Engineering The Interface Of Cu-based Nanocatalysts For The Electrocatalytic Carbon Dioxide Reduction

Electrocatalytic carbon dioxide（CO₂）reduction driven by renewable electricity is a promising route toward value-added carbon dioxide conversion to multiple feedstocks.However,several hinderances remain in the furtherance of this field,such as the undesirable selectivity toward target products,the parasitic hydrogen evolution reaction,and the high required overpotential,which raises the energy consumption.Therefore,the rational design of electrocatalysts with both excellent selectivity and energy efficiency for targeted products has generally believed as the corestone of electrocatalytic CO₂ reduction.Among various catalyst materials currently studied,copper is the only heterogeneous candidate that tends to reduce CO₂ to various compounds,including two-electron reduction pathway and multiple-electron reduction route to generate valuable hydrocarbons and alcohols,thus has been extensively studied.And in view of the broad distribution of possible reduction products,improving the selectivity of Cu-based electrocatalysts in CO₂ reduction has drawn massive attention during the recent years.In this thesis,a series of Cu-based electrocatalysts were designed for different target products.Based on the basic principles of electrocatalytic CO₂ reduction,the engineering of Cu-based catalysts was proceeded from the electronic structure,surface modification,and spatial confinement effect,which leads to different preferred reduction products of carbon monoxide,methane,and ethylene,respectively.The evaluation of the as-prepared Cu-based electrocatalysts was conducted in a flow-cell configuration,which delivers desirable current density and practical relevance.The main content of this thesis can be depicted as follows:1.Electronic engineering through the structural arrangement of AuCu intermetallic electrocatalysts was performed.The well-arranged AuCu bimetal catalyst（o-AuCu）showed the optimal electronic structure,which manifested a high efficiency toward the controllable production of syngas in CO₂ reduction.The partial current density could reach to 78 m A cm^-2at-0.6 V in a flow-cell configuration.A tunable syngas molar ratio of CO/H₂ from 1:3 to 4:1could be derived by changing the applied voltage during electrocatalytic CO₂ reduction.These investigations demonstrated that the transformation in structural arrangement of AuCu bimetallic electrocatalysts plays a decisive role in the controllable syngas production,and the design of well-arranged o-AuCu intermetallic candidate could improve the CO₂ conversion performance toward CO.2.Polymer modification of Cu-based electrocatalyst was performed by combining the amine functional groups in polyaniline（PANI）with the catalytic centers in Cu₂O.Hybrids of Cu₂O/PANI with varied Cu₂O loadings were synthesized to improve the electrocatalytic CO₂reduction to hydrocarbons.In an H-type cell,a commendable FE for methane of 45%could be obtained at-1.4 V over 5%Cu₂O/PANI,and the 20%Cu₂O/PANI delivered a high FE for ethylene of 51%at-1.2 V.The current density can be significantly improved in a flow-cell configuration.The partial current density for methane over 5%Cu₂O/PANI could be raised to49.4 m A cm^-2 at-1.3 V,and in terms of 20%Cu₂O/PANI,the partial current density for ethylene was 163 m A cm^-2 at-1.2 V.It was also demonstrated that the current density can be further improved and the excellent selectivity toward hydrocarbons could be preserved in a membrane electrode assembly（MEA）.The 5%Cu₂O/PANI boosted a partial current density for methane of 100 m A cm^-2 with 46%FE at 2.7 V,and the 20%Cu₂O/PANI exhibited a partial current density for ethylene of 163 m A cm^-2 with 61%FE at the same applied potential.These efforts revealed the importance of PANI modification,which can be attributed to the abundant amine groups that promote the absorption and protonation of CO₂,improving the selectivity toward hydrocarbons.3.Structural engineering was conducted by fabricating a series of CuO nanospheres（m-CuO）with rough and porous surface,which rendered a high efficiency for ethylene production in electrocatalytic CO₂ reduction.The as-prepared m-CuO delivered a 53%FE for ethylene at-1.2 V in a traditional H-type cell with the corresponding partial current density of 4.3 m A cm^-2.When operated in a flow-cell configuration,the m-CuO exhibited a high ethylene partial current density of 308.8 m A cm^-2at-0.98 V.It is therefore reasonable to deduce that the rough CuO surface with porous structure could exposed more active sites for the absorption of CO key intermediates,which facilitates the dimerization of accumulated CO and the production of ethylene.