Rational Design And Performance Study Of Copper-Based Catalysts For Electrocatalytic Carbon Dioxide Reduction

The excessive emission of carbon dioxide has led to many environmental problems such as global warming and acidification of the oceans,which threatens the sustainable development of human society.Electrocatalytic CO2 reduction to produce fuels and chemicals can realize the reduction and utilization of carbon dioxide at the same time,and has many advantages such as mild reaction conditions,tunable product selectivities and easily scaled-up electrolysis devices.Currently,only copper-based catalysts exhibit great potential in electrocatalytic conversion of carbon dioxide into high value-added products at high current densities.However,there are many products of electrocatalytic CO2 reduction on copper-based catalysts,which are difficult to control.Meanwhile,most copper-based catalysts are structurally unstable and will undergo structural reconstruction under electrocatalytic conditions,bringing challenges to the rational design of catalysts.The purpose of this paper is to realize the efficient conversion of carbon dioxide through the reasonable structural design of copper-based electrocatalysts and the optimization of electrolysis devices.In the experimental exploration,we adopted strategies such as superstructure design,support selection and preparation of copper single atoms to improve the selectivity of targeted products,and used various methods such as electron microscopy,synchrotron radiation absorption spectroscopy and theoretical simulation to study the structural changes of catalysts,and employed in situ infrared/Raman spectroscopy and other tests to reveal the reaction mechanism.We also optimized the electrolysis devices to improve the reaction current density and operation stability.The main achievements are as follows:1.We chose Cu2O superparticles as the model catalyst and revealed its structural reconstruction phenomenon under negative potentials through a pre-electroreduction method by using various characterization methods.The results showed that during the pre-electroreduction process,the building blocks inside Cu2O superparticles fused to form Cu aggerates with numerous grain boundaries while those in the outer shell detached to produce many Cu nanoscale/sub-nanoscale gap structures.The resulted gap structures were able to efficiently confine OH-species generated during reaction to induce high local pH.Therefore,the Cu2O superparticle-derived catalyst could combine advantage of grain boundaries and high local pH for accelerating C-C coupling,and achieved Faradaic efficiencies of 53.2%for ethylene and 74.2%for total C2+products finally.2.We adopted a polyol-mediated method to prepare a 2.4 nm CeO2 clustersupported Cu single-atom catalyst.Benefiting from the atomically precise structures of the catalyst system,we could reveal the locating position and loading limit of Cu single atoms on the surface of the CeO2 cluster through various experimental methods and theoretical simulation.The obtained optimal catalyst achieved a maximum Faradaic efficiency of 67%for CH4 and a maximum partial current density of-364 mA/cm2 for CH4 in the flow cell.Also,it could maintain high CH4 selectivity in a wide range of current densities.3.We used the formamide as both the carbon and nitrogen sources,and prepared the Cu-formamide condensate catalyst by introducing the copper nitrate into the formamide condensation reaction.The results of synchrotron radiation absorption spectroscopy and ICP-AES tests indicated that the mass loading for Cu single atoms of the sample with the best performance was up to 5.87 wt%.When the optimal catalyst was used in the flow cell to conduct electrocatalytic reactions,it could obtain the CH4 Faradaic efficiencies of more than 60%in the current density range of-100 to-600 mA/cm2;When used in the MEA cell,the optimal catalyst could get the CH4 Faradaic efficiency of 74.4%at the full cell voltage of 4.1 V and achieve a relatively long-term continuous operation stability.