Overall Electrochemical N2 Fixation to Ammonia and Nitrate by Iridium-Incorporated WO3 Nanorods and Sustainable Zn―N2 Battery Application

Abstract

In this work, an iridium-incorporated tungsten trioxide nanorod (Ir-WO3) electrocatalyst is reported exhibiting bifunctional activity toward fixing N2 into ammonia and nitrate and showing higher activity than the pristine WO3. The 5% Ir-WO3 achieves a maximum ammonia yield rate of 17.60 mu g h-1 mgcat -1 with a faradaic efficiency of 19.42% at -0.4 V. Also, the 5% Ir-WO3 achieves a maximum nitrate yield rate of 20.31 mu g h-1 mgcat -1 at 2.1 V with a faradaic efficiency of 27.34% at 1.9 V. Furthermore, the electrocatalyst possesses cyclic stability up to five consecutive cycles and long-term durability of more than two days for both nitrogen reduction reaction (NRR) and nitrogen oxidation reaction (NOR). The density functional theory (DFT) analysis reveals that the initial protonation and oxidation of the dinitrogen molecule are the potential-determining steps (PDS) for NRR and NOR, respectively. The introduction of Ir atoms boosts the adsorption and activation of N2, diminishes the energy barrier, and improves the yield of ammonia and nitrate. To validate the real-field application, the as-prepared 5% Ir-WO3-based rechargeable aqueous Zn & horbar;N2 battery is assembled, which delivers a maximum power density of 3.79 mW cm-2, a maximum ammonia yield rate of 6.39 mu g h-1 mgcat -1, and a maximum energy density of 143 mWh gzn -1.