Solar-powered systems convert waste into ammonia and glycolic acid

A team of researchers at Unist has developed a new technology that uses solar energy to eliminate carbon dioxide emissions while also producing key components of cosmetics, ammonia and glycolic acid.

A team, co-led with Seungho Cho and Professor Myoung Hoon from UNIST’s Faculty of Materials Science and Engineering, Song, has created a method for converting nitrate contaminants found in wastewater into ammonia through an electrochemical reaction. The process also reduces carbon emissions while generating glycolic acid from plastic waste and effectively converting waste into valuable products.

The findings are published in the journal Nano Letters.

Ammonia is the second most produced inorganic compound in the world, tracking only sulfuric acid, and its production accounts for 1.4% of its carbon dioxide emissions. This underscores the urgent need for eco-friendly alternatives to the traditional Harbor Bosch process.

The researchers have developed a solar electro-electrocatalytic system that uses solar energy to generate ammonia at the cathode and glycolic acid at the anode.

In this system, nitrite (NO2-) in the wastewater is reduced at the anode, but ethylene glycol extracted from plastic waste is oxidized to glycolic acid at the cathode. Because nitrate (NO3-) and nitrite coexist with wastewater, converting nitrite to ammonia requires significantly less energy and time compared to nitrate, optimizing overall efficiency.

The system achieved an impressive energy efficiency of 52.3%, achieving the highest energy efficiency reported based on anode performance alone, with ammonia production rate reaching 146 μmol/cm2H. This showed a 46% improvement over previous records, surpassing the US Department of Energy’s commercialization standard of 58.72 μmol/cm2H.

Researchers have developed an efficient catalyst (RUCO-NT/CF) that selectively reduces nitrites, further increasing the effectiveness of the system. We specifically targeted nitrites and circumvented energy-intensive oxygen evolution reactions, and we fine-tuned the process for better results.

The perovskite solar cells used in the system were designed for high electrical power and durability. As the current density of solar power generation increases, the speed of ammonia production also increases.

Professor Song said, “This study highlights the potential for carbon dioxide-free electrochemical ammonia production using perovskite solar cells that outweigh commercial silicon solar cells.”

The team evaluated the commercialization potential of the technology and found that solar ammonia production rates of 114 μmol/cm2H can be achieved using electrolytes that simulate low-level radioactive wastewater and extract PET materials.

Professor Cho said, “Our research provides a sustainable carbon-neutral energy solution by simultaneously producing green ammonia and glycolic acid from sunlight and waste.”