Research On Preparation And Application In Electrocatalytic Ammonia Production Of Zirconium Based Nanomaterials

Currently,synthesis of ammonia based on electrochemical nitrogen reduction and nitrate reduction at room temperature and pressure has been paid increasing attention,which is regarded as promising green route for ammonia production.However,the sluggish electrochemical process hinders its wide application,so catalysts with high selectivity and high activity are indispensable to improve the performance of ammonia.Zirconium（Zr）based nanomaterials show great potential in the field of electrocatalysis because of their excellent physical and chemical stability and unique surface electronic structure.Therefore,this work carries out research on two aspects of catalyst modification and nitrogen source selection based on Zr-based nanomaterials,and the possible mechanisms of electrocatalytic reactions are investigated by density functional theory calculation.The main contents and experimental results are presented as follows:（1）Oxygen vacancies in ZrO₂ are beneficial to nitrogen adsorption and activation according to the theoretical calculations.Zirconia nanofiber with oxygen vacancies（ZrO₂（V_O）NF）is synthesized by electrospinning and annealing under hypoxia condition and applied in electrocatalytic nitrogen reduction.Compared with ZrO₂ nanoparticles with less contents of oxygen vacancies,ZrO₂（V_O）NF with abundant oxygen vacancy defects and large specific surface area,promotes nitrogen adsorption and electron transfer,thus improving the electrochemical performance of nitrogen reduction.（2）The electrocatalytic activity of zirconium nanofiber modified by copper（Cu-ZrO₂ NF）in nitrogen fixation is further studied.The influence of different impregnating ratios of copper on the surface structure and composition of catalysts are compared by various characterizations.A series of electrochemical tests are conducted,and the results indicate that the specific surface area,oxygen vacancy concentration and nitrogen adsorption properties are strongly dependent on the concentrations of infiltrated copper.When the ratio of copper is 6.3%,the catalyst achieves the highest ammonia productive rate.Theoretical calculations further confirm that the alternating pathway is suitable to Cu-ZrO₂ NF during nitrogen reduction reaction process,and the presence of Cu creates special charge transfer interface and lower desorption barrier.The cooperation between bonding and antibonding of Cu-N is beneficial to the activation of N≡N bond,thus inhibiting the hydrogen evolution reaction,and improving the NRR performance.（3）Considering the high dissociation energy of N≡N bond is not conducive to NRR,nitrate with relatively weak activation bond energy is selected as nitrogen source and reduced to ammonia.In alkaline environment,Cu-ZrO₂ catalyst achieves a high NH₃yield rate of 15.4 mg h^-1 mg^-1_cat.and the Faraday efficiency of 67.6%under the optimal potential condition.The significant improvement in ammonia production efficiency proves that the material system is more suitable for nitrate reduction system.Theory calculations show that the potenial determining step is only 0.49 e V when copper is loaded on the surface of zirconia.