Search

We have characterized polarization switching kinetics of Hf0.5Zr0.5O2 (HZO) at cryogenic temperature (T) down to 100 K. By the nucleation-limited-switching model with Lorentzian distribution fittings, the dependences of the average switching time (log τ1) and switching time distribution (ω) on T are extracted. As T decreases from 300 to 100 K, log τ1 first rapidly decreases and then gradually stabilizes. Meanwhile, ω exhibits different trends under different external electric fields (Eext), decreasing under low Eext while increasing under high Eext, eventually stabilizing at non-zero constants. With the further decrease in T (<100 K), log τ1 and ω exhibited by HZO are almost unchanged, indicating the intrinsic properties of ferroelectric multiple domains, which are different from the prediction in previous literature studies that log τ1 and ω will linearly decrease as T decreases. [ABSTRACT FROM AUTHOR]

Antiferroelectric (AFE) ZrO2-based devices are anticipated to exhibit superior endurance properties in comparison to their ferroelectric (FE) counterparts. Nevertheless, the underlying mechanisms of AFE devices remain elusive. In this study, guided by the dynamic evolution of oxygen vacancies (Vo), we reveal three kinds of fatigue in AFE HfxZr1−xO2 (HZO) during uni-directional cycling. The first mechanism is related to the interfacial Vo charge trapping, which accelerates the switching from the P↓↑ state to the P↓↓ state, leading to extrinsic fatigue, and is demonstrated by electrical stress measurements. The other two mechanisms are Vo-related AFE to FE phase transition (PT) and Vo localization inside the HZO films, which are supported by the first-principles calculations. The highest polarization switching barrier occurs when Vo is localized at the tetra-coordinated oxygen sites inside HZO films. This means that tetra-coordinated Vo accumulation leads to less polarization switching, resulting in AFE to FE PT and Vo localization induced fatigue, i.e., intrinsic fatigue. This work reveals the dynamic evolution of Vo during cycling and its impact on AFE properties, paving the way for developing more durable AFE ZrO2-based devices and contributing to the emergence of diverse recovery methods in the future. [ABSTRACT FROM AUTHOR]

Designing and synthesizing heterostructure‐based catalysis combining two‐dimensional (2D) materials has attracted enormous attention in materials chemistry, especially for electrocatalysis, due to their tunable electronic properties and structure. In this work, a boron carbon nitride (BCN)‐coupled carbon (BCN‐C) heterostructure with improved electronic performance was synthesized starting from C‐ and N‐enriched 2D covalent triazine frameworks (CTFs) via a simple thermal transformation process using NaBH4 as the B source. The characterizations results showed that the B released from NaBH4 reacted with N and C in CTF, forming the BCN‐C heterostructure coupling the BCN and carbon with a strong interfacial effect. The electrocatalytic NRR experiments and density functional theory (DFT) calculation revealed that the interfacial electronic properties and large numbers of active sites of the BCN‐C heterostructure benefited the NRR. The BCN‐C‐1 catalyst showed a high Faradaic efficiency of 27.8% and an NH3 yield of 4.3 μg h−1 mgcat.−1 in 0.1 M HCl electrolyte, owing to its high specific surface area (288 m2/g) with a large number of exposed active sites and the Mott–Schottky effect from the BCN‐C heterostructure. This work highlights the design and synthesis of metal‐free catalysts with high activity and selectivity and makes them excellent candidates for electrocatalytic applications. [ABSTRACT FROM AUTHOR]

Structural optimization is essential to improve the performance of mixing equipment. An efficient optimization strategy based on computational fluid dynamics, machine learning, and the multi‐objective genetic algorithm was proposed to predict and optimize the performance of the stirred tank. Single‐factor analysis was performed to study the effects of structural parameters on power consumption and mixing time, which were reduced by 16.0% and 1.4%, respectively, in the optimized stirred vessel. To further optimize the stirred tank geometries and maximize the integrated performance, XGB coupled NSGA‐ІІ were utilized to minimize the power consumption and mixing time. The optimal design parameters from the Pareto front were identified by two well‐known decision‐making methods (LINMAP and TOPSIS), which decreased power consumption and mixing time by 12.3% and 13.4% compared to the stirred tank with the baseline structure. This research further confirmed the accuracy and reliability of the machine learning‐based optimization method. [ABSTRACT FROM AUTHOR]

Electro‐chemically reducing CO2 in a highly acidic medium is promising for addressing the issue of carbonate accumulation. However, the hydrogen evolution reaction (HER) typically dominates the acidic CO2 reduction. Herein, we construct an efficient electro‐catalyst for CO formation based on a core‐shell structure, where nitrogen‐doped Ni nanoparticles coexist with nitrogen‐coordinated Ni single atoms. The optimal catalyst demonstrates a significantly improved CO faradaic efficiency (FE) of 96.7 % in the acidic electrolyte (pH=1) at an industrial‐scale current density of 500 mA cm−2. Notably, the optimal catalyst maintains a high FE of CO exceeding 90 % (current density=500 mA cm−2) in the electrolyte with a wide pH range from 0.67 to 14. In‐situ spectroscopic characterization and density functional theory calculations show that the local electron density of Ni‐N‐C sites is enhanced by N‐doped Ni particles, which facilitates the formation of *COOH intermediate and the adsorption of *CO. This study demonstrates the potential of a hybrid metal/Ni‐N‐C interface in boosting acidic CO2 electro‐reduction. [ABSTRACT FROM AUTHOR]

Antiferroelectric (AFE) ZrO2-based devices are anticipated to exhibit superior endurance properties in comparison to their ferroelectric (FE) counterparts. Nevertheless, the underlying mechanisms of AFE devices remain elusive. In this study, guided by the dynamic evolution of oxygen vacancies (Vo), we reveal three kinds of fatigue in AFE HfxZr1−xO2 (HZO) during uni-directional cycling. The first mechanism is related to the interfacial Vo charge trapping, which accelerates the switching from the P↓↑ state to the P↓↓ state, leading to extrinsic fatigue, and is demonstrated by electrical stress measurements. The other two mechanisms are Vo-related AFE to FE phase transition (PT) and Vo localization inside the HZO films, which are supported by the first-principles calculations. The highest polarization switching barrier occurs when Vo is localized at the tetra-coordinated oxygen sites inside HZO films. This means that tetra-coordinated Vo accumulation leads to less polarization switching, resulting in AFE to FE PT and Vo localization induced fatigue, i.e., intrinsic fatigue. This work reveals the dynamic evolution of Vo during cycling and its impact on AFE properties, paving the way for developing more durable AFE ZrO2-based devices and contributing to the emergence of diverse recovery methods in the future. [ABSTRACT FROM AUTHOR]

Electro-chemically reducing CO 2 in a highly acidic medium is promising for addressing the issue of carbonate accumulation. However, the hydrogen evolution reaction (HER) typically dominates the acidic CO 2 reduction. Herein, we construct an efficient electro-catalyst for CO formation based on a core-shell structure, where nitrogen-doped Ni nanoparticles coexist with nitrogen-coordinated Ni single atoms. The optimal catalyst demonstrates a significantly improved CO faradaic efficiency (FE) of 96.7 % in the acidic electrolyte (pH=1) at an industrial-scale current density of 500 mA cm -2 . Notably, the optimal catalyst maintains a high FE of CO exceeding 90 % (current density=500 mA cm -2 ) in the electrolyte with a wide pH range from 0.67 to 14. In-situ spectroscopic characterization and density functional theory calculations show that the local electron density of Ni-N-C sites is enhanced by N-doped Ni particles, which facilitates the formation of *COOH intermediate and the adsorption of *CO. This study demonstrates the potential of a hybrid metal/Ni-N-C interface in boosting acidic CO 2 electro-reduction., (© 2023 Wiley-VCH GmbH.)

The electrocatalytic nitrogen reduction reaction (NRR) on metal-free catalysts is an attractive alternative to the industrial Haber-Bosch process. However, the state-of-the-art metal-free electrocatalysts still suffer from low Faraday efficiencies and low ammonia yields. Herein, we present a molecular design strategy to develop a defective boron carbon nitride (BCN) catalyst with the abundant unsaturated B and N atoms as Lewis acid and base sites, which upgrades the catalyst from a single "Lewis acid catalysis" to "frustrated Lewis pairs (FLPs) catalysis." 14 N 2 / 15 N 2 exchange experiments and density functional theory (DFT) calculations reveal that FLPs can adsorb an N 2 molecule to form a six-membered ring intermediate, which enables the cleavage of N 2 via a pull-pull effect, thereby significantly reducing the energy barrier to -0.28 eV. Impressively, BCN achieves a high Faraday efficiency of 18.9 %, an ammonia yield of 20.9 μg h -1  mg -1 cat. , and long-term durability., (© 2022 Wiley-VCH GmbH.)