A rechargeable Al–N2 battery for energy storage and highly efficient N2 fixation

Abstract

Currently developed metal–gas batteries include various metal–CO₂ batteries, but in the area of N₂-based batteries, only Li–N₂ and Na–N₂ batteries have been demonstrated. According to Gibbs free energy calculations, an Al–N₂ electrochemistry system would possess even higher spontaneity, and metallic Al is safe for storage and transportation. However, an Al–N₂ system has not been demonstrated so far. Herein, for the first time, a rechargeable Al–N₂ battery system is proposed and demonstrated with an ionic-liquid electrolyte, a graphene-supported Pd (graphene/Pd) catalyst cathode, and a low-cost Al anode. The battery realizes both energy storage and the production of AlN through sucking up a N₂ feedstock. AlN can be easily further converted to an NH₃-based product, which is essential for the manufacturing of nitrogenous fertilizers and is regarded as an ideal carbon-free energy carrier. In this system, the formation and decomposition of the cathodic AlN product upon cycling are prerequisites for battery rechargeability and cyclability. Remarkably, the battery system exhibits excellent N₂ fixation capabilities with an impressive faradaic efficiency (FE) of 51.2%, far outperforming other systems (FE: ∼5%). This work not only demonstrates the first Al–N₂ battery system enabling energy conversion, but it also offers a promising alternative method for artificial N₂ fixation to the energy-intensive Haber–Bosch process and the low-FE electrochemical N₂ reduction reaction in aqueous electrolytes.