Nanomaterial & Electrocatalysis Laboratory, College of Materials Science and Engineering , Qingdao University of Science and Technology , 53 Zhengzhou Road , 266042 Qingdao , China.
Shanghai Institute of Applied Physics , Chinese Academy of Science , 239 Zhangheng Road , 201204 Shanghai , China.
ACS Appl Mater Interfaces. 2019 Apr 3;11(13):12525-12534. doi: 10.1021/acsami.9b00481. Epub 2019 Mar 25.
Cobalt oxides, including spinel CoO and rock-salt CoO, have been widely reported as promising catalysts for oxygen reduction reaction (ORR). However, three types of cobalt ions, i.e., Co in the tetrahedral site (Co ), Co in the octahedral site (Co ), and Co in the octahedral site (Co ), are included in these oxides, and the roles of cobalt geometric occupancy and valance states have remained elusive. Here, for the first time, we investigated the effects of cobalt geometric occupancy on the ORR activity by substituting Co and Co of CoO with inactive Zn and Al, respectively. The ORR activity decreases in the order of CoO (Co , Co ) < ZnCoO (Co ) ≪ CoAlO (Co ) in accordance with the ORR overpotentials at the current density of 0.1 mA cm. Furthermore, by comparatively investigating the activity and stability of CoO (Co ) and CoO (Co ) nanoparticles, by virtue of the electrochemical technique, the high-resolution transmission electron microscopy, and the in operando fuel cell-X-ray absorption spectroscopy techniques, it was revealed that Co in CoO is the main active site, which under electrochemical conditions tends to transform into Co and form CoO with a hollow structure due to the Kirkendall effect; nevertheless, it retains decent ORR activity due to the formation of the unique hollow structure.
钴氧化物，包括尖晶石 CoO 和岩盐 CoO，已被广泛报道为具有前景的氧还原反应 (ORR) 催化剂。然而，这些氧化物中包含三种类型的钴离子，即四面体位置的 Co（Co ）、八面体位置的 Co（Co ）和 Co（Co ），钴的几何占据和价态的作用仍不清楚。在这里，我们首次通过分别用非活性的 Zn 和 Al 取代 CoO 中的 Co 和 Co ，研究了钴的几何占据对 ORR 活性的影响。按照在 0.1 mA cm 电流密度下的 ORR 过电势，ORR 活性的顺序为 CoO（Co ，Co ）<ZnCoO（Co ）≪CoAlO（Co ）。此外，通过电化学技术、高分辨率透射电子显微镜和在位燃料电池 X 射线吸收光谱技术，比较研究 CoO（Co ）和 CoO（Co ）纳米粒子的活性和稳定性，揭示了 CoO 中的 Co 是主要的活性位，在电化学条件下，由于柯肯达尔效应，Co 倾向于转化为 Co 并形成具有中空结构的 CoO；然而，由于独特的中空结构的形成，它仍然保持着相当的 ORR 活性。
