An ethylene‐bridged copolycarbosilazane precursor of copolysilylethylenediamine (co‐ PSDA ) is synthesized by polycondensation of ethylenediamine with the mixture of vinylmethyldichlorosilane and methyldichlorosilane in the presence of triethylamine as acid absorbing agent. Fourier transform infrared ( FTIR ) and nuclear magnetic resonance ( NMR , 1 H NMR and 13 C NMR ) spectral analysis of the as‐synthesized co‐ PSDA suggests a structure of ethylene‐bridged polycarbosilazane having –Si–N–C–C–N– as backbone chain with – CH = CH 2 , –H and – CH 3 attached to Si as side groups. Co‐ PSDA can be cross‐linked at 80°C using 2, 2‐azobisisobutyronitrile as initiator through the polyaddition of the vinyl group and dehydrogenation/deamination of Si–H and N–H. Then the cross‐linked co‐ PSDA precursor is pyrolyzed at 1000°C in argon, giving out amorphous silicon carbon nitride ( SiCN ) ceramics with a high ceramic yield of 76 wt%. The obtained SiCN ceramics consist of nitrogen‐rich silicon sites of SiN 4 as predominant component and some SiCN 3 sites, which should arise from the breaking of N–C bonds below 600°C and the formation of active N–Si bonds.
Abstract Zinc‐air batteries (ZABs) have recently received tremendous research attention due to their high theoretical energy densities. However, current ZABs suffer from poor energy efficiency and cyclability, mainly owing to the sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) on the air electrode. Therefore, rational design of efficient bifunctional oxygen electrocatalysts with high activity and stability is essential for improving battery performance. Carbon‐based nanomaterials are promising candidates for bifunctional oxygen catalysis. In this review, we present the latest development of carbon‐based bifunctional electrocatalysts for ZABs. Firstly, the related reaction mechanisms of bifunctional ORR/OER catalysts are introduced. Then, the recent advances in developing carbon‐based bifunctional catalysts with tailored structure and promising catalytic performance are introduced following the regulation strategies, e. g., heteroatom doping, defect engineering, and/or hybridizing with other active materials. Finally, the key challenges and perspectives of advanced ZABs are provided to better shed light on future research.
A theoretical study on the spatial configurations of the catalytic dehydrogenation of the pre- and post- Ti-doped NaAlH4(001)2×2×1 supercell surface crystals was performed by using the Car-Parrinello molecular dynamics (CPMD) method at 333 K (60 ℃). It was be found that two of the Al—H bond lengths increased from approximately 1.64 to 1.74 and 1.93 respectively in the AlH4 groups of the Ti-doped alloy. Compared with this change, the four Al—H bond lengths almost kept invariant in the AlH4 group of un-doped alloy, which means that it was easier to dehydrogenate for the Ti-doped alloy than un-doped alloy. There was no bonding tendency between atom Ti and Al observed, which is probably because the temperature in the simulation process is not high enough. Based on the obtained surface crystal configuration, the Ti K-edge x ray absorption near-edge structure (XANES) spectra of the TiAl3, TiH2 crystals and Na8Ti8Al16H64(001) surface crystal have been calculated by using the full-potential linearized augmented plane wave method (FPLAPW). It was also found that the atom Ti may not only exist in the mixture of TiAl3 and TiH2 but also probably partially substitute for the Na atoms in NaAlH4 surface crystal, by comparing the experimental XANES and edge x ray absorption fine structure (EXAFS) spectra.
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