Preparation And Electrochemical Performances Of Carbon-based Non-noble Metal Catalysts

Fossil fuels such as petroleum,coal,and natural gas have greatly promoted the rapid development of human science and technology,but their non-renewability and high pollution have become two major global problems that hinder human development.Therefore,establishing an efficient and clean energy system has become one of the hotspots of the research.In this field,the development of high-efficiency catalysts for various electrode reactions,such as oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）in metal-air fuel cells,and hydrogen evolution reaction（HER）in the field of hydrogen energy have become another important research directions.However,at present,the most effective catalysts are still noble metal materials such as Pt,Ir,Ru,and the shortcomings of low storage and high price have greatly restricted the development of the electrocatalysis field.Therefore,the development of low-cost,high-activity,high-stability catalysts to replace noble metal catalysts has become a very important subject.To this end,this paper studies the preparation and improvement of carbon-based non-noble metal catalysts and their electrocatalytic performance in different electrochemical reactions.The main research contents and results of this article are as follows:（1）Efficient Bifunctional Co/N-doped Carbon Electrocatalysts for Oxygen Reduction and Evolution ReactionsBy changing the type of precursors,the effective control of dimensions was achieved.The electrochemical performances of the obtained carbon-based catalysts with different dimensions were studied,and a dual-functional oxygen catalyst with excellent catalytic performance and good stability was obtained.In this section,three-dimensional Co@N-doped carbon nanotubes（CNTs）and nanosheets（CNSs）composites were prepared by using glucose,g-C₃N₄,and cobalt acetate hydrate as precursors through hydrothermal and pyrolysis processes.The unique three-dimensional structure of the catalyst effectively increases its specific surface area.Besides,the strong interfacial contact between CNSs and CNTs further shortens the electron diffusion distance in the electrochemical reaction,and also ensures the full contact between the reactive material and the electrolyte,and provides an effective transmission path for electrons,oxygen and ions.Pyridine N,Co-N_X and Co nanoparticles as active sites further improve the ORR and OER performance of 3DCo@N/C,with an overvoltage（ΔE）of only 0.80 V.The half-wave potential of 3DCo@N/C is 0.812 V.At a current density of 10 mA cm^-2,the overpotential is only 352 mV.（2）Preparation and electrochemical properties of FeCo₂O₄/NC CatalystA one-step hydrothermal method was used to prepare a FeCo₂O₄/NC dual-functional oxygen catalyst with a spinel structure on a nitrogen-doped carbon nanosheet using Fe³⁺substitution effect.In this structure,the valence state of the iron ion is Fe³⁺and partially replaces the octahedral Co³⁺to form an Fe³⁺-O-Co³⁺bond.Since Fe-O is closer to the Fermi level orbit than Co-O,it is easier to give or obtain electrons in the oxygen reduction reaction.Therefore,the half-wave potential of FeCo₂O₄/NC reaches 0.857 V,which is higher than that of the precious metal Pt/C catalyst（0.856 V）.At the same time,Co²⁺ions occupy the tetrahedral site in spinel Co₃O₄,which helps to formμ-OOH intermediates in OER reactions.When the current density is 10 mA cm^-2,the overpotential is only 348 mV,and the overvoltage（ΔE）between E_OER and E_ORR(ΔE=E_j=10-E_1/2)as low as 0.76 V.（3）Efficient Tuning the Electronic Structure of N-doped Ti-Based MXene to Enhance Hydrogen Evolution ReactionInsufficient electron transport,low chemical activity,and limited active site density inhibit the application of MXene in hydrogen evolution reactions.A simple one-step ultrasonic method was used to synthesize nitrogen-doped titanium carbide（N-MXene-35）at room temperature by using ammonia as a nitrogen source.By adjusting the ultrasonic temperature（5°C,15°C,35°C,55°C,75°C）,MXene with different nitrogen doping content was prepared.The results showed that N-MXene-35 displayed the excellent hydrogen evolution performance.The lowest initial overpotential in the acid electrolyte was 27 mV.When the current density was 10 mA cm^-2,the overpotential was only 162 mV,and the Tafel slope was 69 mV dec^-1.