Preparation Of Carbon-based Catalysts For Electrochemical Ammonia Synthsis

Ammonia is not only an important chemical for the production of fertilizers,but also known as a promising clean energy carrier because of its high hydrogen content,and ease storage and transportation.At present,the Haber-Bosch process is the most important strategy for the ammonia synthesis,but this technology can consume a large amount of energy and emit abundant,which does not meet the requirements of sustainable development.Electrocatalyitic nitrogen reduction reaction（NRR）is regarded as a very attractive strategy for ammonia synthesis because it can be driven by sustainable electricity to produce ammonia using nitrogen gas and water as precursors under ambient condition.Carbon materials have been considered as advanced electrocatalysts in the electrocatalytic field due to their large specific surface area,well-developed porosity and excellent electrical conductivity.Based on the above consideration,this thesis mainly focuses on the design and development of porous Fe₂O₃nanorod array grown on carbon cloth,phosphorus-doped graphene and Pd nanoparticles decorated phosphorus-doped grapheme for the electrochemical ammonia synthesis.The main research contents and results of this thesis are as follows:（1）We synthesize Fe OOH nanorod arrays on carbon cloth by a simple hydrothermal method using iron nitrate nonahydrate and anhydrous sodium sulfate as precursors,followed by calcination in an N₂atmosphere to obtain self-supporting porous Fe₂O₃nanorod array on carbon cloth（p-Fe₂O₃/CC）.Benefiting from the self-supported feather,porous structure and excellent electrical conductivity,the p-Fe₂O₃/CC is served as an excellent catalyst for the electrochemical ammonia synthesis,exhibiting high ammonia yield(6.78μg·h^-1·cm^-2_cat.),Faraday efficiency（7.69%）and good stability.This work provides a facile method for the large-scale synthesis of catalysts,which has a high development prospect in the field of electrochemical synthesis of ammonia.（2）Phosphorus-doped grapheme（PG）has been prepared by high-temperature calcination using graphene oxide as a raw material and phosphoric acid as a phosphorus dopant.Changing the amount of phosphoric acid precursor can regulate the phosphorus amount in graphene.Phosphorus doping would tailor the electric characteristic of carbon material and effect the charge distribution of neighbored carbon atom,leading to enhanced catalytic performance and stability for electrochemical ammonia synthesis.The experimental results show that the PG exhibits excellent ammonia yield(15.12μg·h^-1·mg^-1_cat.),Faraday efficiency（6.47%）and good stability.This method is widely used and easy for massive production,which can promote the application of phosphorus-doped carbon materials in the electrochemical ammonia synthesis.（3）We report a facile approach to synthesize Pd nanoparticles decorated phosphorus-doped grapheme（Pd/PG）by solvothermal method using graphene oxide as a raw material and tetrakis（triphenylphosphine）palladium as dopant.The composition and morphology of the catalyst can be adjusted by changing the ratio of tetrakis（triphenylphosphine）palladium and graphene oxide.Phosphorus doping can modify the electron structure and distribution of carbon material,and the strong interaction among the P,Pd and C elements can induce the synergistic effect,resulting in the more facile for the effective activation of N≡N bond.Therefore,the Pd/PG as an excellent NRR electrocatalyst exhibits excellent ammonia yield of 12.74μg·h^-1·mg^-1_cat.,,and Faraday efficiency of 6.12%,and stability for electrochemical ammonia synthesis.This method can incorporate P and Pd elements into various catalysts,which can significantly improve their catalytic performance for electrochemical ammonia synthesis.