Green ammonia synthesis using CeO 2 /RuO 2 nanolayers on vertical graphene catalyst via electrochemical route in alkaline electrolyte.

The electrochemical synthesis of ammonia at ambient temperature and pressure has the potential to replace the conventional process for the production of ammonia. However, the low ammonia yield and poor long-term stability of catalysts for the synthesis of ammonia hinders the application of this technology. Herein, we endeavored to tackle this challenge by synthesizing 3-D vertical graphene (VG) on Ni foam via a one-step, low-temperature plasma process, which offered high conductivity and large surface area. Subsequently, the vertical graphene on Ni foam was loaded with nanolayers of ruthenium oxide (RuO ₂ , ∼2 nm) and cerium oxide (CeO ₂ , <20 nm) nanoparticles via magnetron sputtering. The incorporation of nanoparticle layers (RuO ₂ and CeO ₂ /RuO ₂ ) on VG significantly increased the NH ₃ yield in KOH electrolyte. Finally, the performance and long-term stability of this composite material were successfully demonstrated by the addition of CeO ₂ /RuO ₂ nanolayers on the VG electrocatalyst. The catalyst achieved an excellent performance with a high ammonia synthesis yield of 50.56 μg mg _{total cat.} ^-1 h ^-1 (1.11 × 10 ^-10 mol cm ^-2 s ^-1 ) during the performance evaluation period of 36 h. This observation was also verified by density functional theory calculation, where CeO ₂ exhibited the best catalytic performance compared to RuO ₂ and pristine graphene.