Plasma-Electrocatalytic Nitrogen Reduction for Ammonia Synthesis

Electrochemical nitrogen reduction under ambient conditions is constrained by the kinetic inertness of N 2 and competition from the hydrogen evolution reaction. Here, we report an integrated plasma–electrolysis membrane-electrode assembly that couples a microstructured nonthermal surface discharge directly to a gas-diffusion cathode, enabling in situ generation and delivery of vibrationally excited N 2, N 2 (ν), to the electrocatalytic interface. Among 14 metal catalysts screened, Ag provided the best balance of activity and selectivity, achieving an NH 3 production rate of 7.7 ± 0.8 nmol s –1 cm –2 with an electrochemical Faradaic efficiency of 86 ± 14% at −0.54 V versus RHE under atmospheric pressure and room temperature. Plasma/electrolysis on–off controls and 15 N 2 isotope-labeling experiments establish that NH 3 formation requires simultaneous plasma activation and electrochemical polarization and originates from the supplied N 2 . Plasma-kinetic modeling indicates strong vibrational excitation in the discharge, with a calculated effective vibrational temperature of approximately 4300 K and 11.8% of N 2 occupying levels (ν = 4–8). Transport modeling further suggests that these comparatively long-lived excited states persist to the membrane–catalyst region. In situ Raman spectroscopy reveals N–N-containing surface intermediates only during coupled operation, while density functional theory shows that vibrational excitation lowers the free-energy requirement for the initial hydrogenation of N 2 to *NNH and shifts the rate-determining step in a catalyst-dependent manner. These findings establish vibrational-state engineering as a strategy for coupling non-equilibrium molecular activation with electrocatalysis for distributed ammonia synthesis under ambient conditions.