High spin state promotes water oxidation catalysis at neutral pH in spinel cobalt oxide

• Main Authors: Ma, Lin, Hung, Sung-Fu, Zhang, Liping, Cai, Weizheng, Yang, Hongbin, Chen, Hao Ming, Liu, Bin
• Other Authors: School of Chemical and Biomedical Engineering
• Format: Article
• Language: English
• Published: 2020
• Subjects: Engineering::Chemical technology; Quantum Dots (QDs); Water Oxidation Catalysis
• Online Access: https://hdl.handle.net/10356/142457
• Institution: Nanyang Technological University

In this work, we present Co3O4 quantum dots (QDs) as a highly efficient and stable oxygen evolution reaction (OER) catalyst at neutral pH. The Co3O4 QDs with a mean size of 5 nm were synthesized by reacting cobalt acetate with benzyl alcohol in the presence of ammonia under reflux conditions. The as-synthesized Co3O4 QDs show extraordinary water oxidation activity with onset overpotential as low as 398 mV and mass activity as high as 567 A/g (at 1.75 V vs RHE) in a 0.2 M phosphate buffer electrolyte (pH ∼7), which are among the most efficient Earth-abundant OER catalysts at neutral pH reported in the literature, reaching a stable current density of 10 mA/cm2 at an overpotential of ∼490 mV with a Tafel slope of 80 mV/decade. Through in-depth investigations by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, the high spin Co2+ and Co3+ cations on the surface of Co3O4 QDs were found to be important to promote the OER kinetics at neutral pH.