Enhanced ammonia synthesis using surface microdischarge with metal-loaded nickel foam electrodes

• The SMD reactor enhances ammonia yields by reducing NH 3 decomposition. • Ni-Co/NF enhances the formation of reactive species in gas-phase reactions. • A correlation between acid sites and ammonia yield was established. • In situ FTIR characterization was conducted under plasma activation. • The Ni-Co catalyst promotes the hydrogenation of intermediates on the surface. Non-thermal plasma (NTP) offers a promising solution for decentralized ammonia synthesis under mild conditions. However, conventional NTP approaches often suffer from limited ammonia synthesis rate and energy yield. Here, we developed a novel water-electrode surface microdischarge (SMD) reactor using nickel foam (NF) as the high-voltage electrode to enhance ammonia synthesis. Different metals were loaded onto the NF (M/NF, M=Ni, Co, Ni-Co) and grown as nanowires/nanosheets on the NF surface, significantly increasing the NH 3 synthesis rate and energy yield. Notably, when Ni-Co/NF was used as the high-voltage electrode, the highest NH 3 synthesis rate of 3390 μmol g -1 h −1 was achieved, representing a 40 % increase compared to NF alone, with an energy yield of ∼ 0.79 g kWh −1 . Plasma diagnostics and catalyst characterizations revealed that in gas-phase reactions, Ni-Co/NF facilitated the formation of active species (N 2 *, N, H α, and NH), while in surface reactions, metal loading increased the number of acidic sites, promoting the generation of NH and NH 2 intermediates on the catalyst surface. In situ plasma-coupled Fourier transform infrared (FTIR) studies further highlighted the role of the Ni-Co/NF catalyst in plasma catalytic ammonia synthesis, emphasizing their ability to enhance the hydrogenation of intermediates and the dissociation of N 2 molecules. This study demonstrates a promising SMD-based plasma catalysis strategy for sustainable ammonia production and provides valuable insights into the interactions between plasma and catalyst, advancing the understanding the N 2 hydrogenation mechanisms.