| With the ever-increasing energy crisis and the rapid aggravation of environment pollution,the exploitation of renewable and clean energy sourceshas become indispensable,whichhas profound significance for reducing the consumption of fossil fuels and promoting the sustainable economic development.Electrocatalytic oxygen evolution reaction(OER)acts a pivotal part in advanced energy conversion and storage technologies like water splitting and rechargeable metal-air batteries.In this context,the development of non-noble metal-based catalysts for replacing the expensive and scarce iridium(Ir)and ruthenium(Ru)-based catalystshas been in the spotlight in recent years.Transition metals(such as Fe,Co and Ni)based catalysts are of great importance in efficient,extensive catalytic applications.In particular,the adjustable structural flexibility and excellent performance of Ni-based catalysts are ideal for meeting the stringent requirements of energy and environmental applications.Besides,the rational morphological and nanostructural design can also bring about important technical advantages for improving the catalytic performance of Ni-based catalysts.However,a clear understanding of the OER mechanism of the electrocatalysts is vital for controllable synthesis ofhigh-performance electrocatalysts based on theoretical guidelines.Herien,this thesis mainly focuses on the active structures of the non-noble-metal based catalysts for oxygen evolution reaction.Particularly,on basis of the vacancies and defects in the crystal structures and the electron transfer structures of the catalysts,the construction strategy of the nickel based nanostructured electrocatalysts and the underlying mechanisms for the performance enhancement of the catalytic activity are carefully investigated and discussed.The main research contents of the thesis are summarized as follows:(1)The Ni(OH)2 nanocages were prepared based on Pearson'shard soft acid-base principle(HSAB),by further ion-exchange reaction with K3Fe(CN)6,Ni Fe Prussian blue compounds(NiFePBAs)were uniformly deposited on the surface of Ni(OH)2 nanocages at room temperature.The double-shelled NiFePBAs nanocage structure was synthesized for the first time through the regulation of Kirkendall effect driven by the crystallinity difference between Ni(OH)2 and NiFePBAs.With further mild thermal activation,carbon-nitrogen(VCN)vacancies could be in situ formed in large quantities in the double-shelled NiFePBAs nanocages without destroying the crystal phase and morphological structure.Theoretical calculation and experimental results prove that the double-shelled NiFePBAs nanocages with an abundance of exposed surfacehave lower energy barrier for the departure of CN groups from NiFePBAs lattices,and thus generate CN vacancies with a concentration ashigh as 18.5%through a mildhermal activation strategy,which far outweigh the CN vacancies content in the solid NiFePBAs nanocubes.The as-prepared NiFePBAs with abundant CN vacancieshave an impressively OER catalytic activity.The oxygen evolution reaction overpotential is as low as 267mV at current density of 20mAcm-2,Tafel slope is only 79mVdec-1 and long-term stability with?2.1%potential value increase for 78h.Post characterizations demonstrate that the opened double-shelled nanocage structure offer fast material transport and charge transfer kinetics.Moreover,the important role of CN vacancies in the suppression of Fe loss during OER process and formation of Fe-O species as the active sites.(2)?-Ni(OH)2 nanocages with uniform morphology are prepared by ions-exchangemethods under alkaline conditions,which NiFePBAs nanocubes were used as self-sacrificial templates,The effects of reactants and reaction time on the composition of the?-Ni(OH)2 nanocage structure during the ion exchange process were studied,and elemental S was compounded at the same time by P2S5 gas-shocked exfoliation at room temperature for?-Ni(OH)2-S nanosheet composite preparation.?-Ni(OH)2-S precatalyst exhibits excellent catalytic activity for oxygen evolution after in-situ electrochemical activation,at current densities of 10 and 20mAcm-2,the overpotential is only 210 and 270mV,the Tafel slope is as low as 73mV dec-1 and exhibits excellent durability.The experimental results show that the precatalyst?-Ni(OH)2-S exhibits an"etch-leaching-reconstruction"strategy in an electrochemical environment.Elemental sulfur is etched and leached from the surface of the nanosheets to cause the self-reconstruction of the surface structure,which promotes the formation of"real catalyst"Ni OOH active sites,which improves electrocatalytic performance.(3)A mild oriented-redox induced wet chemical method to build a core-shellheterostructured Ni3S2@MnO2 array.Ni3S2 nanorod arrays precursor were in-situ synthesized byhydrothermal sulfidation on nickel foil,then dipping in KMnO4 solution by taking advantage of the mixing valence of Ni in Ni3S2[(Ni2+)2(Ni0)(S2-)2],through adjusting the reaction concentration and time can uniformly deposit MnO2 nanosheets layer on the surface of nanorod.Benefiting from multi-dimensional material channels and electron transfer paths,abundant catalytic active sites and a large number of adsorption of OH-radicals,Ni3S2@MnO2 core-shellheterostructure nanoarray electrocatalysts show excellent electrocatalytic oxygen evolution performance.The OER overpotential is only 283mV at current density of 30mAcm-2,and the Tafel slope is as low as 65mV dec-1,and maintains the catalytic activity for more than 30h.In addition,the core-shellheterostructured nanorod arrays directly used as anode materials of lithium-ion batteries demonstrate remarkably improved lithium storage performance.After cycling for 150cycles at a rate of 0.5 C,the discharge specific capacity is 662mAhg-1,and the capacity retention rate reaches 90.7%.The experimental results demonstrate that the enhanced electrochemical performances can be assigned to the generation of stable solid electrolyte interface films and suppression of the transition metal chalcogenide shuttle behavior. |
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