Toward circular nitrogen: Electrochemical ammonia recovery using redox-active materials

Ammonia is an essential chemical commodity for modern agriculture as a fertilizer. It can also be a precursor to oxidized nitrogen compounds, such as nitric acid, which are easily lost in the environment. Meanwhile, ammonia-rich waste streams, such as manure wastewater, are often discharged into farms and cause serious environmental problems, including eutrophication and biodiversity loss. Recovering ammonia from waste streams should provide a sustainable way to close the nitrogen cycle.

Redox-active materials, often solid-state compounds capable of reversible storage of ions and electrons, can selectively uptake ammonium ions in practical waste streams. Dr. Rui Wang from Northwestern University summarizes recent progress in electrochemical ammonia recovery using redox-active materials in Carbon Future on November 20, 2025.

The review highlights two strategies: (1) electrochemical cycles, where renewable electricity drives the uptake and release of ammonium through redox reactions in Prussian blue analogs (PBAs) and related materials; and (2) electrochemical–chemical cycles, in which organic matter in wastewater spontaneously donates electrons to drive ammonium capture, while electrochemical regeneration simultaneously produces value-added chemicals such as hydrogen and hydrogen peroxide.

In particular, the electrochemical–chemical cycle enables efficient nutrient recovery and chemical co-production. For example, in manure wastewater, redox-active materials based on PBAs achieved 84% ammonia recovery and 56% COD removal, with hydrogen peroxide at over 90% Faradaic efficiency. A techno-economic analysis estimated potential annual profits of up to US$200,000 for a 1,000-cow dairy farm, reducing ammonia emissions by 70%.

“Redox-active materials open a new avenue for coupling nitrogen recovery with clean chemical synthesis,” said Dr. Rui Wang, the author of the study. “By investigating electrochemical-chemical pathway, we can simultaneously mitigate pollution and generate valuable products.”

The study also outlines challenges for scaling up, including optimizing ion selectivity, improving material stability, and transitioning from batch to continuous-flow operation. Achieving high-rate recovery with practical energy efficiency will be key for real-world deployment.

“We envision future systems where nutrient recovery, clean energy generation, and wastewater treatment converge through smart electrochemical design,” added Dr. Wang.

This review provides a roadmap for integrating redox-active materials into sustainable ammonia recovery technologies and contributes to a circular nitrogen economy.

About Carbon Future

Carbon Future is an open access, peer-reviewed, and international interdisciplinary journal sponsored by Tsinghua University and published by Tsinghua University Press. It serves as a platform for researchers, scientists, and industry professionals to share their findings and insights on carbon-related materials and processes, including catalysis, energy storage and conversion, as well as low carbon emission process and engineering. It features cutting-edge research articles, insightful reviews, perspectives, highlights, and news and views in the field of carbon. The article publishing charge is covered by the Tsinghua University Press. Carbon Future aims at being a leading journal in related fields.