Cobalt-Based Coordination Polymer for Oxygen Reduction Reaction

Lack of control over the structure and electrically nonconductive properties of coordination polymers (CPs) creates a major hindrance to designing an active electrocatalyst for oxygen reduction reaction (ORR). Here, we report a new semiconductive and low-optical band gap CP structure [{Co 3 (μ 3 -OH)(BTB) 2 (BPE) 2 }{Co 0.5 N(C 5 H 5 )}], 1 , that exhibits high-performance ORR in alkaline medium. The electrical conductivity of compound 1 was measured using impedance spectroscopy and found to be 5 × 10 -4 S cm -1 . The Ketjenblack EC-600JD carbon used as a support for all the electrochemical methods such as cyclic voltammetry, rotating disk electrode, rotating ring-disk electrode and Koutecký-Levich analysis. The as-synthesized Co-based catalyst has the ability to reduce O 2 to H 2 O by a nearly four-electron process. The crystal structure of 1 shows that the trimeric unit {Co 3 (μ 3 -OH)(COO) 5 N 3 } and monomeric unit {Co(COO) 2 (NC 5 H 4 ) 2 } 2+ are linked with BTB and BPE linkers to form a three-dimensional structure. Theoretical calculations predict that the monomeric center acts as an active catalytic site for ORR. This could be due to the efficient overlap of highest occupied molecular orbital-lowest unoccupied molecular orbital between monomer and O 2 molecule. This CP, 1 , shows facile 3.6-electron ORR, and it is inexpensive compared with widely used Pt catalysts. Therefore, this CP can be used as a promising cathode material for fuel cells in terms of efficiency and cost effectiveness.