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(mu(3)-OH)(BTB)(2)(BPE)(2)}{Co0.5N(C5H5)}], 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 x 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 Koutecky-Levich analysis. The as-synthesized Co-based catalyst has the ability to reduce O-2 to H2O by a nearly four-electron process. The crystal structure of 1 shows that the trimeric unit {Co-3(mu(3)-OH)(COO)(5)N-3} and monomeric unit {Co(COO)(2)(NC5H4)(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.