Optimal Geometrical Configuration of Cobalt Cations in Spinel Oxides to Promote Oxygen Evolution Reaction

• Published in: Angewandte Chemie 2020-03, Vol.132 (12), p.4766-4772
• Main Authors: Liu, Zhijuan, Wang, Guangjin, Zhu, Xiaoyan, Wang, Yanyong, Zou, Yuqin, Zang, Shuangquan, Wang, Shuangyin
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Cations; Chemistry; Cobalt; Cobalt oxides; Cobaltkationen; Coexistence; Configurations; Electrocatalysts; Free energy; Geometrische Konfiguration; Gibbs free energy; Oxygen; Oxygen evolution reactions; Sauerstoffentwicklung; Spinelloxide; Tetrahedra
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201914245

MgCo2O4, CoCr2O4, and Co2TiO4 were selected, where only Co3+ in the center of octahedron (Oh), Co2+ in the center of tetrahedron (Td), and Co2+ in the center of Oh, can be active sites for the oxygen evolution reaction (OER). Co3+(Oh) sites are the best geometrical configuration for OER. Co2+(Oh) sites exhibit better activity than Co2+(Td). Calculations demonstrate the conversion of O* into OOH* is the rate‐determining step for Co3+(Oh) and Co2+(Td). For Co2+(Oh), it is thermodynamically favorable for the formation of OOH* but difficult for the desorption of O2. Co3+(Oh) needs to increase the lowest Gibbs free energy over Co2+(Oh) and Co2+(Td), which contributes to the best activity. The coexistence of Co3+(Oh) and Co2+(Td) in Co3O4 can promote the formation of OOH* and decrease the free‐energy barrier. This work screens out the optimal geometrical configuration of cobalt cations for OER and gives a valuable principle to design efficient electrocatalysts. MgCo2O4, CoCr2O4 und Co2TiO4 wurden als Modellkatalysatoren für die Sauerstoffentwicklung untersucht. In diesen Strukturen befindet sich Co3+ in einem Oktaederzentrum (Oh), Co2+ in einem Tetraederzentrum (Td) und Co2+ in einem Oktaederzentrum. Die Co3+(Oh)‐Zentren stellen die beste geometrische Konfiguration dar, und Co2+(Oh)‐Zentren zeigen eine höhere elektrochemische Aktivität als Co2+(Td).