Sustainable nitrogen fixation from synergistic effect of photo-electrochemical water splitting and atmospheric pressure N₂ plasma

Abstract

In this study, nitrogen fixation in the electrolyte was achieved by atmospheric pressure non-thermal plasma generated by a sinusoidal power supply (with an applied voltage of 10 kV and frequency of 33 kHz). Ammonia measurements on plasma exposed electrolyte at several working gas and purging gas conditions revealed that nitrogen plasma on the same gas environment is more favorable for plasma-assisted ammonia synthesis. In addition, photo-electrochemical water splitting was performed by irradiating UV light (316 nm) on a titanium dioxide semiconductor photo-anode to generate hydrogen donor in nitrogen reduction reaction. The amount of ammonia synthesized by this synergistic process of photo-electrochemical water splitting and nitrogen plasma is six times higher than that obtained by nitrogen plasma alone. An increase in the co-synthesized N O X concentrations and background contamination at reaction site reduces the ammonia synthesis rate and Faraday efficiency. However, the ammonia production efficiency was increased up to 72% by using a proton-exchange membrane which prevent the diffusion of oxygen evolved from water splitting into the plasma, and by reducing the axial distance between the plasma electrode and reaction site. The sustainable nitrogen fixation process reported herein can be performed at atmospheric pressure conditions without a direct input of hydrogen gas or any catalyst.

Recent Progress in Applications of Non-Thermal Plasma for Water Purification, Bio-Sterilization, and Decontamination

“…A few examples of thermal plasmas are corona discharge and electric arc [29]. At low pressure, n e of non-thermal atmospheric pressure plasma (NTAPP) is approximately 10 8 -10 14 cm −3 [29][30][31] and the electron-neutral impact energy is not sufficient to reach thermal equilibrium. Consequently, T g is close to room temperature [29], T e remains in the range of a few electron volts, and only a few watts of power are consumed [32][33][34][35].…”

“…Ghimire et al [62,63] discussed the variation of RONS with the gap distance, electrode separation, and plasma propagation length. Yue et al [64] and Lamichhane et al [31] studied the effects of working gas on the concentration of RONS. Similarly, Lim et al [65] and Nguyen et al [66] presented the effects of the applied voltage, frequency, and moisture on atmospheric pressure plasma.…”

Electrical and Optical Characterization of Gliding Arc Discharge (GAD) Operated at Line Frequency (50 Hz) Power Supply

“…The emission profile form 200 to 400 nm is mostly composed of reactive nitrogen as well as oxygen species. In our case, presence of (200-280 nm), OH (309 nm), N 2 second positive system (SPS) (311-380 nm), N 2 first negative system (FNS) around 400 nm [29] in the spectrum suggests that the discharge can form reactive nitrogen and oxygen species (RNOS) above the water during the preparation of Plasma Activated Water (PAW). The formations of these species are due to the collision of energetic electrons with nitrogen and oxygen molecules present in the ambient air.…”

“…As a result it contains more concentration of energetic electrons at lower voltage than that of air. These electrons can excite the particles to transit between the high-energy states and generate more active particles with high energetic electrons [29] resulting more T e in argon environment than in air.…”

Low-Temperature Plasma-Assisted Nitrogen Fixation for Corn Plant Growth and Development

“…The nitrogen fixation process is initiated by the disassociation of the nitrogen molecule (N ≡ N) [6]. The nitrogen triple bond is one of the strongest bonds because of its vibrational excitation energy being 1.5-4 eV (1.4 × 10 5 -3.8 × 10 5 J/mol) [6], bond dissociation energy approximately 9.1 eV (8.7 × 10 5 J/mol) [7], and ionization energy approximately 14.53 eV (1.39 × 10 6 J/mol) [8,9]. Sufficient energy must be supplied to break the bond for artificial nitrogen fixation.…”