Preparation Of Iron-Carbon Nanocomplexes And Their Electrochemical Catalytic Applications

Oxygen reduction reaction is one of the important reactions in electrochemical catalysis,which reduces oxygen to hydrogen peroxide or water by a two-electron（2e^-）or four-electron（4e^-）process,and can be used for the production of hydrogen peroxide and the preparation of metal-air batteries.However,the oxygen reduction reaction is kinetically slow,which severely limits the 2e^-and4e^-ORR reaction effects.To meet the application needs in different fields,the search for new and sustainable catalytic materials and their synthesis methods has become an urgent problem to solve.Currently,the commonly used ORR catalysts are mainly noble metal catalysts such as Pt,Ag and Au.However,their high cost and poor durability have limited their large-scale application in commerce.Transition metal iron-based catalysts have received much attention due to their low cost,abundant resources,and high catalytic activity,and are expected to replace the traditional noble metal catalytic materials.In this thesis,highly active transition metal iron-carbon composites were prepared by electrostatic spinning technique,which solved the problem that metal nanoparticles tend to agglomerate into clumps caused by traditional preparation methods（such as mechanical synthesis,high-energy ball milling,chemical precipitation,etc.）.The catalysts with different morphologies,sizes and dispersions were obtained by designing and regulating the surface morphology of transition metal Fe-Carbon nanocomposites.The main elements are as follows:（1）Preparation and performance study of Fe-PVP-900 compositesThe Fe/C nanocomposites with porous structure were prepared by electrostatic spinning combined with high-temperature carbonization.The effect of different Fe content on the catalyst morphology was investigated by regulating the Fe/C mass ratio,and the electrochemical properties were studied.The experimental results showed that the best ORR performance of Fe-PVP-900 was achieved when the Fe/C mass ratio reached 0.75,and the Faraday efficiency of H₂O₂electrolysis reached 70-80%with a yield of 0.0325 mmol h^-1cm^-2in the voltage range of 0.4-0.6 V.The catalyst was tested for LSV before and after 1000 cycles of CV and I-t The results showed that the catalyst has good cycle durability and stability.In addition,the catalyst has good catalytic performance for the oxygen precipitation reaction,which is close to that of the commercial catalyst Pt/C.The OER potential difference between the catalyst and Pt/C is only 40 m V at a current density of 50 m A cm^-2.（2）Preparation and performance study of Fe-PAN-T compositesPAN nanofibers were prepared by electrostatic spinning,and then Fe-PAN nanofibers were obtained by adsorption of saturated Fe Cl₂,and then the nanocomposites Fe-PAN-T（where T denotes different calcination temperatures）were prepared by different high temperature carbonization.The experimental results showed that the Fe-PAN-T materials exhibited good catalytic activity for the two-electron oxygen reduction catalysts,where Fe-PAN-950 and Fe-PAN-1000 reached a Faraday efficiency of 75%-86%in the voltage interval 0.3-0.5 V with a yield of 0.038 mmol h^-1cm^-2.The results showed that the Fe-PAN-T composites prepared by the electrostatic spinning-adsorption strategy-PAN-T composites with better H₂O₂reduction ability.（3）Preparation and performance study of Fe-phen-PVP-900 compositesTo investigate the effect of elemental doping on oxygen reduction selectivity and catalytic efficiency,different molar percentages of 1,10-o-phenanthroline were complexed with iron nitrate to obtain the orange solid powder Fe-phen,while Fe-phen-PVP composite nanofibers were prepared by electrostatic spinning,and Fe-phen-PVP was pre-oxidized at high temperature and then made by carbonization to produce Fe-phen-PVP-900-n nanocomposites,where n is the molar percentage of1,10-o-phenanthroline to the total amount of substance.It was found that Fe-phen-PVP-900-0.75was superior to Ir O₂in terms of OER potential at a current density of 100 m A cm^-2.In addition,the addition of N elements significantly enhances its oxygen reduction catalytic reaction,making it superior to the commercial catalyst Ir O₂.the ORR limit current density of Fe-phen-PVP-900-0.75reaches 4 m A cm^-2,where a four-electron reduction process occurs.After assembling it into a Zn-Air cell,the specific capacity was up to 760 m Ah g^-1and exhibited excellent multiplicative performance.Meanwhile,the Fe-phen-PVP-900 catalyst showed better cycling stability compared to Pt/C+Ir O₂.Therefore,the addition of N improves the catalytic efficiency and selectivity of the Fe/C composite catalyst for the oxygen reduction process,which gives it excellent performance in zinc-air batteries.