Ab-initio analysis of CrX2 (X = S, Se and Te) monolayers as bifunctional electrocatalysts for oxygen reduction and evolution reaction in nonaqueous lithium-oxygen batteries.

Abstract

Lithium-oxygen batteries are next-generation battery devices due to lightweight nature and high energy density with compared to conventional Li-ion batteries. These batteries consist a metal anode terminal and an oxygen diffused cathode terminal, in which oxygen is used as a reactant with metal atoms from surrounding air. Nonetheless, these systems facing the problems related to sluggish kinetics and higher overpotential due to formation of insoluble products at negative electrode during redox reaction. To address these major issues, the requirement of catalyst materials is raised to enhance the battery performance. Keep this in mind, we have investigated the potential of CrX₂ (X = S, Se and Te) monolayer (ML) as a catalyst material for LiO₂ batteries. Here, we systematically examined the stability and electronic properties of CrX₂ ML using density functional theory (DFT) approach. For the dynamical and thermal stabilities, the phonon dispersion curves and ab initio molecular dynamics (AIMD) simulation were performed. All three materials exhibit outstanding conductivity and are energetically favourable for adsorption of Li atoms and O₂ molecules. The initial nucleation process in all materials begins with the adsorption of Li metal and follows *Li➔*LiO₂ path. Further, analysis the adsorption behaviour, structural geometries and charge distribution of Li_xO_2y reaction intermediates during oxygen reduction reaction mechanism, show that CrX₂ MLs follows four electron pathways, resulting in 2(Li₂O) as the final discharge product. Additionally, we have investigated the free energy for corresponding intermediates involved in both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process. The calculated ORR and OER overpotentials are notably low: CrS₂ (0.27 V and 0.71 V), CrSe₂ (0.22 V and 0.71 V) and CrTe₂ (0.17 V and 0.33 V). Our results shows that CrX₂ MLs are serve as high performance catalyst materials to expedite the catalytic activities for LiO₂ battery systems.