Design And Study Of Controllable Copper-based Catalysts With Highselectivity In Electrochemical Reduction Of CO₂

Carbon capture and utilization technology has recently attracted much attention due to the severe greenhouse gas emissions as well as the challenging shortage of fossil fuel resources.Recycling CO₂ for producing useful fuels,especially electrochemical reduction of CO₂ to carbonaceous products with renewable energy sources,is regarded as an appealing way to control carbon balance.The bimetallic and metal/metal oxide catalysts can improve the activity and selectivity over their monometallic counterparts by tuning the structure,morphology and composition in the electrocatalytic system.However,only a handful of these electrocatalysts were studied in the CO₂ electrochemical reduction reaction?CO₂ER?.In addition,there scarcely was a systematic model to understand the structure-activity relationship for the electrocatalysts on CO₂ER,especially for product tuning process by introduction of second metal or the modification of metal by metal oxide.Thus,it was meaningful to develop the highly selective electrocatalysts and study tuning selectivity origined from the structure and activity.In this dissertation,efforts were mainly focused on the fabrication of the core-shell structured Ag@Cu and the heterostructured Cu/SnO_x?origined from the in-situ electroreduction of mixed CuO_y/SnO_x oxides?and application in CO₂ER system for the first time.Meanwhile,the optimization and adjustment of composition,morphology and structure in bimetallic and metal/metal oxide electrocatalysts can achieve to the selectivity tuning among multiple products in the electrochemical reduction of CO₂.Then the electronic effects and geometric effects have been studied in depth how to influence in the structure-activity relationship.The main points are summarized as follows:?1?The structure,morphology and composition of Ag@Cu bimetallic nanocatalysts were controlled by tuning the heating reaction time in a simple polyol reduction method.Efforts were also focused on the exploration of the addition of Cu as a secondary metal with Ag for a systematic model to study the tuning of selectivity and activity.TEM,UV-Vis,XRD and XPS proved that the NPs endured the process the presence of the dissimilar Cu atoms,surface modification to forming the outer layer and electron transferred from Ag to Cu.Unlike the existing“dilution”effects between Ag and Cu,it was striking that either CO or ethylene endured a volcano-type correlation for the Ag@Cu bimetallic nanocatalysts.For pure Ag and Ag@Cu-5,the FEs for CO were close at-1.06 V?vs.RHE?,which agreed with other reports about bulk Ag materials.The sample of Ag@Cu-7 gave the highest FE towards CO with a value of 82%.Similarly,the sample of Ag@Cu-20 gave the peak activity for ethylene with a value of 28.6%,better than its monometallic counterparts,which was reported for the first time about the electrocatalytic property on the Ag@Cu core-shell structured surface.The influential factors in terms of geometric and electronic effects for Ag@Cu-7 and Ag@Cu-20 were systemically discussed.We expect our study to be particularly beneficial and intuitive as it enables a rational bimetallic catalyst design to CO₂RR.?2?In addition,based on the the conception of metal/metal oxide catalyst which can provide a double active site and have a synergistic effect in the catalytic system,we report one of the first systematic study on composition-dependent influences of metal-oxide interactions on electrocatalytic CO₂ reduction,utilizing Cu/SnO_x heterostructured nanoparticles supported on carbon nanotubes?CNTs?as a model catalyst system?origined from CuO_y/SnO_x-CNT?.By adjusting the Cu/Sn ratio in the catalyst material structure,we can tune the products of the CO₂ electrocatalytic reductionreactionfromhydrocarbon-favorabletoCO-selectiveto formic-acid-dominant.In the Cu-rich regime,SnO_x dramatically alters the catalytic behavior of Cu.The CuO_y/SnO_x-CNT catalyst containing 6.2%of SnO_x converts CO₂ to CO with a high Faradaic efficiency of 89%and a j _CO of 11.3 mA·cm^-2 at-0.99 V?vs.RHE?,in stark contrast to the Cu O_y-CNT catalyst on which ethylene and methane are the main products for CO₂ reduction.In the Sn-richer regime,Cu modifies the catalytic properties of SnO_x.The Cu O_y/SnO_x-CNT catalyst containing30.2%of SnO_x reduces CO₂ to formic acid with a Faradaic efficiency of 77%and a j_HCOOH of 4.0 mA·cm^-2 at-0.99 V,outperforming the SnO_x-CNT catalyst which only converts CO₂ to formic acid in a Faradaic efficiency of 48%.Electronic interactions and geometric synergistic effects at the Cu O_y/SnO_x interface are possibly responsible for the tunable catalytic selectivity.The results add the composition-tunable Cu O_y/SnO_x-CNT materials to the list of product-selective electrocatalysts for CO₂ reduction.In summary,the major product for CO₂ electroreduction can be successfully tailored by the development of bimetallic core-shell structured or metal-metal oxide heterostructured electrocatalysts.We also have a better understanding of the complexed CO₂ electrochemical reduction process,electrochemical properties for the catalysts and the related catalytic mechanism,which provides a theoretical foundation and a technical guidance for the development of new structure CO₂electrochemical reduction catalysts.