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–S4), and Co-BTA (BTA = 1,2,4,5-benzenetetramine,
Co–N4), 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–N4 and Co–S4 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···S).
Interpreting the mechanism of ORR in the coordination sphere provides
a feasible way to improve catalytic activity at an atomic level.