Regulating Electrocatalytic Oxygen Reduction Activity of a Metal Coordination Polymer via d-π Conjugation

Non-noble transition metal complexes have attracted growing interest as efficient electrocatalysts for oxygen reduction reaction (ORR) while their activities still lack rational and effective regulation. Herein, we propose a d-π conjugation strategy for rough and fine tuning of ORR activity of TM-BTA (TM=Mn/Fe/Co/Ni/Cu, BTA=1,2,4,5-benzenetetramine) coordination polymers. By first-principle calculations, we elucidate that the strong d-π conjugation elevates the d_xz /d_yz orbitals of TM centers to enhance intermediate adsorption and strengthens the electronic modulation effect from substitute groups on ligands. Based on this strategy, Co-TABQ (tetramino benzoquinone) is found to approach the top of ORR activity volcano. The synthesized Co-TABQ with atomically distributed Co on carbon nanotubes exhibits a half-wave potential of 0.85 V and a specific current of 127 mA mg_metal ^-1 at 0.8 V, outperforming the benchmark Pt/C. The high activity, low peroxide yield, and considerable durability of Co-BTA and Co-TABQ promise their application in oxygen electrocatalysis. This study provides mechanistic insight into the rational design of transition metal complex catalysts.