Mesoporous nanostructured spinel-type MFe2O4 (M = Co, Mn, Ni) oxides as efficient bi-functional electrocatalysts towards oxygen reduction and oxygen evolution.

Development of excellent bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a key issue for the commercialization of various electrochemical devices such as fuel cells and metal-air batteries. Herein, we report the synthesis and electrocatalytic performance of mesoporous nanostructured spinel-type MFe 2 O 4 (M = Co, Mn, Ni) oxides which can serve as alternative low-cost bi-functional electrocatalysts for ORR/OER. Loaded on XC-72 carbon support, the MFe 2 O 4 spinel oxides show the M-dependent catalytic activities with CoFe 2 O 4 being the most active electrocatalyst followed by MnFe 2 O 4 and NiFe 2 O 4 for ORR. For the OER, however, the activity increases in the order: MnFe 2 O 4 < NiFe 2 O 4 ≈ CoFe 2 O 4 . Additionally, the CoFe 2 O 4 catalyst shows the smallest overpotential between ORR and OER. Compared with commercial IrO 2 , the MFe 2 O 4 catalysts reveal comparable OER activities. Furthermore, the MFe 2 O 4 catalysts exhibit much better methanol tolerance and stability than Pt/C. Meanwhile, both electrochemical measurements and density functional theory (DFT) calculations verify that the ORRs on the MFe 2 O 4 catalysts are a direct 4 e − pathway in the alkaline solution, and expound the reason for the excellent methanol tolerance of MFe 2 O 4 . [ABSTRACT FROM AUTHOR]