Developing cost-effective and controllable technologies beyond traditional overall N2 electrocatalysis is critical for the large-scale production of NH3 through electrochemical N2 reduction reaction (NRR) under ambient conditions. Herein, the aqueous rechargeable Zn-N2 battery, assembled by coupling the bifunctional cobalt phosphate nanocrystals-loaded heteroatoms-doped carbon nanosheets (CoPi/NPCS) as cathode electrocatalyst and the commercial Zn plate as anode with KOH electrolyte, was fabricated for the sustainable reduction of N2 to NH3 and power generation during discharge process. Benefiting from the desirable active components of cobalt phosphate nanocrystals and the synergistic effect between nanocrystals and carbon substrates, the CoPi/NPCS catalyst exhibits the enhanced NRR and oxygen evolution reaction (OER) performance in alkaline electrolyte. And the cobalt phosphates are confirmed as active components through the associative pathway toward NRR. When measured in the flow battery configuration with gas diffusion electrode by flowing N2 during discharge, this CoPi/NPCS-catalyzed Zn-N2 battery enables the high N2-to-NH3 yield rate of 14.7 μg h-1 mgcat.-1 and Faradaic efficiency of 16.35% at 0.6 V vs Zn2+/Zn, which can be able to maintain stable in discharge processes during cycling tests. Moreover, the impressive power output of the peak power density of 0.49 mW cm-2 and the energy density of 147.6 mWh gzn-1 are still achieved by this Zn-N2 battery, which are both higher than those of previously reported Zn-N2 batteries. This work not only provides the guideline for the rational design of robust and active bifunctional NRR-OER catalysts but also develops a reasonable and promising technology for efficient electrochemical N2-to-NH3 and power generation.
Keywords: aqueous Zn−N2 battery; cobalt phosphates; electrochemical N2 fixation; nitrogen reduction reaction; oxygen evolution reaction.