Calixarene-Based {Co₂₆} Burr Puzzle: An Efficient Oxygen Reduction Catalyst

Supramolecular coordination complexes (SCCs) have been investigated extensively as the catalysts. Herein, we synthesize a calixarene-based {Co26} SCC (CIAC-126) for this purpose, which is constructed by 6 shuttlecock-like Co3-TC4A secondary building units, 1 Co8 cubic cluster, and 12 bridging imidazole-4,5-dicarboxylic ligands. CIAC-126 is featured with a three-piece burr puzzle in which each piece is perpendicular to the other two as the axes in a 3D Cartesian coordination system, leading to abundant edge defects. Electrocatalytic studies show that the composite of CIAC-126 and the commercial ordered mesoporous carbon (CMK-3), CIAC-126&CMK-3 (1:3, w/w), exhibits Pt-like electrocatalytic oxygen reduction activity in basic media due to the synergistic effect of the two components which provides both approachable active sites and electrical conductivity. It has higher stability than the commercial Pt/C catalyst, and there is almost no change in the oxygen reduction reaction (ORR) polarization curve after 3000 cycles. Furthermore, the nickel precursor instead of the cobalt feed leads to the formation of an open icosahedral {Ni36} coordination cage (CIAC-127) which displays modest ORR activity.