Kumar Anuj, Vashistha Vinod Kumar
Beijing University of Chemical Technology Beijing China-100096.
Department of Chemistry, GLA University Mathura UP-281406 India
RSC Adv. 2019 Apr 30;9(23):13243-13248. doi: 10.1039/c9ra02169h. eCollection 2019 Apr 25.
The major concerns in the design of macrocycle based-ORR catalysts are: (i) understanding the macrocyclic, π-conjugation, central metal and substituent effects on ORR electrocatalysis; and (ii) the use of macrocycles on the electrode surface for the retention of ORR activity because of their poor stability. In this work, we demonstrated the aromaticity/π-electron conjugation effect on ORR activity by using the same macrocycles [HMTAA-14 and 16 (hexamethyltetraaza [14] and [16] annulenes)] with a difference in their macrocyclic cavity/π-electron conjugation. The macrocycles CoHMTAA-14 and CoHMTAA-16 and their nanocomposites with highly conductive carbon black were prepared by a microwave-assisted method and characterized by using multiple spectroscopy techniques. Comparative redox and oxygen reduction activity studies of CoHMTAA-14 and CoHMTAA-16 were undertaken by using cyclic voltammetry and linear sweep voltammetry in an alkaline medium. The composite CoHMTAA-16@C showed good ORR activity compared to CoHMTAA-14@C in O-saturated KOH electrolyte. Since the CoHMTAA-14 and CoHMTAA-16 systems have a similar central atom and substituents, the shift of the ORR peak position in the +ive potential region for HMTAA-16 can be attributed to the difference in the size of the macrocyclic cavity (macrocyclic effect) and the extra stability of HMTAA-16 annulene due to its aromaticity.
基于大环的氧还原反应（ORR）催化剂设计中的主要关注点包括：（i）理解大环、π共轭、中心金属和取代基对ORR电催化的影响；（ii）由于大环在电极表面稳定性较差，如何利用大环来保持ORR活性。在这项工作中，我们通过使用具有不同大环腔/π电子共轭的相同大环[HMTAA - 14和16（六甲基四氮杂[14]和[16]轮烯）]，证明了芳香性/π电子共轭对ORR活性的影响。通过微波辅助法制备了大环CoHMTAA - 14和CoHMTAA - 16及其与高导电性炭黑的纳米复合材料，并使用多种光谱技术对其进行了表征。在碱性介质中，通过循环伏安法和线性扫描伏安法对CoHMTAA - 14和CoHMTAA - 16进行了比较氧化还原和氧还原活性研究。在O饱和的KOH电解液中，复合CoHMTAA - 16@C比CoHMTAA - 14@C表现出更好的ORR活性。由于CoHMTAA - 14和CoHMTAA - 16体系具有相似的中心原子和取代基，HMTAA - 16在正电位区域的ORR峰位置的移动可归因于大环腔尺寸的差异（大环效应）以及HMTAA - 16轮烯因其芳香性而具有的额外稳定性。
