High-valent Transition Metal Research Articles

Oxygen Plasma Triggered Co-O-Fe Motif in Prussian Blue Analogue for Efficient and Robust Alkaline Water Oxidation.

In the context of oxygen evolution reaction (OER), the construction of high-valent transition metal sites to trigger the lattice oxygen oxidation mechanism is considered crucial for overcoming the performance limitations of traditional adsorbate evolution mechanism. However, the dynamic evolution of lattice oxygen during the reaction poses significant challenges for the stability of high-valent metal sites, particularly in high-current-density water-splitting systems. Here, we have successfully constructed Co-O-Fe catalytic active motifs in cobalt-iron Prussian blue analogs (CoFe-PBA) through oxygen plasma bombardment, effectively activating lattice oxygen reactivity while sustaining robust stability. Our spectroscopic and theoretical studies reveal that the Co-O-Fe bridged motifs enable a unique double-exchange interaction between Co and Fe atoms, promoting the formation of high-valent Co species as OER active centers while maintaining Fe in a low-valent state, preventing its dissolution. The resultant catalyst (CoFe-PBA-30) requires an overpotential of only 276 mV to achieve 1000 mA cm-2. Furthermore, the assembled alkaline exchange membrane electrolyzer using CoFe-PBA-30 as anode material achieves a high current density of 1 A cm-2 at 1.76 V and continuously operates for 250 hours with negligible degradation. This work provides significant insights for activating lattice oxygen redox without compromising structure stability in practical water electrolyzers.

Design of Highly Electrophilic and Stable Metal Nitrido Complexes.

ConspectusMetal oxo (M═O) and nitrido (M≡N) complexes are two important classes of high-valent transition metal complexes. The use of M═O as oxidants in chemical and biological systems has been extensively investigated. Nature makes use of M═O in enzymes such as cytochrome P450 to oxidize a variety of substrates. Highly oxidizing oxo species have also been synthesized and they have been shown to oxidize organic and inorganic substrates via one-electron oxidation, O atom transfer, and H atom abstraction pathways. In contrast, the oxidation chemistry of M≡N is much less investigated. Although a variety of nitrido complexes are known, most of them are inert and do not show appreciable oxidizing properties, which is not unexpected since the N3- ligand is much more electron-donating than the O2- ligand. In principle, highly electrophilic/oxidizing nitrido complexes may be designed by using weakly coordinating ancillary ligands and/or by increasing the oxidation state of the metal centers. A number of such species have been generated in solution at low temperatures. However, attempts to isolate them are often hampered by their ease of decomposition via bimolecular N···N coupling to generate N2. In some cases, decomposition occurs by intramolecular nitrogenation of the ancillary ligand.In this account, we describe our recent efforts into the design of nitrido complexes that are highly oxidizing but stable enough so they can be isolated and characterized, and their reactivity toward organic substrates can be readily investigated.We have successfully isolated and determined the structure of the first stable manganese(VI) nitrido complex bearing an oxidation-resistant macrocyclic tetraamido TAML ligand, [MnVI(N)(TAML)]- (H4TAML = 3,3,6,6,9,9-hexamethyl-3,4,8,9-tetrahydro-1H-benzo[e][1,4,7,10] tetraazacyclotridecine-2,5,7,10(6H,11H)-tetraone). This complex readily undergoes direct aziridination of alkenes; it also abstracts hydrides from NADH analogues via a Separated CPET mechanism. Coupling of the nitrido ligands to give dinitrogen is a major decomposition pathway for electrophilic nitrido complexes. In order to shut down this pathway, we made use of a bulky trianionic corrole ligand TTPPC (H3TTPPC = 5,10,15-tris(2,4,6-triphenylphenyl)corrole) to prepare manganese nitrido complexes. Remarkably, we were able to isolate and determine the structures of [MnV(N)(TTPPC)]- and its one- and two-electron ligand-oxidized products, [MnV(N)(TTPPC+•)] and [MnV(N)(TTPPC2+)]+ ("TTPPC" has a 3- charge, 'TTPPC+•' has an overall 2- charge and 'TTPPC2+' has an overall 1- charge). Although [MnV(N)(TTPPC2+)]+ is formally a manganese(V) complex, it was found to be the most electrophilic among isolated metal nitrido complexes. The use of the bulky corrole ligand effectively prevents the decomposition of Mn≡N by N···N coupling.A number of luminescent M═O species that possess highly oxidizing excited states are known. We have also developed a strongly luminescent osmium(VI) nitrido complex, [OsVI(N)(L)(CN)3]- (OsN, HL = 2-(2-hydroxy-5-nitrophenyl)benzoxazole), that absorbs visible light to generate a highly oxidizing/electrophilic excited state. The excited state readily reacts with a wide variety of organic and inorganic substrates, many of these reactions are unprecedented. Notably, it reacts with cyclohexane to give an osmium(IV) cyclohexyliminato product, and with benzene to give an osmium(IV) p-benzoquinone iminato species.

Nucleophilic Aromatic Substitution of Halobenzenes and Phenols with Catalysis by Arenophilic π Acids.

ConspectusLewis π acids, particularly high-valent transition metals with vacant orbitals, can coordinate with unsaturated compounds such as alkynes and alkenes by means of π-bonding. The coordination enhances the electrophilicity of the bound compounds, thereby facilitating reactions─such as nucleophilic addition─that take place at the ligated carbon-carbon multiple bonds. This activation phenomenon occurs at the ligand rather than at the metal atom, and it has been extensively utilized in the development of catalytic methods. In addition to alkynes and alkenes, aromatic compounds featuring a phenyl ring can be activated by an electrophilic transition-metal unit (e.g., Cr(CO)3, [Mn(CO)3]+, [CpFe]+, or [CpRu]+, where Cp = cyclopentadienyl) through π coordination. Over the past several decades, remarkable advances have been achieved in the development of reactions occurring on bound arenes, capitalizing on the highly electron-withdrawing nature of these transition-metal units and on the thermodynamic stability of η6-arene complexes. A prime example is the extension of nucleophilic aromatic substitution (SNAr) reactions to electron-neutral and -rich halobenzenes. Such arenes, which are normally inert to classical SNAr, can undergo sequences involving complex formation, substitution, and complex decomposition. Despite the successes achieved through the utilization of preformed complexes, the application of reversible arene coordination to catalytic systems has seen only limited progress. Consequently, in π-coordination activation, transition-metal units are commonly considered to be components of bound arene complexes rather than π-acid catalysts.In this Account, we summarize our recent research on catalytic SNAr reactions of halobenzenes and phenols enabled by reversible π-coordination of the arenes with electrophilic Ru or Rh catalysts, which we refer to as arenophilic π-acids. First, we developed a method for SNAr amination of fluorobenzenes with catalysis by a Ru(II) complex with a hemilabile P,O-bidentate ligand. The use of the hemilabile ligand significantly enhanced catalytic efficiency, allowing electron-rich and -neutral arenes to undergo amination without the need of excess fluorobenzenes. In a subsequent study of hydroxylation and alkoxylation reactions, we found that Rh(III) catalysts bearing a Cp-type ligand had a substantial activating effect. In addition, by isolating an η5 complex as the reaction intermediate, we obtained evidence in support of the long-standing hypothesis that SNAr of η6-arene complexes proceeds via a stepwise mechanism. Next, we extended the Rh-catalyzed SNAr to chloro- and bromobenzenes, which are abundant and readily available but are less reactive than corresponding fluorides toward SNAr. When the weakly nucleophilic alcohol hexafluoroisopropanol was used as a reaction partner, we were able to synthesize hexafluoroisopropyl aryl ethers, which are challenging to obtain by means of conventional approaches. Beyond halobenzenes, we successfully applied π-coordination strategy to achieve umpolung substitution reactions of phenols, which are typically nucleophilic. We found that an arenophilic Rh or Ru catalyst activated the phenol ring by π coordination instead of κ-O coordination, generating transient η5-phenoxo complexes that subsequently underwent carbonyl-amine condensation to produce anilines without the need for an exogenous oxidant or reductant. We anticipate that our research on catalyst development and reactions involving π-coordination activation will facilitate further advances in the application of arenophilic π acids.

Lattice Oxygen Activation through Deep Oxidation of Co4N by Jahn-Teller-Active Dopants for Improved Electrocatalytic Oxygen Evolution.

Triggering the lattice oxygen oxidation mechanism is crucial for improving oxygen evolution reaction (OER) performance, because it could bypass the scaling relation limitation associated with the conventional adsorbate evolution mechanism through the direct formation of oxygen-oxygen bond. High-valence transition metal sites are favorable for activating the lattice oxygen, but the deep oxidation of pre-catalysts suffers from a high thermodynamic barrier. Here, taking advantage of the Jahn-Teller (J-T) distortion induced structural instability, we incorporate high-spin Mn3+ ( ) dopant into Co4N. Mn dopants enable a surface structural transformation from Co4N to CoOOH, and finally to CoO2, as observed by various in situ spectroscopic investigations. Furthermore, the reconstructed surface on Mn-doped Co4N triggers the lattice oxygen activation, as evidenced experimentally by pH-dependent OER, tetramethylammonium cation adsorption and online electrochemical mass spectrometry measurements of 18O-labelled catalysts. In general, this work not only offers the introducing J-T effect approach to regulate the structural transition, but also provides an understanding about the influence of the catalyst's electronic configuration on determining the reaction route, which may inspire the design of more efficient catalysts with activated lattice oxygen.

Mo4+-Doped CuS Nanosheet-Assembled Hollow Spheres for CO2 Electroreduction to Ethanol in a Flow Cell.

Electrocatalytic CO2 reduction reaction (CO2RR) to ethanol has been widely researched for potential commercial application. However, it still faces limited selectivity at a large current density. Herein, Mo4+-doped CuS nanosheet-assembled hollow spheres are constructed to address this issue. Mo4+ ion doping modifies the local electronic environments and diversifies the binding sites of CuS, which increases the coverage of linear *COL and produces bridge *COB for subsequent *COL-*COH coupling toward ethanol production. The optimal Mo9.0%-CuS can electrocatalyze CO2 to ethanol with a faradaic efficiency of 67.5% and a partial current density of 186.5 mA cm-2 at -0.6 V in a flow cell. This work clarifies that doping high valence transition metal ions into Cu-based sulfides can regulate the coverage and configuration of related intermediates for ethanol production during the CO2RR in a flow cell.

Oxidation state regulation of iron-based bimetallic nanoparticles for efficient and simultaneous electrochemical detection of Pb2+ and Cu2+

In this work, bimetallic nanocomposites were synthesized by an emulsion hydrothermal method, and the electronic structure of the nanocomposite’s surface was adjusted to make it optimal by introducing different transition metal salts, providing more active adsorption sites for detecting heavy metal ions (HMIs). The results showed that different transition metal cations underwent redox reactions with Fe3+ at high temperature, resulting in generation of more Fe2+ as well as high valence transition metal ions. And this process formed more oxygen vacancies (OVs) on the material surface, enhancing the adsorption properties of HMIs. Among these nanocomposites, CoFe2O4 produced the most Fe2+ (Fe2+/Fe3+ = 1.29) and Co3+ (Co3+ = 44.0%) at a high temperature, suggesting the generation of the most active sites on the material surface. The corresponding modified electrode CoFe2O4 (CoFe2O4/GCE) also exhibited good electrochemical performance for simultaneously detecting Pb2+ and Cu2+, with the limit of detections of 3.94 and 8.27 nM, respectively. Compared with other nanocomposites, adsorption experiments showed that the CoFe2O4/GCE had the largest adsorption capacity of Pb2+ and Cu2+ (QPb2+=49.82 μC, QCu2+=48.88 μC). Therefore, this work showed that the interaction between metal ions in bimetallic nanomaterials can regulate the electronic structures of the material surface at high-temperature treatment, improve the adsorption capacity of nanomaterials, and lead to good electrochemical detection performance of HMIs.

Combining Donor Strength and Oxidative Stability in Scorpionates: A Strongly Donating Fluorinated Mesoionic Tris(imidazol-5-ylidene)borate Ligand.

Strongly donating scorpionate ligands support the study of high-valent transition metal chemistry; however, their use is frequently limited by oxidative degradation. To address this concern, we report the synthesis of a tris(imidazol-5-ylidene)borate ligand featuring trifluoromethyl groups surrounding its coordination pocket. This ligand represents the first example of a chelating poly(imidazol-5-ylidene) mesoionic carbene ligand, a scaffold that is expected to be extremely donating. The {NiNO}10 complex of this ligand, as well as that of a previously reported strongly donating tris(imidazol-2-ylidene)borate, has been synthesized and characterized. This new ligand's strong donor properties, as measured by the υNO of its {NiNO}10 complex and natural bonding orbital second-order perturbative energy analysis, are at par with those of the well-studied alkyl-substituted tris(imidazol-2-ylidene)borates, which are known to effectively stabilize high-valent intermediates. The good donor properties of this ligand, despite the electron-withdrawing trifluoromethyl substituents, arise from the strongly donating imidazol-5-ylidene mesoionic carbene arms. These donor properties, when combined with the robustness of trifluoromethyl groups toward oxidative decomposition, suggest this ligand scaffold will be a useful platform in the study of oxidizing high-valent transition-metal species.

The Nature of the Chemical Bonds of High-Valent Transition-Metal Oxo (M=O) and Peroxo (MOO) Compounds: A Historical Perspective of the Metal Oxyl-Radical Character by the Classical to Quantum Computations.

This review article describes a historical perspective of elucidation of the nature of the chemical bonds of the high-valent transition metal oxo (M=O) and peroxo (M-O-O) compounds in chemistry and biology. The basic concepts and theoretical backgrounds of the broken-symmetry (BS) method are revisited to explain orbital symmetry conservation and orbital symmetry breaking for the theoretical characterization of four different mechanisms of chemical reactions. Beyond BS methods using the natural orbitals (UNO) of the BS solutions, such as UNO CI (CC), are also revisited for the elucidation of the scope and applicability of the BS methods. Several chemical indices have been derived as the conceptual bridges between the BS and beyond BS methods. The BS molecular orbital models have been employed to explain the metal oxyl-radical character of the M=O and M-O-O bonds, which respond to their radical reactivity. The isolobal and isospin analogy between carbonyl oxide R2C-O-O and metal peroxide LFe-O-O has been applied to understand and explain the chameleonic chemical reactivity of these compounds. The isolobal and isospin analogy among Fe=O, O=O, and O have also provided the triplet atomic oxygen (3O) model for non-heme Fe(IV)=O species with strong radical reactivity. The chameleonic reactivity of the compounds I (Cpd I) and II (Cpd II) is also explained by this analogy. The early proposals obtained by these theoretical models have been examined based on recent computational results by hybrid DFT (UHDFT), DLPNO CCSD(T0), CASPT2, and UNO CI (CC) methods and quantum computing (QC).

Interstitial atom-doped NiFe alloy as pre-catalysts boost direct seawater oxygen evolution

NiFe-based materials are excellent OER electrocatalysts. However, it is difficult to stabilize anions and cations during reconstruction, which also leads to the problem of high valence metals at low levels and poor stability in direct seawater. Herein, we propose the strategy of using interstitial P atom-doped NiFe alloys (P4.8-NiFe ANs-400) as pre-catalysts to stabilize anions and cations, thereby promoting the formation of abundant high-valent metal species and excellent activity and stability in direct seawater. The reconstructed P4.8-NiFe ANs-400 catalyst generates a large amount of high-valence transition metal Ni4+, which contributed to its low overpotential (214 mV) and long-term stability (100 h) in a seawater electrolyte at 100 mA cm−2. Experiments and theoretical calculations show that the interstitially doped P atoms share the charge around the Fe and the active Ni sites, optimizing the free energy of the OER intermediate and making the chlorine evolution reaction (CER) difficult to proceed.

Prussian blue analogues-derived zero valent iron to efficiently activate peroxymonosulfate for phenol degradation triggered via reactive oxygen species and high-valent iron-oxo complexes

It is of great significance to develop the effective technique to treat phenol-containing wastewater. Herein, Fe-based prussian blue analogues-derived zero valent iron (ZVI) was successfully synthesized by one-step calcination method. Owing to high specific surface area and rich active sites, ZVI-2 possessed excellent performance in charge transfer. Notably, in comparison with conventional ZVI and Fe2+, ZVI-2 can effectively activate peroxymonosulfate (PMS) for achieving rapid degradation of phenol, and the highest removal efficiency of phenol reached 94.9% within 24 min. More importantly, developed ZVI-2/PMS oxidation system with good stability displayed strong anti-interference capability. Interestingly, Fe0 loaded on the surface of ZVI-2 can efficiently break the O–O bond of PMS to generate reactive oxygen species (i.e., SO4•−, OH•, O2•− and 1O2). As main adsorption sites of PMS, the existence of oxygen vacancy promote the formation of high-valent transition metal complexes (namely ZVI-2≡Fe4+=O). Under the combined action of reactive oxygen species and ZVI-2≡Fe4+=O, phenol can be eventually degraded into CO2 and H2O. The possible degradation pathways of phenol were also investigated. Furthermore, proposed ZVI-2/PMS oxidation system displayed great potential for application in the field of wastewater treatment. All in all, current work provided a valuable reference for design and application of Fe-based catalysts in PS-AOPs.

High-Valence Surface-Modified LMO Cathode Materials for Lithium-Ion Batteries: Diffusion Kinetics and Operando Thermal Stability Investigation.

Lithium manganese oxide (LiMn2O4) is a prevalent cathode material for lithium-ion batteries due to its low cost, abundant material sources, and ecofriendliness. However, its capacity fade, low energy density, and fast auto-discharge hinders its large-scale commercialization. Consequently, scientists are urged to achieve high-performance LMO cathodes through material doping and surface modification using a wide range of transition metals, polymers, and carbon precursors. Few studies have considered the potential of high-valence transition metal oxides in stabilizing the LMO's cycling process and enhancing the overall battery performance. In this work, we report the synthesis of surface-modified lithium manganese oxide using high-valence tungsten oxide (WVIO3). Different WO3 wt % were investigated before settling for 0.5%WO3-LMO as the synergic surface-modified LMO. Using galvanostatic charge-discharge, 0.50 WO3-LMO exhibited better rate capability by retaining 51% of its initial capacity at a 20C rate, compared to 34% for the pristine LMO. Furthermore, cyclic voltammetry at different scan rates showed that 0.50 WO3-LMO possesses better ion diffusion than pristine LMO, around 10-11 and 10-13 cm2·s-1 respectively. Finally, using in situ Raman spectroscopy, reaction mechanisms during cycling were investigated, and operando accelerating rate calorimetry (ARC) visualized the surface-modified LMO's cycling thermal stability and highlighted its potential use for safe high-voltage lithium-ion batteries in automotive applications.

Urea-assisted synthesis of nickel sulfide arrays with enriching high-valence W species to boost Ni3+ active sites for water oxidation

Introduction of high-valence transition metal in nickel sulfides is an effective strategy to boost Ni3+ active sites, resulting in excellent OER performance. However, it is a challenge to enhance the amount of high-valence transition metal for ensuring Ni3+-rich specie in nickel sulfides. In this work, one-pot urea-assisted synthesis method was applied to fabricate Ni3+-rich W,V co-modified nickel sulfide nanohorn arrays grown on nickel foam (W, V-NiS@NF-UR1) as OER electrocatalyst in alkaline media. Urea can not only improve the crystallinity of electrocatalysts but also regulate their composition, which is favorable for the formation of the high content of W6+ species in the electrocatalyst, consequently increasing the Ni3+ active sites and enhancing the electrocatalytic OER performance. As a result, a small overpotential of 214 mV is required for a current density of 10 mA cm−2 by the as-prepared W, V-NiS@NF-UR1 electrocatalyst and a small Tafel slope of 69 mV dec−1 is observed in 1 M KOH. Meanwhile, the introduction of V species is also beneficial to keeping the high-valence W6+ in the electrocatalyst during the sulfurization process. For comparison, the counterpart electrocatalysts were also investigated systematically without urea.

Electrochemical Oxidation of Methane to Methanol on Electrodeposited Transition Metal Oxides

Electrochemical partial oxidation of methane to methanol is a promising approach to the transformation of stranded methane resources into a high-value, easy-to-transport fuel or chemical. Transition metal oxides are potential electrocatalysts for this transformation. However, a comprehensive and systematic study of the dependence of methane activation rates and methanol selectivity on catalyst morphology and experimental operating parameters has not been realized. Here, we describe an electrochemical method for the deposition of a family of thin-film transition metal (oxy)hydroxides as catalysts for the partial oxidation of methane. CoOx, NiOx, MnOx, and CuOx are discovered to be active for the partial oxidation of methane to methanol. Taking CoOx as a prototypical methane partial oxidation electrocatalyst, we systematically study the dependence of activity and methanol selectivity on catalyst film thickness, overpotential, temperature, and electrochemical cell hydrodynamics. Optimal conditions of low catalyst film thickness, intermediate overpotentials, intermediate temperatures, and fast methanol transport are identified to favor methanol selectivity. Through a combination of control experiments and DFT calculations, we show that the oxidized form of the as-deposited (oxy)hydroxide catalyst films are active for the thermal oxidation of methane to methanol even without the application of bias potential, demonstrating that high valence transition metal oxides are intrinsically active for the activation and oxidation of methane to methanol at ambient temperatures. Calculations uncover that electrocatalytic oxidation enables reaching an optimum potential window in which methane activation forming methanol and methanol desorption are both thermodynamically favorable, methanol desorption being favored by competitive adsorption with hydroxide anion.

In Situ Structure of a Mo-Doped Pt-Ni Catalyst during Electrochemical Oxygen Reduction Resolved from Machine Learning-Based Grand Canonical Global Optimization.

Pt-Ni alloy is by far the most active cathode material for oxygen reduction reaction (ORR) in the proton-exchange membrane fuel cell, and the addition of a tiny amount of a third-metal Mo can significantly improve the catalyst durability and activity. Here, by developing machine learning-based grand canonical global optimization, we are able to resolve the in situ structures of this important three-element alloy system under ORR conditions and identify their correlations with the enhanced ORR performance. We disclose the bulk phase diagram of Pt-Ni-Mo alloys and determine the surface structures under the ORR reaction conditions by exploring millions of likely structure candidates. The pristine Pt-Ni-Mo alloy surfaces are shown to undergo significant structure reconstruction under ORR reaction conditions, where a surface-adsorbed MoO4 monomer or Mo2O x dimers cover the Pt-skin surface above 0.9 V vs RHE and protect the surface from Ni leaching. The physical origins are revealed by analyzing the electronic structure of O atoms in MoO4 and on the Pt surface. In viewing the role of high-valence transition metal oxide clusters, we propose a set of quantitative measures for designing better catalysts and predict that six elements in the periodic table, namely, Mo, Tc, Os, Ta, Re, and W, can be good candidates for alloying with PtNi to improve the ORR catalytic performance. We demonstrate that machine learning-based grand canonical global optimization is a powerful and generic tool to reveal the catalyst dynamics behavior in contact with a complex reaction environment.

Co3+-rich CoFe-PBA encapsulated in ultrathin MoS2 sheath as integrated core-shell architectures for highly efficient OER

Highly active and stable oxygen evolution reaction (OER) electrocatalyst is the key component of sustainable water splitting reaction. Controllable core-shell engineering is one of the most effective strategies for modulating the local electronic structure of active sites to enhance catalytic activity. Herein, we design a nano-cube of Co3+-rich CoFe Prussian blue analogues coated with controllable MoS2 shell heterostructures as OER electrocatalyst by simple solvothermal method, named as CoIIIFe-PBA/MoS2. Importantly, CoIIIFe-PBA/MoS2 possesses an extremely low overpotential of 306 mV at the current density of 100 mA cm−2, a small Tafel slope of 36.2 mV dec−1 and excellent stability for OER. The results of spectroscopic characterizations reveal that the Co3+ species with more 3d electron orbits origin from the charge transfer between CoFe-PBA and MoS2 core-shell interface, which promotes the electron accepting and results in the higher electrochemical activity. This research offers unique insight to design other advanced electrocatalysts with high-valent transition metal ions and core-shell structure.

Rational regulation of peroxymonosulfate activation over porous Co3O4 with carbon coating to boost utilization efficiency of peroxymonosulfate and achieve rapid removal of pollutants

It is of great significance to regulate rationally the activation mechanism of persulfate for promoting the development of sulfate radical-based advanced oxidation processes in wastewater treatment. Herein, carbon coated porous Co3O4 with hollow structure was synthesized. Notably, the formation of porous hollow structure improved specific surface area of Co3O4 and offered more redox couples of Co2+/Co3+, thereby reducing electron transfer resistance. Thus, the generation of reactive oxygen species and the role of high-valent transition metal complexes (namely Co3O4Co4+) were improved. The formation of carbon layer on the Co3O4 surface can avoid the release of Co ion during reaction process. Benefiting from the role of carbon layer in electron transport, catalyst-mediated the direct electron transfer from pollutant to PMS was boosted. Radical and nonradical pathways worked in coordination each other and realized the rapid removal of various organic pollutants in the presence of a little PMS. In short, current work revealed that modulating rationally the microstructure of catalyst was an efficient strategy for achieving controllable regulation of PMS activation process. More significantly, whether the direct electron transfer process can occur or not depended on both catalyst structure and electronic density of pollutants.

Enhanced oxygen bulk diffusion of La0.6Sr0.4FeO3-δ fuel electrode by high valence transition metal doping for direct CO2 electrolysis in solid oxide electrolysis cells

Solid oxide electrolysis cell (SOEC) is a promising energy conversion device for the efficient conversion of CO2 into valuable chemicals by using renewable energy sources. Fe-based perovskite oxides are highly active for CO2 electrochemical reduction as fuel electrodes in SOECs. Herein, high valence cations doped La0.6Sr0.4FeO3-δ oxides (La0.6Sr0.4FeO3-δ, La0.6Sr0.4Fe0.9Sc0.1O3-δ, La0.6Sr0.4Fe0.9Ta0.1O3-δ, La0.6Sr0.4Fe0.9W0.1O3-δ) are used as fuel electrodes in SOECs for CO2 electrolysis, and the crystal structure, electrical conductivity, chemical surface exchange coefficient (Kchem), chemical bulk diffusion coefficient (Dchem) and electrolysis performance are investigated for CO2 electrolysis. In addition, we determine the electrochemical processes on half cells and single cells with La0.6Sr0.4FeO3-δ series fuel electrodes by distribution of relaxation times (DRT) analysis, respectively. The results show that W-doping introduces more highly oxidative oxygen species O22−/O− and decreases the activation energy of lattice oxygen diffusion, thus accelerating the oxygen ion diffusion kinetics. The value of Dchem for La0.6Sr0.4Fe0.9W0.1O3-δ reaches to 4.671 × 10−4cm2 S−1 at 800 °C, and this value is 3.8 times than that of La0.6Sr0.4FeO3-δ (1.216 × 10−4cm2 S−1). DRT analysis indicates the different rate-limiting steps for CO2 reduction reaction (CO2RR) on half cells and single cells, which are the dissociation of carbonate intermediate process on half cells, and the exchange and diffusion of oxygen ions process on single cells. W-doping remarkably improves the oxygen ion transport property, thus enhancing the single cell performance for CO2 electrolysis. The single cell with La0.6Sr0.4Fe0.9W0.1O3-δ fuel electrode demonstrates a high current density of 1.48 A cm−2 at 800 °C and 1.5 V, with the polarization resistance (Rp) of 0.527 Ω cm2 at open circuit voltage (OCV). Meanwhile, the single cell exhibits good stability for 50 h at an applied voltage of 1.2 V. This work reveals the difference in electrochemical processes on half cells and single cells, and provides a strategy to accelerate the CO2RR kinetics of La0.6Sr0.4FeO3-δ-based materials.

Oxidative Cleavage of Alkenes by Photosensitized Nitroarenes

This article highlights the recent seminal findings on the possibility to use photoexcited nitroarenes as modular and easily dosable reagents which can mimic the reactivity of ozonolysis for the oxidative conversion of alkenyl bonds into carbonyl groups in a highly selective fashion.

Oxidative Cleavage of Alkenes by Photosensitized Nitroarenes

AbstractOxidative cleavage of alkenes into carbonyl molecules mainly relies on either ozonolysis or Lemieux‐Johnson oxidation involving high valent transition metal oxides. Safety, technical concerns and highly oxidizing conditions of both these procedures limited their adoption in streamlined synthesis. Like ozone, photosensitized nitroarenes can deliver similar types of [3+2] cycloaddition products with alkenes through biradical formation and the resulting “N‐doped” ozonides can safely be converted to the corresponding carbonyl compounds through hydrolysis. The high prevalence of nitroarenes with diverse electronic and steric profiles combined with the mild oxidizing power allow to modulate site‐selectivity and tolerate highly sensitive functional groups ideal for application in complex molecular setup.

Recycling of valuable metals from spent cathode material by organic pyrolysis combined with in-situ thermal reduction

From the perspective of environmental protection and resource recovery, recycling of spent lithium-ion batteries is a meaningful process. In this study, the removal of organics, liberatioin of electrode material, and reduction of high valence transition metal, as the key points in recycling efficiency of valuable metals, have been firstly achieved simultaneously by low temperature heat treatment recycling process. Pyrolysis characteristics of organics, phase transition behavior of spent cathode material and the thermal reduction mechanism were evaluated in the meantime. Results demonstrate that organics can be removed and the liberation of electrode materials can be improved by pyrolysis. High-valence transition metals in cathode materials are synchronously reduced to CoO, NiO, MnO, Ni, and Co based on the reducing action of organics, aluminum foil and conductive additives. At the same time, Li element exists in the form of Li2CO3, LiF and aluminum-lithium compound that can be recycled by water-leaching in the water impact crushing process while transition metals can be recycled by acid leaching without reducing agents. 81.26% of Li can be recycled from water-leaching process while the comprehensive recovery rate of Ni, Co, Mn is 92.04%, 93.01%, 92.21%, respectively. This study may provide an environmentally-friendly recycling flowchart of spent lithium-ion batteries.