Chain ether-based electrolyte enables long-term continuous ammonia electrosynthesis

Abstract

Abstract Ammonia is essential to the fertilizer and chemical industries and is seen as a carbon-free fuel1. The ammonia electrosynthesis from nitrogen under ambient conditions is an attractive alternative to the centralized Haber-Bosch process2,3. The lithium-mediated nitrogen reduction (Li-NRR) has been demonstrated as a promising approach for continuous-flow ammonia electrosynthesis, where nitrogen reduction is coupled with hydrogen oxidation4. This provides a genuine pathway for converting nitrogen and hydrogen into ammonia, but the long-term ammonia production is impeded by the polymerization and volatility of ring ether-based solvent, tetrahydrofuran (THF, with a boiling point of 66 °C), in a continuous-flow electrolyzer. Here we show that a chain ether-based electrolyte enables long-term continuous ammonia synthesis. We find that a chain ether-based solvent offers not only non-polymerization properties and high boiling point (162 °C) but also the formation of a compact solid-electrolyte interphase (SEI) layer on the gas diffusion electrode (GDE), facilitating the release of produced ammonia in the gas phase and ensuring long-term stability of the electrolyte. We demonstrate 300 hours continuous operation in a flow electrolyzer at 1 bar and room temperature, and achieve a current-to-ammonia efficiency of 64% (repeated twice) with unprecedented gas phase ammonia of ~98%. Our work highlights the crucial role of the solvent in long-term continuous ammonia synthesis, and these findings will guide the development of a durable and efficient process for sustainable ammonia production.