Synthesis,Assembly And Catalytic Performance Of Two-Dimensional Nickel-Based Nanomaterials

Due to the atomic thickness and infinite planar size,two-dimensional nanomaterials show great advantages in the field of catalysis due to their high specific surface areas,many exposed surface active sites and excellent electron transfer capability.Among them,the two-dimensional transition metal oxide is widely concerned due to the structural advantages of two-dimensional sheets and the high activity of transition metals combining with its rich source,low cost and high activity.And how to use simple and effective synthesis method to control the catalytic active sites,reduce the agglomeration and deactivation of the two-dimensional nanosheets during the catalytic reaction and improve the structural stability,ensure excellent electron transfer ability,is the key to obtain advanced two-dimensional catalytic materials.In this thesis,a series of nano-sheet assembly structures with special morphology and novel structure were prepared by delving into two-dimensional nickel-based(hydrogen)oxides.The application of the products in the field of catalysis(especially electrocatalysis)have been explored.The structure-activity relationship between the material structure and catalytic performance provides theoretical and experimental basis for rational design of advanced catalytic materials with excellent stability,high porosity and good electrical conductivity.Research in this paper includes the design and preparation of three kinds of nickel-based nanosheet assembly materials with different structures and compositions and their catalytic applications.The main conclusions are sumerized as follows:(1)The layered a-Ni(OH)2 assembled from ultrathin nanosheets were prepared by a mild one-step hydrothermal method using a solvent-induced intercalation technique.During the synthesis procedure,the solvent not only played the role as a structure-directing agent to promote the formation of the hierarchical structure,but also was used as an intercalating agent to control the interlayer spacing of the ultrathin nanosheet.The assembled hierarchical structure avoided the reunion of the ultrathin nanosheets while retaining their atomic-scale thickness and high surface area.The intercalation of the diatomic alcohol molecules provided larger interlayer spacing and further more internal active sites were exposed,which guaranteed the high activity of the catalysts.The as-obtained hierarchical a-Ni(OH)2 exhibited excellent catalytic performance in the reduction of p-nitrophenol.(2)Novel 3D self-supported porous NiO@NiMoO4 core-shell nanosheets are grown on nickel foam through a facile stepwise hydrothermal method.Ultrathin NiO nanosheets on the nickel foam cross-linked to each other are used as the core and tinny NiMoO4 nanosheets are further engineered to be immobilized uniformly on the NiO nanosheets to form the shell.This step-by-step construction of the architecture composed of ultrathin primary and secondary nanosheets efficiently avoids the agglomeration problems of individual ultrathin nanosheets and endows the heterostructure with high electrical conductivity,which improve structural stability greatly during the electrochemical processes.The demonstrated outstanding electrochemical performance for NiO@NiMoO4 nanosheets may first be ascribed to the poor crystallinity and ultrathin features,increasing the degree of structural disorder which leads to the appearance for more active sites.In addition,the large active surface area due to the two ultrathin nanosheets with the highly porous configuration further promotes the exposure of catalytic active sites and offers numerous diffusion channels between the electrolyte ions and the electrocatalyst.In addition,the high proportion of oxygen vacancies for NiO@NiMoO4 nanosheets also helps to improve the electrochemical performance.(3)Hollow NiFe hydroxide assembled from nanosheets was successfully fabricated as the OER electrocatalyst via a simple and gentle self-templating strategy,which includes two steps:the synthesis of Ni(OH)2 nanospheres precursor and its further transformation to the final hollow-spheres after the adding of iron source.This unique structure achieved numerous mass transfer channels for electrolytes and O2,ideal pathways for ions and electrons,and a high specific surface area,leading to the improved performance for the product during the electrocatalytic reaction.In addition,the electrical conductivity and structural stability of the architecture have been greatly improved after the adding of Fe3+,which guaranteed high electrochemical performance toward OER.