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