The Roles of Composition and Mesostructure of Cobalt‐Based Spinel Catalysts in Oxygen Evolution Reactions

• Published in: Chemistry : a European journal Vol. 27; no. 68; pp. 17038 - 17048
• Main Authors: Rabe, Anna, Büker, Julia, Salamon, Soma, Koul, Adarsh, Hagemann, Ulrich, Landers, Joachim, Friedel Ortega, Klaus, Peng, Baoxiang, Muhler, Martin, Wende, Heiko, Schuhmann, Wolfgang, Behrens, Malte
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 06-12-2021; John Wiley and Sons Inc
• Subjects: Aluminum; Ammonium; Ammonium nitrate; Anisotropy; Carbon dioxide; Catalysts; Catalytic activity; Cations; Cerium ammonium nitrate; Chemistry; co-precipitation; Cobalt; Cobalt ferrites; Cobalt oxides; cobalt spinels; Composition; crystalline precursor decomposition approach; Decomposition; Decomposition reactions; Electrochemistry; Hydrogen peroxide; Magnesium; Oxidation; Oxygen; oxygen evolution reaction; Oxygen evolution reactions; Spinel; structure-reactivity relationship; Substitution reactions; Valence
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202102400

By using the crystalline precursor decomposition approach and direct co‐precipitation the composition and mesostructure of cobalt‐based spinels can be controlled. A systematic substitution of cobalt with redox‐active iron and redox‐inactive magnesium and aluminum in a cobalt spinel with anisotropic particle morphology with a preferred 111 surface termination is presented, resulting in a substitution series including Co3O4, MgCo2O4, Co2FeO4, Co2AlO4 and CoFe2O4. The role of redox pairs in the spinels is investigated in chemical water oxidation by using ceric ammonium nitrate (CAN test), electrochemical oxygen evolution reaction (OER) and H2O2 decomposition. Studying the effect of dominant surface termination, isotropic Co3O4 and CoFe2O4 catalysts with more or less spherical particles are compared to their anisotropic analogues. For CAN‐test and OER, Co3+ plays the major role for high activity. In H2O2 decomposition, Co2+ reveals itself to be of major importance. Redox active cations in the structure enhance the catalytic activity in all reactions. A benefit of a predominant 111 surface termination depends on the cobalt oxidation state in the as‐prepared catalysts and the investigated reaction.
The particle anisotropy and cobalt content in spinel oxides is systematically varied and the impact on oxygen evolving reactions is investigated. For chemical and electrochemical water oxidation as well as H2O2 decomposition the reactivity changes with the cobalt‐to‐metal ratio and the degree of anisotropy. Furthermore, the importance of the interplay of redox pairs and different active sites are highlighted.