Imagine a world where harmful industrial waste is not just reduced, but repurposed into something valuable. That vision is becoming a reality, thanks to new research from Washington University in St. Louis. A team led by Feng Jiao, the Lauren and Lee Fixel Distinguished Professor in the McKelvey School of Engineering, has developed a groundbreaking electrochemical method to convert nitric oxide (NO)—a major contributor to acid rain—into concentrated nitric acid (HNO₃), a widely used industrial chemical.
Published in Nature Catalysis, the study presents a low-energy, cost-effective approach that could reshape how industries manage nitrogen waste, while contributing to a circular economy.
“We’ve created an electrochemical solution that transforms NO, a toxic waste gas, into useful nitric acid,” said Jiao. “Our main focus is tackling emissions from mining operations, where nitric acid is heavily used to extract metals. Our system allows NO emissions to be converted on-site, then reused in the same process, creating a closed-loop system that’s both sustainable and economical.”
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The team’s method uses a carbon-based catalyst to drive NO oxidation, in combination with a single-metal oxygen reduction catalyst developed by Gang Wu, Professor of Energy, Environmental & Chemical Engineering at WashU. This enables the system to operate efficiently at near-room temperature, eliminating the need for high heat, harsh chemicals, or complex purification processes.
Designed as a modular, “plug and play” system, the technology can be deployed without major infrastructure investment or reliance on costly materials like precious metals. It is scalable for small- and medium-sized operations and maintains over 90% faradaic efficiency when using pure NO. Even at lower concentrations, it achieves more than 70% efficiency, making it adaptable to various industrial settings.
The system produces nitric acid at concentrations of up to 32% by weight—directly from NO and water—without added electrolytes or post-processing. This simplifies production while opening the door to cleaner, more efficient chemical manufacturing.
Beyond mining, the approach has promising applications across other industries and strong commercial potential. A techno-economic analysis conducted by the team shows that the process consumes less energy and cuts costs compared to conventional nitric acid production methods.
“Transforming pollutants into valuable products makes both environmental and economic sense,” Jiao noted. “The nitric acid we generate can go straight into mining or other chemical processes. We've already achieved impressive efficiency and purity, and our next steps involve optimizing performance and scaling up the technology for broader use.”
With continued development, the researchers aim to help establish a nitrogen circular economy—one that supports more sustainable agriculture, manufacturing, and resource management by turning industrial waste into a valuable resource.