A high-energy aqueous Zn||NO₂ electrochemical cell: a new strategy for NO₂ fixation and electric power generation

Air pollution by nitrogen oxides (NO₂) from exhaust gas is a deep-seated problem, thus urgently calling for new capture and abatement technologies. Meanwhile, the electrocatalytic conversion of NO₂ to value-added chemicals is a promising strategy for mitigating human-caused imbalances of the global nitrogen cycle. Here, we propose an electrochemical cell based on an aqueous Zn||NO₂ system with a nano-NiO catalyst deposited as the cathode, a metallic Zn foil as the anode and a ZnCl₂ aqueous solution as the electrolyte. Importantly, the electrolyte can efficiently capture NO₂, then convert it to NO₂^- and eventually to value-added NH₃, while simultaneously producing electric power. As proof of concept, a battery has been fabricated, which exhibits bifunctional activity and stability (>100 h) towards reversible NO₂ reduction and evolution reactions. A high cell-level energy density of 553.2 W h kg^-1_cell/1589.6 W h L^-1_cell from pouch cells (2.4 Ah) has been achieved. As an additional green feature, the produced NO₂^- by the Zn||NO₂ cell is subsequently converted to NH₃ by a self-powered mechanism, thereby servicing multiple key conversion steps in the nitrogen cycle all within a single device, paving the way to scalable, highly integrated solutions. © 2023 The Royal Society of Chemistry.