摘要
Spinel Co 3 O 4 , comprising two types of cobalt ions: one Co 2+ in the tetrahedral site (Co 2+ Td ) and the other two Co 3+ in the octahedral site (Co 3+ Oh ), has been widely explored as a promising oxygen evolution reaction (OER) catalyst for water electrolysis. However, the roles of two geometrical cobalt ions toward the OER have remained elusive. Here, we investigated the geometrical-site-dependent OER activity of Co 3 O 4 catalyst by substituting Co 2+ Td and Co 3+ Oh with inactive Zn 2+ and Al 3+ , respectively. Following a thorough in operando analysis by electrochemical impedance spectroscopy and X-ray absorption spectroscopy, it was revealed that Co 2+ Td site is responsible for the formation of cobalt oxyhydroxide (CoOOH), which acted as the active site for water oxidation.