Preparation Of Metal Silver Phosphonate Materials And Their Catalytic Performance For CO₂ Conversion

The concentration of carbon dioxide（CO₂）in the atmosphere is increasing with the development of modern industry.To capture CO₂in the atmosphere and convert it into new renewable energy has attracted people’s attention.Coordination polymer materials have shown advantages in the field of chemical fixation of CO₂due to their diversity of structures and functions.In this paper,silver phosphonate materials were synthesized under hydrothermal condition,and were applied to the catalytic conversion of CO₂both in the cycloaddition reaction of CO₂and epoxides,and in the electrocatalytic reduction of CO₂to CO.All of the results show that the silver phosphonate materials possess excellent catalytic activity for the catalytic conversion of CO₂.Firstly,a new coordination polymer named[Ag₁₀（H₃L）₂（H₂O）₂（4,4’-bipy）]was synthesized under hydrothermal condition using silver nitrate and（ethene-1,1,2,2-tetrayltetrakis（benzene-4,1-diyl））tetraphosphonic acid as raw materials.It is a three-dimensional network composed of extended···Ag-O-P-O···chains and organic linkers.The X-ray single crystal diffraction analysis shows that the compound is in a triclinic system with a space group of1.The compound consists of five crystallographically independent Ag⁺ions,one deprotonated H₃L^5-with half of4,4’-bipyridine molecule and one H₂O molecule.Three of the four phosphonate groups of the organic ligand are protonated,which makes the silver phosphonate material have abundant proton acid sites.Secondly,the catalytic performance of silver phosphonate material was investigated by the cycloaddition reaction of epoxide and CO₂.The loading of the catalyst is a 0.05%ratio based on the epoxide.The reactions were carried out at 100 ^oC under 1 MPa CO₂pressure..the condition of 3 h reaction time,yield is 93.6%,It showed good catalytic activity for different epoxides.Furthermore,the catalytic activity of the silver phosphonate material was well maintained after five runs of cyclic experiments,which proved the heterogeneous nature of the catalyst.Finally,the silver phosphonate was loaded onto a carbon paper and used as the electrocatalyst for electrochemical CO₂reduction.Then the performance of the electrocatalyst was tested in an aqueous solution system,and the reduction products,faraday efficiency（FE）and electrocatalytic stability were also evaluated.The silver phosphonate cathode exhibits great difference in the electrochemical behaviors between saturated Ar electrolyte and saturated CO₂electrolyte.The current density of the saturated CO₂electrolyte is significantly higher than that of the saturated Ar one,indicating the CO₂reduction occurs.The mainly reduction product is carbon monoxide（CO）,and mainly by-product is hydrogen（H₂）.The CO selectivity reach the maximum at a potential of-1.0 V vs.RHE,the FE_COis as high as 97.6%.The double layer electric capacitance test showed that the silver phosphonate based electrode has a high electrochemical active surface area（1014μF/cm²）,further indicating that the high electrocatalytic kinetic of silver phosphonate.Furthermore,the silver phosphonate exhibits an excellent electrocatalytic stability,the reduction current maintains without great decease during 4h electrochemical test,and the CO selectivity keeps above 90%.