Efficient Construction Of Metal/Oxides Interface And Its Application In Environmental And Energy Catalysis

Environmental pollution and energy crisis have greatly influenced on existence and living condition of human beings.Among these,water and air pollution have a more profound influence.Heterogeneous catalysis can not only be applied in treatment of waste water,which efficiently degrades the pollution in water to harmless products,but also be employed in energy storage and conversion devices for clean and efficient utilization of renewable energy sources,which can solve the air pollution caused by low-efficient ultilization of fossil energy from the source,meanwhile,ease the shortage crisis of traditional fossil energy.Metal/oxides composite is one kind of widely researched heterogeneous catalytic materials,although metal/oxides catalysts have made series of progress in wastewater treatment and energy storage and conversion,there are still some issues remained in current research as follows:(1)Noble-based composites materials are lack of appropriate interface environment and active sites in specific reaction system,resulting in the low reaction activity;(2)Despite the activity of noble-based composite materials is generally high compared to non-noble-based counterpart so far,the noble-based composite materials with high-cost and poor-stability could hardly be commercialized;(3)The designed non-noble-based metal composites with excellent single-functional catalytic performance could hardly be used in the electrochemical storage devices which need the bi-functional catalysts.Therefore,it is of great significance to develop highly efficient,low-cost,highly stable,single-functional or bi-functional heterogeneous catalysts applied in environment and energy.Based on these issues of composites materials in environment and energy discussed above,this dissertation takes metal/oxides composites as research object and studies their application in catalytic reduction of nitrate in water and the ORR and OER through optimized designing and efficient constructing of metal/oxides interface.The specific research contents are as follows:(1)Firstly,to replace the dangerous and low-efficiency reducing agent(H2)in catalytic reduction of nitrate,the more economical and highly efficient HCOOH was employed as reducing agent precursor.Secondly,given that the traditional supported PdCu catalysts are lack of suitable interface environment and active sites,the SiO2 support was modified by-NH2 to improve the interface environment of metal/oxides and uniformly disperse the Pd nanoparticles.Herein,the PdAg alloy nanoparticles supported on SiO2-NH2 were obtained by a controlled surface reaction to load Ag.For the first time,the PdAg/SiO2-NH2 catalyst was found to be able to effectively reduce nitrate.On the one hand,its enhanced nitrate reduction performance could be attributed to the modification of-NH2 on the metal/oxides interface,which can not only uniformly disperse active phases,but also promote the HCOOH decomposition.On the other hand,the better nitrate reduction performance could attributed to the easier transfer of electrons from Ag to Pd than that from other metals due to the larger difference of work function between Ag and Pd.Both these two aspects were beneficial for the catalytic HCOOH decomposition to provide the in situ sources of the reducing agent of H2 and buffer of CO2 for the catalytic nitrate reduction process.(2)The former work showed that noble metal-based materials exhibited excellent catalytic performance,in fact,noble metal-based catalysts could also display high activity in electrocatalytic ORR,however,the scarce,high-cost,poor-stability noble metal-based materials could hardly be applied in practice.Thus,to replace the noble-based ORR electrocatalysts,the non-noble metal ORR electrocatalysts with superior activity,stability and endurance for methanol to commercial Pt/C were developed in this part.Firstly,to meet the need of porosity as electrocatalysts,Co-based ZIFs with hollow polyhedral structure were employed as in-situ template,the volatile Zn element was introduced into the ZIFs precursor,thus the Co3O4/Co@N-C composites electrocatalyst with large specific surface area and appropriate pore structure was achieved.Secondly,the metallic Co can facilitate the electron transfer between carbon supports and oxides by efficient constructing the metal/oxides(Co/Co3O4)interface,leading to the improved conductivity of oxides.Finally,the structure characterization and performance comparison showed that the Co3O4/Co@N-C electrocatalyst exhibited superior ORR activity,stability and endurance for methanol to commercial Pt/C due to the efficient interface between Co3O4 and Co for electron transfer,large surface area and appropriate pore structure.(3)The non-noble-metal-based meal/oxides electrocatalysts with better ORR performance were developed in section(2),however,some storage devices need the electrocatalysts with ORR and OER performance simultaneously.Therefore,based on the former work,this part developed a non-noble-metal-based ORR&OER bi-functional electrocatalyst by directly reducing carbonized glucose-coated urchin-like Co3O4 microspheres through the carbon-thermal processing with NH3 reducing environment.Similarly,to furnish with high porosity and conductivity as electrocatalyst,on the one hand,urchin-like Co3O4 microspheres were served as the in situ template without removal requirement for the creation of hierarchically porous N-doped carbon microsphere matrix with abundant macropores and mesopores for efficient mass diffusion.On the other hand,urchin-like Co3O4 microspheres were employed as Co source for deriving nano-CoO/Co active phase with efficient interface for electrons transfer,promoting the fast transmission of electrons between oxides and carbon matrix.In brief,the efficient Co/CoO interface and synergetic effect among these three components endowed a superior bifunctional performance towards both ORR and OER to the CoO/Co@N-C electrocatalyst over the commercially available Pt/C and Ir/C electrocatalysts.