| With the continuous advancement of society and science and technology,non-renewable energy sources such as petroleum are consumed in large quantities,followed by more and more serious greenhouse effect and frequent outbreaks of environmental problems.At present,while looking for other clean energy to replace fossil fuels,the conversion of CO2 into high-value chemical products through various means is an important means to alleviate energy and environmental problems,such as electrocatalysis,thermal catalysis,biocatalysis,etc,among which electrochemistry Carbon dioxide reduction reaction(CO2RR)is a more economical and environmentally friendly method,which has important practical significance.The raw material carbon dioxide and water have abundant reserves on the earth,and the reaction conditions are mild.The energy required for the reaction process can be converted from renewable energy such as solar energy and wind energy.Due to these advantages,CO2RR is now an important research hotspot in the world.There are many kinds of catalysts for electro-reduction of carbon dioxide.Among them,transition metal complex catalysts have good catalytic performance,easy-to-control molecular structure and selectivity,and are cheaper than precious metal elemental atom catalysts,which have attracted a lot of attention from many scholars.In this article,we first synthesized eight palladium complexes that have been reported by our group:complex 1.[Pd(C6H4CH=NC6H3-2,6-i-Pr2)((?)-Cl)]2;complex 2.[Pd{(4-MeO)C6H4CH=NC6H3-2,6-i-Pr2}((?)-Cl)]2;complex3.[Pd{(4-MeO)C6H3CH=NC6H3-2,6-i-Pr2}]2((?)-C2O4);complex4.[Pd{(4-MeO)C6H4CH=NC6H3-2,6-i-Pr2}((?)-SCN)2];complex5.[Pd(C6H4CH=NC6H3-2,6-i-Pr2)(Cl)]2((?)-bpt);complex6.[Pd2{(4-MeO)C6H4CH=NC6H3-2,6-i-Pr2}2((?)-dppp)(SCN)2];complex 7.[Pd2{(4-MeO)C6H4 CH=N C6H3-2,6-i-Pr2}2((?)-dppb)(SCN)2];complex8.[Pd{(4-MeO)C6H3CH=NC6H3-2,6-i-Pr2}(NO3)]2((?)-dppb);[Pd{(4-MeO)C6H3CH=NC6H3-2,6-i-Pr2}(Cl)]2((?)-dppb).The complex was loaded on a carbon cloth to perform a heterogeneous catalytic electro-reduction performance test in an aqueous solution,and it was found that the reduction products were hydrogen,carbon monoxide and formic acid.Among them,the performance of the nitrate-coordinated organophosphine bridged palladium complex 7 is the best.Under the applied voltage of-0.4 V(vs RHE),the HCOOH reaches the Faraday efficiency of 51.8%;at-0.9 V(vs RHE)CO reaches a Faraday efficiency of 61.9%under voltage,and depending on the ligand,it affects the efficiency,selectivity,and stability of CO2 reduction.Among them,complex 8(FEHCOOH=44.2%,FECO=53.1%)>coordination Compound 1(FEHCOOH=39.6%,FECO=50.1%)>Complex 2(FEHCOOH=28.8%,FECO=42.5%)>Complex 6(FEHCOOH=19.5%,FECO=18.7%)>Complex5(FEHCOOH=13.4%,FECO=12.1%)>complex 3(FEHCOOH=9.7%,FECO=6.6%)>complex 4(FEHCOOH=5.4%,FECO=8.6%).In order to further explore the catalytic performance of the most effective complex 7 under other reaction conditions,the complex 7 was dissolved in a 0.1 M tetrabutylamine hexafluorophosphate DMF solution for homogeneous catalysis.It was found that the catalyst was reduced to produce a diameter of Palladium particles between 50 nm and 2000 nm prove that they are not stable in homogeneous electrocatalytic systems.Subsequently,we synthesized a sheet-shaped reduced graphene oxide(RGO)with a diameter of 4(?)m-15(?)m.RGO and complex 7 were loaded on a carbon cloth and dried as a working electrode.After testing,it was found that the electrode material loaded with RGO-complex reached a maximum Faraday efficiency of 65.7%for HCOOH at an applied voltage of-0.4 V(vs RHE).,CO achieves a Faraday efficiency of 63.4%at the applied voltage of-0.9 V(vs RHE);it may be due to the special structure and abundant groups of the reduced graphene oxide itself,which is more current than the carbon cloth loaded with the complex alone.The higher the density,the better the suppression of the hydrogen evolution reaction,and the higher the selectivity to formic acid. |
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