Search

Since the discovery in 2000, conversion‐type materials have emerged as a promising negative‐electrode candidate for next‐generation batteries with high capacity and tunable voltage, limited by low reversibility and severe voltage hysteresis. Heterogeneous construction stands out as a cost‐effective and efficient approach to reducing reaction barriers and enhancing energy density. However, the second term introduced by conventional heterostructure inevitably complicates the electrochemical analysis and poses great challenges to harvesting systematic insights and theoretical guidance. A model cell is designed and established herein for the conversion reactions between Na and TMSA−SnO2, where TMSA−SnO2 represents single atom modification of eight different 3d transition elements (V, Cr, Mn, Fe, Co, Ni, Cu or Zn). Such a model unit fundamentally eliminates the interference from the second phase and thus enables independent exploration of activation manifestations of the heterogeneous architecture. For the first time, a thermodynamically dependent catalytic effect is proposed and verified through statistical data analysis. The mechanism behind the unveiled catalytic effect is further elucidated by which the active d orbitals of transition metals weaken the surface covalent bonds and lower the reaction barriers. This research provides both theoretical insights and practical demonstrations of the advanced heterogeneous electrodes. [ABSTRACT FROM AUTHOR]

Hydrazine hydrate and hydrogen peroxide are both important raw materials for industrial production and have a wide range of applications in several fields. Owing to their damage to the human body and cellular functions by excessive exposure or ingestion, it is essential to develop an efficient and rapid assay for the detection of hydrazine hydrate and hydrogen peroxide. Fluorescence switches have been applied in many fields including for metal ion detection. However, the assembly of Prussian blue (PB) and carbon quantum dots (CDs) has never been reported for the fabrication of a fluorescence switch for the detection of hydrazine and hydrogen peroxide. In this work, a fluorescent switch PB@CD/SiO2 based on PB and CDs was constructed, which could be used as a detection platform for hydrazine hydrate and hydrogen peroxide. The surface of PB was coated with a silica layer, which contained CDs to fabricate PB@CD/SiO2 nanoparticles. The composite demonstrated reversible switching between fluorescence quenching and recovering states through the mutual conversion of PB and Prussian white (PW). The prepared composite was utilized for the detection of N2H4 and H2O2 by fluorescence spectroscopy and UV-vis absorption spectroscopy. It is worth-mentioning that the detection limit for N2H4 is calculated to be 0.15 μM (fluorescence) and the detection limit for H2O2 can reach 0.93 μM (UV). Moreover, both detection methods showed low detection limits, wide detection ranges and a short response time for N2H4 and H2O2. The proposed fluorescence switch system exhibits good performance towards the dual-spectral determination of hydrazine and hydrogen peroxide by fluorescence spectroscopy and UV-vis spectroscopy, which may be beneficial for further application in practical fields. [ABSTRACT FROM AUTHOR]

Spin state is often regarded as the crucial valve to release the reactivity of energy‐related catalysts, yet it is also challenging to precisely manipulate, especially for the active center ions occupied at the specific geometric sites. Herein, a π–π type orbital coupling of 3d (Co)‐2p (O)‐4f (Ce) was employed to regulate the spin state of octahedral cobalt sites (CoOh) in the composite of Co3O4/CeO2. More specifically, the equivalent high‐spin ratio of CoOh can reach to 54.7 % via tuning the CeO2 content, thereby triggering the average eg filling (1.094) close to the theoretical optimum value. The corresponding catalyst exhibits a superior water oxidation performance with an overpotential of 251 mV at 10 mA cm−2, rivaling most cobalt‐based oxides state‐of‐the‐art. The π–π type coupling corroborated by the matched energy levels between Ce t1u/t2u‐O and CoOh t2g‐O π type bond in the calculated crystal orbital Hamilton population and partial density of states profiles, stimulates a π‐donation between O 2p and π‐symmetric Ce 4fyz2 orbital, consequently facilitating the electrons hopping from t2g to eg orbital of CoOh. This work offers an in‐depth insight into understanding the 4f and 3d orbital coupling for spin state optimization in composite oxides. [ABSTRACT FROM AUTHOR]

Lattice oxygen in metal oxides plays an important role in the reaction of diesel oxidation catalysts, but the atomic-level understanding of structural evolution during the catalytic process remains elusive. Here, we develop a Mn2O3/SmMn2O5 catalyst using a non-stoichiometric exsolution method to explore the roles of lattice oxygen in NO oxidation. The enhanced covalency of Mn–O bond and increased electron density at Mn3+ sites, induced by the interface between exsolved Mn2O3 and mullite, lead to the formation of highly active lattice oxygen adjacent to Mn3+ sites. Near-ambient pressure X-ray photoelectron and absorption spectroscopies show that the activated lattice oxygen enables reversible changes in Mn valence states and Mn-O bond covalency during redox cycles, reducing energy barriers for NO oxidation and promoting NO2 desorption via the cooperative Mars-van Krevelen mechanism. Therefore, the Mn2O3/SmMn2O5 exhibits higher NO oxidation activity and better resistance to hydrothermal aging compared to a commercial Pt/Al2O3 catalyst. This work reports on an exsolved Mn2O3/SmMn2O5 diesel oxidation catalyst competitive with current commercial materials in reactivity and hydrothermal aging resistance and further clarifies the catalytic mechanism for lattice oxygen as the reactive center [ABSTRACT FROM AUTHOR]

Understanding the microstructure of materials and their impact on performance is crucial for new electronic devices design. The strong interaction between multiple degrees of freedom (spin, orbit, charge, and lattice) within perovskite type oxides can generate rich electron phase diagrams. The microscopic modulation of manganese ions electron states in rare earth manganate perovskites is the root of many novel macroscopic quantum behaviors, such as giant magnetoresistance phenomenon. For ABO3 type perovskites, the differences of radii and valence states of A‐site ions are used to regulate the coexistence of B site manganese multivalent states (Mn3+, Mn4+, Mn5+), and its ordered structure in the metastable state will create a new combination of electronic states. The ordered arrangement of the multi‐dimensional space of electronic states can induce unique transport properties. Therefore, the preparation of manganate perovskites will provide strong chemical support to construct new generation quantum devices. This review summarizes the challenges and difficulties on constructing trivalent coexisting metastable phase in manganate perovskites through disproportionation reactions, and discusses the status and potential of designing ideal rectified p‐n junctions taking advantage of this unique structure. Finally, the foregrounds of new quantum states driven by this chemical reaction are prospected. [ABSTRACT FROM AUTHOR]