Using the fermi level as a predictive indicator of the electrocatalytic activities displayed by single-atom catalysts in sulfur cathode reactions

Abstract

Single-atom catalysts (SACs) have emerged as promising candidates for promoting sulfur cathode kinetics. Despite the growing popularity, the literature is devoid of general guidelines for predicting the electrocatalytic effects exerted by novel SACs. Herein, a series of SACs immobilized on N-doped graphene were prepared from metal (Mn, Ni, Cu, or Zn) porphyrins. The Fermi levels of the catalysts were found to be inversely correlated with their electrocatalytic effects. For example, the Ni-based SACs exhibited the lowest Fermi level but showed the strongest binding affinity to sulfur. As a result, Li-S cells containing Ni SACs exhibited a high specific capacity (10.0 mA h cm-2 at 0.05 C), excellent cycling stability (6.7 mA h cm-2 at 0.1 C after 100 cycles) and other remarkable performance metrics even at a high sulfur loading of 9.6 mg cm-2. The methodology offers a way to evaluate the catalytic activities of SACs rapidly and efficiently, particularly in electrocatalytic systems.