Despite the importance of stem cells in plant and animal development, the common mechanisms of stem cell maintenance in both systems have remained elusive. Recently, the importance of hydrogen ...peroxide (H2O2) signaling in priming stem cell differentiation has been extensively studied in animals. Here, we show that different forms of reactive oxygen species (ROS) have antagonistic roles in plant stem cell regulation, which were established by distinct spatiotemporal patterns of ROS‐metabolizing enzymes. The superoxide anion (O2·−) is markedly enriched in stem cells to activate WUSCHEL and maintain stemness, whereas H2O2 is more abundant in the differentiating peripheral zone to promote stem cell differentiation. Moreover, H2O2 negatively regulates O2·− biosynthesis in stem cells, and increasing H2O2 levels or scavenging O2·− leads to the termination of stem cells. Our results provide a mechanistic framework for ROS‐mediated control of plant stem cell fate and demonstrate that the balance between O2·− and H2O2 is key to stem cell maintenance and differentiation.
Synopsis
Superoxide regulates plant stem cell fate, and the balance between superoxide and H2O2 serves as a key switch for stem cell maintenance versus differentiation by antagonistically regulating expression of stem cell fate transcription factor WUSCHEL.
Superoxide specifically accumulates in plant stem cells to determine the stem‐cell fate.
H2O2 is enriched in the differentiating peripheral zone to promote plant stem cell differentiation.
Repression of superoxide dismutases and activation of peroxidases establishes the high superoxide and low H2O2 distribution patterns in plant stem cells.
H2O2 negatively regulates superoxide accumulation in stem cells by inhibiting key enzymes in superoxide anabolism.
The superoxide/H2O2 balance controls plant stem cell fate by antagonistically regulating WUSCHEL expression.
Superoxide regulates plant stem cell fate, and the balance between superoxide and H2O2 serves as a key switch for stem cell maintenance versus differentiation by antagonistically regulating expression of stem cell fate transcription factor WUSCHEL.
Because of growing environmental concerns, the development of lead-free piezoelectric materials with enhanced properties has become of great interest. Here, we report a giant piezoelectric ...coefficient (d 33) of 550 pC/N and a high Curie temperature (T C) of 237 °C in (1–x–y)K1–w Na w Nb1–z Sb z O3– xBiFeO3– yBi0.5Na0.5ZrO3 (KN w NS z -xBF-yBNZ) ceramics by optimizing x, y, z, and w. Atomic-resolution polarization mapping by Z-contrast imaging reveals the intimate coexistence of rhombohedral (R) and tetragonal (T) phases inside nanodomains, that is, a structural origin for the R–T phase boundary in the present KNN system. Hence, the physical origin of high piezoelectric performance can be attributed to a nearly vanishing polarization anisotropy and thus low domain wall energy, facilitating easy polarization rotation between different states under an external field.
We report a greatly enhanced thermoelectric performance in a BiCuSeO system, realized by improving carrier mobility through modulation doping. The heterostructures of the modulation doped sample make ...charge carriers transport preferentially in the low carrier concentration area, which increases carrier mobility by a factor of 2 while maintaining the carrier concentration similar to that in the uniformly doped sample. The improved electrical conductivity and retained Seebeck coefficient synergistically lead to a broad, high power factor ranging from 5 to 10 μW cm–1 K–2. Coupling the extraordinarily high power factor with the extremely low thermal conductivity of ∼0.25 W m–1 K–1 at 923 K, a high ZT ≈ 1.4 is achieved in a BiCuSeO system.
Microstructure manipulation plays an important role in enhancing physical and mechanical properties of materials. Here a high figure of merit zT of 1.2 at 357 K for n‐type bismuth‐telluride‐based ...thermoelectric (TE) materials through directly hot deforming the commercial zone melted (ZM) ingots is reported. The high TE performance is attributed to a synergistic combination of reduced lattice thermal conductivity and maintained high power factor. The lattice thermal conductivity is substantially decreased by broad wavelength phonon scattering via tuning multiscale microstructures, which includes microscale grain size reduction and texture loss, nanoscale distorted regions, and atomic scale lattice distotions and point defects. The high power factor of ZM ingots is maintained by the offset between weak donor‐like effect and texture loss during the hot deformation. The resulted high zT highlights the role of multiscale microstructures in improving Bi2Te3‐based materials and demonstrates the effective strategy in enhancing TE properties.
Hot deformation is directly applied to zone melted Bi2Te3−xSex ingots to optimize the thermoelectric performance. The induced multiscale microstructures, including microscale grain refinement, nanoscale distorted regions, and atomic‐scale point defects, reduce the lattice thermal conductivity but maintain the high power factor, resulting in a high figure of merit of zT ≈ 1.2 at 357 K.
Exploration of cheap, efficient, and highly durable transition-metal-based electrocatalysts is critically important for the renewable energy chain, including both energy storage and energy ...conversion. Herein, we have developed cobalt (Co) single atoms anchored in porous nitrogen-doped carbon nanoflake arrays, synthesized from Co-MOF precursor and followed by removal of the unwanted Co clusters. The well-dispersed Co single atoms are attached to the carbon network through N–Co bonding, where there is extra porosity and active surface area created by the removal of the Co metal clusters. Interestingly, compared with those electrocatalysts containing excess Co nanoparticles, a single Co atom alone demonstrates a lower oxygen evolution reaction (OER) overpotential and much higher oxygen reduction reaction (ORR) saturation current, showing that the Co metal clusters are redundant in driving both OER and ORR. Given the bifunctional electrocatalytic activity and mechanical flexibility, the electrocatalyst assembled on carbon cloth is employed as the air cathode in a solid-state Zn–air battery, which presents good cycling stabilities (2500 min, 125 cycles) as well as a high open circuit potential (1.411 V).
A major limitation of MnO2 in aqueous Zn/MnO2 ion battery applications is the poor utilization of its electrochemical active surface area. Herein, it is shown that by generating oxygen vacancies (VO) ...in the MnO2 lattice, Gibbs free energy of Zn2+ adsorption in the vicinity of VO can be reduced to thermoneutral value (≈0.05 eV). This suggests that Zn2+ adsorption/desorption process on oxygen‐deficient MnO2 is more reversible as compared to pristine MnO2. In addition, because of the fact that fewer electrons are needed for ZnO bonding in oxygen‐deficient MnO2, more valence electrons can be contributed into the delocalized electron cloud of the material, which aids in enhancing the attainable capacity. As a result, the stable Zn/oxygen‐deficient MnO2 battery is able to deliver one of the highest capacities of 345 mAh g−1 reported for a birnessite MnO2 system. This excellent electrochemical performance suggests that generating oxygen vacancies in MnO2 may aid in the future development of advanced cathodes for aqueous Zn ion batteries.
A major limitation of MnO2 in aqueous Zn/MnO2 ion battery applications is the poor utilization of its electrochemical active surface area. Herein, the superiority of Zn ion batteries engineered with oxygen vacancy in MnO2 framework is proposed and demonstrated. More accessible electrochemical active surface area and more electrons are available for electrochemical process, which aids in enhancing the attainable capacity.
Lead-based piezoelectric materials are currently facing global restrictions due to their lead toxicity. Thus it is urgent to develop lead-free substitutes with high piezoelectricity and temperature ...stability, among which, potassium-sodium niobate (K,Na)NbO3, KNN has the most potential. It is very difficult to simultaneously achieve high piezoelectric performance and reliable stability in KNN-based systems. In particular, the structural/physical origin for their high piezoelectricity is still unclear, which hinders property optimization. Here we report the achievement of high temperature stability (less than 10% variation for electric field-induced strain from 27 degree C to 80 degree C), good fatigue properties (stable up to 106 cycles) as well as an enhanced piezoelectric coefficient (d33) of 525 pC N-1 in (1 - x)(K1-yNay)(Nb1-zSbz)O3-xBi0.5(Na1-wKw) 0.5HfO3 (KNNS-BNKH) ceramics through manipulating the rhombohedral-tetragonal (R-T) phase boundary. The structural origin of their high piezoelectric performance can be attributed to a hierarchical nanodomain architecture, where the local structure inside nanodomains comprises R and T nanotwins. The physical origin can be attributed to low domain wall energy and nearly vanishing polarization anisotropy, facilitating easy polarization rotation among different states. We believe that the new breakthrough will open a window for the practical applications of KNN-based ceramics.
Piezoelectric materials interconvert between electrical energy and mechanical strain and are widely used for electronic and electromechanical devices. Owing to growing environmental concerns, ...development of lead‐free piezoelectric materials with enhanced properties becomes of great interest. Key to the academic problem is a lack of fundamental understanding on the actual mechanisms involved at the microscopic (unit cell) level. While it is well known that giant responses occur near structural phase boundaries, and it has long been proposed that polarization rotation and nanodomains are major determinants, so far, atomistic understanding of the origin of the response has come mostly from theoretical simulations. Recently, notable breakthroughs have been achieved in improving the properties of piezoceramics and thin films. Precise mapping of atomic displacements by atomically resolved Z‐contrast imaging has demonstrated that gradual polarization rotation bridges the coexisting nanophases. These structural features, which take place on a length scale of just a few nanometers, now visible through aberration‐corrected microscopy, provide a new pivotal understanding on the outstanding piezoelectric behavior that has been obtained in all systems. They also provide key guiding principles for the development of lead‐free piezoelectrics, especially in the form of thin films, which remain far behind bulk ceramics at the time being. Coexistence of nanophases with flexible interconversion, introduced via phase boundary engineering, holds much promise for achieving high performance in other material systems with phase transitions.
With aberration‐corrected scanning transmission electron microscopy (STEM), directly seeing and tuning atomic‐scale local polarization inside nanodomains for piezoelectrics has now become possible. Precise mappings of atomic displacements demonstrate gradual polarization rotations among coexisting nanophases. These atomic‐scale structural features provide a new pivotal understanding of the outstanding piezoelectric behaviors that have been obtained for all piezoelectric systems.
Highly active and durable air cathodes to catalyze both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for rechargeable metal–air batteries. In this ...work, an efficient bifunctional oxygen catalyst comprising hollow Co3O4 nanospheres embedded in nitrogen‐doped carbon nanowall arrays on flexible carbon cloth (NC‐Co3O4/CC) is reported. The hierarchical structure is facilely derived from a metal–organic framework precursor. A carbon onion coating constrains the Kirkendall effect to promote the conversion of the Co nanoparticles into irregular hollow oxide nanospheres with a fine scale nanograin structure, which enables promising catalytic properties toward both OER and ORR. The integrated NC‐Co3O4/CC can be used as an additive‐free air cathode for flexible all‐solid‐state zinc–air batteries, which present high open circuit potential (1.44 V), high capacity (387.2 mAh g−1, based on the total mass of Zn and catalysts), excellent cycling stability and mechanical flexibility, significantly outperforming Pt‐ and Ir‐based zinc–air batteries.
An efficient bifunctional oxygen catalyst comprising hollow Co3O4 nanospheres embedded in N‐doped carbon nanowall arrays (NC‐Co3O4) is facilely fabricated from a metal–organic framework. The additive‐free NC‐Co3O4 electrode can be directly utilized as an efficient air cathode for a flexible solid‐state Zn–air battery, which demonstrates much improved cycling stability and mechanical flexibility over Pt‐ and Ir‐based zinc–air batteries.
High thermoelectric performance of n-type PbTe is urgently needed to match its p-type counterpart. Here, we show a peak ZT ∼ 1.5 at 723 K and a record high average ZT > 1.0 at 300–873 K realized in ...n-type PbTe by synergistically suppressing lattice thermal conductivity and enhancing carrier mobility by introducing Cu2Te inclusions. Cu performs several outstanding roles: Cu atoms fill the Pb vacancies and improve carrier mobility, contributing to an unexpectedly high power factor of ∼37 μW cm–1 K–2 at 423 K; Cu atoms filling Pb vacancies and Cu interstitials both induce local disorder and, together with nano- and microscale Cu-rich precipitates and their related strain fields, lead to a very low lattice thermal conductivity of ∼0.38 Wm–1 K–1 in PbTe-5.5%Cu2Te, approaching the theoretical minimum value of ∼0.36 Wm–1 K–1. This work provides an effective strategy to enhance thermoelectric performance by simultaneously improving electrical and thermal transport properties.
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