Surface/Interface Regulation Of Nickel-based Alloys And Its Application In Electrocatalytic Energy Conversion

Hydrogen energy is an important clean fuel and plays an indispensable role in the process of achieving the peak of carbon dioxide emission and carbon neutrality.Electrocatalytic water splitting is considered as an efficient routine to produce green hydrogen.However,the slow kinetics and high thermodynamic energy barrier of the anodic oxygen evolution reaction(OER)as well as the relatively low value of the evolved oxygen,greatly increase the cost of electrocatalytic water splitting for hydrogen production,which seriously restricts its industria(?)application.Therefore,realizing the efficient generation and utilization of oxygen is of grea(?)significance for the large-scale application of electrocatalytic water splitting to produce hydrogen.In addition,the selection of low-value organic small molecules for electro-oxidation to replace OER can also reduce the overall energy consumption of hydrogen production from water splitting,and at the same time,it is expected to obtain high value-added chemicals However,the key to realize the energy-saving hydrogen production and efficient preparation of high value-added chemicals lies in designing the corresponding reaction system and developing efficient and inexpensive non-precious metal-based catalysts to drive the corresponding electrochemical reactions.Nickel-based alloys have high electrical conductivity,easily tunable electronic structure,and excellent corrosion resistance,which makes them have broad application prospect in the field of electrocatalytic energy conversion.By adjusting the surface/interface properties of Nibased alloys,their catalytic properties can be further optimized and their application range expanded.In this regard,our works were carried out from the perspective of reaction pathway(oxygen evolution,oxygen utilization,and substitution of oxygen evolution),taking nickelbased alloys(Ni-Fe,Ni-B,Ni-N)as the main research object,combining the key factor of the above specific reactions,taking advantage of methods for nanostructure design and microstructure regulation,optimizing the surface/interface properties of nickel-based alloys by adjusting the electronic and geometric structure,combining theoretical calculation to study their structure-activity relationship in depth,and finally realizing the efficient electrocatalysis of hydrogen fuel and high value-added chemicals(hydrogen peroxide,benzonitrile,formic acid).The main research contents of this paper are as follows:In chapter 1,the significance of electrocatalytic energy conversion is briefly introduced,and then the basic principles and evaluation indexes of water splitting,ORR and electrooxidation of organics coupling hydrogen evolution are elaborated.Subsequently,the research progress of nickel-based materials in electrocatalytic energy conversion is(?)described,and the classification,preparation methods and basic strategies to optimi(?)electrocatalytic properties of nickel-based alloys are systematically introduced.By anal the shortcomings of nickel-based alloys in the current electrocatalytic application,a res idea to further optimize the catalytic properties of nickel-based alloys based on the regu of electronic structure and geometric structure towards its surface/interface is proposed.In chapter 2,in consideration of the slow kinetics of OER,from the perspecti increasing the number of active sites and improving the intrinsic catalytic ability of NiFe a the highly dispersed and surface fluorinated NiFe alloy(NiFe-F)was prepared via flori(?)stategy from NiFe-PBAs precursors.Compared to that of the adhesive NiFe alloy obtain traditional pyrolysis from NiFe-PBA,the NiFe-F alloy has a larger specific surface are stronger mass transfer capacity.In addition,along with the migration of F ions,the NiFe-F undergoes dramatic surface reconstruction during the OER process,which result i generation of many F-doped NiFeOOH nanosheets on the its surface.Compared NiFeOOH,F-NiFeOOH nanosheets exhibit superior electrical conductivity,stronger int catalytic ability,and more favorable adsorption of oxygen-containing intermediates.advantages enable NiFe-F alloys to exhibit excellent OER activity and stable operation at current densities.In chapter 3,in view of the relatively low value of oxygen,the Ni-B alloying strateg(?)used to tune the electronic structure of the metal Ni and optimize its ORR pathway,(?)realized the efficient electrosynthesis of H2O2 via two-electron oxygen reduction.Based(?)instability of interstitial atoms at high temperature,Ni3B alloys were subjected to temperature dealloying treatment,and experiments showed that the reaction gra(?)progressed toward the four-electron oxygen reduction pathway as the dealloying pr progressed.In addition,by alloying nickel and boron at high temperature,it is found that the increase of alloying degree,the reaction is more inclined to the two-electron ox reduction pathway.Through the process of dealloying and alloying,we experimentally rev that the synergistic effect between Ni and B is critical for 2e-ORR.Furthermore,the de functional theory(DFT)calculations indicate that the inner B atoms with high electronega decrease the state density of Ni-3d orbital near the Fermi level relative to elemental Ni,(?)optimizes the binding energy of OOH*and makes Ni3B as a highly efficient and stable ca(?)for 2e-ORR.In chapter 4,in view of the high thermodynamic energy barrier of OER,the benzylamine oxidation reaction(BOR)was selected to replace OER.Based on using interstitial atoms t(?)control the electronic structure of metal sites in the previous chapter,we further successfully realized the controllable insertion and migration of N interstitial atoms from Ni3N alloy throug(?)precise nitridation engineering,and prepare the Ni3N alloy and Ni-Ni3N heterostructures.XPS and UPS results show that the insertion and migration of N atoms achieves the continuous regulation of the electronic structure for Ni sites.Among them,the Ni3N alloy exhibits the excellent activity and selectivity for electrosynthesis of benzonitrile via BOR,and the overpotential is significantly reduced compared to the OER.Experiments and theoretica calculations show that the amino group on the benzylamine molecule has a lone pair of electrons and the N atom embedded in the Ni lattice will enhance the electrophilicity of the Ni site Therefore,the formation of Ni-N bonds is beneficial for the adsorption of benzylamin(?)molecules and the subsequent activation process.In addition,due to the strong electronic interaction between Ni and Ni3N at the heterointerface,the adsorption and desorption energy of H*intermediates on Ni3N electrode are further optimized,and the Ni-Ni3N heterostructure exhibits significant HER activity and stability.Finally,the two-electrode system composed o(?)Ni3N and Ni-Ni3N catalysts driven by solar panels realizes the efficient benzonitrile generation and energy-saving hydrogen production.In chapter 5,the microplastic upgrading reaction is selected to replace OER,and we creatively combine the electro-reforming of plastics coupled with HER in seawater.The 3D sponge-like Ni3N/W5N4 Janus heterostructure was designed via "transition metal nitridesinducing growth" strategy.Benefiting from the unique structural and compositional advantages of Ni3N/W5N4 Janus electrode:Hierarchical nanostructures,barrier-free Janus interface,confinement effect and synergistic effect,the Ni3N/W5N4 electrode displays Pt-like HER performance in deionized water/seawater,and the outstanding stability for～300 h under large current of 100-200 mA.Furthermore,Ni3N/W5N4 Janus nanostructure also exhibits the high activity and selectivity toward electro-reforming of plastics,showing an ultralow overpotential of 1.33 V(η10).Meanwhile,the value-added HCOOH is obtained with the high Faradic efficiency of～85%.Ultimately,the Ni3N/W5N4 bifunctional electrode realizes the efficient upgrading of microplastics and energy-saving hydrogen production in seawater,which is of great significance for marine environmental engineering and energy engineering.In chapter 6,the main research contents and the innovation points of this paper are summarized.Besides,the deficiencies are pointed out,and the future work is prospected.