N₂ Fixation Enabled By Mechanical-Energy-Driven Triboelectric Plasma Jet

Artificial N₂ fixation,one of the most crucial chemical reactions,enables food growth for 48%of the global population and has made indelible contributions to the development of human civilisation.In the process of industrialisation,the Haber–Bosch（H–B）process is the most important artificial nitrogen-fixation method;the nitrogen-fixation products produced in this process promote the development of agriculture.However,the H–B process requires high temperatures and pressures and harsh reaction conditions,resulting in an urgent need to develop an environment-friendly nitrogen-fixation method to replace the traditional H–B process.Mechanical-energy-driven N₂ fixation using air as the raw material is a promising and ideal way to synthesise N-containing compounds.Mechanical energy,including water,wind,tidal and wave energy,is one of the most common renewable energies,with abundant reserves and numerous sources.However,its intermittency and irregularity are difficult to be compatible with the harsh conditions required for traditional large-scale H–B processes,resulting in a lack of direct use of mechanical energy for N₂ fixation.The triboelectric nanogenerator（TENG）is a recent innovative device that efficiently converts mechanical energy into electrical energy,offering a promising method for converting mechanical energy into chemical energy.To form a mechanical-energy-driven electrochemical N₂-reduction system,one common approach is to couple a TENG with electrochemical N₂-reduction devices.However,owing to a high output voltage of TENGs and low voltage of the electrochemical system,low solubility of N₂ in aqueous solutions,and competitive hydrogen-evolution reactions,the activity of the electrochemical N₂-reduction system driven by TENGs is extremely low(approximately 0.01–0.21μmol h^-1).To address these challenges,triboelectric plasma can be generated using the high voltage from a TENG,which can excite gases such as N₂ and O₂.The triboelectric plasma can directly connect the TENG and the chemical reaction,reducing the energy loss caused by electrical energy management and storage.Moreover,the high substrate concentration and fast reaction speed in gas plasma effectively solve the problems of low substrate concentrations and hydrogen evolution in aqueous solutions.Mechanical-energy-driven triboelectric plasma has several advantages,including the ability to switch at any time,mild reaction conditions,fast response speeds and potential compatibility with intermittent and irregular mechanical energy.Therefore,it is expected to provide a small-scale N₂-fixation method with high efficiencies and zero CO₂ emissions as no fossil fuels are required.The research content of this thesis mainly includes the following two parts:1.Development of a mechanical-energy-driven jet plasma N₂-oxidation-reaction system.This system comprises two components,namely,a friction nanogenerator（TENG）and a jet-type triboelectric plasma N₂-oxidation reactor.The high voltage output of the TENG creates gas discharge and plasma.The electrical output curve of the jet plasma N₂-oxidation-reaction system varies with parameters such as the speed,distance,discharge mode,N₂/O₂ gas ratio and N₂/O₂ gas flow rate.The experiments show that the highest activity of the N₂-oxidation reaction is 4.82μmol h^-1 when the discharge distance is 2.0 mm,discharge mode is negative and TENG rotation speed is 300 rpm.The highest efficiency of converting electrical energy to chemical energy is 4.92%;the lowest energy consumption is 1.76 MJ mol^-1 N^-1.The system enables nitrogen fixation at normal temperatures and pressures and exhibits good compatibility with fluctuating mechanical energy and gas flow rates.The efficiency of converting mechanical energy to chemical energy of the N₂-oxidation reaction is 0.11‰,as measured by the dynamic-torque-testing system.2.Investigation of the mechanism of the jet plasma N₂-oxidation reaction driven by the TENG.The experiment using ¹⁵N₂ and ¹⁸O₂ isotopes and the control experiment demonstrate that the N and O atoms in the product NO_X originate from N₂ and O₂ in the raw material rather than from the pollution in the raw material or the system.The triboelectric jet plasma reactions exhibit higher conversion efficiencies and lower energy consumptions compared to those of static and flow triboelectric plasma reactions.The results indicate that gas flow and nozzles play a crucial role in N₂ oxidation.Emission spectra and plasma simulation results suggest that the low average energy of electrons in the plasma is responsible for the high activity and efficiency of mechanical-energy-driven triboelectric plasma,which facilitates the vibrationally excited dissociation process of low energy barriers.Herein,a jet-type triboelectric plasma system is constructed that is driven by mechanical energy to achieve nitrogen fixation at normal temperatures and pressures.Our reaction system is compatible with fluctuations in mechanical energy and gas velocity.The N₂-oxidation rate obtained using this system is 4.82μmol h^-1,which is the highest activity value reported for N₂-fixation systems driven by TENGs at normal temperatures and pressures.The energy consumption is 1.76 MJ mol^-1 N^-1,which is the lowest energy consumption reported for plasma N₂-oxidation reactions at room temperature and pressure.The emission spectra and plasma simulation results show that the high activity and efficiency of mechanical-energy-driven triboelectric plasma is due to the low average energy of electrons in the plasma,which facilitates the vibrationally excited dissociation process of low energy barriers.Finally,wind-driven N₂-oxidation reactions were conducted using wind energy in the environment;it is found that our system can efficiently utilise this wind energy.This study provides an effective means and strategy for nitrogen fixation using mechanical energy.