Application Of Graphene And Its Composites In Energy Storage And Single Atomic Catalysis

To solve the problems of fossil fuel depletion and the ever-increasing environmental pollution,great efforts have been devoted exploring efficient renewable energy types and catalytic conversion of organics techniques.However,realization of the above goals is highly reliant on the development of material science,as a result,advanced materials featured by well-designed structures and feasibility are needed.Carbon has the most abundant reserves on Earth only next to oxygen.During recent decades,researchers have constructed enormous carbon-based materials,which has significantly boosted the development of energy storage,energy conversion and catalysis fields,among which graphene has attracted great attention due to its extraordinary physical/chemical properties.However,construction of graphene is often accompanied by high energy consumption and serious environmental pollution,which limits large scale applications of such materials.Moreover,lacking of precise structural tailoring approaches has bottle-necked the development of several fields in which graphene is supposed to play a key role,which further limits the development of carbon technology.Based on the above,in this work,we focused on optimizing the structures of graphene,which mainly refers to the construction of graphene-based materials with advanced structures via simple and highly efficient methods,meanwhile,the capability of these materials as substrates or active materials are also test in energy storage/conversion and catalysis applications,the main results are summarized as follows:(1)At present,the relative catalytic capability of metallic atomic clusters and their single atomic counterparts is still unknown to people,which limits further enhancing of various chemical reactions.Based on the above,we proposed in this work that tailoring the structure of nitrogen dopants to achieve optimization of the structure of anchoring points in graphene,which further enables controllable synthesizing of Pt atomic clusters and Pt single atoms.As the catalysts of electrocatalytic hydrogen evolution reactions(HER),we found that Pt atomic clusters are intrinsically more active and stable than their single atomic counterparts.DFT calculations prove that the nitrogen dopants in graphene can not only optimize the electronic structure of Pt atomic clusters which decreases the adsorption/desorption energy barriers of hydrogen,but also promotes mutual charge transfer which further enhances the catalytic stability of Pt atomic clusters.We achieved for the first time that optimizing the structure and catalytic capability of active centers by tailoring the dopant structure of carbon substrates,which provides a novel strategy for constructing highly efficient HER catalysts.(2)Due to the incapability of current synthesis methods in controlling the valence states of single atoms,we tailor the moderate interaction between Pd single atoms and graphene via photodeposition,which further leads to optimization of the coordination structure between Pd single atoms and graphene substrates.As a result,we achieved for the first time that precise control of Pd single atoms between 0-+2.As the catalysts of C-C coupling reactions(Suzuki and Sonogashira reactions),we found that the valence state of Pd has a huge influence on the catalytic effect of the reactions,and Pd0 is intrinsically more active than its+2 counterparts.This work proposed for the first time that controlling the coordination structure of active centers by tailoring the functionalization degree of carbon substrates,which shed light on further enhancing the catalytic performance of numerous chemical reactions.(3)For the first time,graphene was achieved from cellulose,the most abundant natural polymer on Earth,by a combined mechanocatalytic and molten-salt route in large scale.In-situ XRD and DFT calculation techniques proved that the"dehydration-condensation" growing mechanism of the porous graphene material is not only favorable for the formation of graphene-like structure,but also benefits precise controlling of the pore sizes.As electrode material of electrical double-layer capacitors,this porous graphene delivers a specific capacitance of 422 F g-1 at 1 A g-1,and maintained 97%of the initial specific capacitance after 20000 cycles.This work provides guidance for tailoring the pore sizes of different carbon materials as well as enhancing the performances of various carbon-based energy storage devices.