Preparation Of Transition Metal/heterogeneous Element Modified Lead-based Catalysts And Performance Study Of Carbon Dioxide Reduction To Formic Aci

Electrocatalytic carbon dioxide（CO₂）reduction reaction（CO₂RR）is an emerging and feasible CO₂conversion and utilization strategy that can transform CO₂into formic acid（HCOOH）,carbon monoxide（CO）,methane（CH₄）and other valuable industrial chemical raw materials.Among them,HCOOH is an important industrial raw material for tanning leather and food additives,and its effective synthesis is favored by researchers.The synthesis of HCOOH by CO₂RR can effectively alleviate the huge increase of CO₂emissions caused by the extensive development of fossil fuels,the energy shortage in today’s society and the problems of global warming.Metallic lead（Pb）based electrocatalyst is considered as a promising catalyst for the synthesis of HCOOH from CO₂RR due to its preferential adsorption to the important intermediate（HCOO*）in the aqueous electrolyte.However,due to the formation of competitive CO and H₂in the CO₂RR process,Pb-based electrocatalysts adsorbed important intermediates in CO path（*COOH）and H₂path（H*）,which often posed threats and challenges to the selectivity of HCOOH path.At the same time,due to the oxidation of Pb active sites in electrolyte and the simultaneous self-reduction(Pb（?）Pb²⁺)in the process of CO₂RR,the valence state is often unstable,so the true electronic structure of Pb active site is still uncertain.In addition,the lack of outer orbital electrons of high valence of Pb ions will also affect the delocalized electrons,which is not conducive to the activation of*CO₂,resulting in low catalytic performance.It is obvious that*CO₂can be activated effectively and HCOO*formation can be driven by regulating the electronic structure of the active site of Pb in the Pb-based electrocatalyst and giving sufficient electronic environment optimization.This paper aims to prepare stable and efficient Pb-based electrocatalyst that synthesizes CO₂RR into HCOOH,and uses metal elements（such as cobalt（Co））and heterogeneous elements（such as phosphorus（P）,sulfur（S）,and nitrogen（N））to regulate the active site of Pb-based electrocatalyst,so as to optimize its electronic structure and improve its catalytic performance.Specific research contents are as follows:1.Study on CO₂RR synthesis of HCOOH enhanced by Co doping/interfacial regulation of Pb²⁺active site electronic structure.In this work,sodium alginate was used as precursor,alginate-Co-Pb hydrogel was obtained by ion exchange.After freeze-drying,Co modified lead oxide（Pb O）/carbon nanosheet catalyst（Co-Pb O@CNS）was obtained by carbonizing in Ar atmosphere at high temperature.Co modified lead carbonate（Pb CO₃）/carbon nanosheet electrocatalyst（Co-Pb CO₃@CNS）was prepared by immersion in CO₂-saturated 0.1 M KHCO₃electrolyte.There is an intermetallic electronic interaction between Co and Pb²⁺base structure.For Co-Pb CO₃@CNS,the regulation of the content of Co and Pb makes the external electron-deficient structure of Pb get the most moderate supplement adjustment due to the addition of Co,and the best catalytic activity and stability is shown when Co:Pb=0.09:1.The Faraday efficiency of formic acid(FE_fomate)at-0.7 V vs.RHE reached 98.15%,and the current density reached9.65 m A cm^-2.After 20 h stability test,FE_fomatedecreased only 3.86%and current density decreased only 13.47%.The catalyst showed excellent selectivity and catalytic stability of HCOOH.2.Study on the regulation of heterogeneous elements on Pb-based catalyst and its performance of CO₂RR synthesis of HCOOH.In this work,sodium alginate was also used as the precursor,alginate-Pb hydrogel was obtained through ion exchange,and after freeze-drying,it was carbonized at high temperature in Ar atmosphere to obtain the precursor of Pb O/carbon nanosheet structure（Pb O@CNS）.Then,the Pb O@CNS was modified by vapor deposition method,the sodium hypophosphite as phosphorus（P）source,thiourea as sulfur（S）source,melamine as nitrogen（N）source,and the mass ratio was 1:10.P,S,N heteroelements doping,so as to obtain Pb₉（PO₄）₆@CNS,Pb S@CNS and Pb N_2.5@CNS with Pb²⁺as the main ordering state.Subsequently,Pb₉（PO₄）₆@CNS,Pb S@CNS and Pb N_2.5@CNS were reduced in hydrogen and argon mixture atmosphere for 0.5 h～3.0 h at different time lengths,and finally the target products Pb/Pb₉（PO₄）₆@CNS,Pb/Pb S@CNS and Pb/Pb N_2.5@CNS were obtained.The composition did not change significantly after soaking in CO₂-saturated 0.1 M KHCO₃electrolyte,Pb²⁺was used as the active site.By comparing the modification of Pb based catalysts with different heterogeneous elements,the prepared Pb/Pb₉（PO₄）₆@CNS showed the best catalytic performance,FE_fomatereached 94.74%at-0.8 V vs.RHE,and the current density reached 17.25 m A cm^-2.After 20 h stability test,FE_fomatedecreased only 1.2%.The electrocatalyst also showed outstanding selectivity and catalytic stability for CO₂RR synthesis of HCOOH.