction. Experiments were performed in vivo, using a live microcirculatory preparation (extensor digitorum longus); the local oxygen environment was tightly controlled (custom stage insert) and capillary RBC kinetics monitored in mice lacking endothelial KIR2.1 or connexin 40. Dropping PO2 on the muscle surface (53 mmHg to 15 mmHg or 0 mmHg (3 min)) induced a stark microvascular response in control animals (RBC supply rate, velocity and hematocrit increased by 56%, 28% an 18%, respectively) without diminishing mitochondrial respiration. This blood flow response failed to materialize in connexin 40−/− mice. As this response was absent, capillary RBC O2 saturation was lower under normal conditions in the connexin 40−/− animals. In contrast, endothelial KIR2.1−/− mice reacted normally to O2 challenges, with RBC supply rate, velocity and hematocrit rising by 43%, 28%, and 11%, respectively. These findings show that coupling O2 demand‐to‐O2 supply requires coordinated electrical signaling among cells connected by gap junctions comprised of connexin 40. They also show that endothelial KIR2.1 channels are not responsible for initiating the hyperpolarization needed to drive conduction. These findings begin the process of restructuring our understanding of blood flow regulation and how O2 initiates this process independent of metabolite production.Support or Funding InformationThis work was funded by NSERC Discovery grants to CGE and to DGW.