Effect Of Ion Doping On The Electrocatalytic Performance Of PrBaCo₂O_5+? Perovskite

Owing to increase in the fossil fuel consumption and carbon emission,we aim to primarily develop clean and sustainable energy in future.Hydrogen(H₂)energy is considered to be one of the most potential candidates,and the most environment alfriendly way for producing hydrogen is the water electrolysis.Nowadays,precious metal-based materials have been used as highly efficient catalysts for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).However,the scarce reserves,expensive price,and weak cycling stability limit their large-scale applications.Therefore,it is necessary to rationally design source-plentiful and cost-cheap electrocatalysts.The perovskite oxides have attracted much attention due to high electrical conductivity,flexible element components,and modulated electronic structures.In this thesis,the cation and anion-doped Pr Ba Co₂O_5+?perovskite catalysts have been syntheszied,and their electrocatalytic HER and OER performance are studied.(1)Pr_xLa_1-xBa Co₂O_5+?(x=0-0.6)perovskite catalysts are synthesized by a glycine-nitrate firing method.Among all components,Pr_0.5La_0.5Ba Co₂O_5+?(P0.5LBC)exhibits the best alkaline HER activity.The overpotentials of P0.5LBC are 233 and 298 m V at10 and 50 m A cm^-2,respectively.The smaller Tafel slope means fast HER kinetics.The P0.5LBC catalyst possesses the highest double-layer capacitance(4.32 m F cm^-2)and mass activity(255 m A mg^-1).X-ray photoelectron(XPS)results indicate that the average valence state of Co ion is+3.32 in P0.5LBC.The high oxidation state of Co ion facilitates the charge trasnfer and adsorption of H₂O molecule,leadin to outstanding electrocatalytic performance.Furthermore,the Pr doping significantly promotes the long-term stability of the perovskite catalysts.(2)Combined with electrospinning and phosphatizing methods,P-doped Pr_0.5La_0.5Ba Co₂O_5+?nanofibers(P-PLBC-F)are successfully synthesized.Spherical aberration correction transmission electron microscopy(AC-TEM)and XPS results demonstrate that the phosphorous element exists in the form of P^3-ions that are coordinated with the Co ions.The overpotential of P-PLBC-F reaches as low as 307 m V at 500 m A cm^-2toward HER in a basic media,which is superior to that of commercial Pt/C catalyst.The Tafel slope of P-PLBC-F(only 32.9 m V dec^-1)is very close to that of the Pt/C benchmark.The electrolyzer with the P-PLBC-F and Ni Fe-layered double hydroxide(Ni Fe-LDH)electrodes delivers a voltage of 1.84 V at 500 m A cm^-2for overall water splitting.The density functional theory calculations reveal that the P doping not only enhances the hybridization of Co 3d-O 2p orbitals but also realizes the low charge transfer energy of Co 3d-P 3p,while remarkably reducing the Gibbs free energy for the H^*desorption.(3)Pr_0.5La_0.5Ba Co_2-x-yFe_xNi_yO_5+?(x=0-0.8 and y=0-0.6)perovskites are synthesized by a glycine-nitrate firing method.The results indicate that Pr_0.5La_0.5Ba Co Fe_0.6Ni_0.4O_5+?(PLBCF0.6N0.4)has the best catalytic OER activity.The overpotential of PLBCF0.6N0.4 is 361 m V at 10 m A cm^-2in a basic media,and its OER activity outperforms that of the Ir O₂benchmark at a large current density(>90 m A cm^-2).The excellent electrochemical performance of PLBCF0.6N0.4 benefits from abundant active sites,increased surface oxygen vacancies,and low charge transfer resistance.The current density of the electrolyzer with bifunctional PLBCF0.6N0.4 electrodes exceeds200 m A cm^-2at a voltage of 1.9 V,which is better than that of commercial Ir O₂and Pt/C couple.