Theoretical Research On Optimizing Metal-based Electrocatalysts For Hydrogen Evolution/Oxidation Reaction Through Surface And Interfacial Regulation

Water electrolysis and hydrogen fuel cell are two important devices in the circulation and utilization of hydrogen energy.Pt group noble metal materials are efficient electrocatalysts for cathodic hydrogen evolution reaction(HER)in water electrolysis and anodic hydrogen oxidation reaction(HOR)in fuel cells.However,their high cost and low abundance hinder their large-scale application and commercial development of hydrogen energy devices.Therefore,developing cheap and high performance HER/HOR electrocatalysts is of great significance to promote the development of hydrogen energy.Designing and optimizing catalysts form the perspective of composition and structures are useful strategies for developing high-performance electrocatalysts.And deeply understanding the effects of strategies based on adjusting composition,modifing surface structures and constructing phase interfaces on the geometric and electronic structures of catalysts,the adsorption of intermediates and the reaction mechanism can not only contribute to the screening of electrocatalysts,but also provide theoretical guidence for rational design high-performance electrocatalysts.Based on this background,by means of theoretical calculation and experiment,this thesis mainly focuses on exploring the effects of elemental composition,surface strain and interfacial interaction on geometric structures,electronic structures and activities of electrocatalysts,so as to identify the relationship between the surface or interface properties and activities of electrocatalysts,and futher to screen out high-performance HER/HOR electrocatalysts.This thesis mainly contains the following four parts of work:(1)In view of the interaction between nonmetallic atom(X)and Ni in Nickle compound(Ni X)and the role of X in enhancing HER catalytic activity of Ni X are still ambiguous,a series of X/Ni(100)(X=B,C,N,O,S,Se,Te)composite models were built to decipher the contribution of X in catalytic activity of Ni X,and a series of Ni-Ni X catalysts with different X contents were synthesized to verify the calculated results.Results indicat that the electronegativity(?_X)and the principle quantum number(n _X)of X are two important descriptors for evaluating and predicting the HER catalytic activities of Ni X catalysts.The X atoms in VIA group can enhance the HER activity of X/Ni(100)more significant than theose in second period due to the large?_X or n _X.At relative low X coverage,the S/Ni(100)owns the best HER activity among all X/Ni(100),and the optimum surface S:Ni atomic ratio is about 22%?33%.Further,the experiment demonstrated that the Ni-Ni₃S₂ catalyst with surface S:Ni atomic ratio of 28.9%exhibits the best catalytic activity.(2)As the absence of rational design strategies toward nonmetallic atoms doping in Ni-based compounds HER electrcatalysts,a series of X doped Ni₃S₂(X-Ni₃S₂,X=B,C,N,O,P)electrocatalysts are explored to uncover the effects of nonmetallic dopants(X=B,C,N,O,P)on surface stability,electronic structures,H adsroption,H₂O dissociation and HER performance of Ni₃S₂ were investigated,and the alkaline HER activities of X-Ni₃S₂ were studied to screen high performance X-Ni₃S₂.Results illustrate that X doping in Ni₃S₂ can alter surface electronic states,change active sites,boost H₂O dissociation and optimize H ad-desorption.Especially,due to the strong C/O-Ni interaction,which induces favorable charge transfer and facilitates the formation of specific optimal active sites for H₂O dissociation and H ad-desorption,O-Ni₃S₂and C-Ni₃S₂ exhibit superior alkaline HER activities,which only require very low overpotentials of 68.4 and 85.5 m V,respectively,to deliver a geometrical current density of 10 m A cm^-2.(3)Aiming at the unexplained phenomenon of tensile strain weaken the adsorption of species on certain metal surfaces as the compressive strain do,Pt low-index surfaces were used as modles to explor the effect of strain on the species adsorption on different low index surface.Results confirmed that tensile strain on the close-packed Pt(111)and Pt(100)surfaces enhances species adsorption,while tensile strain on the open Pt(110)surface weakens species adsorption.The adsorption behaviors on strained surfaced are relate to the asynchronous change in the five 5d orbitals due to the inconsistency between interlayer contraction and biaxial stretching.And The dramatic contraction of interlayer spacing on the tensile strained Pt(110)surface sharply downshifts the d_z2center,then weakens species adsorption.Thus,due to the different roles of the five 5d orbitals in binding species,the inconsistent change in the five d orbitals is the intrinsic mechanism of the effects of strain on metal catalysts.(4)Considering the fuzzy role of interfacial interaction between metal(M)and transition metal oxides(TMO)in activities of M/TMO electrocatalysts,Pt/TiO₂composite models with interfacial Pt-Ti and Pt-O bonds were constructed respectively as examples to clarify the interface effect on electronic structures,species ad-desorption and migration properties,HER and HOR mechanism through DFT calculations.The results indicat that interfacial Pt-Ti metallic interaction causes more delocalized electron on Pt cluster,which strengthens H and OH adsorption,facilitates H*migration and H₂O dissociation.While interfacial Pt-O covalent interaction affects the localized electronic structure of Pt with deficient electron,which results in optimum H ad-desorption and complicated H*migration processes.The interface sites and non-interface sites jointly provide an efficient H migration channel and reaction pathway.For HER,Pt-O interaction benefits the Tafel step,and Pt-Ti interaction is favorable for the Volmer step.For HOR,Pt-O interaction contributes to a higher HOR activity and an anti-oxidation ability than Pt-Ti.