Design And Preparation Of Novel Catalysts Towards Electrochemistry Reduction Reaction

The design of efficient electrocatalysts is of great significance to the realization of green and sustainable national development strategy.Hydrogen is expected to replace traditional fossil fuels as a clean and energy-dense chemical source.The main industrial method of producing hydrogen is to extract it from fossil fuels,but in recent decades,producing hydrogen through electrochemical water splitting has attracted our attention as it is an efficient and clean method.Now,the application of electrochemical water splitting is limited by the high energy consumption,so the development of highly efficient HER catalyst is the key to break through this bottleneck.Fuel cells will occupy a place in the new energy market in the future.At present,Pt-based materials are the main catalysts for the oxygen reduction reaction in fuel cells.However,the high cost limits its extensive commercial application,so it is urgent to develop the non-precious metal-based catalysts with excellent ORR catalytic performance.Converting CO2 to usable clean energy can turn waste into treasure as well as mitigate the greenhouse effect.CO2 can be transferred into commercially valuable hydrocarbons via electrochemical methods.However,the selectivity and yield of final products are affected by the performance of catalyst.At present,the reportd catalysts that can reduce CO2 to hydrocarbon products(CH4,C2H4,etc.)mainly include only Cu and Cu-based materials,but it is difficult to accurately design the structure of Cu to achieve the highly selectivity of target product.To solve the above three problems,we designed non-Ptbased ORR catalysts,novel HER catalysts and non-Cu-based CO2RR catalysts.1.Biological Heme-copper oxidases(HCOs)play a critical role in the fourelectron,four-proton reduction of O2 to H2O in biosystem.The HCOs exhibit high enzymatic activity due to their natural structure with heme-nonheme metal active sites,and the nonheme metal plays a role in conferring and fine-tuning O2 reduction activity of the HCOs.Inspired by this binucleus active enzyme,herein we designed an efficient electrocatalyst(Fe,Mn-N/C)for oxygen reduction reaction,which contains two types of Metal-Nx active sites incorporated within the graphene frameworks of porous carbon.The catalysts displayed remarkable ORR performance with a half-potential of 0.904V and kinetic current density of 33.33mA cm-2 that was 4.9 times as that of 20%Pt/C(6.76 mA cm-2).When Fe,Mn-N/C catalyst was applied as air electrode in Zn-air battery,it exhibited a superior performance compared to commercial Pt/C.Its discharge curve showed the change in output voltage was negligible at 20mA cm-2 for 23000 seconds(6.4 h).The first principle calculations revealed that Fe,Mn-N/C needs less energy for the protonation of O*to OH*in ORR procedure compared with Fe-N/C.This catalyst with bimetal reactive center mimicking metal enzyme will pave a new way to design efficient electrocatalysts for ORR in fuel cells.2.In comparison to other electrocatalysts,graphene possesses two distinguished merits of superior electrical conductivity and anticorrosion performance.However,graphene and graphene oxide are electrocatalytically inert in hydrogen evolution reaction(HER)due to their electronic properties.Herein,we first report a highly active and stable graphene oxide electrocatalyst for HER.The catalyst of graphene oxide encapsulated IrNi alloy(IrNi@OC)was prepared by pyrolysis of Ir-doped Ni-BTC,exhibiting excellent electrocatalytic activity for HER,achieving 100 raA cm-2 at a low overpotential of 95 mV in 0.5 M H2SO4 and 10 mA cm-2 at 27 mV in 1 M KOH,which is superior to that of commercial Pt/C.DFT calculations reveal that electrons are transferred from IrNi alloy core to graphene shell,and this process becomes more facile as graphene was decorated with O species,tuning the electronic structure of carbon atoms favorable for forming C-H bond,thereby decreasing ΔGH*of HER.3.The electrochemical reduction of CO2 into high-value hydrocarbon CH4 has a great prospect for commercial application.At present,the catalysts reported to achieve this goal mainly included Cu-based materials.Herein,we prepared a metal-free molecular catalyst for electrochemical reduction of CO2 to CH4 through an extremely method.Based on the fact the ethylenediaminetetraacetic acid disodium salt(Na2EDTA)can dissolve in KHCO3 thus producing EDTA2-,which is adsorbed on carbon nanotube(CNT)due to the electrostatic interaction,we in situ synthesis EDTA/CNT.The experimental characteristics reveal that EDTA is atomically dispersed on the surface of CNT.This catalyst exhibits a high Faradaic efficiency(FE)of 61.6%toward CH4,a partial current density of-16.5 mA cm-2 at a potential of-1.3 V versus saturated calomel electrode.DFT calculation also proved that the abundant carboxyl group in EDTA molecule is the active site in CO2RR.Compared with copper-based materials,EDTA/CNT not only has higher catalytic activity,but also has a more definite and adjustable molecular structure.Therefore,we can design rational molecular materials for CO2RR according to the structure-activity relationship in the future.