Antioxidant treatment strategy by scavenging reactive oxygen species (ROS) is a highly effective disease treatment option. Nanozymes with multiple antioxidant activities can cope with the diverse ROS ...environment. However, lack of design strategies and limitation of negative correlation for nanozymes with multiple antioxidant activities hindered their development. To overcome these difficulties, here we used ZnMn2O4 as a model to explore the role of Mn valency at the octahedral site via a valence‐engineered strategy, and found that its multiple antioxidant activities are positively correlated with the content of Mn4+. Therefore, through this strategy, a self‐cascading antioxidant nanozyme LiMn2O4 was constructed, and its efficacy was verified at the cellular level and in an inflammatory bowel disease model. This work not only provides guidance for the design of multiple antioxidant nanozymes, but also broadens the biomedical application potential of multiple antioxidant nanozymes.
A valence‐engineered strategy to develop self‐cascading nanozymes with simultaneous multiple antioxidant activities has been proposed. Nanozyme LiMn2O4 (LM), as the final optimized material, exhibits the best SOD‐like, CAT‐like, GPx‐like, and hydroxyl radical scavenging activities. The outstanding antioxidant capacity of LM was demonstrated at the cellular level and in the treatment of inflammatory bowel disease in mice.
To generate red emissions, manganese (IV) ions have recently gained recognition as potent non-rare-earth activators. However, the oxide and fluoride hosts that offer suitable environments for Mn4+ ...require careful preparation, involving precise control of reaction parameters like redox equilibrium and temperature. In the current work, we show simultaneous oxidation of Mn2+ to Mn4+ by devitrification of glassy Na2Ge4O9: Mn under moderate atmospheric conditions and under the argon atmosphere. The G-sample was devitrified via thermal treatment after the parent glass, which shares the same chemical formula as dilithium tetragermanate (Na2Ge4O9), was created through the use of traditional melt-quenching (MQ). Optical spectroscopy and electron paramagnetic resonance (EPR) spectroscopic are utilized to confirm the Mn2+ oxidation to Mn4+ from glass stat to glass ceramic after thermal treatment. Due to the transition from Mn2+ to Mn4+, a sharp 668 nm emission peak is recorded whereas the red emission peaking at 611 nm monitored in glass is steadily reduced. The temperature-dependent PL spectra of the Na2Ge4O9:0.1Mn+4, red-emitting GC in the temperature range ∼295–490 K were recorded. The PL emission intensity decreases gradually with increasing the temperature. The technique showcased for producing Na2Ge4O9:Mn4+ phosphors could be expanded to synthesize other phosphors incorporating activators possessing a high oxidation state.
A highly active graphdiyne heterojunction with highly efficient photocatalysis is designed and fabricated. This catalyst demonstrates transformative properties on photocatalysis for ammonia ...synthesis. Such excellent properties are reigned from graphdiyne incorporating Fe site‐specific magnetite resulting in a valence state transition within the catalyst. Our results show the strong advantages of graphdiyne in effectively regulating magnetite activity and coordination environments and also indicate that magnetite can selectively form two different valence tetrahedral coordination Fe and octahedral coordination Fe. The catalysts show remarkable catalytic performance for ammonia synthesis by photocatalysis, indicating transformative photocatalytic activity with an ammonia yield (YNH3
) of unprecedented level of 1762.35±153.71 μmol h−1 gcat.−1 (the highest YNH3
could reach up to 1916.06 μmol h−1 gcat.−1). This work makes full use of the structural and property features of graphdiyne and opens up a new direction for photocatalysis in the field of catalysis.
A graphdiyne heterojunction photocatalyst for ammonia synthesis reaches reaction rates of 1762.35±153.71 μmol h−1 gcat.−1 (the highest YNH3
could reach up to 1916.06 μmol h−1 gcat.−1). Our results demonstrated that the excellent properties originated from graphdiyne incorporating Fe site‐specific magnetite, resulting in a valence state transition in the catalytic process.
Transition metal‐based electrocatalysts will undergo surface reconstruction to form active oxyhydroxide‐based hybrids, which are regarded as the “true‐catalysts” for the oxygen evolution reaction ...(OER). Much effort has been devoted to understanding the surface reconstruction, but little on identifying the origin of the enhanced performance derived from the substrate effect. Herein, we report the electrochemical synthesis of amorphous CoOOH layers on the surface of various cobalt sulfides (CoSα), and identify that the reduced intermolecular energy gap (Δinter) between the valence band maximum (VBM) of CoOOH and the conduction band minimum (CBM) of CoSα can accelerate the formation of OER‐active high‐valent Co4+ species. The combination of electrochemical and in situ spectroscopic approaches, including cyclic voltammetry (CV), operando electron paramagnetic resonance (EPR) and Raman, reveals that Co species in the CoOOH/Co9S8 are more readily oxidized to CoO2/Co9S8 than in CoOOH and other CoOOH/CoSα. This work provides a new design principle for transition metal‐based OER electrocatalysts.
The reduced intermolecular energy gap between the valence band maximum of CoOOH and the conduction band minimum of Co precursors can promote the formation of oxygen evolution reaction (OER)‐active high‐valent Co4+ species, and enhance the OER performance. This finding provides a new design principle for transition metal‐based OER electrocatalysts.
Developing efficient electrocatalysts for the oxygen evolution reaction (OER) is highly challenging for hydrogen production from water splitting, due to the high energy barrier for OO bond formation ...and the restriction of the scaling relation between the multiple reaction intermediates. In order to simultaneously address these concerns, an Ir/Ni(OH)2 heterostructure with abundant heterointerfaces is deliberately designed as an efficient electrocatalyst system, with Ir nanoparticles (NPs) homogeneously confined on the Ni(OH)2 nanosheets. The strong electronic interaction and chemical bonding across the interface between the Ir and Ni(OH)2 can effectively stabilize the metastable electrophilic Ir(V) species, which is vital to boost the formation of OO bonds. Meanwhile, the adsorption of the multiple intermediates is synergistically optimized at the heterointerface, which breaks the restrictive scaling relation and substantially accelerates the OER kinetics. In addition, the severe agglomeration of Ir species is greatly mitigated by the confinement effect, ensuring the structural integrity of the catalyst and the constant exposure of active sites. Owing to its well‐defined multifunctional interfaces, the Ir/Ni(OH)2 heterostructure exhibits exceptional OER activity and durability in alkaline media. The present results highlight the significance of heterostructure interface engineering toward the rational design and development of advanced electrocatalysts for the OER and beyond.
A highly efficient Ir/Ni(OH)2 heterostructured electrocatalyst is designed for the oxygen evolution reaction (OER). The heterointerface not only stabilizes the metastable electrophilic Ir(V) species but also breaks the scaling relation, thereby substantially promoting the OER kinetics. The results highlight the significance of heterostructure interface engineering toward the rational design of advanced electrocatalysts for the OER and beyond.
A nitrogen‐stabilized single‐atom catalyst containing low‐valence zinc atoms (Znδ+‐NC) is reported. It contains saturated four‐coordinate (Zn‐N4) and unsaturated three‐coordinate (Zn‐N3) sites. The ...latter makes Zn a low‐valence state, as deduced from X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory. Znδ+‐NC catalyzes electrochemical reduction of CO2 to CO with near‐unity selectivity in water at an overpotential as low as 310 mV. A current density up to 1 A cm−2 can be achieved together with high CO selectivity of >95 % using Znδ+‐NC in a flow cell. Calculations suggest that the unsaturated Zn‐N3 could dramatically reduce the energy barrier by stabilizing the COOH* intermediate owing to the electron‐rich environment of Zn. This work sheds light on the relationship among coordination number, valence state, and catalytic performance and achieves high current densities relevant for industrial applications.
A nitrogen‐anchored low‐valence Zn single‐atom catalyst, containing coordinately unsaturated Zn‐N3 active sites, can boost electrochemical CO2 reduction to industrial application levels.
Electrochemical water splitting is a critical energy conversion process for producing clean and sustainable hydrogen; this process relies on low‐cost, highly active, and durable oxygen evolution ...reaction/hydrogen evolution reaction electrocatalysts. Metal cations (including transition metal and noble metal cations), particularly high‐valence metal cations that show high catalytic activity and can serve as the main active sites in electrochemical processes, have received special attention for developing advanced electrocatalysts. In this review, heterogenous electrocatalyst design strategies based on high‐valence metal sites are presented, and associated materials designed for water splitting are summarized. In the discussion, emphasis is given to high‐valence metal sites combined with the modulation of the phase/electronic/defect structure and strategies of performance improvement. Specifically, the importance of using advanced in situ and operando techniques to track the real high‐valence metal‐based active sites during the electrochemical process is highlighted. Remaining challenges and future research directions are also proposed. It is expected that this comprehensive discussion of electrocatalysts containing high‐valence metal sites can be instructive to further explore advanced electrocatalysts for water splitting and other energy‐related reactions.
High‐valence metal cations, including transition metal and noble metal cations, exhibit high catalytic activity and serve as the main active sites in electrochemical processes. This review discusses the design strategies, advances, challenges, and future directions of heterogenous electrocatalysts based on high‐valence metal sites for the application of electrochemical water splitting.
The ability of resonant X‐ray emission spectroscopy (XES) to recover physical oxidation state information, which may often be ambiguous in conventional X‐ray spectroscopy, is demonstrated. By ...combining Kβ XES with resonant excitation in the XAS pre‐edge region, resonant Kβ XES (or 1s3p RXES) data are obtained, which probe the 3dn+1 final‐state configuration. Comparison of the non‐resonant and resonant XES for a series of high‐spin ferrous and ferric complexes shows that oxidation state assignments that were previously unclear are now easily made. The present study spans iron tetrachlorides, iron sulfur clusters, and the MoFe protein of nitrogenase. While 1s3p RXES studies have previously been reported, to our knowledge, 1s3p RXES has not been previously utilized to resolve questions of metal valency in highly covalent systems. As such, the approach presented herein provides chemists with means to more rigorously and quantitatively address challenging electronic‐structure questions.
Assigning transition‐metal physical oxidation states is a major goal of X‐ray spectroscopy. However, competing influences of covalency and d‐count on Kβ XES spectra often make assignments ambiguous. It is now shown that resonant Kβ X‐ray emission spectroscopy (RXES) yields unambiguous oxidation‐state determinations for iron monomers, dimers, cubanes, and metalloenzymes.
Based on a description of bond valence as a function of valence electron density, a systematic bond softness sensitive approach to determine bond-valence parameters and related quantities such as ...coordination numbers is elaborated and applied to determine bond-valence parameters for 706 cation-anion pairs. While the approach is closely related to the earlier
parameter set, the new
parameters proposed in this work may be simpler to apply in plausibility checks of crystal structures, as they follow the first coordination shell convention. The performance of this
bond-valence parameter set is compared with that of the previously derived
parameter set that also factors in contributions from higher coordination shells, and with a benchmarking parameter set that has been optimized following the conventional choice of a universal value of the bond-valence parameter
. The results show that a systematic adaptation of the bond-valence parameters to the bond softness leads to a significant improvement in the bond-valence parameters, particularly for bonds involving soft anions, and is safer than individual free refinements of both
and
from a limited number of reference cation environments.
Vanadium‐based materials are fascinating potential cathodes for high energy density Zn‐ion batteries (ZIBs), due to their high capacity arising from multi‐electron redox chemistry. Most ...vanadium‐based materials suffer from poor rate capability, however, owing to their low conductivity and large dimension. Here, we propose the application of V2C MXene (V2CTx), a conductive 2D nanomaterial, for achieving high energy density ZIBs with superior rate capability. Through an initial charging activation, the valence of surface vanadium in V2CTx cathode is raised significantly from V2+/V3+ to V4+/V5+, forming a nanoscale vanadium oxide (VOx) coating that effectively undergoes multi‐electron reactions, whereas the inner V‐C‐V 2D multi‐layers of V2CTx are intentionally preserved, providing abundant nanochannels with intrinsic high conductivity. Owing to the synergistic effects between the outer high‐valence VOx and inner conductive V‐C‐V, the activated V2CTx presents an ultrahigh rate performance, reaching 358 mAh g−1 at 30 A g−1, together with remarkable energy and power density (318 Wh kg−1/22.5 kW kg−1). The structural advantages of activated V2CTx are maintained after 2000 cycles, offering excellent stability with nearly 100% Coulombic efficiency. This work provides key insights into the design of high‐performance cathode materials for advanced ZIBs.
An effective strategy to unleash the potential of V2C MXene for fast Zn‐ion storage is developed via regulating the valence of surface vanadium while preserving the inner 2D conductive V‐C‐V layers, which forms a VOx/V2CTx heterostructure. This heterostructure not only offers abundant active sites for Zn2+ storage, but also provides ordered nanochannels for rapid electron/ion transfer.
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