We studied the evaporation-driven crystallization in the droplets of sodium acetate anhydrous (CH3COONa) aqueous solution, which were deposited on superhydrophobic substrates. The results reveal distinct crystallization behaviors between saturated and unsaturated droplets under identical experimental conditions. Specifically, unsaturated droplets could form a quasi-spherical crystal shell on the superhydrophobic substrate, while saturated droplets could develop crystal legs between the droplet and substrate when the crystal shell formed. Subsequently, the saturated droplet was lifted off the substrate by the growing crystal legs. The formation of crystal shell was closely associated with the evaporation from the droplet surface and the internal convection inside the droplet. The formation of crystal legs was induced by the heterogeneous nucleation effect caused by the substrate of SiO2nanoparticles. These findings provide valuable insights into regulating the morphology of salt crystallization through adjustments in salt solution concentration and substrate surface structure.Keywords:superhydrophobic substrate;droplet evaporation;crystallization;internal convection;crystallization pressure
Pt-based alloy catalysts are popular for fuel cell oxygen reduction reactions (ORRs) because of their high activity and low cost. However, during the preparation and reaction processes, metal nanoparticles tend to aggregate, which affects the activity and stability of the catalyst. To address this issue, this work uses Zeolite-type imidazolic acid framework material (ZIF) crystal shells to coat PtCu alloy catalysts, and N-doped nanoporous carbon layers derived from ZIFs are used to protect individual metal nanoparticles . The appropriate thickness of the ZIF-derived carbon protective layer is reported to effectively inhibit the aggregation of metal nanoparticles during high-temperature calcination , improve the utilization rate of Pt atoms and enhance the activity and stability of Pt-based catalyst. N-doping stabilizes the metal nanoparticles by enhancing their interaction with carriers. Electrochemical test results demonstrated that the mass activity of the prepared 3-Co-PtCu/NC is 6.9 times and 4.3 times that of commercial Pt/C and PtCu/C, respectively. Furthermore, the excellent half-wave potential is maintained even after 10,000 cycles. In single-cell test, the performance of 3-Co-PtCu/NC is better than Pt/C. This study provides a strategy for controlling the aggregation and detachment of metal nanoparticles in metal-based catalysts, which is conducive to improving the performance of catalysts.
危险品化学品经营许可证（带存储）