Phosphorene as a Catalyst for Highly Efficient Nonaqueous Li-Air Batteries

Li-air batteries can yield exceptionally high predicted energy densities. However, for this technology to become realizable, round-trip efficiency issues and slow kinetics at the cathode require implementation of a catalyst. With design parameters not well understood and limitations on material selection, choosing an ideal catalyst is complex. In Li-air batteries, energy storage is achieved by reactions between Li and O (oxygen reduction reaction for discharge and oxygen evolution reaction for charge). Here, phosphorene is proposed as a solution through simulations of its catalytic behavior toward discharge initiated via either O₂ dissociation or Li adsorption. After obtaining intermediate geometries for both nucleation paths leading to either Li₂O₂ or 2(Li₂O), free-energy diagrams are generated to predict the promoted discharge product of Li₂O₂. Furthermore, considering a final product of Li₂O₂, the overpotentials are predicted to be 1.44 V for discharge and 2.63 V for charge. Activation barriers for the catalytic decomposition of Li₂O₂ (during charge) are found to be 1.01 eV for phosphorene versus 2.06 eV for graphene. This leads to a major difference in reaction rate up to 10¹⁷ times in favor of phosphorene. These results, complemented by electronic analysis, establish phosphorene as a promising catalyst for Li-air batteries.