Nanocomposite Materials Interfacial Electron Transfer Effects On The Catalytic Performance Of Photocatalysis And Electrocatalysis

Nanocomposite material is one kind of the most important functional materials. It is composited of different structural units in the micro and nanoscale or molecular complex. According to the complementation of the properties of components and their related synergistic effect, the nanocomposite materials are with excellent catalytic properties. Based on the unique feature of structure, the nanocomposite materials have widely applications in various fields of our lives. In catalysis, it is a consensus that interfacial electrons can be transferred among the intrinsic structural units and occluded reactants during catalytic reactions. The determination of the mechanism of interfacial electron transfer of nanocomposite catalysts during the catalytic reactions is crucial for the improvement of catalytic performance.Based on above considerations, in this dissertation we attempted to synthesize a serious of novel nanocomposite materials with unique structure and excellent performance guided by catalytic application. With investigation of photo- and electron-driven interfacial electron transfer processes in various catalytic reactions of nanocomposite catalysts, we aim to establish the relationship between the nanocomposite materials interfacial electron transfer processes and catalytic property. The following are detailed research contents:First, 3D porous nitrogen doped graphene highly integrated carbon nanofiber composite catalysts（CNF@NG） were successfully synthesized through a simple heating procedure by using natural biomass template as raw materials. The nitrogen doped graphene pieces were in situ grown on the carbon nanofibers, constructing seamlessly connected nanocarbon composites via covalent bonds. The highly integrated structure is favor for interfacial electrons transfer between the structure units. Meanwhile, the rigid CNF also make CNF@NG monoliths robust enough to retain the porous 3D structure, favoring a better mass transfer for catalytic reaction. Therefore, the resulting CNF@NG nanocomposite materials exhibit high activity, excellent selectivity, and superior stability in the oxygen reduction reaction of fuel cell cathode.Second, we synthesized ultrathin MoS₂ nanosheets decorated 3D graphene-carbon nanofiber papers（MoS₂-CPs） through an improved chemical deposition approach. It is found that there is a great amount defects inside or on the surface of the decorated MoS₂ nanosheets, ensuring the abundance of exposed edges for increasing the active sites for hydrogen evolution reaction（HER）. More importantly, the strong coupled interface between MoS₂ nanosheets and CPs also facilitated the interfacial electron transfer for improving the HER activity of the MoS₂-CPs. Additionally, the 3D porous structure also promoted the reactant and production diffusion behavior. As a result, the directly using MoS₂-CPs work electrode showed ultra-high activity and stability in both acid and basic medium for HER.Third, we synthesized “Branch” liked graphene-tethered carbon fiber composite papers（GCCP） through a simple heating procedure by using waste paper（such as printing paper, filter paper, kraft paper, napkin, newspaper and calendar papar） as raw materials. The GCCP is composited of nanoscale nitrogen doped graphene integrated carbon nanofiber composite layer with microscale carbon fiber. The subunit of GCCP is of hierarchical structure like a carbon tree with carbon fibers as the trunk and branches and in situ grown graphene as leaves. The hierarchical structures from nanometer to micrometerscale were built in GCCP, promising their superhydrophobic property. Therefore, GCCP can be directly using as separator and exhibited extremely high separation efficiency（> 95%） with all investigated oil-water mixtures. Meanwhile, highly carbonized GCCP composite papers display very high conductivity and can be directly used as conductive wires. And the flexible GCCP/PDMS composite papers also exhibit good electrical conductivity as well as their good mechanical properties, indicating a great potential as flexible conductors. In addition, the hierarchical structure make GCCP an electrocatalyst for ORR, OER and HER with good activity and super stability.Additionally, we also investigated the crystallinity effect on photocatalytic properties of mesocrystalline composite oxides. We choose mesocrystalline BaZrO₃ hollow nanospheres as a perfect model for investigating the crystallinity effect of mesocrystal for photocatalytic activity. Through a simple calcinations approach, the crystallinity of BaZrO₃ gradually increased and the defects among the grain boundaries decreased. Thus the highly crystalline mesocrystalline BaZrO₃ hollow nanospheres exhibit high photocatalytic activity for hydrogen production from water splitting and methyl orange degradation. It is found that the high crystalline sample can function as “highway” for electron transport, resulting in better charge separation and thus photocatalytic performance.