Computational screening on two-dimensional metal-embedded poly-phthalocyanine as cathode catalysts in lithium-nitrogen batteries

• The MPPc-based cathode catalysts in Li-N 2 battery were computationally screened. • ScPPc exhibits the lowest η DC (0.24 V) and η C (0.35 V) among all the screened MPPcs. • The ScPPc and FePPc could fully reduce the adsorbed N 2 into Li 6 N 2 * mediated by Li +. • ΔG ads of N 2 is an indicator to evaluate the catalytic performance in Li-N 2 battery. Despites the high theoretical energy density, there still lacks of sufficient theoretical insight into the lithium-nitrogen (Li-N 2 ) batteries, which limits their further development. Here we performed computational studies on screening of the two-dimensional metal-embedded poly-phthalocyanines (MPPcs) for electro-catalysis of Li-mediated nitrogen reduction reaction (NRR) in cathode of Li-N 2 batteries. After the calculations on adsorption free energies ( ΔG ads ) of N 2 molecule on MPPcs, the Li-mediated NRR process was simulated by plotting the free energy profiles of Li x N 2 * intermediates along two different pathways. It is found that only parts of the MPPcs could fully reduce N 2 * into the final product Li 6 N 2 *, whose catalytic performance was compared by the discharge/charge overpotential ( η DC / η C ). Along with the end-on pathway, FePPc shows considerably low η DC (0.37 V) and η C (0.42 V), while along with the side-on pathway, ScPPc exhibits the lowest η DC (0.24 V) and η C (0.35 V) among all the screened MPPcs. The ΔG ads of N 2 is found to be suitable indicator to evaluate the catalytic performance of MPPc in Li-N 2 batteries, which should be negative and close-to-zero. This work not only proposes FePPc and ScPPc as the promising cathode catalysts, but also provides theoretical insight into the microscopic mechanism in Li-N 2 batteries.