Molybdenum Carbide Electrocatalysts for Electrochemical Synthesis of Ammonia from Nitrogen: Activity and Stability

Abstract

Ammonia production has increased from few thousand tons in 1908 to above 200 million tons per year today, revolutionizing the fertilizer industry thanks to the Haber-Bosch (HB) process. However, the HB process is highly energy intensive consuming about 1.4% of fossil energy generated worldwide and releasing 1.87 tons of CO2 per ton of ammonia produced. This further reduces ammonia’s scope as a carrier fuel for the hydrogen economy. Hence, finding alternative energy efficient ways to synthesize ammonia is important from more than one perspective. Ammonia synthesis from its constituent nitrogen and hydrogen gases is mainly hampered by the nitrogen reduction reaction (NRR) due to the strong N≡N bond (945 kJ mol−1). Electrochemical synthesis (ES) routes in this regard offer a milder approach. However, ES of ammonia under different temperatures, utilizing different electrolytes and catalysts has not yet reliably produced ammonia at viable rates and efficiencies. We report an origami-like Mo2C cathode catalyst for NRR that achieved a maximum synthesis rate of 2.16 × 10−11 mol cm−2 s−1 and a faradaic efficiency of 1.8% at 30 °C using Nafion-212 as electrolyte. Origami-like morphology containing numerous kinks appears to improve electrocatalytic activity and show a promising route for fabricating NRR catalysts with higher catalytic activity.

Electrocatalytic nitrogen reduction directed through the p-band center of boron on BSAC@Mo2C

“…18 Mo clusters and SACs, on the other hand, require a conducting/semi-conducting support for further usage as electrocatalysts. 19,20,22,27 In this regard, Mo-based 2D materials such as MoS 2 , 24,[28][29][30][31] MXenes (Mo 2 C) [32][33][34] and MBenes (Mo 2 B 2 ) 35,36 are appealing electrocatalysts owing to their high electrical conductivity and presence of active Mo metal centres. These 2D materials not only show high hydrophilicity, stability and conductivity but are interesting from the catalytic aspect of nitrogen reduction as the Mo metal is accessible to the nitrogen molecule.…”

Tailored p‐Orbital Delocalization by Diatomic Pt‐Ce Induced Interlayer Spacing Engineering for Highly‐Efficient Ammonia Electrosynthesis

“…[1] Currently, the ammonia synthesis methods of the traditional Haber-Bosch process and electrochemical nitrogen reduction reaction (eNRR) have limited application conditions, such as harsh operating requirements and highly stable nonpolar NN bonds with high dissociation energy (945 kJ mol −1 ). [2][3][4][5] Consequently, the electrochemical nitrate reduction reaction (eNO 3 RR) to convert nitrate into ammonia is generally a more efficient synthesis scheme. It is considered one of the best pathways to an ammonia economy.…”

Electrocatalytic activity of CoFe1.9Mo0.1O4-Ce0.8Gd0.18Ca0.02O2-δcomposite cathode for ammonia synthesis from water and nitrogen

“…indirect hydrogen storage medium). As a fuel, it is anticipated that ammonia will play a vital role in the future owing to its ease of liquefaction, storage and transportation, as well its high energy density (11.5 MJ L À1 ) compared to hydrogen (4.5 MJ L À1 ) at 15°C and 690 bar (Lan et al, 2012;Qing et al, 2016;Ramaiyan et al, 2020). Therefore, ammonia is used as a potential fuel for direct ammonia fuel cells (DAFCs).…”

“…In this context, several materials have been used as electrocatalysts for the ammonia synthesis including; precious metals (e.g. Pt, Ru) (Skodra and Stoukides, 2009;Yun et al, 2015), perovskites (Kosaka et al, 2017;Wang et al, 2010;Yun et al, 2015), spinel (Amar et al, 2011a), nitride (Amar et al, 2015a) and carbide (Ramaiyan et al, 2020). However, the electrocatalyst that selectively reduces nitrogen into ammonia and simultaneously suppresses the competing hydrogen evolution reaction (HER) remain elusive (Hao et al, 2019).…”