DARPA moves to decentralize critical nitric acid production

A top-secret US government body called the Defense Advanced Research Projects Agency (DARPA) has launched a new solicitation seeking proposals for a high-rate, energy-efficient method of producing nitric acid directly from air and water.

The initiative, known as the High-Efficiency Nitrogen Oxidation, or HNO3 program, is aimed at protecting critical U.S. defense-industrial supply chains and reshaping how energetics are produced in contested environments.

According to DARPA, the agency is requesting “innovative proposals in the foundational technologies to enable high-rate, energy efficient, decentralized nitric acid manufacturing to protect critical supply chains in the defense industrial base.”

The notice states that DARPA is seeking research approaches that “enable revolutionary advances in science, devices, or systems,” and explicitly excludes work that would result only in evolutionary improvements.

The agency outlines nitric acid as a chemical at the center of both civilian and military production. The background section notes that global annual production reaches between 60 and 70 million tons, with the majority used for fertilizer. Nitric acid also plays a central role in synthesizing explosives and propellants for defense purposes, and remains essential for producing polymers such as nylon and polyurethane.

DARPA underscores supply-chain vulnerability tied to the traditional Haber-Bosch/Ostwald process, which begins with ammonia. The notice explains that “the United States’ reliance on imported ammonia… represents a significant vulnerability,” adding that roughly 2.5 million tons are imported each year. A disruption to this supply chain, the document says, would carry broad consequences “ranging from munitions production to food supply.”

Current industrial nitric acid production is energy intensive, requiring about 600 kJ per mole—over six times the thermodynamic minimum for the nitrogen-oxidation reaction. DARPA explains that energy demands increase sharply as production scales down, making distributed nitric acid manufacturing inefficient under the traditional model. The agency notes that direct nitrogen oxidation via plasma offers limited efficiency and shows no clear path to rapid improvement. Early electrochemical methods have demonstrated potential but remain constrained by low production rates and reaction competition that reduces efficiency.

The HNO3 program is designed to explore a new route that bypasses ammonia entirely. The notice emphasizes that “direct nitrogen oxidation via electrochemical approaches” has shown early promise, while also acknowledging technical obstacles tied to catalysts, reaction pathways, and competing side reactions. DARPA cites evidence that rate and efficiency could be improved through dynamic catalysis, reactor redesign, improved electrolytes, and better nitrogen solubility.

According to the program description, HNO3 is structured as a 42-month effort divided into a 12-month Phase 1a, a 12-month Phase 1b option, and an 18-month Phase 2 option. Phase 1 aims to produce a sub-scale reactor capable of generating one liter per day of lab-grade nitric acid using only air and water. Phase 2 culminates in a field demonstration of a system capable of producing 50 liters per day. DARPA outlines detailed performance metrics for each phase, including reaction rates, energy efficiency, production rates, and system power limits.

Catalyst development is a major component of the effort. Performers must develop catalysts that suppress unwanted oxygen evolution while promoting nitrogen oxidation. Reactor design must address mass transport, nitrogen solubility, and overall size, weight, and power. DARPA will use an independent verification and validation team to test catalysts and evaluate reactor performance at multiple stages.

Nitric acid is central to U.S. munitions, industrial chemicals, and global food production. The country’s reliance on imported ammonia creates a supply-chain risk that could affect both defense readiness and civilian needs.