Efficient Fe-Co-N-C Electrocatalyst Towards Oxygen Reduction Derived from a Cationic Co(II)-based Metal-Organic Framework Modified by Anion-Exchange with Potassium Ferricyanide.

Fe-Co-N-C electrocatalysts have proven superior to their counterparts (e.g. Fe-N-C or Co-N-C) for the oxygen reduction reaction (ORR). Herein, we report on a unique strategy to make Fe-Co-N-C-x (x refers to the pyrolysis temperature) electrocatalysts which involves anion-exchange of [Fe(CN)6]3- into a cationic Co(II)-based metal-organic framework precursor prior to heat treatment. Fe-Co-N-C-900 exhibits the optimal ORR catalytic performance in alkaline electrolyte with the comparable onset potential (Eonset: 0.97 V) and the half-wave potential (E1/2: 0.86 V) to the commercial Pt/C (Eonset = 1.02 V; E1/2 = 0.88 V), which also far outperforms the corresponding Co-N-C-900 (Eonset = 0.92 V; E1/2 = 0.84 V) derived from the same MOF precursor without anion-exchange modification. This is the first example of Fe-Co-N-C electrocatalysts fabricated from a cationic Co(II)-based MOF precursor that dopes the Fe element via anion-exchange, and our current work provides a new entrance towards MOF-derived transition-metal (e.g. Fe or Co) and nitrogen-codoped carbon electrocatalysts with excellent ORR activity.