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

Abstract

Air pollution by nitrogen oxides (NO<inf>2</inf>) from exhaust gas is a deep-seated problem, thus urgently calling for new capture and abatement technologies. Meanwhile, the electrocatalytic conversion of NO<inf>2</inf> 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‖NO<inf>2</inf> system with a nano-NiO catalyst deposited as the cathode, a metallic Zn foil as the anode and a ZnCl<inf>2</inf> aqueous solution as the electrolyte. Importantly, the electrolyte can efficiently capture NO<inf>2</inf>, then convert it to NO<inf>2</inf>⁻ and eventually to value-added NH<inf>3</inf>, while simultaneously producing electric power. As proof of concept, a battery has been fabricated, which exhibits bifunctional activity and stability (>100 h) towards reversible NO<inf>2</inf> reduction and evolution reactions. A high cell-level energy density of 553.2 W h kg⁻¹<inf>cell</inf>/1589.6 W h L⁻¹<inf>cell</inf> from pouch cells (2.4 Ah) has been achieved. As an additional green feature, the produced NO<inf>2</inf>⁻ by the Zn‖NO<inf>2</inf> cell is subsequently converted to NH<inf>3</inf> 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.