Design,Synthesis And Catalytic Performance Of Cerium Oxide Based Nanocomposites

Due to the continuous and extensive use of fossil fuels,energy shortage and environmental pollution are still the two major scientific problems facing the present.Using electrochemical technology to develop sustainable new energy sources and prepare chemicals with green and low energy consumption have become two important research directions to solve the above problems,because electrochemical technology can realize the effective conversion and storage between electric energy and chemical energy,and the process is highly efficient and pollution-free.However,the slow reaction kinetics of the electrode surface limit its electrochemical performance,so finding efficient electrocatalysts is the primary task to improve electrochemical performance.Although noble metal catalysts exhibit excellent catalytic performance,their high cost and scarce reserves limit their large-scale application,so it is important to develop non-precious metal catalysts with abundant reserves and low prices.However,the catalytic activity of non-noble metal catalysts is limited,and it is necessary to explore suitable cocatalysts to effectively regulate the activitity of nonprecious metal catalysts.China is a big country in rare earth,where cerium is abundant and cheap,and cerium dioxide（CeO₂）is a typical rare earth oxide,which has abundant oxygen vacancies due to its reversible conversion of surface valence states,which can be used as a cocatalyst to construct CeO₂ and non-precious metal nanocomposites to improve the catalytic performance of catalysts.Based on this,this dissertation studies the application of a series of cerium oxide based non-noble metal nanocatalysts in improving the electrocatalytic activity and stability.Specific research contents are as follows:1.Study on electrocatalytic OER performance in seawater by CeO₂ doped NiCo mixed metal phosphide.CeO₂-doped Ni-Co bimetallic phosphide（CeO₂-Co2xNixP@C）was obtained by phosphating CeO₂-NiCo-MOF hollow nanospheres using a hard template synthesis method.Benefiting from the characteristics of composition and structure,CeO₂-Co2-xNixP@C exhibited better oxygen evolution reaction（OER）performance than Co2-xNixP@C in 1 M KOH,with an overpotential of 295 mV at 10 mA cm-2 and a Tafel slope of 69.7 mV dec-1.More importantly,the catalytic activity and stability were well preserved after the fresh water electrolyte was changed into seawater electrolyte.The excellent OER performance of CeO₂-Co2-xNixP@C in both fresh and seawater can be attributed to the following:（ⅰ）The introduction of CeO₂ effectively regulated the surface state of the catalyst,and CeO₂ could form abundant oxygen vacancy and increase the electrochemical active site of the catalyst;（ⅱ）CeO₂ can adjust the surface electron state of the catalyst and reduce the energy barrier of OER reaction;（ⅲ）The activity of the contrast sample Co2-xNix P@C decreased sharply in the seawater electrolyte,indicating that CeO₂ can effectively inhibit the adsorption of Clto the catalyst,thereby inhibiting the Cl-oxidation reaction.2.Study on the effect of CeO₂ on the surface electronic structure of molybdenum nitride on electrocatalytic nitrogen reduction.The nanocomposite of CeO₂ and molybdenum nitride（CeO₂-MoN）was prepared by molten salt method.The morphology and structure of CeO₂-MoN composite were characterized,and the electrochemical catalytic nitrogen reduction（NRR）performance of CeO₂-MoN was tested.The results showed that the introduction of CeO₂ effectively enhanced the NRR activity of MoN material,and the ammonia yield was 27.5 μg h-1 mg-1 and Faraday efficiency was 17.2%at the optimal voltage of-0.3 V（vs.RHE）.Density functional theory（DFT）calculation showed that the oxygen vacancy in CeO₂ played an important role in the electrocatalytic nitrogen fixation of CeO₂-MoN nanocomposite.Specifically,the oxygen vacancy of CeO₂ can expand the electron-deficient region at the MoN nitrogen vacancy site,and the expanded electron-deficient region is more favorable to accommodate the lone pair electrons in N2,thus promoting the adsorption and activation of N2 molecules,and achieving excellent electrocatalytic nitrogen fixation efficiency.3.Study on electrocatalytic nitrogen reduction performance of graphenesupported strongly coupled CeO₂-Mo2C composites.Graphene-supported CeO₂/MO₂C nanocomposites（CeO₂/MO₂C@rGO）were prepared by calcination heat treatment and applied to electrocatalytic NRR reaction.The results of NRR experiments showed that CeO₂/MO₂C@rGO exhibited an ammonia yield of 22.3 μg h-1mg-1 and a Faraday efficiency of 12.7%at low overpotential of-0.3 V（vs.RHE）,and its NRR performance was several times better than that of the comparison sample Mo2C@rGO,indicating that the introduction of CeO₂ had an effective synergistic and promoting effect on electrocatalytic nitrogen fixation.DFT calculation further proved that the introduction of CeO₂ optimized the electronic structure of CeO₂/Mo2C@rGO,and the oxygen vacancy in CeO₂ effectively promoted the activation of nitrogen adsorbed on the surface of the material,so that CeO₂/Mo2C@rGO composite exhibited excellent electrocatalytic nitrogen fixation performance.