Direct electrosynthesis and separation of ammonia and chlorine from waste streams via a stacked membrane-free electrolyzer.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39349480.
- Also identified by DOI 10.1038/s41467-024-52830-4 and PMC identifier 11443043.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Electrosynthesis, a viable path to decarbonize the chemical industry, has been harnessed to generate valuable chemicals under ambient conditions. Here, we present a membrane-free flow electrolyzer for paired electrocatalytic upcycling of nitrate (NO<sub>3</sub><sup>-</sup>) and chloride (Cl<sup>-</sup>) to ammonia (NH<sub>3</sub>) and chlorine (Cl<sub>2</sub>) gases by utilizing waste streams as substitutes for traditional electrolytes. The electrolyzer concurrently couples electrosynthesis and gaseous-product separation, which minimizes the undesired redox reaction between NH<sub>3</sub> and Cl<sub>2</sub> and thus prevents products loss. Using a three-stacked-modules electrolyzer system, we efficiently processed a reverse osmosis retentate waste stream. This yielded high concentrations of (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> (83.8 mM) and NaClO (243.4 mM) at an electrical cost of 7.1 kWh per kilogram of solid products, while residual NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup> (0.3 mM), NO<sub>2</sub><sup>-</sup> (0.2 mM), and Cl<sub>2</sub>/HClO/ClO<sup>-</sup> (0.1 mM) pollutants in the waste stream could meet the wastewater discharge regulations for nitrogen- and chlorine-species. This study underscores the value of pairing appropriate half-reactions, utilizing waste streams to replace traditional electrolytes, and merging product synthesis with separation to refine electrosynthesis platforms.