Understanding the Impact of Peripheral Substitution on the Activity of Co Phthalocyanine in Sulfur Reduction Catalysis

Abstract

AbstractCatalytic materials are effective in promoting sulfur utilization in lithium‐sulfur batteries. Co phthalocyanine (CoPc) presents a unique planner single‐molecular structure with a highly active Co‐N4 center for sulfur reduction catalysis. The high flexibility of phthalocyanines offers rich opportunities for electronic structure modulation toward enhanced catalytic activities. To guide future design and screening, this study aims to understand the impact of peripheral substitution, the most common method to obtain CoPc derivatives, by examining two typical substituents: the electron‐withdrawing nitro and electron‐donating amino groups. Co tetranitrophthalocyanine (CoTnPc) presents a significantly higher activity in promoting the liquid‐solid transition process than Co tetraaminophthalocyanine (CoTaPc). Substitution alters the stable binding geometry of Li2S4 by influencing the electrostatic potential and Li─bond, making the Co─S bond energetically favorable with the bridging S atoms on CoTnPc. CoTnPc also enables a greater electron donation from the S 3pz orbital to the singly occupied Co 3 orbital, significantly weakening the bridging S─S bond to enhance the reactivity of Li2S4 for the subsequent liquid‐solid transition. A framework of theoretical calculation is tested, providing descriptors for the screening of related materials. The potential of CoPc derivatives is demonstrated by pouch cells with CoTnPc under high sulfur loading and limited electrolyte addition.