Preparation And Performance Of Non-precious Metal Carbon-based Nanocatalysts For Electrocatalytic Oxygen And Nitrogen

Energy shortage and environmental pollution are two urgent problems facing the world.The overwhelming reliance on conventional energy sources such as oil,coal,and natural gas for human activities not only seriously damages the environment which the human beings depend on for living,but also makes it difficult to sustain human society.Exploiting green clean energy and green preparation of chemical technologies provides a new perspective for human sustainable development,such as fuel cells,rechargeable zinc-air batteries,are clean energy conversion technologies that are expected to replace traditional energy,and effectively convert chemical energy into electrical energy.Catalytic nitrogen reduction of synthetic ammonia under ambient condition is a very promising green preparation chemical technology.If it can replace the industrial synthetic ammonia process,it will greatly reduce the environmental pollution of the synthetic ammonia industry.The sluggish kinetics of the above energy conversion technologies between chemical energy and electrical energy,such as oxygen reduction reaction?ORR?,oxygen evolution reaction?OER?and nitrogen reduction reaction?NRR?,need to be overcome by developing the highly efficient electrocatalysts.At present,noble metal catalysts are the best for the above mentioned reactions,but high price and scarce reserves severely hinder their large-scale commercial application.Therefore,the development of abundant and efficient non-noble metal catalysts for the above-mentioned electrode reactions is of great significance for improving the current energy shortage and environmental pollution problems.In this thesis,two types of highly efficient and stable catalysts for oxygen and nitrogen electrode reactions are designed and synthesized by using non-noble metals?Fe,Mo?and heteroatom?N,P?doped carbon,which are rich in reserves.The performance is improved by tuning the morphology,composition and structure of the catalysts,and the relationship of microstructure and performance is revealed.The main results are as follows:?1?Preparation and performance FeMo-based electrocatalyst for ammonia synthesis by the reduction of nitrogen.The metal organic framework?MOF?precursor with regular spherical structure is synthesized from 2,5-dimethylterephthalic acid and iron and molybdenum metal salts,and then the catalyst MoFe-PC porous microspheres?PC,phosphorus-doped carbon?is obtained by phosphating the precursor using a temperature-controlled tube furnace.After studying the relationship of structure and performance,we conclude that Fe,Mo oxide and phosphorus-doped carbon are the main active components,which synergistically catalyze the reduction of nitrogen to ammonia.In an acid medium,the ammonia yield and Faraday efficiency?FE?are about34.23?g h^-11 mg^-11 _cat.and 17.0%,respectively,which are better than those of many reported NRR electrocatalysts.Meanwhile,Faraday efficiency and ammonia yield of the catalyst almost remain unchanged after many cycling tests,indicating an excellent stability.?2?Preparation and performance of a highly efficient metal-free bifunctional electrocatalyst for OER,ORR and rechargeable zinc-air battery.Using CsCl as a template,phytic acid as a carbon and phosphorus source,and NH₃ as a nitrogen source,a nitrogen and phosphorus co-doped porous nanocarbon catalyst?NPC-"Cs"?is synthesized.The metal Cs is removed by acid etching at high temperature.The catalyst contains abundant C=O,P=O hydrophilic groups and microporous channels which are favorable for full contact between the electrolyte and electrodes,as well as full exposure of active sites inside and outside of microspheres.In 0.1 M KOH,the NPC-"Cs"exhibit excellent bifunctional catalytic activity for the both ORR and OER.The half-wave potential of the ORR is 0.85 V?vs.RHE?,which is comparable to that of commercial Pt/C.In addition,In 1M KOH,the overpotential of OER is 343 mV,which is lower than that of commercial IrO₂.The catalyst also is assembled into rechargeable zinc-air battery that show excellent performance.Among them,the specific capacitance of zinc-air battery is 697 mAh g_Zn^-1,and the corresponding energy density is about 864 Wh Kg_Zn^-1,which are compared with those of commercial Pt/C.The rechargeable zinc-air battery shows better performance than that of the battery assembled with?Pt/C+IrO₂?.The battery assembled with the catalyst shows excellent stability and energy efficiency,indicating by almost the unchanged sum of overpotentials after cycling test of charge and discharge are carried out more than 20hours.