Researchers at Princeton University and the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have uncovered a surprising new pathway for ammonia synthesis by combining non-thermal plasma activation with tungsten oxide/oxynitride catalysts. In our earlier news coverage, we explored how this discovery not only slashes catalyst fabrication time from two days to 15 minutes, but also reveals an unexpected heterogeneous interfacial complexion (HIC) structure that could redefine the design rules for plasma-responsive catalytic materials.
Now, we sat down with Professor Yiguang Ju (Princeton University / PPPL) to explore the origins of this concept, the role of vacancies and plasma chemistry in enabling ammonia formation at ambient conditions, and the broader implications for distributed, renewable-powered ammonia production. In this interview, he walks us through the experimental challenges, the diagnostic techniques that validated the HIC structure, and the technological hurdles that must be overcome to scale this approach toward practical reactors.
You can view the full research this interview pertains to here:
Zhang, Z., Kondratowicz, C., Smith, J., Kucheryavy, P., Ouyang, J., Xu, Y., Desmet, E., Kurdziel, S., Tang, E., Adeleke, M., Lele, A. D., Martirez, J. M., Chi, M., Ju, Y., & He, H. (2025). Plasma-Assisted Surface Nitridation of Proton Intercalatable WO 3 for Efficient Electrocatalytic Ammonia Synthesis. ACS Energy Letters, 10(7), 3349–3358. https://doi.org/10.1021/acsenergylett.5c01034
The following interview is presented unedited to preserve his original responses and provide an unfiltered look into how the team combined plasma physics, catalysis, and advanced microscopy to uncover a catalyst structure that may accelerate progress toward carbon-neutral ammonia synthesis.
Acknowledgments from the team: The collaborative effort of this study is supported by the US National Science Foundation (Award#: 2428523). HH would also like to acknowledge the support of Rutgers Research Council. YJ would like to acknowledge the support from the DOE Plasma-Enhanced H2 Production (PEHPr) Energy Earthshot Research Center (EERC) at Princeton Plasma Physics Laboratory under contract DEAC0209CH11466 for plasma reactors and DOE FES DE-SC0025371 grant for diagnostics. Microscopy was partially conducted at the Center for Nanophase Materials Science, Oak Ridge National Laboratory, supported by the U.S. Department of Energy, Office of Science, and in part at the Analytical Instrumentation Facility (AIF) at NCSU, which is supported by the State of North Carolina and the National Science Foundation (award number ECCS-2025064). Participation of Princeton Plasma Physics Laboratory, a national laboratory operated by Princeton University for the U.S. Department of Energy under Prime Contract No. DE-AC02-09CH11466, is made possible via the Strategic Partnership Projects program.
What inspired your team to combine plasma activation with tungsten oxide/oxynitride catalysts, and how did you arrive at that heterogeneous interfacial complexion (HIC) structure as a promising design?
Non-thermal plasma enables new reaction pathways through plasma-generated radical species and excited molecules, thereby lowering the synthesis temperature of ammonia and improving energy efficiency. Moreover, plasma-assisted ammonia synthesis offers a promising solution for large-scale, long-duration renewable electricity storage and decarbonization, presenting an exciting opportunity for our team. We developed the concept of plasma activation with tungsten oxide for ammonia synthesis based on two hypotheses. First, tungsten oxide can suppress the hydrogen evolution reaction during water electrolysis by promoting the formation of surface-bound hydrogen atoms instead of H₂, thereby increasing faradaic efficiency. Second, tungsten oxide can form tungsten nitride or oxynitride under nitrogen plasma, potentially reducing the energy barrier for nitrogen adsorption and dissociation. Unexpectedly, we discovered the formation of a heterogeneous interfacial complexion (HIC) on the tungsten oxide surface. Using high-resolution transmission electron microscopy, we observed an amorphous tungsten nitride/oxynitride HIC structure—a surprising and fortunate finding.
The new method reduces catalyst fabrication time from about two days to 15 minutes; what process steps are eliminated or accelerated, and how is catalyst quality still maintained?
The synthesis of tungsten oxide nanostructures via the conventional hydrothermal method is typically slow due to the temperature limitation of water. By introducing microwave interaction with a carbon support, the surface temperature can be elevated, significantly accelerating the process and dramatically reducing the synthesis time.
How does the production rate or yield of ammonia achieved with the plasma-activated HIC catalyst compare quantitatively to those of standard thermal Haber-Bosch or other plasma-catalytic systems under similar conditions?
The ammonia production with plasma can be done at room temperature and atmospheric pressure. However, the Haber-Bosch process is high temperature and high pressure (200-300 atm). Therefore, the current plasma assisted ammonia synthesis rate is still far lower than Haber-Bosch. However, if we can design an efficient plasma-responsive catalysis using the HIC structure, plasma assisted ammonia synthesis has the potential to be more efficient for distributed ammonia synthesis with renewable electricity.
What are the primary energy and operational cost trade-offs when using this low-temperature plasma method, particularly considering electrode configuration, plasma power input, and catalyst stability?
The advantages of the low temperature plasma synthesis method are room temperature, atmospheric pressure, and small-scale distribution production. It can also be run intermittently to adjust peaks of renewable electricity. Since the HIC structure can be regenerated by plasma, it has a higher stability compared to conventional nitride catalysts. The electrode scale-up remains a big challenge because of the plasma instability at atmospheric pressure. Novel plasma sources such as the pulsed ferroelectric discharge need to be developed.
How have you characterised the role of nitrogen vacancies and active hydrogen sites on this catalyst in promoting ammonia formation, and what diagnostics (spectroscopy, microscopy) were crucial in verifying them?
The nitrogen and oxygen vacancy can be characterized by using X-ray photoelectron spectroscopy by examining the charge numbers of tungsten, oxygen, and nitrogen atoms. In addition, high resolution TEM can also see the vacancy formation. In situ XPS and high resolution TEM are critical to verifying them.
In scaling towards practical, distributed ammonia production, what challenges do you foresee in reactor design, gas handling, and durability of the catalyst under continuous plasma exposure?
The biggest challenges for practical production in commercial scale are hydrogen transport across the electrode and the plasma stability and chemistry control.
Looking forward, what are your next steps in refining this technology? For example, altering catalyst compositions, optimizing plasma parameters, integrating renewable electricity, or deploying pilot reactors?
We aim to address the above three major challenges. One is to design a new plasma responsive catalyst which can enhance the formation of HIC. The second is to design an electrode membrane which can transport H atom more efficiently. The third is to develop a novel plasma source which can control plasma chemistry and plasma-surface interaction.
Hassan graduated with a Master’s degree in Chemical Engineering from the University of Chester (UK). He currently works as a design engineering consultant for one of the largest engineering firms in the world along with being an associate member of the Institute of Chemical Engineers (IChemE).
