Catalyst Design And Performance Of Transition Metal-based Hybrid Materials For CO₂ Conversion

Converting CO₂ into valuable products by utilizing solar energy or electricity is a promising strategy to remedy the problems of excessive CO₂ emissions and global warming.To promote the reaction rates and reduce energy requirements for this process,efficient photo-/electrocatalytic materials are indispensable.In the heterogeneous catalysis system,one of the most essential issues is the interface between catalysts and reaction environment.Many processes,such as adsorption and activation of molecules,energy transfer and mass transport,are involved at the interface.These processes can be highly influenced by the electronic behavior and surface structure of the catalysts.It is thus of great importance for catalyst design to understand the relationship between surface feature and catalytic performance.In addition,nanoscale materials with a small size have a relatively high proportion of surface atoms.The overall performance will be remarkably influenced by the surface atoms of nanoscale catalysts.Moreover,this feature offers a convenient way to acquire the information of surface atoms for fundamental studies.In this dissertation,a series of hybrid catalysts have been successfully developed to fulfill the requirements for CO₂ conversion.By combining theoretical simulation,advanced characterization techniques,and precise synthetic strategies,we have systematically investigated the effect of surface structure on the adsorption and activation of molecules,as well as the relationship between catalytic performance and energy delivery/mass transport across the interface in hybrid structures.The main results can be summarized as follows:1.The arrangement of metallic alloy atoms results in different surface structures on catalysts,affecting the catalytic process.We developed highly selective sites for photocatalytic conversion of CO₂ to CH4 by isolating Cu atoms in Pd lattice.The isolation of Cu atoms in Pd lattice provided paired Cu-Pd sites for the enhanced CO₂ adsorption and suppressed H2 evolution,as well as elevated the d-band center of Cu for CO₂ activation.This work offers novel perspectives on constructing catalytic sites for highly efficient and selective photocatalytic CO₂ conversion,and highlights the importance of catalyst lattice engineering at atomic scale to catalytic performance.2.Small particle size usually generates more interfaces,which may enhance the catalytic performance.To increase the density of active sites,atomically thin TiO2 nanosheets were decorated with ultrasmall Cu2O clusters via a one-step hydrothermal method.Further more,the photo-induced carriers in each component are well controlled by maneuvering the ratio of the two semiconductors,leading to an ideal photocatalytic CO₂ conversion.3.The complicated bonding state and uncertain chemical environment make it difficult to investigate the relationship between surface structure and reaction kinetics,even in the case of clusters with the size of several nanometers.Single atoms located on well-defined substrates cannot only help us learn the interaction between catalyst surface and performance,but also improved the atomic economy.By controlling synthetic conditions,we successfully produced single atom Ni sites in different coordinative modes on hollow nano fibers,leading to the improved capabilities for CO₂ adsorption and activation of CO₂.As a result,the optimized catalyst exhibits remarkable selectivity under more strict conditions.4.Oxygen evolution reaction?OER?is the half reaction on counter electrode for electrochemical CO₂ reduction?CO₂RR?and hydrogen evolution reaction?HER?,which will certainly influence the overall performance.An outstanding electrode should possess high density of active sites,excellent conductivity and mass-transport ability.Based on these principles,a self-supported membrane electrode with excellent OER performance was carefully designed.Benefitting from the 3D structure and in-situ fabrication method,this membrane was free of the conductive polymer that may block the mass-transport channel,and possessed large surface area.This work offers a rational strategy for designing efficient electrodes for complex situations.These works help develop improved catalysts and provide new insights into CO₂ conversion.