Study On The Carbon And Carbon Composites For Electrochemical Energy Storage And Catalysis

electrochemical energy storage systems including batteries,supercapacitors and methanol fuel cells,have been widely used in many fields such as transportation and mobile communications.Carbon and carbon composites play an important role in electrochemical energy storage and electrocatalysis due to their large specific surface area,diverse structure,excellent electrical conductivity,controllable morphology and strong chemical stability.Their application in electrochemical energy storage and electrocatalysis has become one of the research hotspots.There are four parts in our work:1.Methanol Oxidation Reaction Performance on Graphene-Supported PtAg Alloy NanocatalystIn Pt-based alloy catalyst,the electrocatalytic performance is highly related to the Pt d-band center,whose position can be modulated by the synergetic interaction of electronic and geometric effects.In this study,graphene-supported PtAg?PtAg@graphene?alloy nanocatalyst was prepared by a facile galvanic replacement reaction.Due to the introduction of Ag component,the PtAg@graphene exhibits a higher specific/mass activity(1.48 mA cm^–2,580 mA mg_Pt^–1)and better CO tolerance?CO stripping potential:0.45 V vs.Ag/AgCl?than those of commercial Pt/C catalyst(0.86 mA cm^–2,270 mA mg_Pt^–1,0.50 V vs.Ag/AgCl)when being applied for catalyzing methanol oxidation reaction?MOR?.On the basis of component and structure characterization,the PtAg alloy catalyst model was constructed,and first-principles density function theory calculation was applied to study the relative influence of electronic and geometric effects on the Pt d-band center and CO binding energy,respectively.It is found that the electronic effect,i.e.the charge transfer from Ag to Pt,is the decisive factor to enhance the electrocatalytic performance of PtAg alloy towards MOR.2.The Enhanced Lithium-Storage Performance for MnO Nanoparticles Anchored on Electrospun Nitrogen-Doped Carbon FibersManganese monoxide?MnO?is a promising anode material in lithium-ion battery.However,its application is impeded by poor rate capability and rapid capacity fading.In this work,a MnO/carbon hybrid material,in which small-sized MnO nanoparticles are tightly anchored on carbon fibers?denoted as MnO@CFs?,is prepared by annealing the electrospun precursor fibers at 650°C.When being applied as the anode materials of Li-ion battery,the small size of MnO shortens Li-ion diffusion path,and the carbon fibers not only greatly improve the conductivity but also efficiently buffer MnO structure strain during charge-discharge process,endowing MnO@CFs electrode a good rate capability(185 mAh g^?1 at 5 A g^?1)and cyclic stability(406 mAh g^?1 after 500 cycles at 1.0 A g^?1).3.Nitrogen/Oxygen Co-doped Carbon Monolithic Electrode Derived from melamine foam for Supercapacitor with High Capacitance and CyclabilityA novel monolithic carbon sponge is prepared by ZnCl₂-assisted pyrolysis of commercial melamine foam?MF?at 800°C.The as-prepared nitrogen/oxygen co-doped carbon sponges?NOCSs?can be directly applied as monolithic electrode for supercapacitor without using any additives.It is found that ZnCl₂ activation plays an important role in improving the supercapacitance behavior.Compared with the NOCS without ZnCl₂activating treatment,the optimal NOCS-1/10,obtained with ZnCl₂/MF weight ratio of 1:10,has the best supercapacitance performance due to its unique porosity architecture,rich pseudocapacitance-active species,and good electron/ion transfer feature.It exhibits a high specific capacitance(245 F g^?1 at a current density of 0.5 A g^?1 and 345 F g^?1 at a scan rate of 10 mV s^?1)and electrochemical stability(97.0%after 10000 cycles at 5.0 A g^?1).When being assembled into all-solid-state supercapacitors?PVA/KOH electrolyte?,it delivers an energy density of 4.33 Wh kg^?1 at a power density of 250 W kg^?1 and 3.13 Wh kg^?1 at a power density of 3 kW kg^?1.4.Enhanced Capacity and Rate Capability of Nitrogen/Oxygen Dual-Doped Carbon for Potassium-Ion Battery AnodePotassium-ion batteries attract tremendous attention for large scale application due to the abundance of K resources.Herein,a nitrogen/oxygen dual-doped porous hard carbon derived from melamine foam?MF?is investigated.Specifcally,the nitrogen/oxygen co-doped carbon sponges?NOCS?electrode delivers high reversible capacities of 382 and 118mA h g^-1 at 50 and 1000 mA g^-1,respectively.Due to its unique three-dimensional communication architecture,rich pseudocapacitance-active species,and good electron/ion transfer feature.it exhibits enhanced electrochemical performance,such as the high capacity,good cycling stability,and superior rate capability.Quantitative analysis reveals that mixed mechanisms,including capacitance and diffusion,account for the K-ion storage,in which the capacitance plays a more important role.