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Surface-interface Engineering And Electrocatalytic N2 Reduction Of Metal Oxides

Posted on:2021-05-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:J L LvFull Text:PDF
GTID:1361330602496207Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Electrochemical catalytic reaction can convert abundant small molecules into high value-added products to obtain great economic and social benefits by using clean energy in ambient conditions.The catalytic activity of catalysts results from the superficial unsaturated atoms,which enables the solid surface to absorb and activate molecules in the surroundings.Therefore,the basic catalytic research is inextricably caught up with the surface science.As for electrocatalytic N2 reduction reaction(NRR),the main problems are the slow N2 adsorption kinetics,strong H2 evolution competition reaction(HER),and unclear catalytic reaction mechanism.Interface modulation and defect engineering can optimize the spin configuration,increase conductivity and electronic interaction,to improve the surface chemisorption capacity of N2 and reaction intermediates,reduce the reaction energy barrier and enhance catalytic performance.In addition,the interface between two different components possess more active centers than a single component to stabilize the catalytic sites due to synergistic effects.Therefore,the surface-interface regulation is an improve way to facilitate the activity,selectivity and stability of NRR catalysts,and in-depth study the mechanism of electrocatalytic N2 fixation.Laser ablation in liquid(LAL)technology and Laser irradiation in liquid(LIL)technology can create the extreme high temperature and high-pressure non-equilibrium conditions based on the interaction between laser and matter.The characteristics of rapid quenching,photo-reduction and impact destruction can not only produce highly active and rich defective substrate materials,but also is conducive to regulate the surface defects,components and structures,so as to improve the catalytic activity of materials.In this dissertation,we mainly focus on the surface and interface regulation of NRR materials combined with laser technology in liquid.Metal oxide heterojunction preparation,metal carbide heterojunction synthesis,and metal oxide surface defects regulation are relized by using LAL and LIL technology to improve the NRR activity.The main research contents and conclusions are as follows:1.Preparing highly active and rich defective TiOx colloid by using the LAL was to construct Pt/TiO2 and Pd/TiO2 heterojunctions for exploring the activity and selectivity of NRR for different precious metals.Electrocatalytic results concluded that although enhanced activity surely needs more electrons and protons to participate in the reaction,the limited protons and electrons furnishing could restrain HER and improve selectivity of NRR.Comparing with Pt/TiO2 and TiO2,Pd-based catalyst was beneficial to balance H2 evolution and N2 activation,thus improving the N2 chemisorption capacity and NH3 synthesis efficiency.Therefore,the Faraday efficiency of NRR of Pd/TiO2 was 1.63 and 2.01 times higher than that of Pt/TiO2 and TiO2,respectively.2.Inducing PdO reduction was used to prepare PdO/Pd/CNTs heterojunctions and construct PdO-Pd interface through modulating irradiation time to control reduction degree of PdO,for studing the NRR activity enhancement mechanism of interface.Electrochemical tests proved that PdO/Pd/CNTs irradiated for 10 min had the optimal mass ratio of Pd(18%)to PdO(82%)and abundant PdO-Pd interfaces,its Faradaic efficiency reached up to 11.5%and NH3 yield was 18.2 μg mg-1 cacal.h-1 at 0.1 V vs reversible hydrogen electrode(RHE).Pd phase on one side absorbed N2 to form chemisorbed Pd-N2 bonds,and PdO phase on the other side transmitted protons to form α-PdH and broke the N≡N bond.The synergistic effect of Pd and PdO efficiently decreased the transition distance of protons and the over-potential of chemical reaction,and thus improving the catalytic NRR performance.3.The concentration of surface oxygen defects of CeO2 was regulated by using LIL to study the impacts of oxygen defects concentration for wettability and NRR activity.Compared to original CeO2,laser irradiated CeO2(L-CeO2)presented a reduced oxygen defects concentration but a large ambient N2-to-NH3 transformation rate of 1748.0 μg g-1cat.h-1 with an optimal Faradaic efficiency of 11.6%at-0.3 V in 0.5 M Na2SO4,which are almost about 2.76 and 5.9 times higher than that of CeO2.The superior performance of the obtained L-CeO2 toward NRR could be attributed to its specific hydrophobic-aerophilic structure,inducing an appropriate three phase boundary of solid-liquid-gas,the superior protons activation and N2 adsorption capability,and effective H2 suppression reaction.This work provides a guidance for designing efficient electrocatalysts for NRR based the LIL technology of oxygen defects concentration.4.Combing the technology of LIL and chemical method developed a ternary hybrid composite of Au/Mo2C/NCNTs to study the different effect mechanism of multi-component catalytic sites in NRR.Electrocatalytic testing displayed that Au/Mo2C/NCNTs exhibited improved electrocatalytic performance of NRR,in which the NH3 yield was 2.28 and 2.36 times higher than that of Au/NCNTs and Mo2C/NCNTs,and the Faraday efficiency was 1.74 and 3.20 times higher than that of Au/NCNTs and Mo2C/NCNTs,respectively.Further DFT calculations showed that thee superficial ultrafine Mo2C nanocrystals could facilitate N2 adsorption and the cleavage of N≡N bond,and the modified Au NPs with unique electronic structure could facilitate charges transfer and the protonation of intermediates during a whole hydrogenation reaction,thereby efficiently limiting the unnecessary side reaction of HER to improve the rate of NH3 formation.Moreover,the doped N species not only restrained the aggregation of surface nanoparticles during the carbonization and reduction process,but also provided more active sites for N2 adsorption and activation,thus promoting the NRR reaction.
Keywords/Search Tags:Electrocatalytic N2 reduction reaction(NRR), Surface-interface regulation, Metal oxides/carbide, Laser technology in liquid
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