Tuning the Coordination Microenvironment of Central Fe Active Site to Boost Water Electrolysis and Oxygen Reduction Activity

In heterogeneous catalysis, single-atom catalysts are the frontier and important prototypes for many reactions, and revealing the intrinsic structure–activity relationship is presently a critical task, but remains challenging. In this work, water electrolysis and oxygen reduction performances of FeXY_iN_3-i (X, Y = B, C, O, P and S; i = 0, 1) moiety in Fe–porphyrin are studied by the first-principles calculations, aiming at unraveling how and why tuning the coordination microenvironment of the active metal atom can improve the activity. It can be concluded that breaking the coordination shell symmetry breaks the well-accepted standard scaling relationship, adjusts *O adsorption behavior and thus optimizes the oxygen evolution reaction (OER) activity, for example, to an extremely low overpotential of 0.17 V. In combination with the Fe atom spin configuration and ligand field theory, the dramatically improved OER activity can be well explained. In the present work, the significance of the coordination microenvironment of central metal atom in studies of electrocatalysis is highlighted.     

Synthesis and Structure of Mixed-Cation Salts with [NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the general composition NaM₂[NpO₄(OH)₂]·4H₂O, where M = Rb (I, II) and Cs (III), were synthesized and structurally characterized. The compounds differ from each other in the structural organization. The Np central atom in [NpO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with the O atoms of hydroxide ions in the apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb cations with 10- and 12-vertex coordination polyhedra, and in the structures of II and III the framework of large cations is built of 12-vertex Rb and Cs polyhedra. The coordination polyhedra of the Np and Na atoms, sharing a common edge (I, III), or chains of the coordination polyhedra of the Np and Na atoms, sharing common vertices (II), are accommodated in the channels of the frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [NpO₄(OH)₂]^3– anions.     

Cation off-stoichiometric SrMnO<Subscript>3−δ</Subscript> thin film grown by pulsed laser deposition

The laser energy density (laser fluence) dependency of the Sr/Mn ratio was investigated for SrMnO_3−δ (SMO) thin films grown by pulsed laser deposition (PLD). It was found that the Sr/Mn ratio showed a steep increase followed by a gradual increase as the laser fluence was increased. However, the Sr/Mn ratio always showed Mn-excess under the present laser fluence condition as long as stoichiometric SrMnO₃ targets were used. In order to obtain cation stoichiometric SMO films, it was necessary to use Sr-excess SrMnO₃ targets in addition with laser fluence tuning. The crystal quality of the SMO thin film was found to vary with the Sr/Mn ratio. In stoichiometric or Sr-excess SMO thin films, epitaxial thin films could be obtained, whereas Mn-excess thin films showed very low crystallinity. Sr-excess films were also found to have some extra SrO planes. In addition, they exhibited out-of-plane lattice expansion which electron energy loss spectroscopy analysis revealed was due to Mn vacancies. The variation of film growth was closely related to point defects due to excess cations included in growing thin films.     

Synthesis and structure of dodecamolybdates of tetravalent cerium,thorium, uranium,neptunium, and plutonium

A series of isostructural compounds of the composition Na₇H[EMo₁₂O₄₂]·12H₂O, where E(IV) = Ce, Th, U, Np, or Pu, were synthesized and structurally characterized. In the [EMo₁₂O₄₂]^8– heteropolyanion (HPA), the central E(IV) atom is surrounded by six Mo₂O₉ groups, each constituted by two octahedra sharing a common face. The coordination polyhedron (CP) of the central atom is a weakly distorted icosahedron with the mean E(IV)–О bond lengths of 2.498, 2.529, 2.500, 2.490, and 2.488 Å for Ce, Th, U, Np, and Pu, respectively. In the structure of the compounds Na₇H[EMo₁₂O₄₂]·12H₂O, there are two crystallographically independent sodium atoms: Na(1) and Na(2). The oxygen surrounding of the Na(1) atom is formed by the terminal oxygen atoms of two heteropolyanions adjacent along [001], and its coordination polyhedron is an octahedron. The surrounding of the Na(2) atom (a six-vertex polyhedron) is formed by three terminal oxygen atoms of three Mo₂O₉ groups belonging to the same HPA and by three water molecules. The coordination polyhedra of the Na(2) atoms are linked with each other via common oxygen atoms of O_w(2) water molecules to form a chain “winding” around the 3₁ screw axis. The heteropolyanions and Na⁺ cations in the crystal form a framework constructed in a fashion characteristic of Dexter–Silverton type anions, with the coordination via three terminal oxygen atoms of three Mo₂O₉ groups. Excess negative charge of HPA is compensated by the proton localized on one of the six bridging O atoms. In the Mo₂O₉ doubled octahedra, the Mo–O bonds with the О atoms bonded to E(IV) and forming the edge of the common face are sensitive to the kind of the central atom.     

Linear Conjugated Coordination Polymers for Electrocatalytic Oxygen Evolution Reaction

Conjugated coordination polymers (CCPs) have attracted extensive attention for various applications related to energy storage and conversion in the past few years, despite that there are many CCPs with unclear chemical states and structures. Here, linear CCPs (LCCPs), with metal–O₄ active sites grown on carbon paper (CP) for oxygen evolution reaction (OER), are presented. The LCCPs with high crystallinity and simple structures exhibit the order of electrocatalytic activity of Co–O₄ > Ni–O₄ > Fe–O₄ in terms of the metal–O₄ centers. The Co-based LCCP shows higher OER performance (263 mV at 10 mA cm⁻²) and better durability (90 h at 30 mA cm⁻²) than commercial IrO₂/CP. The structures and chemical states of LCCPs are carefully investigated, and density functional theory is used to reveal the mechanism of OER at the central metal site. This investigation into LCCPs provides new sights for a better understanding of CCPs and expands the applications of LCCPs with metal–O₄ sites.     

NiCo2O4-Based Nanosheets with Uniform 4 nm Mesopores for Excellent Zn–Air Battery Performance

Herein, a strategy is reported for the fabrication of NiCo₂O₄-based mesoporous nanosheets (PNSs) with tunable cobalt valence states and oxygen vacancies. The optimized NiCo_2.148O₄ PNSs with an average Co valence state of 2.3 and uniform 4 nm nanopores present excellent catalytic performance with an ultralow overpotential of 190 mV at a current density of 10 mA cm⁻² and long-term stability (700 h) for the oxygen evolution reaction (OER) in alkaline media. Furthermore, Zn–air batteries built using the NiCo_2.148O₄ PNSs present a high power and energy density of 83 mW cm⁻² and 910 Wh kg⁻¹, respectively. Moreover, a portable battery box with NiCo_2.148O₄ PNSs as the air cathode presents long-term stability for 120 h under low temperatures in the range of 0 to −35 °C. Density functional theory calculations reveal that the prominent electron exchange and transfer activity of the electrocatalyst is attributed to the surface lower-coordinated Co-sites in the porous region presenting a merging 3d–e_g–t_2g band, which overlaps with the Fermi level of the Zn–air battery system. This favors the adsorption of the *OH, and stabilized *O radicals are reached, toward competitively lower overpotential, demonstrating a generalized key for optimally boosting overall OER performance.     

Synthesis,characterization and in situ monitoring of the mechanochemical reaction process of two manganese(II)-phosphonates with N-containing ligands

Two divalent manganese aminophosphonates, manganese mono(nitrilotrimethylphosphonate) (MnNP₃) and manganese bis(N-(carboxymethyl)iminodi(methylphosphonate)) (Mn(NP₂AH)₂), have been prepared by mechanochemical synthesis and characterized by powder X-ray diffraction (PXRD). The structure of the novel compound Mn(NP₂AH)₂ was determined from PXRD data. MnNP₃ as well as Mn(NP₂AH)₂ exhibits a chain-like structure. In both cases, the manganese atom is coordinated by six oxygen atoms in a distorted octahedron. The local coordination around Mn was further characterized by extended X-ray absorption fine structure. The synthesis process was followed in situ by synchrotron X-ray diffraction revealing a three-step reaction mechanism. The as-prepared manganese(II) phosphonates were calcined on air. All samples were successfully tested for their suitability as catalyst material in the oxygen evolution reaction.     

Local ordering structure of meta-kaolinite and meta-dickite by the X-ray radial distribution function analysis

X-ray diffraction measurements on the structure of meta-kaolinite and meta-dickite have been carried out to obtain the radial distribution function (RDF). The distances and corresponding coordination numbers for Si-O and Al-O pairs were estimated by applying the pair function method. The SiO₄ tetrahedron remains unchanged in the dehydrated samples presently investigated, and the oxygen coordination number around aluminium was also found to be four. This implies the overall preference of AlO₄ tetrahedron at the expense of the parent AlO₂ (OH)₄ octahedron.     

O‐, N‐Atoms‐Coordinated Mn Cofactors within a Graphene Framework as Bioinspired Oxygen Reduction Reaction Electrocatalysts

Manganese (Mn) is generally regarded as not being sufficiently active for the oxygen reduction reaction (ORR) compared to other transition metals such as Fe and Co. However, in biology, manganese‐containing enzymes can catalyze oxygen‐evolving reactions efficiently with a relative low onset potential. Here, atomically dispersed O and N atoms coordinated Mn active sites are incorporated within graphene frameworks to emulate both the structure and function of Mn cofactors in heme–copper oxidases superfamily. Unlike previous single‐metal catalysts with general M‐N‐C structures, here, it is proved that a coordinated O atom can also play a significant role in tuning the intrinsic catalytic activities of transition metals. The biomimetic electrocatalyst exhibits superior performance for the ORR and zinc–air batteries under alkaline conditions, which is even better than that of commercial Pt/C. The excellent performance can be ascribed to the abundant atomically dispersed Mn cofactors in the graphene frameworks, confirmed by various characterization methods. Theoretical calculations reveal that the intrinsic catalytic activity of metal Mn can be significantly improved via changing local geometry of nearest coordinated O and N atoms. Especially, graphene frameworks containing the Mn‐N₃O₁ cofactor demonstrate the fastest ORR kinetics due to the tuning of the d electronic states to a reasonable state.     

Heterojunction‐Assisted Co3S4@Co3O4 Core–Shell Octahedrons for Supercapacitors and Both Oxygen and Carbon Dioxide Reduction Reactions

Expedition of electron transfer efficiency and optimization of surface reactant adsorption products desorption processes are two main challenges for developing non‐noble catalysts in the oxygen reduction reaction (ORR) and CO₂ reduction reaction (CRR). A heterojunction prototype on Co₃S₄@Co₃O₄ core–shell octahedron structure is established via hydrothermal lattice anion exchange protocol to implement the electroreduction of oxygen and carbon dioxide with high performance. The synergistic bifunctional catalyst consists of p‐type Co₃O₄ core and n‐type Co₃S₄ shell, which afford high surface electron density along with high capacitance without sacrificing mechanical robustness. A four electron ORR process, identical to the Pt catalyzed ORR, is validated using the core–shell octahedron catalyst. The synergistic interaction between cobalt sulfide and cobalt oxide bicatalyst reduces the activation energy to convert CO₂ into adsorbed intermediates and hereby enables CRR to run at a low overpotential, with formate as the highly selective main product at a high faraday efficiency of 85.3%. The remarkable performance can be ascribed to the synergistic coupling effect of the structured co‐catalysts; heterojunction structure expedites the electron transfer efficiency and optimizes surface reactant adsorption product desorption processes, which also provide theoretical and pragmatic guideline for catalyst development and mechanism explorations.     

Facile,Room Temperature,Electroless Deposited (Fe1−x,Mnx)OOH Nanosheets as Advanced Catalysts: The Role of Mn Incorporation

Herein, bimetallic iron (Fe)–manganese (Mn) oxyhydroxide ((Fe_1−x,Mn_x)OOH, FeMnOOH) nanosheets on fluorine‐doped tin oxide conducting substrates and on semiconductor photoanodes are synthesized by a facile, room temperature, electroless deposition method as catalysts for both electrochemical and photo‐electrochemical (PEC) water splitting, respectively. Surprisingly, Mn‐doped FeOOH can significantly modulate the nanosheet morphology to increase the active surface area, boost more active sites, and augment the intrinsic activity by tuning the electronic structure of FeOOH. Due to the 2D nanosheet architecture, the optimized FeMnOOH exhibits superior electrochemical activity and outstanding durability for the oxygen evolution reaction with a low overpotential of 246 mV at 10 mA cm⁻² and 414 mV at 100 mA cm⁻², and long‐term stability for 40 h without decay, which is comparable to the best electrocatalysts for water oxidation reported in the literature. By integrating with semiconductor photoanodes (such as α‐Fe₂O₃ nanorod (NR) arrays), bimetallic FeMnOOH catalysts achieve solar‐driven water splitting with a significantly enhanced PEC performance (3.36 mA cm⁻² at 1.23 V vs reversible hydrogen electrode (RHE)) with outstanding long‐term stability (≈8 h) compared to that of the bare Fe₂O₃ NR (0.92 mA cm⁻² at 1.23 V vs RHE).     

Ionic Exchange of Metal−Organic Frameworks for Constructing Unsaturated Copper Single‐Atom Catalysts for Boosting Oxygen Reduction Reaction

Regulating the coordination environment of atomically dispersed catalysts is vital for catalytic reaction but still remains a challenge. Herein, an ionic exchange strategy is developed to fabricate atomically dispersed copper (Cu) catalysts with controllable coordination structure. In this process, the adsorbed Cu ions exchange with Zn nodes in ZIF‐8 under high temperature, resulting in the trapping of Cu atoms within the cavities of the metal?organic framework, and thus forming Cu single‐atom catalysts. More importantly, altering pyrolysis temperature can effectively control the structure of active metal center at atomic level. Specifically, higher treatment temperature (900 °C) leads to unsaturated Cu–nitrogen architecture (Cu? N₃ moieties) in atomically dispersed Cu catalysts. Electrochemical test indicates atomically dispersed Cu catalysts with Cu? N₃ moieties possess superior oxygen reduction reaction performance than that with higher Cu–nitrogen coordination number (Cu? N₄ moieties), with a higher half‐wave potential of 180 mV and the 10 times turnover frequency than that of CuN₄. Density functional theory calculation analysis further shows that the low N coordination number of Cu single‐atom catalysts (Cu? N₃) is favorable for the formation of O₂* intermediate, and thus boosts the oxygen reduction reaction.     

Heterogeneous Phase Equilibria in Rare Earth–Mn–O Systems in Air

The phase relations in rare earth–Mn–O systems in air are considered. Most of the phase diagrams of these systems fall into two distinct groups: R"–Mn–O (R" = Y, Ho–Lu) and R"–Mn–O (R" = Pr, Nd, Sm–Dy). In addition, the Sc–Mn–O, La–Mn–O, and Ce–Mn–O systems have phase-diagram features of their own. The Ce–Mn–O system contains no ternary oxides or solid solutions: there are only mixtures of cerium and manganese oxides. The Sc–Mn–O system has phase-diagram features in common with both the R"–Mn–O and M–Mn–O (M = Mg, Al, 3d transition metal) systems. The La–Mn–O phase diagram can be thought of as a degenerate diagram of the R"–Mn–O group, since LaMn₂O₅ exists at oxygen pressures higher than atmospheric pressure. The R"–Mn–O and R"–Mn–O systems contain two chemical compounds, RMnO₃ and RMn₂O₅, but differ in the crystal structure of RMnO₃: hexagonal in the R" group and orthorhombic perovskite-like in the R" group. A key role in determining the structure of RMnO₃ is played by the size factor. In both groups, the RMn₂O₅ compounds dissociate in air by the reaction \({\text{RMn}}_{\text{2}} {\text{O}}_{\text{5}} {\text{ = RMnO}}_{\text{3}} + \frac{1}{3}{\text{RMn}}_{\text{3}} {\text{O}}_{\text{4}} + \frac{1}{3}{\text{O}}_{\text{2}} \). The dissociation temperature of RMn₂O₅ is shown to correlate with the atomic number of R, the total number of 4f electrons, the number of unpaired 4f electrons, and the ionic radius of R³⁺.     

Preparation,characterisation and catalytic property of ultrafine Ce–La–Mn mixed oxides

Using cerium carbonate, lanthanum oxide and manganese nitrate as raw materials, ultrafine particles of Ce–La–Mn mixed oxides were prepared by the sol–gel method combined with supercritical drying technology. The prepared materials were characterised by thermo-gravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscope. The catalytic properties of ultrafine Ce–La–Mn mixed oxides were tested by the reaction ‘2CO?+?2NO?=?2CO₂?+?N₂’. The key aim was to examine the effect of supercritical fluid drying technology and Ce-doping on the crystal structure, morphology and catalytic activity of ultrafine Ce–La–Mn mixed oxides. The results show that at 260°C, Ce–La–Mn mixed oxides are brown loose flocculent powders with good dispersibility. The particles are spherical about 10?nm in size. The main crystal components are CeO₂, MnO, La₅O₇NO₃ and La(OH)₂NO₃. After thermal treating at 850°C, Ce–La–Mn mixed oxides were made up of plenty of quasi-global grains smaller than 20?nm; the main crystal components of the Ce–La–Mn mixed oxides are LaMnO_{3+ λ} , La₂O₃ and CeO₂; heat treatment can enhance the crystallinity of the materials. Cerium-doped mixtures just exist as crystal CeO₂, which contributes to the crystallisation of Ce–La–Mn mixed oxides in the process of supercritical fluid drying at 260°C, enhancing the catalytic activity of ultrafine Ce–La–Mn mixed oxides which are thermal treated at 850°C.     

Facet-controlled Pt–Ir nanocrystals with substantially enhanced activity and durability towards oxygen reduction

Nanocrystals made of Pt–Ir alloys are fascinating catalysts towards the oxygen reduction reaction (ORR), but the lack of control over their surface atomic structures hinders further optimization of their catalytic performance. Here we report, for the first time, a class of highly active and durable ORR catalysts based on Pd@Pt–Ir nanocrystals with well-controlled facets. With an average of 1.6 atomic layers of a Pt₄Ir alloy on the surface, the nanocrystals can be made in cubic, octahedral, and icosahedral shapes to present Pt–Ir {1 0 0}, {1 1 1}, and {1 1 1} plus twin boundaries, respectively. The Pd@Pt–Ir nanocrystals exhibit not only facet-dependent catalytic properties but also substantially enhanced ORR activity and durability relative to a commercial Pt/C and their Pd@Pt counterparts. Among them, the Pd@Pt–Ir icosahedra deliver the best performance, with a mass activity of 1.88 A·mg⁻¹_Pt at 0.9 V, which is almost 15 times that of the commercial Pt/C. Our density functional theory (DFT) calculations attribute the high activity of the Pd@Pt–Ir nanocrystals, and the facet dependence of these activities, to easier protonation of O* and OH* under relevant OH* coverages, relative to the corresponding energetics on clean Pd@Pt surfaces. The DFT calculations also indicate that incorporating Ir atoms into the Pt lattice destabilizes OH–OH interactions on the surface, thereby raising the oxidation potential of Pt and greatly improving the catalytic durability.     

Bifunctional Transition Metal Hydroxysulfides: Room‐Temperature Sulfurization and Their Applications in Zn–Air Batteries

Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal–air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn–air batteries. By simply immersing Co‐based hydroxide precursor into solution with high‐concentration S^2?, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as‐obtained Co‐based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm^?2 OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half‐wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co₃FeS_1.5(OH)₆ hydroxysulfides are employed in the air electrode for a rechargeable Zn–air battery with a small overpotential of 0.86 V at 20.0 mA cm^?2, a high specific capacity of 898 mAh g^?1, and a long cycling life, which is much better than Pt and Ir‐based electrocatalyst in Zn–air batteries.     

Achieving Long-Enduring High-Voltage Oxygen Redox in P2-Structured Layered Oxide Cathodes by Eliminating Nonlattice Oxygen Redox

Triggering reversible lattice oxygen redox (LOR) in oxide cathodes is a paradigmatic approach to overcome the capacity ceiling determined by orthodox transition-metal (TM) redox. However, the LOR reactions in P2-structured Na-layered oxides are commonly accompanied by irreversible nonlattice oxygen redox (non-LOR) and large local structural rearrangements, bringing about capacity/voltage fading and constantly evolving charge/discharge voltage curves. Herein, a novel Na_0.615Mg_0.154Ti_0.154Mn_0.615◻_0.077O₂ (◻ = TM vacancies) cathode with both Na O Mg and Na O ◻ local configurations is deliberately designed. Intriguingly, the activating of oxygen redox at middle-voltage region (2.5–4.1 V) via Na O ◻ configuration helps in maintaining the high-voltage plateau from LOR (≈4.38 V) and stable charge/discharge voltage curves even after 100 cycles. Hard X-ray absorption spectroscopy (hXAS), solid-state NMR, and electron paramagnetic resonance studies demonstrate that both the involvement of non-LOR at high-voltage and the structural distortions originating from Jahn–Teller distorted Mn³⁺O₆ at low-voltage are effectively restrained in Na_0.615Mg_0.154Ti_0.154Mn_0.615◻_0.077O₂. Resultantly, the P2 phase is well retained in a wide electrochemical window of 1.5–4.5 V (vs Na⁺/Na), resulting in an extraordinary capacity retention of 95.2% after 100 cycles. This work defines an effective approach to upgrade the lifespan of Na-ion battery with reversible high-voltage capacity provided by LOR.     

Synthesis and Structure of Mixed-Cation Salts with [PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.     

Soft chemistry synthesis and crystal structure of MgxCu3−xV2O6(OH)4·2H2O

Mg_xCu_3−xV₂O₆(OH)₄·2H₂O (x ∼ 1), with similar crystal structure as volborthite Cu₃V₂O₇(OH)₂·2H₂O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V₂O₅ with few mL of 30 vol.% H₂O₂ followed by addition of distilled water). When ammonium hydroxide NH₄OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO₄ to trigonal bipyramidal VO₅, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu₃V₂O₈ phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu₃V₂O₈ phases.     

Less-Coordinated Atomic Copper-Dimer Boosted Carbon–Carbon Coupling During Electrochemical CO2 Reduction

This work reports a metal–organic framework (MOF) with less-coordinated copper dimers, which displays excellent electrochemical CO₂ reduction (eCO₂RR) performance with an advantageous current density of 0.9 A cm⁻² and a high Faradaic efficiency of 71% to C₂ products. In comparison with MOF with Cu monomers that are present as Cu₁ O₄ with a coordination number of 3.8 ± 0.2, Cu dimers exist as O₃Cu₁···Cu₂O₂ with a coordination number of 2.8 ± 0.1. In situ characterizations together with theoretical calculations reveal that two *CO intermediates are stably adsorbed on each site of less-coordinated Cu dimers, which favors later dimerization via a key intermediate of *CH₂CHO. The highly unsaturated dual-atomic Cu provides large-quantity and high-quality actives sites for carbon–carbon coupling, achieving the optimal trade-off between activity and selectivity of eCO₂RR to C₂ products.