Design And Synthesis Of Iron Group Metals Based Nanomaterials For Energy Conversion And Storage

Energy crisis and environment pollution make the development and utilization of new renewable energy remarkably attractive.However,the output of new energies,such as solar energy and wind energy,is not stable.Therefore,the improvement of energy conversion and storage technology is crucial to realize the flexible utilization of renewable energy Electrolyzed water splitting and lithium ion batteries play important roles in the clean energy transfer chain of ’solar energy to electric energy to hydrogen energy to fuel cell to user’Nonetheless,the practical application of water splitting and lithium-ion batteries is limited by the cost of noble metal catalysts and the low capacity of anode materials.Herein,we synthesized iron group metal-based nanomaterials with excellent water electrolysis and lithium storage performance through modulating the morphology and electrode structure We also analyze the intrinsic structure-activity relationship between materials and performance by employing(quasi)in-situ technology and density functional theory(DFT)calculations.Main results of this paper are as follows1.Developing earth-abundant catalysts for overall water splitting is important for sustainable energy conversion technologies.However,selectively exposing active surface and judiciously optimizing nanostructure remain challenging for high-performance electrocatalysts.Herein,(003)-facet-oriented Ni3S2 nanoporous thin films(NTFs)on nickel foil are synthesized through anodization and vapor-sulfurization strategies.The Ni3S2 NTFs exhibit low onset overpotentials of 48 and 152 mV,and require overpotentials of 135 and 175 mV to achieve a benchmark of 10 mA cm-2 towards alkaline hydrogen and oxygen evolution,respectively.Remarkably,an electrolyzer assembled by Ni3S2 NTFs as both anode and cathode can deliver a water-splitting current density of 10 mA cm-2 at 1.611 V.Experimental and theoretical results indicate that the controllable hollow nanoporous spheres and low-coordinated Ni3-triangles on Ni3S2(003)facet synergistically contribute to the electrocatalytic activity2.Exploiting high-performance electrocatalysts for oxygen evolution reaction(OER)is pivotal for renewable energy storage and conversion.The surface reconstruction of catalyst surface has been proven favorable for OER,whereas how to promote the active species generation and identifying the active site remain vague.Here,we report the synthesis of CoNi incorporated ε-Fe3N nanotubes(CoxNi1-x/ε-Fe3N,0≤x≤1)in situ on iron foil through anodization/electrodeposition/nitridation process.The synergistic CoNi doping induces the lattice expansion and up shifts the d-band center of ε-Fe3N,which enhances OH-adsorption and facilitates the generation of active Co0.5Ni0.5/FeOOH on surface.DFT calculations further reveal that the Ni site in Co0.5Ni0.5/FeOOH modulates the adsorption of OER intermediates and delivers a lower overpotential than those from Fe and Co sites,serving as the real active site for excellent OER performance.As a result,the optimized Co0.5Ni0.5/ε-Fe3N catalyst requires an overpotential of only 285 mV at a current density of 10 mA cm"2 with a Tafel slope of 34 mV dec-1,outperforming commercial RuO2 catalysts.This study provides valuable insights into the intrinsic catalytic mechanism of transition-metal based catalysts for water oxidation.3.High electronic conductivity and fast lithium ion diffusion are essential for the anode materials of lithium ion battery.We synthesized a series of FeXn(X=S,Se,Te)nanotubes on iron foil through anodization and chemical vapor deposition.Different anions result in different crystal structures,physical properties,nanotubular secondary structures and lithium storage performances.By tailoring the reaction condition of sulfuration/selenization/tellurization,FeSn and FeSen with different crystal phases and chemical ratios were obtained,including orthogonal FeS2,FeSe2,monoclinic Fe7S8,Fe3Se4,and teragonal FeTe.The decrease of electronegativity of X atoms enhances the conductivity of FeXn and Li2X;and the increase of anoionic radius improves the reversibility of lithiation and delithiation.Due to the Kirkendall effect,Te and Se elements with larger atomic mass induce more holes and defects on the wall of FeXn nanotubes.Under the synergetic effect of theoretical specific capacity,crystal configuration and secondary morphology of nanotubes,the lithium storage capacity of FeXn nanotubes reveals the following trend:Fe7S8<FeS2≈Fe3Se4<FeSe2/Fe3Se4<FeTe.Futher,FeXn nanotubes was coated with carbon layer by vapor deposition technology.After charging and discharging at different current densities,FeTe&C exhibits a capacity of 610 mAh g-1 at the current density of 1 A g-1,the corresponding volume specific capacity is 1403 mAh cm-3,closing to the twice of commercial graphite electrode.These results highlight the importance of anions on transition metal-based anode materials,and provide a good idea for the development of batteries with higher energy density.