Preparation Of Metal-organic Framework-based Composite Materials And Their Electrocatalytic CO₂ Reduction Performance

Converting CO2 into serviceable high valued energy products or chemicals is of great significance for the sustainable development of human beings,due to the continuous combustion of fossil fuels in human life and industrial production has resulted in a sharp increase of CO2 level and serious environmental pollution.Currently,the electroreduction of carbon dioxide was regarded as one of the potential strategies to achieve this goal,owing to selectively reducing carbon dioxide to available single or multi-carbon products.However,the electrochemical conversion of CO2 still remained considerable kinetic barrier required by the intrinsically thermodynamic stability and low electron affinity of the CO2 molecule,meanwhile the accompanying competitive H2 evolution is always hindering the generation of aiming product,which was resulting in the low electrocatalytic CO2 reduction reaction(CO2RR)efficiency and selectivity.MOFs has been paid great interests in ascendant CO2RR electrocatalysts,attributing to structural merits commonly involved in open Lewis acid metal sites in favor of adsorbing CO2 molecule,as well as well-defined catalytic environments suitable for mechanism explanation.Unfortunately,the current MOFs was limited in poor electrical conductivity and electron-donating capability and little interests was paid in structural modification of novel MOFs materials.Considering the accomplishment of necessary multiple electron transfer process for obtaining any reductive products in CO2RR.It’s urgent to develop an effective approach to improve the selectivity and efficiency of CO2RR,integrating electron-rich unit,electron mobility and active component related to specifically electrocatalytic CO2 reduction product.Based on the research of our group,we concentrated on the preparation of MOFs based composites and their performances in CO2 electroreduction.From the point of view of material design structure,combined with theoretical simulation and advanced characterization,we have earried out the following research:(1)We inplant metallocene in MOFs through a facile chemical vapor deposition method and thus-obtained catalysts present excellent CO2 reduction reaction electrocatalysis performances.For instance,the FEco of CoCp2@MOF-545-Co can be as high as 97%at-0.7 V.The high performances might be attributed to the strong binding-interaction between metallocene and metalloporphyrin that can largely reduce the adsorption energy of CO2 as revealed by density functional theory calculations.The introduction of metallocene can serve as electron donator and carrier to create continuous electron transfer channel in MOFs and provide strong binding-interaction with metalloporphyrin during CO2RR process to enhance the CO2RR activity.(2)In order to verify the universality of the previous methods,we prepared a series of composite materials by depositing MCp2 into MOF-525-Co channels by vapor deposition.The materials present excellent CO2RR catalytic performances.For instance,the FEco of FeCp2@MOF-525-Co can be as high as 85.1%at-0.7 V.The universality of the method described above is verified.The results also show that the intramolecular multi-electron transfer of the catalyst itself is beneficial to the improvement of the CO2RR performances.(3)We synthesized a new In－MOF based on trinuclear indium cluster in situ hydrothermal method.After the further annealing in nitrogen,we obtained a serious of composites for electrocatalytic CO2RR.The In-g-C3N4(2:1)composites can selectively reduce CO2 to CH3COOH and the FE can reach up to 50%at-0.8 V.The excellent performance is attributed to the synergistic effect of In and g-C3N4.