Theoretical evaluation of pristine, single B- and N-doped, and BN co-doped graphenylene as metal-free cathode catalysts for nonaqueous Li–O2 batteries

Abstract

Rechargeable non-aqueous lithium–oxygen (Li–O₂) batteries, owing to their high specific capacity and energy density, are among the most promising next-generation energy storage systems. However, their practical application is hindered by sluggish electrochemical kinetics and high charge/discharge overpotentials, highlighting the need for novel catalysts. In this study, first-principles calculations were employed to theoretically investigate the catalytic potential of pristine, B-doped, N-doped, and BN co-doped graphenylene (GP) nanosheets as metal-free cathode electrocatalysts. Optimized geometries along two nucleation pathways (leading to Li₄O₄ and Li₄O₂) and free energy profiles were computed to elucidate mechanisms and predict final discharge products, revealing that Li₄O₄ formation is thermodynamically favored in all structures. Charge/discharge voltages lie within a safe range preventing electrolyte decomposition. Among the catalysts, B-BNGP exhibits enhanced stability compared to the other configurations and graphene, with the lowest discharge/charge overpotentials (0.280 and 0.293 V), making it the most efficient cathodic catalyst for the ORR/OER. Adsorption patterns in the rate-determining step (RDS) serve as overpotential descriptors, while reduced adsorption energy correlates with lower overpotential. Using B-BNGP as a reference, activation barriers for catalytic decomposition of Li₂O₂ and Li₄O₄ were 1.627 and 1.769 eV, respectively, significantly lower than that for Li₂O₂ decomposition on graphene (2.06 eV), yielding a 1.9 × 10⁷-fold increase in the reaction rate. Additionally, B-BNGP can mitigate the tendency toward Li₂CO₃ formation and dimethyl sulfoxide (DMSO) electrolyte decomposition, thereby enhancing cycling reversibility. Electronic structure analysis confirms the conductivity of these structures, highlighting GP-based nanosheets as promising bifunctional cathodic electrocatalysts for non-aqueous Li–O₂ batteries.