RESUMO
Constructing multiheteroatom coordination structure in carbonaceous substrates demonstrates an effective method to accelerate the oxygen reduction reaction (ORR) of supported single-atom catalyst. Herein, the novel etching route assisted by potassium thiocyanate (KCNS) is developed to convert metal-organic framework to 2D defect-rich porous N,S-co-doped carbon nanosheets for anchoring atomically dispersed iron sites as the high-performance ORR catalysts (Fe-SACs). The well-designed KCNS-assisted etching route can generate spatial confinement template to direct the carbon nanosheet formation, etching condition to form defect-rich structure, and additional sulfur atoms to coordinate iron species. Spectral and microscopy analysis reveals that the iron element in Fe-SACs is highly isolated on carbon nanosheet and anchored by nitrogen and sulfur atoms in unsymmetrical Fe-S1N3 structure. The optimized Fe-SACs with large specific surface area could show remarkable alkaline ORR performances with a high half-wave potential of 0.920 V versus RHE and excellent durability. The rechargeable zinc-air battery assembled with Fe-SACs air electrodes delivers a large power density of 350 mW cm-2 and a stable voltage platform during charge and discharge over more than 1300 h. This work proposes a novel strategy for the preparation of single-atom catalysts with multiheteroatom coordination structure and highly exposed active sites for efficient ORR.
RESUMO
Defect chemistry in carbon matrix shows great potential for promoting the oxygen reduction reaction (ORR) of metal single-atom catalysts. Herein, a modified pyrolysis strategy is proposed to tune carbon defects in copper single-atom catalysts (Cu-SACs) to fully understand their positive effect on the ORR activity. The optimized Cu-SACs with controllable carbon defect degree and enhanced active specific surface area can exhibit improved ORR activity with a half-wave potential of 0.897 VRHE , ultrahigh limiting current density of 6.5 mA cm-2 , and superior turnover frequency of 2.23 e site-1 s-1 . The assembled Zn-air batteries based on Cu-SACs can also show well-retained reversibility and voltage platform over 1100 h charge/discharge period. Density functional theory calculations reveal that suitable carbon defects can redistribute charge density of Cu-N4 active sites to weaken the O-O bond in adsorbed OOH* intermediate and thus reduce its dissociation energy. This discovery offers a universal strategy for fabricating superior single-atom catalysts with high-efficiency active sites toward energy-directed applications.
RESUMO
A centimeter-sized bearing fault probe based on dual-fiber Bragg grating vibration sensing is proposed. The probe can provide multi-carrier heterodyne vibration measurements based on swept source optical coherence tomography technology and the synchrosqueezed wavelet transform method to obtain a wider vibration frequency response range and collect more accurate vibration data. For the sequential characteristics of bearing vibration signals, we propose a convolutional neural network with long short-term memory and transformer encoder. This method is proven in bearing fault classification under variable working conditions, and the accuracy rate reaches 99.65%.