Mechanochemical Synthesis of Fluorine-Containing Co-Doped Zeolitic Imidazolate Frameworks for Producing Electrocatalysts

Max Rautenberg; Marius Gernhard; Jörg Radnik; Julia Witt; Christina Roth; Franziska Emmerling

doi:10.3389/fchem.2022.840758

Mechanochemical Synthesis of Fluorine-Containing Co-Doped Zeolitic Imidazolate Frameworks for Producing Electrocatalysts

Front Chem. 2022 Mar 14:10:840758. doi: 10.3389/fchem.2022.840758. eCollection 2022.

Authors

Max Rautenberg^{1

2}, Marius Gernhard³, Jörg Radnik¹, Julia Witt¹, Christina Roth³, Franziska Emmerling^{1

2}

Affiliations

¹ BAM Federal Institute of Materials Research and Testing, Berlin, Germany.
² Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany.
³ Fakultät für Ingenieurwissenschaften, Lehrstuhl für Werkstoffverfahrenstechnik, Universität Bayreuth, Bayreuth, Germany.

Abstract

Catalysts derived from pyrolysis of metal organic frameworks (MOFs) are promising candidates to replace expensive and scarce platinum-based electrocatalysts commonly used in polymer electrolyte membrane fuel cells. MOFs contain ordered connections between metal centers and organic ligands. They can be pyrolyzed into metal- and nitrogen-doped carbons, which show electrocatalytic activity toward the oxygen reduction reaction (ORR). Furthermore, metal-free heteroatom-doped carbons, such as N-F-Cs, are known for being active as well. Thus, a carbon material with Co-N-F doping could possibly be even more promising as ORR electrocatalyst. Herein, we report the mechanochemical synthesis of two polymorphs of a zeolitic imidazole framework, Co-doped zinc 2-trifluoromethyl-1H-imidazolate (Zn_0.9Co_0.1(CF₃-Im)₂). Time-resolved in situ X-ray diffraction studies of the mechanochemical formation revealed a direct conversion of starting materials to the products. Both polymorphs of Zn_0.9Co_0.1(CF₃-Im)₂ were pyrolyzed, yielding Co-N-F containing carbons, which are active toward electrochemical ORR.

Keywords: MOF (Metal–Organic framework); XRD; electrocatalysis; mechanochemistry; mixed metal.