Synthesis And Applications Of Non-precious Metal Electrocatalysts

Developing sustainable,fossil-free pathways to produce fuels and chemicals of global importance could play a major role in reducing contaminant emissions while providing the increasing feedstocks needed to make the fuel and products we use on a daily basis.One prospective direction for sustainable energy conversion system,is to develop electrochemical conversion processes that can convert rich substance in the nature(e.g.,water,biomass,carbon dioxide,and nitrogen)into higher-value products(e.g.,hydrogen,hydrocarbons and ammonia)by coupling to renewable energy(e.g.wind energy,solar energy).It has been discovered electrocatalysts play a key role in these energy conversion and storage technologies because they increase the rate,efficiency,and selectivity of the chemical transformations involved.However,considering high-performance but expensive and resource-poor precious metal electrocatalysts,many clean energy technologies have been limited large-scale applications.The grand challenge and important research topic is to develop advanced electrocatalysts with the practical value and the enhanced performance needed to enable widespread penetration of clean energy technologies.To establish the true sense of 'zero emission'clean energy conversion system based on 'water','hydrogen' and 'oxygen',the main goal of the thesis is to design and construct advanced non-precious metal electrocatalysts with practical,stable,high efficiency features,thus further facilitate the development of efficient and high-valuable application such as electrolysis of water for hydrogen production technology,metal-air battery technology and so on.The main research contents and results are summarized as follows:1.We rational design and develop porous carbon-based electorcatalysts with multiple active sites by using shrimp-shell derived N-doped carbon nanodots(N-CNs)as precursors,thus this means successfully realize the functionalzed proecss of biomass shrimp-shell "turning waste to treasure".The N-CNs with N-rich(14.4%)content is obtained from the cutting and carbonization of shrimp-shell power by hydrothermal method.Then,the N-CNs and metal(M)ions are assembled into particle-like aggregates by a simple polymerization reaction of pyrrole,finally the resulting composites are thermally treated by a facile pyrolysis approach to successfully obtain(M/MOx nanoparticles encapsulated in)M-N codoped porous graphitic carbon materials.The Fe,N-doped porous graphitic carbon(Fe-N-PGC-800)material with diplopore size distribution centered at?1.97 nm and?2.8 nm and a surface area of 806.7 m2 g-1,is obtained from thermally treating N-CN/polypyrrole composites by a facile pyrolysis approach.As an electrocatalyst for oxygen reduction reaction(ORR)in alkaline media,Fe-N-PGC-800 shows superior ORR catalytic activity,which is comparable to that of commercial Pt/C catalysts.Co/CoO nanoparticles immobilized on Co-N-doped carbon(Co/Co9S8@SNGS-1000)are successfully developed using shrimp-shell derived N-CNs and Co ions as precursors by a combined approach of polymerization and pyrolysis,as electrocatalysts exhibiting trifunctional catalytic activities toward oxygen reduction,oxygen evolution and hydrogen evolution reactions.We carefully study the realationship between structure and performance on the as-obtained carbon-based electrocatalysts with multiple active sites and high suface area.Further,the application value of the as-prepared cabon-based materials is evaluated as electrocatalysts for(rechearable)znic-air batteries and overall water splitting:2.The novel method is developed to prepare multiple active sites and multifunctional electrocatalyst by using MOFs as precursor.The Co/Co9S8 core-shell structures anchored onto Co,N,S co-doped porous graphene sheets(Co/Co9S8@SNGS)are prepared by high temperature pyrolysis of S-containing and N-containing dual organic ligands assembled Co-based metal-organic frameworks(Co-MOFs)in situ grown on graphene oxide sheets(Co-MOFs@GO).We carefully study the effects of the proportion of dual organic ligands and pyrolysis temperatures on the structure and activities of as-prepared Co-MOFs derived electrocatalysts.The synergistic mechanism of multiple catalytic sites is investigated by controlling the synthesis of single active site electrocatalysts.As electrocatalyst,Co/Co9S8@SNGS-1000 exhibited superiorly bifunctional electrocatalytic activities toward both OER and HER in alkaline solution,As electrode material for full water splitting,the Co/Co9S8@SNGS-1000 electrodes exhibit high O2 and H2 generation efficiencies with nearly 100%Faradaic yield.The findings in this work would be helpful to design and develop high performance bifunctional MOFs derived non-precious electrocatalysts for practical energy applications.3.By utilizing urea oxidation reaction(UOR)instead of high overpotential OER as research way of thinking in the chapter,a new type energy-saving rechargeable zinc-air battery is designed and developed.The multifunctional Mn-Ni(OH)2/CFC electrocatalysts are successfully fabricated by a facile room-temperature solution route.The Mn-Ni(OH)2/CFC as an electrocatalyst exhibit bifunctional electrocatalytic activities of ORR and OER,as well as a superior UOR activity.We carefully study the mechanism of electrocatalytic activity for UOR and OER of Mn incorporation Ni(OH)2 electrocatalysts.When assemble into Zn-air battery with Mn-Ni(OH)2/CFC as the air cathode,the Zn-air battery without urea(oxidation of water)exhibits higher charging voltages at different current densities(almost 0.3 V higher at the current densities over 15 mA cm-2)compared to the urea introduced Zn-air battery,delivering 12-21%energy saving in the charging process of the Zn-air battery;And along the same lines the hydrogen production technology of electrocatalytic electrolysis is developed.The nanocrystalline Ni2P on CFC(Ni2P/CFC)with excellent HER,UOR and OER catalytic activity,is successfully fabricated by a facile VPH method.Compared to the pure water-spitting,the urea electrolysis system significantly reduce the cell voltage by about 0.29 V to reach benchmark current densities(10 mA cm-2),which could attribute to the more favourable thermodynamics and kinetics of UOR than OER catalyzed by Ni2P/CFC electrode.The research work provides a new research strategy for how to further improve the energy conversion efficiency of electrochemical energy devices and the degradation of environmental organic pollutants.4.The self-supported nano-structure transition metal phosphides(Cu3P/CFC or Ni2P/CFC)on carbon fiber cloth are facile obtained by in-situ vapor phase hydrothermal method.The furfural electrocatalytc conversion system is designed and developed by using water as the hydrogen source in a membrane separated H-type reactor,catalyzed by Ni2P/CFC and Cu3P/CFC electrodes.Our results show that Cu3P/CFC electrode demonstrated highly Faradic efficiency,current density and selective electrocatalytic conversion of furfural to furfuryl alcohol in the competitive reaction of electrocatalytic furfural hydrogenation and electrocatalytic hydrogen production.DFT calculations show the excellent furfural electrocatalytic hydrogenation activity on Cu3P/CFC electrode,could attribute to the high concentration Had and higher H2 desorption energy,which inhibit the of the H2 generation,therefore improve the Faraday efficiency and selectivity for furfural hydrogenation.Those results not only give guiding significance to how to design high catalytic activity,but also provide high value guidance for the design of electrocatalytic synthesis system.