Assessing the efficacy of an atmospheric air DC glow discharge system for sustainable nitrogen fixation: A vibrational coherent anti-Stokes Raman scattering study

In addressing the substantial greenhouse gas emissions produced by the energy-intensive Haber-Bosch (HB) synthesis, this study investigates the viability of sustainable nitrogen fixation (NF) via low-temperature plasma systems energized by renewable sources. Utilizing vibrational coherent anti-Stokes Raman scattering (CARS) as a diagnostic tool, we probed the nitrogen rovibrational temperature and population dynamics within a DC glow discharge in atmospheric air, a setting with considerable promise for eco-friendly fertilizer production. Besides, density for atomic N, O, and NO molecule was quantified by laser-induced fluorescence (LIF) or two-photon absorbed lase-induced fluorescence (TALIF) methods. Our findings reveal a quasi-equilibrium between rotational and vibrational energy states in the DC glow discharge environment, reaching an approximate value of 3500 K at the discharge core. The discharge parameters, discharge current, air flow rate, and discharge gap influence the rovibrational temperature, density distribution of species of interest, and the NF energy cost. However, the influences induced by these parameters are of limitations. Further analysis implies that the high gas temperature and its induced vibrational-rotational (V-R) and vibrational-translational (V-T) energy exchange are mainly responsible for the non-ideal NF energy cost.