Fabricating Highly Efficient Palladium-Based Nano-Electrocatalysts For Enhancing Carbon Dioxide Reduction Reaction

Electrochemically converting carbon dioxide to the value-addded products is considered as a promising way to deal with the CO2 excessive emission problem.Up to now,Palladium-based catalysts,as one of the highly efficient catalysts,can transform CO2 to formic acid or carbon monoxide.Due to its versatility,it has received the wicdespread attention.However compared with metals like Au and Ag,Pd-based catalysts still have been limited to the high overpotential for CO production,requiring approximately-0.8 V vs.RHE to attain the maximum Faradaic efficiency(FE)of around 90%since 2015.In addition,by reason of CO poisoning on the Pd-based catalysts surface,the overall performance will be lowerecd in a short time.Based on the fact that the above-mentioned obstacles block the application and industrialization of Pd-based catalysts,this study explores synthesizing partially oxidized nanostructured Pd electrocatalysts and aims to design and develop high performance catalysts employing diverse strategies.Firstly,Pd(OH)2 precursor was synthesized by the hydrolysis of H2PdCl4 and then the adding of H2O2 caused the further reaction of Pd(OH)2 transforming to partially oxidized Pd/PdOx catalysts.Through the calcination process with Ar/H2 reaction atmosphere in the tube furnace and with air in the muffle furnace,catalysts with different surface oxidation state were successfully synthesized.The structure-function relationship between different catalyst surface oxidation state and catalytic activity was discussed.We prepared Pd-based catalyst of highly oxidized surface and after assembling this catalyst into a three-electrode system,the Faradaic efficiency of 91.7%could be obtained.The overpotential required was merely-0.45 V vs.RHE.The preparation method adopted in this chapter is sustainable without any surfactant,has the advantages of high efficiency and good repeatability,and provides a valuable reference for the large-scale preparation of Pd-based catalysts of partially oxidized surface.Secondly,in view of the fact that high Faradaic efficiency could only be obtained in a narrow potential range and effective strategies have yet to be developed for the time being,we presented a surface modification strategy,by doping Bi element into Pd/PdOx catalyst to greatly improve its Faradaic efficiency and broaden its potential window with high Faradaic efficiency(over 90%).The metal element Bi improves Faradaic efficiency of CO by inhibiting the competitive reaction of hydrogen evolution reaction.This discovery provides a new perspective to modulate the catalytic performance.In the last chapter,we proposed to introduce non-metallic elements to regulate electronic structure,shift the reaction barrier,further stabilize intermediate products and thus significantly improve the electrochemical properties of CO2RR.Iin the H2PdCl4 aqueous solution,sulfur element was introduced by adding Na2S solution as sulfur source.After adjusting reaction parameters and changing the reaction metal source,the electrocatalyst with excellent catalytic performance was fabricated.This method provides a modified process for the fabrication of efficient and stable catalysts.