Synthesis And Electrocatalytic Properties Of Graphene Aerogel-metal Nanoparticle Composites

Due to the energy and environmental problems,new energy conversion approaches（such as fuel cells and electrochemical hydrogen production）have attracted wide attention.The cathode oxygen reduction reaction（ORR）and cathode hydrogen evolution reaction（HER）are key half-reaction in fuel cells and water electrolysis devices,respectively.Therefore,the design of high-performance and cheap ORR and HER electrocatalysts are essential for the commercial development of these new energy conversion systems.Compared with noble metal-based nanomaterials,supported catalysts can effectively reduce the metal loading and consequently save cost.Graphene aerogel has many advantages,such as large specific surface area and excellent conductivity.When using as supporting materisl,graphene aerogel can provide abundant sites for anchoring metal nanoparticles.Meanwhile,its three-dimensional（3D）porous interconnected structure is conducive to the transfer of reactants/products.During the synthesis,polyallylamine（PAA）can act as the surfactant,anchor molecule and functional molecule,which can effectively reduce the size of nanoparticles,and increase their electrocatalytic activity and durability.In this thesis,N-doped or surface-functionalized reduced graphene oxide aerogel are used as supporting materials to anchor Co,Rh,and Ru nanoparticles,respectively.Furthermore,the physical-chemical properties of these graphene aerogel-metal nanoparticles composites are characterized detailedly and their electrocatalytic performance are investigated systematically.The main results are as follows:1.The three-dimensional N-doped porous graphene aerogel supported Co nanoparticles composites（Co/N-GA-h）are successfully synthesized by calcination at high-temperature.Co/N-GA-h have excellent electrocatalytic activity for ORR in alkaline medium,which is comparable to the electrocatalytic activity of commercially available Pt/C electrocatalyst.Meanwhile,Co/N-GA-h also show significant tolerance to CO and methanol oxidation due to its excellent ORR selectivity.The three-dimensional interconnected structure of graphene aerogel,N doping,uniform dispersion of Co nanoparticles,and the porous structure of graphene all conduce to the high ORR activity of Co/N-GA-h.2.The three-dimensional graphene aerogel（GA）supported polyallylamine（PAA）functionalized ultrafine Rh nanoparticles composites（PAA@Rh-uNPs/GA）are synthesized by the surface adsorption and chemical reduction method.Electrochemical measurements show that the molecular weight of PAA affects the HER activity of PAA@Rh-uNP.The molecular weight optimized PAA@Rh-uNPs/GA with 10%Rh content has higher HER activity than the commercially available 20%Pt/C electrocatalyst in the full pH range,which is attributed to the proton enrichment at the electrode/solution interface.3.The nitrogen-doped graphene aerogel supported Ru nanoparticles composites（Ru/N-GA）are successfully prepared by high-temperature pyrolysis.Due to its porous network structure,high surface area,and nitrogen doping,Ru/N-GA with optimized composition show excellent electrocatalytic activity and durability for HER in alkaline medium,which is comparable to commercially available Pt/C electrocatalyst.