A Conjugated Porous Polymer Complexed with a Single-Atom Cobalt Catalyst as An Electrocatalytic Sulfur Host for Enhancing Cathode Reaction Kinetics

Abstract

© 2021Conjugated microporous polymers (CMPs) have shown great promise for use in contemporary energy applications owing to their unique structures and tunable functionality. Here, we report a CMP embedded with a single-atom Co catalyst (Co-CMP) as an electrocatalytic sulfur host for promoting the cathode reactions of lithium−sulfur (Li−S) batteries. The Co-CMP was synthesized by copolymerizing a dibromo salcyen Co complex with tris(ethynylthiophene)triazine using standard Sonogashira coupling methodology. In addition to featuring a single-atom catalyst (SAC), the Co-CMP possesses a high quantity of pyridinic nitrogen atoms and relatively large pore sizes that collectively facilitate sulfur cathode chemistry. The performance displayed by Li−S cells fabricated with the Co-CMP was outstanding when compared with cells that were devoid of a SAC, particularly in terms of specific capacity (1404 vs. 1338 mA h g−1 at 0.1 C), rate capability (766 vs. 613 mA h g−1 at 2 C), and cycling stability (549 vs. 314 mA h g−1 after 1000 cycles at 0.5 C). Density functional theory calculations in conjunction with X-ray absorption near-edge structure spectroscopy measurements revealed that the single-atom Co catalyst lowers the cathode reaction energies by forming bonding interactions with the polysulfide anions as well as the Li cations that are present in sulfur cathodes. Since the methodology is modular and obviates the extreme steps required by other approaches, it can be employed to synthesize new classes of CMPs containing SACs with predictable structures and functions for use in a broad range of contemporary catalytic applications.