Atomic-Level Modulation-Induced Electron Redistribution in Co Coordination Polymers Elucidates the Oxygen Reduction Mechanism

Regulating the atomic arrangement and electron redistribution is beneficial for tuning catalytic oxygen reduction reaction (ORR) performance and deciphering the intrinsic mechanism. Herein, we modulate the charge density around Co centers by designing and synthesizing three Co coordination polymer catalysts, including Co-DABDT (DABDT = 2,5-diaminobenzene-1,4-dithiol, Co-N2S2), Co-BTT (BTT = 1,2,4,5-tetramercaptobenzene, Co-S-4), and Co-BTA (BTA = 1,2,4,5-benzenetetramine, Co-N-4), to explore the structure-activity relationship between the coordination environment and ORR performance. Because of the high electronegativity of S compared to N atoms, the charge density of Co increases in the order of Co-BTA -> Co-DABDT -> Co-BTT. Experimentally, Co-DABDT@CNTs with Co-N2S2 delivers a remarkable half-wave potential of 0.85 +/- 0.002 V, outperforming Co-N-4 and Co-S-4 and even Pt/C (0.84 +/- 0.003 V). Zinc-air batteries using Co-DABDT@CNTs as the air cathode catalyst also demonstrate excellent power density and stability. The systematic characterization and theoretical simulation reveal that the charge redistribution on Co and S sites of Co-N2S2 would both effectively optimize and stabilize the key intermediate (OOH*) with the assistance of hydrogen bonding interactions between intermediates and active S atoms (*OO-H center dot center dot center dot S). Interpreting the mechanism of ORR in the coordination sphere provides a feasible way to improve catalytic activity at an atomic level.

Automated summary

By modulating the charge density around the cobalt centers, three cobalt coordination polymer catalysts were designed and synthesized to optimize the performance of the oxygen reduction reaction (ORR). Experimental results show that Co-DABDT@CNTs with Co-N2S2 exhibits a high half-wave potential and outperforms other catalysts, including Pt/C. Systematic characterization and theoretical simulations reveal the mechanism behind this optimization.