Design Of Interface Engineering And Electrolytic Water Performance Research On Iron-triad Nanomaterials

With the depletion of fossil energy and the worsening of the environment,it is imperative to develop new energy sources without pollution.Hydrogen energy(H2),due to its high combustion heat and pollution-free product characteristics,will become a favorable alternative to fossil fuels in the future.Hydrogen production by water electrolysis is currently one of the most efficient and ideal strategies for producing hydrogen energy.However,high overpotential always causes additional energy consumption and reduces energy conversion efficiency.Electrocatalysts can significantly reduce overpotential,reduce energy consumption,and improve production efficiency.Noble metal Pt based materials,Ru based materials,and Ir based materials are considered as benchmarks for the current HER and OER catalysts,respectively.However,its low reserves and high preparation costs seriously restrict its future industrial application.Non-noble transition metal materials have received widespread attention from researchers due to their high earth reserves and flexible composition and structure.However,its weak intrinsic conductivity,poor catalytic activity,and limited number of surface active sites make it impossible to meet the demands of future production applications when used alone.Based on iron-triad metal nanomaterials,this paper constructs heterogeneous interfaces through interface engineering to overcome some of their inherent shortcomings and achieve better electrocatalytic activity.In this paper,heterogeneous interfacial electrocatalysts,such as metal-supported,hierarchical,heterojunction,and atomic interfacial electrocatalysts,have been designed,and their common synthesis methods have been briefly described.Based on advanced characterization techniques and theoretical simulation calculations,the origin of better catalytic activity at interface sites has been revealed.Due to the different Fermi energy levels between heterogeneous phases,when the two are combined,it is bound to cause electron transfer between the two phases,which not only improves the energy transfer of charge at the interface,but also optimizes the adsorption energy of interface sites on reaction intermediates,thereby improving catalytic activity.The specific contents is as follows:Part Ⅰ:Interface engineering is an effective strategy for controlling the surface properties of materials and improving their catalytic activity.We have developed an interface engineered catalyst with a core-shell structure of FeP@CoP,which can achieve 10 mA/cm2 with only 50 mV and a low Tafel slope of 51.1 mV/dec in 1 M KOH.This layered structure is not only conducive to improving the specific surface area,but also conducive to exposing more surface active sites.The unique selfsupported structure ensures good contact between the CoP nanowires and the conductive Ni foam,improves the electron transfer and mass transfer capabilities of the electrode,and is conducive to demonstrating good mechanical stability during the electrolytic reaction process.Density functional theory(DFT)simulation shows that the interfacial effect between FeP nanosheets and CoP nanowires will significantly adjust the electronic structure of the active sites,optimize the H*adsorption free energy,and obtain better catalytic performance.In addition,assembled NiFe LDH@Co3O4/NF‖FeP@CoP/NF electrolytic cells require only 1.50 and 1.70 V voltages at 1 M KOH to achieve 10 and 100 mA/cm2.The electrolyzer also exhibits excellent catalytic performance in alkaline seawater electrolytes.And it can also be driven by commercial Si solar panels under illumination conditions of AM 1.5 G 100 mW/cm2.Part Ⅱ:Transition metal phosphides(TMPs)are considered as substitutes for Pt-based catalysts used in electrochemical hydrogen evolution reactions(HER),but their low conductivity and limited catalytic activity hinder their application.Interface engineering is a feasible way to enhance the catalytic activity of TMPs in the HER process.Here,Ni2P/Ni5P4 heterojunction 2D porous nanosheets with interface engineering have been developed through a simple solvothermal method and controllable low-temperature phosphating treatment.DFT calculation results show that the active sites on the Ni2P/Ni5P4 heterojunction interface have a more ideal H*adsorption/desorption free energy compared to single-phase Ni2P and Ni5P4,which can lead to electron redistribution and optimization of electronic structure,thereby improving the HER catalytic activity of Ni2P/Ni5P4 heterojunction nanosheets.In addition,layered porous structures increase their close contact with electrolytes and can more effectively utilize exposed active sites.The experimental results show that Ni2P/Ni5P4 heterojunction nanosheets exhibit excellent HER performance in the universal pH range.By assembling it with the NiFeCH anode,we have built a NiFeCH‖Ni2P/Ni5P4 electrolyzer,which requires only 1.52 V to obtain a current density of 10 mA/cm2 in 1 M KOH.Even in complex seawater systems,the electrode and assembled electrolyzer exhibit excellent electrocatalytic hydrogen production performance.Part Ⅲ:Fabricating a functional heterogeneous interface to enhance the catalytic performance is quite significant for developing high-efficient electrocatalysts.Herein,we designed a coral-like Ni2P@CeO2 hybrid nanoarrays on nickel foam via selective-phosphorization of Ni(OH)2@CeO2.Benefiting from CeO2 as the "electron pump",it leads to electrons transfer from Ni2P to CeO2 side,and induces the electrons redistribution in interface boundary,thereby optimizing the H*adsorption free energy in HER process.As proposed,owing to the superior affinity to oxygen-containing species of CeO2,the H2O molecule will preferentially adsorb on CeO2 side,and easily decompose into OH*and H*with lower energy barrier.Subsequently,benefiting from the lower H*adsorption free energy of Ni2P phase,the generated H*will transfer to Ni2P side through spillover process.Contributing to the synergistic effect of double-active sites,the Ni2P@CeO2/NF electrode exhibits brilliant catalytic performance for HER with 62 mV to attain 10 mA/cm2 and exceptional durability over 100 h in 1 M KOH solution under～100 mA/cm2.Meanwhile,attributing to the similar interface electrons redistribution effect,the precursor Ni(OH)2@CeO2/NF also displays excellent OER electrocatalytic performance,it only requires 229 mV to arrive 10 mA/cm2,even better than benchmark RuO2.Hence,the assembled Ni(OH)2@CeO2/NF‖Ni2P@CeO2/NF system only needs 1.53 V to achieve 10 mA/cm2 in alkaline solution.Moreover,the electrolyzer also presents brilliant electrocatalytic activity and stability in natural seawater alkaline electrolyte with higher reserves on earth.Part Ⅳ:Heteroatoms Fe,F co-doped NiO hollow spheres(Fe,F-NiO)was designed,which simultaneously integrates promoted thermodynamics by electronic structure modulation with boosted reaction kinetics by nano-architectonics.Benefiting from the electronic structure co-regulation of Ni sites by introducing Fe and F atoms in NiO lattice,as the rate-determined step(RDS),the Gibbs free energy of OH*intermediates(ΔGOH*)for Fe,F-NiO catalyst is significantly decreased to 1.87 eV in OER process compared with pristine NiO(2.23 eV),which reduces the energy barrier and improves the reaction activity.Besides,DOS result verifies that the bandgap of Fe,F-NiO(100)is significantly decreased compared with pristine NiO(100),which is more beneficial to promoting electrons transfer efficiency in electrochemical system.Profiting by the synergistic effect,the Fe,F-NiO hollow spheres only requires the overpotential of 215 mV for OER at 10 mA/cm2 and extraordinary durability under alkaline condition.And the assembled Fe,FNiO‖Fe-Ni2P system only needs 1.51 V to reach 10 mA/cm2,also exhibits outstanding electrocatalytic durability for continuous work up to 100 h.More importantly,replacing the sluggish OER by advanced sulfion oxidation reaction(SOR)not only can realize the energy saving H2 production and toxic substances degradation,but also bring additional economic benefits.Part Ⅴ:Interface engineering and cation doping engineering are verified as the effective methods to improve the sluggish electrocatalytic performance of transition metal-based electrocatalysts.Here,we synthesized a self-supported heterostructure of Ce doped Co(OH)2 nanosheets/CoP nanowires on the support of nickel foam(Ce-Co(OH)2/CoP/NF)by simple hydrothermal method,lowtemperature phosphorization method.The Ce atom doping can lead to lattice distortion and abundant superficial defects on crystal surface,which will generate more active sites and faster charges transformation.The heterointerface between Ce-Co(OH)2 and CoP also can lead to electronic structure modulation at interface domain,which not can induce much fresh active sites in this area,but can optimize the active sites to the optimal state for superior catalytic activity.Benefitting from these,it shows much enhancement than single-phased samples.As the bifunctional electrocatalyst for two-electrode system,it also exhibits outstanding overall water splitting performance in alkaline natural electrolyte,along with excellent catalytic long-time durability.In addition,the Ce-Co(OH)2/CoP/NF-based electrolyzer also could achieve energy-saving hydrogen production,and simultaneously oxidative degradation of organic materials or biomass upgrading at anode under lower voltages.Part Ⅵ:Modulation the interfacial interaction of metal-support has been recognized as an effective strategy to improve the electrocatalytic performance of supported-type catalysts.Here,we have successfully synthesized the electrocatalyst of Ni2NPs anchored on B,N co-doped graphite-like carbon nanosheets(Ni2P@B,N-GC),and disentangled the main mechanism by B atoms doping effect on the enhancement of electrocatalytic HER process.The 2D opening porous structure of graphite-like carbon support ensures abundant growing sites for Ni2P NPs and decrease the particles agglomeration.The B atoms with unique electron donor characteristic will modulate the electronic structure of carbon skeleton,and modulate the interaction between Ni2P and carbon-based support,which will lead to the increased available electrons density of Ni2P.This improvement is conducive to accelerating the proton transfer and promoting the reactive activity.As revealed.the Ni2P@B,N-GC catalyst with B atoms doping exhibits much superior performance than Ni2P@N-GC catalyst in universal pH range of acidic,neutral and alkaline solutions.Besides,the assembled Ni(OH)2@B,N-GC‖Ni2P@B,N-GC electrolyzer displays prominent overall water splitting performance for hydrogen production.It only requires 1.57 V to reach 10 mA/cm2,even in complicated natural seawater electrolyte,it also needs as low as 1.59 V.Hence,the B atoms doping strategy shows the significant enhancement for HER electrocatalysis.