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 prepare 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 an optimal ORR catalytic performance in an alkaline electrolyte with an onset potential (E_onset : 0.97 V) and half-wave potential (E_1/2 : 0.86 V) comparable to that of commercial Pt/C (E_onset =1.02 V; E_1/2 =0.88 V), which outperforms the corresponding Co-N-C-900 sample (E_onset =0.92 V; E_1/2 =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.