Synthesis And Electrochemical Performance Of Carbon-Supported Metal/Metal Oxide Composites

Recently,research and application of metals and metal oxides in the fields such as catalysts,lithium batteries,electrochemical sensors and supercapacitors are more and more extensive due to their unique structure,physical and chemical properties.However,the poor conductivity of metal oxides and the easy of agglomeration for metal nanomaterials make their application limited,especially in the fields of electrocatalysis and lithium batteries.Carbon nanomaterials,especially porous carbon materials,have the advantages of excellent electrical conductivity,good structural stability,high specific surface area,low cost,environmental friendliness and being convenient for functional modification.When combined with metals or metal oxides,carbon nanomaterials can not only effectively increased the specific surface area of the active component and the conductivity of the material,but also serve as the substrate to fasten the active nanoparticles and prevent them from aggregating.Therefore,carbon-based metals and metal oxide composites have great potential in the field of electrochemistry.In this paper,a series of carbon-based nanocomposites with specific structures and functions were designed and synthesized based on the soluble salt template method,and served as electrocatalyst or anode materials for Li-ion batteries.The main research contents of this paper are as follows:1.Synthesis of FeCo/N-doped 3D porous carbon nanosheets composite via NaCl template-assisted method:Iron-based and cobalt-based catalysts have good catalytic activity toward ORR and OER,respectively.The formation of iron-cobalt alloys can synergistically combine the advantages of both to obtain efficient bifunctional oxygen catalysts.In this work,a FeCo/N-doped porous carbon nanosheets composite was synthesised as a double-effect catalyst for oxygen reduction?ORR?and oxygen evolution?OER?catalyst in situ via a NaCl template-assisted strategy.The results show that this strategy assists in generating the 3D interconnected nano-thickness carbon nanosheets network with hierarchical pores and a larger specific surface area through stencil effect.In the KOH solution,the FeCo/NPC catalyst shows excellent electrocatalysis activity for both ORR and OER:a high onset potential of 0.92 V?vs.RHE?,a high half-wave potential of 0.81 V?vs.RHE?,the high current retention of 95.7%after stability test of 20000 s for ORR and the potential of 1.68V?vs.RHE?for OER at 10 mA·cm^-2.X-ray photoelectron spectroscopy?XPS?results show that Fe 2p_3/2 and Co 2p_3/2 core-level binding energy?BE?of FeCo/NPC catalyst exhibits a positive shift compared with monometallic catalysts,which is associated with that alloying downshifts the d-band position of metal and weakens the interaction between the oxygenic species and metal surfaces,thereby improving the catalytic activity.2.Synthesis of MgFe₂O₄/N-doped 3D hierarchical porous carbon nanosheets composite via water-soluble salt template method:Although MgFe₂O₄ has been researched as a high-capacity anode material for Li-ion battery,there are some problems of it,such as low initial efficiency,poor cycle stability and rate performance.By combining with carbon materials,the above problems can be well solved.In this paper,a 3D nitrogen-doped carbon nanosheet with a hierarchical porous structure was synthesized by using NaCl and Na₂SiO₃ as templates.Then,the MgFe₂O₄/carbon nanosheet composite was prepared via solvothermal method as an anode material for lithium ion batteries.As expected,the as-synthesized composite exhibits outstanding cycle stability,rate performance and high initial coulombic efficiency at different current densities.When cycling260 cycles at 0.5 A·g^-1,its specific capacity can maintained 1337.7 mAh·g^-1,and the initial coulombic efficiency is 78.3%.At the current density of 1 A·g^-1,the initial coulombic efficiency can reach 81.2%and the specific capacity is 1042.1 mAh·g^-1 after 200 cycles.The reversible specific capacity of 530.3 mAh·g^-1can still be maintained at a high current density of 5 A·g^-1 in a prolonged charge-discharge process?1500cycles?.Its superior battery performance can be attributed to the combination of both magnesium ferrite and carbon nanosheets and their unique three-dimensional structure.The good conductive network of carbon nanosheets not only enhances the electrical conductivity of the material,but also alleviates the aggregation and volume expansion of MgFe₂O₄ nanoparticles during a continuous charge-discharge process,and maintains the structural integrity of the electrode.The unique 3D structure with a high specific surface area and a hierarchical porous structure is more conducive to the sufficient contact of electrolyte with the active material and shorten the diffusion distance of lithium ions.3.Synthesis of MgFe₂O₄/N-doped 3D carbon nanosheets supported Pt catalyst:The poor stability of carbon-supported platinum catalysts has been a major obstacle for their application.The strong interaction between oxide and platinum can effectively alleviate the agglomeration and dissolution of platinum nanoparticles.In this paper,for the first time,the MgFe₂O₄/N-doped 3D carbon nanosheets were used as carriers to deposit active metal Pt particles by ethylene glycol reduction method as a highly efficient and stable ORR catalyst.XPS results show that the binding energy of Fe 2p and Mg 2p is positively shifted and Pt 4f is negatively shifted for Pt/MgFe₂O₄/carbon nanosheet composite compared with that of MgFe₂O₄/carbon nanosheet composite and Pt/carbon nanosheet composite.It is proved that there is a strong metal-support interaction between MgFe₂O₄ and Pt,which facilitates the transfer of electrons from the carrier to the Pt catalyst and stabilizes the Pt catalyst.The ORR test showed that the catalyst possesses comparable catalytic activity,excellent stability and methanol tolerance to commercial Pt/C in an alkaline solution.The current retention reaches 87.0%after the 20,000 s of stability test,which was significantly higher than that of the commercial Pt/C?46.9%?and Pt/carbon nanosheet composite?76.4%?.