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

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