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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Pendent Relay Enhances H 2 O 2 Selectivity during Dioxygen Reduction Mediated by Bipyridine-Based Co–N 2 O 2 Complexes

Generally, cobalt–N 2 O 2 complexes show selectivity for hydrogen peroxide during electrochemical dioxygen (O 2 ) reduction. We recently reported a Co(III)–N 2 O 2 complex with a 2,2'-bipyridine-based ligand backbone which showed alternative selectivity: H 2 O was observed as the primary reduction product from O 2 (71 ± 5%) with decamethylferrocene as a chemical reductant and acetic acid as a proton donor in methanol solution. We hypothesized that the key selectivity difference in this case arises in part from increased favorability of protonation at the distal O position of the key intermediate Co(III)–hydroperoxide species. To interrogate this hypothesis, in this study we have prepared a new Co(III) compound that contains pendent –OMe groups poised to direct protonation toward the proximal O atom of this hydroperoxo intermediate. Mechanistic studies in acetonitrile (MeCN) solution reveal two regimes are possible in the catalytic response, dependent on added acid strength and the presence of the pendent proton donor relay. In the presence of stronger acids, the activity of the complex containing pendent relays becomes O 2 dependent, implying a shift to Co(III)–superoxide protonation as the rate-determining step. Interestingly, the inclusion of the relay results in primarily H 2 O 2 production in MeCN, despite minimal difference between the standard reduction potentials of the three complexes tested. EPR spectroscopic studies indicate the formation of Co(III)–superoxide species in the presence of exogenous base, with greater O 2 reactivity observed in the presence of the pendent –OMe groups.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Elucidating the Role of Halides and Iron during Radiolysis-Driven Oxidative Etching of Gold Nanocrystals Using Liquid Cell Transmission Electron Microscopy and Pulse Radiolysis

Graphene liquid cell transmission electron microscopy (TEM) has enabled the observation of a variety of nanoscale transformations. Yet understanding the chemistry of the liquid cell solution and its impact on the observed transformations remains an important step toward translating insights from liquid cell TEM to benchtop chemistry. Gold nanocrystal etching can be used as a model system to probe the reactivity of the solution. FeCl 3 has been widely used to promote gold oxidation in bulk and liquid cell TEM studies, but the roles of the halide and iron species have not been fully elucidated. In this work, we observed the etching trajectories of gold nanocrystals in different iron halide solutions. We observed an increase in gold nanocrystal etch rate going from Cl - - to Br - - to I - -containing solutions. Furthermore, this is consistent with a mechanism in which the dominant role of halides is as complexation agents for oxidized gold species. Additionally, the mechanism through which FeCl 3 induces etching in liquid cell TEM remains unclear. Ground-state bleaching of the Fe(III) absorption band observed through pulse radiolysis indicates that iron may react with Cl 2 · - radicals to form an oxidized transient species under irradiation. Complete active space self-consistent field (CASSCF) calculations indicate that the FeCl 3 complex is oxidized to an Fe species with an OH radical ligand. Together our data indicate that an oxidized Fe species may be the active oxidant, while halides modulate the etch rate by tuning the reduction potential of gold nanocrystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Factors Governing Oxygen Vacancy Formation in Oxide Perovskites

The control of oxygen vacancy (V O ) formation is critical to advancing multiple metal-oxide-perovskite-based technologies. In this work, we report the construction of a compact linear model for the neutral V O formation energy in ABO 3 perovskites that reproduces, with reasonable fidelity, Hubbard-U-corrected density functional theory calculations based on the state-of-the-art, strongly constrained and appropriately normed exchange-correlation functional. We obtain a mean absolute error of 0.45 eV for perovskites stable at 298 K, an accuracy that holds across a large, electronically diverse set of ABO 3 perovskites. Our model considers perovskites containing alkaline-earth metals (Ca, Sr, and Ba) and lanthanides (La and Ce) on the A-site and 3d transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) on the B-site in six different crystal systems (cubic, tetragonal, orthorhombic, hexagonal, rhombohedral, and monoclinic) common to perovskites. Physically intuitive metrics easily extracted from existing experimental thermochemical data or via inexpensive quantum mechanical calculations, including crystal bond dissociation energies and (solid phase) reduction potentials, are key components of the model. Beyond validation of the model against known experimental trends in materials used in solid oxide fuel cells, the model yields new candidate perovskites not contained in our training data set, such as (Bi,Y)(Fe,Co)O 3 , which we predict may have favorable thermochemical water-splitting properties. The confluence of sufficient accuracy, efficiency, and interpretability afforded by our model not only facilitates high-throughput computational screening for any application that requires the precise control of V O concentrations but also provides a clear picture of the dominant physics governing V O formation in metal-oxide perovskites.

08 HYDROGEN↗
DOE OSTI2025

Mechanical-Bond-Enabled Highly Efficient Charge Separation in a Light-Harvesting Hetero[2]Catenane

Photodriven charge separation is a key process for converting solar energy into chemical energy. However, it remains a challenge to develop artificial light-harvesting materials that can simultaneously achieve ultrafast charge separation and a long-lived charge-separated state with low energy loss. In contrast to conventional strategies based on covalent or noncovalent interactions, we employed a mechanical bond to forcibly assemble two strongly electron-deficient cationic chromophores (TTzBo x4+ and PDI-C 2+ ), which have very similar reduction potentials and exhibit limited noncovalent interactions, into a hetero[2]catenane (TTzPCat 6+ ). This design provides efficient π electronic couplings, enabling ultrafast charge separation (<2.3 ps) even with a low driving force (|ΔG CS | ≈ 160 meV). Furthermore, the adaptive molecular conformation of TTzPCat 6+ , in combination with the Marcus inverted region effect, successfully prolongs the charge-separated state lifetime (k CS /k CR > 1000), surpassing the conventional trade-off between driving force and charge separation efficiency in heterogeneous donor–acceptor systems. The photocatalytic system based on TTzPCat 6+ exhibits an over 2-fold enhancement in selective oxidation of aryl sulfides under mild conditions, demonstrating the potential of mechanical bonding for preparing photocatalytic materials. This investigation not only highlights a strategy for achieving highly efficient charge separation with low energy loss but also offers fresh insights into developing efficient solar energy conversion systems.

Charge transfer↗
DOE OSTI2021

Selective cobalt and nickel electrodeposition for lithium-ion battery recycling through integrated electrolyte and interface control

Abstract Molecularly-selective metal separations are key to sustainable recycling of Li-ion battery electrodes. However, metals with close reduction potentials present a fundamental challenge for selective electrodeposition, especially for critical elements such as cobalt and nickel. Here, we demonstrate the synergistic combination of electrolyte control and interfacial design to achieve molecular selectivity for cobalt and nickel during potential-dependent electrodeposition. Concentrated chloride allows for the speciation control via distinct formation of anionic cobalt chloride complex (CoCl 4 2- ), while maintaining nickel in the cationic form ([Ni(H 2 O) 5 Cl] + ). Furthermore, functionalizing electrodes with a positively charged polyelectrolyte (i.e., poly(diallyldimethylammonium) chloride) changes the mobility of CoCl 4 2- by electrostatic stabilization, which tunes cobalt selectivity depending on the polyelectrolyte loading. This strategy is applied for the multicomponent metal recovery from commercially-sourced lithium nickel manganese cobalt oxide electrodes. We report a final purity of 96.4 ± 3.1% and 94.1 ± 2.3% for cobalt and nickel, respectively. Based on a technoeconomic analysis, we identify the limiting costs arising from the background electrolyte, and provide a promising outlook of selective electrodeposition as an efficient separation approach for battery recycling.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Sustained bacterial N 2 O reduction at acidic pH

Nitrous oxide (N 2 O) is a climate-active gas with emissions predicted to increase due to agricultural intensification. Microbial reduction of N 2 O to dinitrogen (N 2 ) is the major consumption process but microbial N 2 O reduction under acidic conditions is considered negligible, albeit strongly acidic soils harbor nosZ genes encoding N 2 O reductase. Here, we study a co-culture derived from acidic tropical forest soil that reduces N 2 O at pH 4.5. The co-culture exhibits bimodal growth with a Serratia sp. fermenting pyruvate followed by hydrogenotrophic N 2 O reduction by a Desulfosporosinus sp. Integrated omics and physiological characterization revealed interspecies nutritional interactions, with the pyruvate fermenting Serratia sp. supplying amino acids as essential growth factors to the N 2 O-reducing Desulfosporosinus sp. Thus, we demonstrate growth-linked N 2 O reduction between pH 4.5 and 6, highlighting microbial N 2 O reduction potential in acidic soils.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Demand-side solutions to climate change mitigation consistent with high levels of well-being

Mitigation solutions are often evaluated in terms of costs and greenhouse gas reduction potentials, missing out on the consideration of direct effects on human well-being. Here, we systematically assess the mitigation potential of demand-side options categorized into avoid, shift and improve, and their human well-being links. Here we show that these options, bridging socio-behavioural, infrastructural and technological domains, can reduce counterfactual sectoral emissions by 40–80% in end-use sectors. Based on expert judgement and an extensive literature database, we evaluate 306 combinations of well-being outcomes and demand-side options, finding largely beneficial effects in improvement in well-being (79% positive, 18% neutral and 3% negative), even though we find low confidence on the social dimensions of well-being. Implementing such nuanced solutions is based axiomatically on an understanding of malleable rather than fixed preferences, and procedurally on changing infrastructures and choice architectures. Results demonstrate the high mitigation potential of demand-side mitigation options that are synergistic with well-being.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Multi-objective goal-directed optimization of de novo stable organic radicals for aqueous redox flow batteries

Abstract Advances in the field of goal-directed molecular optimization offer the promise of finding feasible candidates for even the most challenging molecular design applications. One example of a fundamental design challenge is the search for novel stable radical scaffolds for an aqueous redox flow battery that simultaneously satisfy redox requirements at the anode and cathode, as relatively few stable organic radicals are known to exist. To meet this challenge, we develop a new open-source molecular optimization framework based on AlphaZero coupled with a fast, machine-learning-derived surrogate objective trained with nearly 100,000 quantum chemistry simulations. The objective function comprises two graph neural networks: one that predicts adiabatic oxidation and reduction potentials and a second that predicts electron density and local three-dimensional environment, previously shown to be correlated with radical persistence and stability. With no hard-coded knowledge of organic chemistry, the reinforcement learning agent finds molecule candidates that satisfy a precise combination of redox, stability and synthesizability requirements defined at the quantum chemistry level, many of which have reasonable predicted retrosynthetic pathways. The optimized molecules show that alternative stable radical scaffolds may offer a unique profile of stability and redox potentials to enable low-cost symmetric aqueous redox flow batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Regulating electrodeposition morphology of lithium: towards commercially relevant secondary Li metal batteries

Lithium, the lightest and most electronegative metallic element, has long been considered the ultimate choice as a battery anode for mobile, as well as in some stationary applications. The high electronegativity of Li is, however, a double-edged sword—it facilitates a large operating voltage when paired with essentially any cathode, promising a high cell-level energy density. It is also synonymous with a high chemical reactivity and low reduction potential. The interfaces a Li metal anode forms with any other material (liquid or solid) in an electrochemical cell are therefore always mediated by one or more products of its chemical or electrochemical reactions with that material. The physical, crystallographic, mechanical, electrochemical, and transport properties of the resultant new material phases (interphases) regulate all interfacial processes at a Li metal anode, including electrodeposition during battery recharge. This Review takes recent efforts aimed at manipulating the structure, composition, and physical properties of the solid electrolyte interphase (SEI) formed on an Li anode as a point of departure to discuss the structural, electrokinetic, and electrochemical requirements for achieving high anode reversibility. An important conclusion is that while recent reports showing significant advances in the achievement of highly reversible Li anodes, e.g. as measured by the coulombic efficiency (CE), raise prospects for as significant progress towards commercially relevant Li metal batteries, the plateauing of achievable CE values to around 99 ± 0.5% apparent from a comprehensive analysis of the literature is problematic because CE values of at least 99.7%, and preferably >99.9% are required for Li metal cells to live up to the potential for higher energy density batteries offered by the Li metal anode. On this basis, we discuss promising approaches for creating purpose-built interphases on Li, as well as for fabricating advanced Li electrode architectures for regulating Li electrodeposition morphology and crystallinity. Considering the large number of physical and chemical factors involved in achieving fine control of Li electrodeposition, we believe that achievement of the remaining ~0.5% in anode reversibility will require fresh approaches, perhaps borrowed from other fields. We offer perspectives on both current and new strategies for achieving such Li anodes with the specific aim of engaging established contributors and newcomers to the field in the search for scalable solutions.

25 ENERGY STORAGE↗
DOE OSTI2020

Modulation of crystal growth and structure within cerium-based metal–organic frameworks

The intriguing catalytic properties of cerium-based materials have motivated the development of Ce-based metal–organic frameworks (MOFs). However, the controlled crystallization of Ce MOFs remains nascent due to complications with the high reduction potential of Ce 4+ species. Modulators offer a route in other well-studied coordination networks to slow down crystallization processes to allow for corrective, uniform crystal growth. Herein, we report an investigation of modulator identity and concentration on the synthesis of a Ce-UiO-type MOF with 2,6-naphthalenedicarboxylic acid (NDC) as a linker. At low concentrations using both benzoic acid and trifluoroacetic acid, we observed a mononuclear Ce 3+ MOF (NU-350) through single-crystal X-ray diffraction studies. Higher modulator concentrations yielded pure-phase Ce-UiO-NDC, with uniform particle sizes observed with utilizing benzoic acid as a modulator. Moreover, we demonstrated the transferability of this synthesis through the pure-phase synthesis of Ce-UiO-66 with benzoic acid as a modulator. High-resolution transmission electron microscopy showed a single crystalline domain within Ce-UiO-NDC.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Passivation-driven speciation, dealloying and purification

Thin passivating surface oxide layers on metal alloys form a dissipation horizon between dissimilar phases, hence harbour an inherent free energy and composition gradient. We exploit this gradient to drive order and selective surface separation (speciation), enabling redox-driven enrichment of the core by selective conversion of low standard reduction potential (E°) components into oxides. Additionally, coupling this oxide growth to volumetric changes during solidification allows us to create oxide crystallites trapped in a metal (‘ship-in-a-bottle’) or extrusion of metal fingerlings on the heavily oxidized particle. We confirm the underlying mechanism through high temperature X-ray diffraction and characterization of solidification-trapped particle states. We demonstrate that engineering the passivating surface oxide can lead to purification via selective dealloying with concomitant enrichment of the core, leading to disparate particle morphologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Using molten salts to probe outer-coordination sphere effects on lanthanide( III )/( II ) electron-transfer reactions

Controlling structure and reactivity by manipulating the outer-coordination sphere around a given reagent represents a longstanding challenge in chemistry. Despite advances toward solving this problem, it remains difficult to experimentally interrogate and characterize outer-coordination sphere impact. Here, this work describes an alternative approach that quantifies outer-coordination sphere effects. It shows how molten salt metal chlorides (MCl n ; M = K, Na, n = 1; M = Ca, n = 2) provided excellent platforms for experimentally characterizing the influence of the outer-coordination sphere cations (M n+ ) on redox reactions accessible to lanthanide ions; Ln 3+ + e 1– → Ln 2+ (Ln = Eu, Yb, Sm; e 1– = electron). As a representative example, X-ray absorption spectroscopy and cyclic voltammetry results showed that Eu 2+ instantaneously formed when Eu 3+ dissolved in molten chloride salts that had strongly polarizing cations (like Ca 2+ from CaCl 2 ) via the Eu 3+ + Cl 1– → Eu 2+ + ½Cl 2 reaction. Conversely, molten salts with less polarizing outer-sphere M 1+ cations (e.g., K 1+ in KCl) stabilized Ln 3+ . For instance, the Eu 3+ /Eu 2+ reduction potential was >0.5 V more positive in CaCl 2 than in KCl. In accordance with first-principle molecular dynamics (FPMD) simulations, we postulated that hard M n+ cations (high polarization power) inductively removed electron density from Ln n+ across Ln–Cl···M n+ networks and stabilized electron-rich and low oxidation state Ln 2+ ions. Conversely, less polarizing M n+ cations (like K 1+ ) left electron density on Lnn+ and stabilized electron-deficient and high-oxidation state Ln 3+ ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Evaluating the photophysical and photochemical characteristics of green-emitting cerium(III) mono-cyclooctatetraenide complexes

The photophysical and photochemical reactivity of the organometallic mono(cyclooctatetraenide)-Ce(III) complexes: [(C 8 H 8 )Ce(μ-X)(THF) 2 ] 2 X = O 3 SCF 3 - (1), Cl - (2), were studied. Here, in the course of these studies, a new polymorph of [(C 8 H 8 )Ce(μ-O 3 SCF 3 )(THF) 2 ] 2 (1) was described. Photoluminescence (PL) studies of 1 and 2 showed characteristic excitation and emission bands in the visible region, with bright green light emission under light irradiation from states corresponding to the 5d → 4f transition. Complexes 1 and 2 exhibit relatively long lifetime of 205.4 ± 0.2 and 145.8 ± 0.4 ns respectively. And the quantum yields (Φ) for 1 and 2 are 0.180 and 0.068 respectively. Electrochemical studies were performed on complexes 1 and 2 with a reversible Ce(III)/Ce(IV) redox couple recorded at $E_{1/2}$ = -1.53 V versus the Fc/Fc + for 2. Complex 1 shows an irreversible Ce(III/IV) oxidation wave. Complexes 1 and 2 revealed strongly-reducing, estimated, excited state reduction potentials ($E^*_{1/2}$) of -3.31 and -4.02 V versus the Fc/Fc + respectively, with small Stokes shifts of 0.12 eV. With their associated relatively long lifetimes, small Stokes shifts and large, negative $E^*_{1/2}$ values, both complexes were evaluated as potential photosensitisers for halogen atom transfer (XAT) using a test reaction of the dehalogenation of benzyl chloride.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Pre-equilibrium reactions involving pendent relays improve CO 2 reduction mediated by molecular Cr-based electrocatalysts

Homogeneous earth abundant transition-metal electrocatalysts capable of carbon dioxide (CO 2 ) reduction to generate value-added chemical products are a possible strategy to minimize rising anthropogenic CO 2 emissions. Previously, it was determined that Cr-centered bipyridine-based N 2 O 2 complexes for CO 2 reduction are kinetically limited by a proton-transfer step during C–OH bond cleavage. Therefore, it was hypothesized that the inclusion of pendent relay groups in the secondary coordination sphere of these molecular catalysts could increase their catalytic activity. Here, it is shown that the introduction of a pendent methoxy group favorably impacts a pre-equilibrium protonation prior to the catalytic resting state, resulting in a significant increase in catalytic activity without a loss of product selectivity for generating carbon monoxide (CO) from CO 2 . Interestingly, combining the pendent methoxy group with a cationic acid causes a positive shift of the catalytic reduction potential of the system, while maintaining increased activity and quantitative selectivity. This work suggests that tuning the secondary coordination sphere with respect to cationic proton sources can result in activity improvements by modifying the kinetic and thermodynamic aspects of proton transfer in the catalytic cycle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Electroanalytical characterization of Np( VI )/Np( V ) redox in a pentadentate ligand environment and stabilization of [Np V O 2 ] + by hydrogen bonding

The redox chemistry of the actinyl cations (AnO 2 n+ ) heavily influences their reactivity and speciation in solution, but the redox properties of the actinyls in non-aqueous media have received far less attention than they deserve. Here, the non-aqueous electrochemistry of a chemically reversible Np(VI)/Np(V) redox manifold is reported in both protic (CH 3 OH) and aprotic (CH 3 CN) organic media. Using a neutral Np(VI) complex supported by a chelating and strongly donating pentadentate ligand that was fully characterized in prior work, a clean Np(VI)/Np(V) redox couple was found to be accessible under ambient conditions. Coupled electrochemical and spectroscopic studies, as well as simulations of cyclic voltammetry data, confirm the 1e− nature of this couple and establish it to be chemically reversible and nearly electrochemically reversible as well. Bulk electrolysis of a solution of the neutral Np(VI) complex facilitated isolation of the corresponding anionic and monomeric Np(V) species. Data from X-ray diffraction analysis as well as optical and vibrational spectroscopies provide strong evidence in support of metal-centered reduction and the Np(V) oxidation state, findings that are in accord with the measured reduction potentials. Distinctive hydrogen bonding interactions between the terminal (yl) oxo groups and water molecules appear to stabilize the isolated Np(V) species in the solid state, providing insight into the features that afford the uncommon chemically reversible redox encountered in this system.

Mikeska, Emily R.↗
DOE OSTI2024

The role of an intramolecular hydrogen bond in the redox properties of carboxylic acid naphthoquinones

A bioinspired naphthoquinone model of the quinones in photosynthetic reaction centers but bearing an intramolecular hydrogen-bonded carboxylic acid has been synthesized and characterized electrochemically, spectroscopically, and computationally to provide mechanistic insight into the role of proton-coupled electron transfer (PCET) of quinone reduction in photosynthesis. The reduction potential of this construct is 370 mV more positive than the unsubstituted naphthoquinone. In addition to the reversible cyclic voltammetry, infrared spectroelectrochemistry confirms that the naphthoquinone/naphthoquinone radical anion couple is fully reversible. Calculated redox potentials agree with the experimental trends arising from the intramolecular hydrogen bond. Molecular electrostatic potentials illustrate the reversible proton transfer driving forces, and analysis of the computed vibrational spectra supports the possibility of a combination of electron transfer and PCET processes. The significance of PCET, reversibility, and redox potential management relevant to the design of artificial photosynthetic assemblies involving PCET processes is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

A comprehensive approach for elucidating the interplay between 4f n +1 and 4f n 5d 1 configurations in Ln 2+ complexes

Lanthanides (Ln) are typically found in the +3 oxidation state. However, in recent decades, their chemistry has been expanded to include the less stable +2 oxidation state across the entire series except promethium (Pm), facilitated by the coordination of ligands such as trimethylsilylcyclopentadienyl, C 5 H 4 SiMe 3 (Cp'). The [LnCp' 3 ] complexes have been the workhorse for the synthesis and theoretical study of the fundamental aspects of divalent lanthanide chemistry, where experimental and computational evidence have suggested the existence of different ground state (GS) configurations, 4f n+1 or 4f n 5d 1 , depending on the specific metal. Standard reduction potentials and 4f n+1 to 4f n 5d 1 promotion energies have been two factors usually considered to rationalize the occurrence of these variable GS configurations, however the driving force behind this phenomenon is still not clear. In this work we present a comprehensive theoretical approach to shed light on this matter using the [LnCp 3 ] - model systems. We begin by calculating 4f n+1 to 4f n 5d 1 promotion energies and successfully correlate them with existing experimental data. Furthermore, we analyze how changes in the GS charge distribution between the Ln ions, LnCp 3 and the reduced [LnCp 3 ] - complexes (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) correlate with experimental trends in redox potentials and the calculated promotion energies. For this purpose, a comprehensive theoretical work that includes relativistic ligand field density functional theory (LFDFT) and relativistic ab initio wavefunction methods was performed. This study will help the rational design of suitable environments to tune the different GS configurations as well as modulating the spectroscopic properties of new Ln 2+ complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗