Design Of Efficient Gold-Based Nanocatalysts For Electroreduction Of Carbon Dioxide

The CO₂ electroreduction driven by clean electricity can effectively convert CO₂into high value-added products.This method not only solves the environmental problems caused by carbon imbalance,but also alleviate the energy crisis,which thus received much attentions.During CO₂ electroreduction reaction,the catalysts can reduce the reaction barrier,optimize the reaction pathway and increase the product selectivity.Therefore,the choice of catalysts plays an important role in this field.Au-based nanocatalysts have shown great potential for the CO₂ electroreduction reaction,due to their advantages in activity and stability.However,it still has some challenges,such as high cost and poor selectivity.In order to solve these shortcomings,this thesis optimizes Au-based nanomaterials via constructing the bimetallic synergies,core-shell structure,and unconventional crystal phase.In the first work,the disordered Au Cu alloy nanoparticles were prepared by wet-chemical method.By adjusting the amount of precursors,we achieved precise control of the chemical composition.The CO₂ electroreduction test has shown that the catalytic performance of Au Cu_0.4was the best.At-0.8 V vs.RHE,the selectivity of CO is 75%,and the mass activity reaches 10.1 A/g.It is significantly improved compared to nanoparticles with other ingredients.The research found that through the control of the chemical composition,the synergistic effect can be adjusted,the center position of the d-band can be optimized,and the optimized adsorption of the intermediate*COOH in the reduction process can be achieved.As a consequence,it improves the selectivity and activity.Although the activity and selectivity of the Au Cu alloy catalyst have been improved,the poor stability limits the further application.In order to further improve the catalytic stability of Au-based catalysts,the ordered Au Cu intermetallic nanoparticles were preared by annealing the disordered Au Cu_0.9 nanoparticles.Notably,the Au Cu intermetallic nanoparticles had o-Au Cu@Au Core-shell structure with ordered Au Cu as the core and 3 to 4 layers of Au atoms as the shell.We found that the selectivity of o-Au Cu@Au core-shell nanoparticles reached 83%and the mass activity reached 24A/g at-0.8 V vs.RHE.Compared to Au nanoparticles,the performance is significantly improved,while the catalytic stability can be maintained for more than 20 h.Mechanism studies have shown that the mismatch of the interplanar spacing between the core-shell of o-Au Cu@Au nanoparticles can introduce 2.9%surface compressive stress,which can accelerate the generation of intermediate*COOH and lead to the enhanced activity.Meanwhile,the existence of Au shell leads to good stability of the catalyst.Through the combination of composition and stress control,in the fifth chapter of this article,we continue to change the chemical composition and increase the surface stress.It could introduce the outer layer of Au to undergo a phase change,and successfully prepared an unconventional metastable crystals fct Au.Its catalytic performance is excellent,and the selectivity of CO up to 94.5%at-0.8 V vs.RHE.The mass activity reache 73 A/g,which is 18.2 times higher than fcc Au.Based on the d-band theory,DFT calculation and in-situ synchrotron radiation infrared spectroscopy,we found that the phase transition from fcc Au to metastable fct Au can further optimize the electronic structure,make the catalyst adsorb the intermediate*COOH to the best value,and significantly reduce the barrier of reaction rate determination,thereby it could improve the catalytic performance.Our studies provide a new idea for the design of low-cost,high-performance catalytic materials,and provides some insight for the subsequent research of CO₂electroreduction reactions.In the meantime,in terms of material synthesis,the concept of interfacial strain-stabilized metastable fct Au was proposed for the first time,which can be extended to synthesize othermetal nanocrystals with metastable phases.