Fabrication And Electrocatalytic Performance Of Transition Metal-based Sulfide And Boride For Oxygen Evolution Reaction

The application of fossil fuels promotes rapid socio-economic growth,but it also leads to various environmental and energy problems,which have seriously threatened the healthy development of human society and ecosystem.Nowadays,countries around the world seek a green development path and make unremitting innovations to achieve carbon neutrality.In the future,clean and sustainable energy alternatives to traditional fuels are inevitable to the public.Electrocatalytic water splitting is the clean and efficient new energy technology,which achieves continuous hydrogen production regardless of weather,geography and other environmental factors.The anodic process—oxygen evolution reaction（OER）leads to increasing voltage and limited application of water splitting due to the sluggish kinetic and the high energy barrier of O=O formation.OER catalysts are often used to accelerate the electrolysis process and reduce its energy consumption.The noble metal-based catalysts,such as Ir O₂ and Ru O₂ materials,are considered to exhibit excellent OER activity,but the scarcity and high cost make them difficult to be used by the general public.Therefore,the exploration on cheap,high-efficient and stable OER catalysts is significant for the sustainable development of water splitting.The dissertation focuses on the morphology and electronic structure modification of transition metal sulfides and borides by introducing heteroatoms,3D metal substrate and metal organic framework precursor.The self-assembled flower-like active materials,multi-metal coordinated electronic structure modification,"d-f electron ladder"at self-oxidizing interface,and metal framework-derived self-supporting boride electrode have been prepared and exhibit good electroactivity and stability.The mechanism of enhanced OER performance have also been investigated in depth.The main research contents and results are as follows.（1）The preparation of Bi atom-induced self-assembled flower-like catalysts.Based on the metal Ni foam（NF）,the self-assembled flower-like bismuth sulfide/nickel sulfide（Bi₂S₃/Ni₃S₂/NF）catalyst has been constructed by the simple solvothermal method.The self-supporting electrode has been prepared with optimal solvents,which avoids the decrease of conductivity aroused from adhesives and ensures the tight bonding of catalysts to substrate,thus enhancing the mass transfer and long-term stability during the catalytic reaction.Meanwhile,the introduction of Bi atom modifies the morphology of catalyst with charge rearrangement around the Ni atom,which provides more active sites for the reaction intermediates.It is shown that Bi₂S₃/Ni₃S₂/NF exhibits good OER performance with a low overpotential of 268 m V at the benchmark current density of 10m A·cm^-2 in 1.0 M KOH solution.Additionally,Bi₂S₃/Ni₃S₂/NF delivers stable oxygen production at high current density for 12 h,suggesting good stability in alkaline solution.（2）The electronic structure modification of multi-metal sulfides.Based on the self-supporting electrode strategy above,a simple one-pot solvothermal method has been used to construct bismuth-iron atoms synergistically modified ternary nickel-iron-bismuth sulfide（NFBS/NF）catalyst.The conductive NF substrate ensures fast mass transfer process and charge transfer process.The electronic structures and active centers have been synergistically modified by the multi-metal interaction,promoting adsorption/desorption process.Additionally,detailed characterization and analysis of the surface reconstruction and OER mechanism have been investigated for NFBS/NF catalyst.The results show that the surface reconstruction exposes abundant electrocatalytic active centers and provides sufficient reaction sites for the active intermediates.The high-valence Ni Fe species are responsible for the intrinsic electroactivity of NFBS/NF.Compared with other transition metal-based sulfides,NFBS/NF exhibits superior electrocatalytic OER performance with an overpotential of only 219 m V@10 m A·cm^-2,whereas NFS/NF and NBS/NF catalysts exhibit relatively higher overpotential of 243 and314 m V,respectively.Besides,NFBS/NF shows good stability for 20 h OER process.（3）The construction of"d-f electron ladder"at the self-oxidation interface of metal boride.The amorphous ternary Ni-Ce-B nanoparticle catalysts have been prepared by chemical reduction method.Due to the autoxidation of catalysts during the OER process,Ce O2-x（f orbitals）forms and acts as the electron acceptor on the surface of Ni-Ce-B（d orbitals）,resulting in"d-f electron ladder"at the Ni-Ce-B@Ce O_2-x heterogeneous interfaces.At the optimal Ce content of 5%,the Ni-Ce-B-5/NF catalyst exhibits the lowest overpotential of 240 m V@10 m A·cm^-2,which is 90 m V lower than that of Ni-B/NF（330m V）.Compared with Ni-B/NF catalyst,the stability of Ni-Ce-B-5/NF is significantly improved.The mechanism investigation shows that electrons first dive to Ce 4f orbitals and then bounce rapidly to Ni species（d orbitals）through the"d-f electron ladder"to promote the formation of high-valence Ni species,thus achieving efficient and stable electrocatalytic performance.（4）The construction of self-supporting metal boride electrode.The metal boride materials prepared by chemical reduction method are mostly in powder form,which leads to complicated electrode fabrication process and the usage of adhesive materials.The design and preparation of self-supporting metal boride electrode are significant for the research of electrocatalytic water splitting.Prussian blue analog-derived self-supporting cobalt-iron-based boride（CoFe-PBA-B）electrode has been successfully constructed on NF substrate using the solid-phase boronization engineering.The boronization method both improves the morphology and electronic structure of catalyst and also ensures the integrated structure of self-supporting metal boride electrode.CoFe-PBA-B shows outstanding OER activity among the boride catalysts,which only requires an overpotential of 255 m V to reach 10 m A·cm^-2.In addition,CoFe-PBA-B exhibits a long-term stability for 40 h in alkaline solution.