Molybdenum carbide has immense potential as an active catalyst for reaction systems such as synthesis of important chemicals like ammonia. However, the carbide is not used as a commercial catalyst or support as the current synthesis processes produce low surface area material or have contaminants such as excess carbon and surface and chemisorbed oxygen. Moreover, attempts to refine the synthesis pathways are usually not supported by any thermochemical modeling. In this study, a facile and reproducible method to synthesize high surface area molybdenum carbide was developed with the help of thermochemical modeling to better understand molybdenum‐carbon phase behavior. We have synthesized 2‐5 nm particles of MoxC with surface areas of up to 360 m2/g as characterized using a variety of techniques including X‐ray diffraction and electron microscopy.

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Ammonia synthesis by the Haber-Bosch (HB) process paved the way for rapid increase in crop production and sustained the needs of population growth. However, HB process is cost and energy intensive and releases about 260 million tons of CO2 every year. Considering the threat associated with CO2, finding an alternative, cheap and environmentally benign methodology for ammonia synthesis is highly desirable. Electrochemical synthesis through renewable electricity offers a viable alternative, although the synthesis rates reported are far from adequate. This is mainly due to the strong NºN bond (941 kJ mol-1) that poses a severe challenge for mild condition synthesis of ammonia. Several attempts toward electrosynthesizing ammonia at low and high temperatures included a variety of electrode materials ranging from glassy carbon electrode to precious metals and different proton and oxide ion conducting electrolytes [1]. Rates on the order of 10-9 mols-1cm-2 have been reported for both low and high temperature systems. This rate is still three orders of magnitude lower than the required rates for commercialization. We have achieved ammonia synthesis rates of 1x10-8 mols-1cm-2 at 200 °C in a simple fuel cell configuration using a Sn2P2O7 – nafion composite membrane and Pt based catalyst [2]. Here we will present our results obtained with alternate electrocatalysts and discuss the role of applied potential and back pressure measurements on the synthesis rates of ammonia. References V. Kyriakou, I. Garagounis, e. Vasileiou, A. Vourros, and M. Stoukides, Catalysis Today, 2017, 286, 2-13. K. P. Ramaiyan, S. Maurya, Y. S. Kim, F. H. Garzon, R. Mukundan, C. R. Kreller, Meeting Abstracts, ECS 231st meeting. Issue 31, 1464-1464. Acknowledgements This project is supported by ARPA-E under Award No. DE-AR0000687.

Ammonia offers potential as a carbon-free energy carrier with a high hydrogen content and if fully oxidized, the products nitrogen and water are environmentally benign. It also serves as the major feedstock for fertilizer production and a building block for nitrogen containing chemicals and polymers. Ammonia is readily liquefied and conveniently stored in low cost steel tanks. It may function as a high energy density storage medium for hydrogen produced by renewable energy derived electricity. Ammonia synthesis is currently carried out in a few very large Haber-Bosch plants, mostly fueled from natural gas. The current large-scale Haber-Bosch (H-B) technology needs to run at constant inputs of energy and reactants. The economics dictate very large process reactors and separation systems, consequently the technology does not downscale well to small sized plants, nor does it work with interruptible energy supplies. Even though the ammonia synthesis efficiency can be considered low at ~70%, these efficiencies are only obtained in large-scale integrated facilities. Highly efficient ammonia synthesis in small-scale H-B systems does not exist, thus stimulating research towards a low temperature and pressure processes. Electrosynthetic pathways for NH3 production theoretically offer higher efficiency and scalability but, the challenges are quite foreboding as the dinitrogen triple bound is extremely stable and most known nitrogen dissociation catalysts are deactivated by oxygen or water [1]. We are currently engaged in a DOE ARPA-e funded program to develop electrochemical methods for ammonia synthesis. We are developing and evaluating intermediate NH3 synthesis processes, one based on the spontaneous electro-reduction of nitrogen in lithium ion systems where the potential for lithium is close to metal deposition and the subsequent formation of lithium nitride. The other utilizes proton conducting, anhydrous metal pyrophosphate/polymer composite membranes for protonation of nitrogen [2]. The advantage of the lithium process is the reaction is autocatalytic, however the reaction of Li3N with water to form NH3 and LiOH is exothermic, with an amount of enthalpy of -581.62 kJ mol-1 and thus presents challenges for the design of an energy efficient process. The direct protonation process is thermodynamically favorable at modest potentials near hydrogen evolution potentials, however it requires suitable electrocatalysts that dissociate dinitrogen but inhibit the parasitic hydrogen evolution reaction (HER). Using proprietary Li ion solid electrolytes, we have demonstrated lithium nitride formation at high coulombic efficiency and ammonia evolution upon hydrolysis. We have also demonstrated intermittent ammonia production at >8% efficiency using Pt catalysts, however the coulombic efficiency is limited by HER. We are exploring the use of carbon supported Ru, MoxC and Ru/MoxC catalysts to limit current efficiency losses due to HER. References: J. Van der Ham, M. T. Koper , D. G. Hetterscheid , Chem. Soc. Rev., 2014, 43, 5183 F. Garzon, C. R. Kreller, M. S. Wilson, R. Mukundan, H. Pham, N. J. Henson, M. Hartl, L. Daemen, ECS Transactions 2014, 61, 159-168.

Theoretical and computational approaches play a key role in developing and optimizing new materials and devices for energy storage and conversion applications. Here we use several examples to illustrate how theory and computations can help accelerate the design and development of materials for fuel cell and electrolyzers by addressing the issue of their durability. We emphasize computational studies of different processes that can lead to decreased durability of fuel cells and electrolyzers under operating conditions. These studies, for instance, include catalyst corrosion [1], the change in the catalyst structure at different cell potentials and pH [2], poisoning of the catalyst with a crossover fuel or fragments from the ionomeric binder [3,4], and phosphoric acid leaching in acid-doped high temperature fuel cell polymer electrolytes [5].We first illustrate how combination of experimental and first principles thermochemical data can be used to predict and understand the stability of catalytic materials in aqueous media as a function of pH, cell potential, and temperature. Examples will include transition metal carbides and nitrides [1] and the size effect on the stability diagrams of precious metal catalysts [2]. Secondly, we discuss how first principles calculations can be used in the design of high temperature membrane fuel cells. The specific example will include a study of cluster energetics between phosphoric acid, water, and proton-accepting or hydroxide-donating bases, which are explored in the design of acid-doped polymer electrolytes [5].[1] I. Matanovic, F. H. Garzon, N. J. Henson, J. Phys. Chem. C, 115, 10640–10650 (2011).[2] I. Matanovic, F. H. Garzon, J. Electrochem. Soc. 167, 046518 (2020).[3] D. Sebastián, A. Serov, I. Matanovic, K. Artyushkova, P. Atanassov, A.S. Aricò, V. Baglio, Nano Energy, 34, 195-204 (2017).[4] I. Matanovic, S. Maurya, E. J. Park, J. Y. Jeon, C. Bae, Y. S. Kim, Chem. Mater, 31, 11, 4195-4204 (2019). [5] I. Matanovic, A. S. Lee, Y.-S. Kim, J. Phys. Chem. B, 124, 7725-7734 (2020).