Ammonia is an essential gas in agriculture and industry, and it has the potential to serve as a zero-carbon fuel for various energy conversion and storage technologies. Unfortunately, the traditional methods for ammonia production are very energy-consuming, accounting for about 1.8% of the world’s CO2 emissions. A research team has turned its attention to spinel cobalt oxides, uncovering how enhancing and understanding these catalysts could help tackle this issue.
A major advancement has been made by researchers in creating catalysts for the electrochemical nitrate reduction reaction (eNO3RR) to convert nitrate into ammonia. This process holds significant potential for sustainable energy, agriculture, and industrial uses.
Ammonia is vital for food production globally and shows promise as a zero-carbon fuel because of its high energy density, non-polluting combustion products, and pre-existing storage and transport systems. The existing approach to make ammonia, known as the Haber-Bosch process, is energy-demanding and generates around 1.8% of global CO2 emissions.
In their latest research, the team investigated spinel cobalt oxides (Co3O4), a new class of cost-effective, highly active, and selective catalysts for eNO3RR. They developed various Co3O4 nanostructures with distinct crystallographic facets — {100}, {111}, {110}, and {112} — to see how these facets impact ammonia production performance. The results showed that the {111} facet of Co3O4 performed exceptionally well, achieving a remarkable ammonia Faradaic efficiency of 99.1% and a yield rate of 35.2 mg h−¹ cm−².
“Our results indicate that the {111} facet of Co3O4 is highly effective at converting nitrate to ammonia,” stated Dr. Heng Liu, co-first author of the study and a Specially Appointed Assistant Professor at the Advanced Institute for Materials Research (WPI-AIMR), Tohoku University. “This efficiency is attributed to the rapid creation of oxygen vacancies and Co(OH)2 on this facet, greatly improving the catalyst’s performance.”
Moreover, the team identified that the catalyst undergoes changes during the reaction, transitioning from Co3O4 to a form with oxygen vacancies, evolving into a Co3O4−x-Ov/Co(OH)2 hybrid, and finally stabilizing as Co(OH)2. This transformation was most evident on the {111} facet, further contributing to its outstanding performance.
“Understanding the structural changes we observed is vital for comprehending the catalyst’s activity,” added Professor Hao Li, the corresponding author and an associate professor at WPI-AIMR. “These findings will assist in designing more efficient catalysts by optimizing exposed facets.”
Beyond its agricultural significance, ammonia is a potential zero-carbon fuel and an important element in energy conversion and storage. The eNO3RR serves as a sustainable substitute for the Haber-Bosch process, converting nitrate waste into valuable ammonia while also supporting environmental cleanup efforts.
“This research establishes a strong groundwork for developing more effective and sustainable catalysts,” Li noted. “As we progress, our aim is to regulate the final stages of the catalyst’s transformation to boost its activity, selectivity, and durability.”
This breakthrough in the comprehension and optimization of Co3O4 catalysts might lead to cleaner and more sustainable industrial methodologies, aiding global initiatives to reach carbon neutrality by the 2050s.
