Catalysts Of LaMO₃(M=Fe?Co?Ni?Mn) Perovskite Oxides:Surface Engineering And Electronic Structure Regulation

With the progress and development of the society,the demand for energy in human production and life is growing.In addition,the depletion of traditional energy such as coal,oil and natural gas and the environmental pollution caused by its combustion are becoming increasingly serious.It is urgent to explore and develop clean energy with low cost and high efficiency.Among them,electrochemical energy storage and conversion devices such as rechargeable metal air battery,fuel cell and water splitting are especially concerned by scientists and industry.It is worth pointing out that oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are the most important reaction processes of the above energy storage and conversion devices.Therefore,it is an urgent need to develop efficient,stable,cheap and abundant non-noble metal catalysts with ORR and OER performance.In this article,we focuse on the surface modification,nanostructure design and electronic regulation of perovskite oxide based on transition metal,and revealing the reasons of enhanced catalytic performance and the corresponding electrochemical reaction mechanisms in the electrochemical process.Finally,the electrocatalyst with high activity and strong durability for zinc-air battery is developed,and the comprehensive evaluation from material to device performance is realized.The detailed research achievements are described as follows:(1)We report our findings in the development of a bifunctional catalyst based on phosphorus-doped La Fe O_3-?for ORR and OER in alkaline solutions.The remarkable electrocatalytic performance for ORR and OER is attributed to a large amount of O₂^2-/O^-species,trace amount of Fe⁴⁺species,and optimized e_g electron filling(?1).Both the mass activity and the specific activity are nearly doubled after P-doping.Density functional theory calculations also confirm that the phosphorus doping can not only increase intrinsic electrical conductivity but also increase the valence state of Fe ions.These are the main reason for the increased catalytic activity of ORR and OER.Therefore,P-doping is an effective strategy to regulate the electrocatalytic activity of La Fe O_3-?,and this method is also applicable to other 3d transition metal oxide perovskite oxides,such as La Ni O₃ and La Co O₃.(2)One-dimensional La Fe_1-xNi_xO₃(x=0,0.25,0.5,0.75 and 1)nanofibers((LNFO NFs)with different Ni/Fe ratio were prepared by a feasible electrospinning route and its further implemented post-annealing.We found that OER performance was best when the ratio of Ni/Fe was 3:1(La Fe_0.25Ni_0.75O₃).In addition,we also fabricated Se-doped La Fe_0.25Ni_0.75O₃(LFNOSe-III)NFs,the result shows that the Se-doping can not only replace oxygen atoms to improve intrinsic electronic conductivity of LNFO which will facilitate the charge transfer,but also introduce abundant oxygen vacancies to uplift the O2p band center close to the Fermi level to accelerating reaction kinetics and optimizing the adsorption energy of intermediates in the OER process,which is further confirmed by density functional theory calculation.The result of valence band spectrum test also confirmed that the d-band center of Ni/Fe was positively shifted,which enhanced the hybridization degree of Ni/Fe 3d and O 2p,and further optimized the adsorption energy of intermediates in the OER process.Consequently,the as-prepared LFNOSe-III NFs exhibits outstanding OER activity and long-term stability.(3)A feasible strategy is developed for boosting the oxygen evolution reaction(OER)kinetics of La_0.6Sr_0.4Co_0.8Fe_0.2O₃nanofibers(LSCF NFs)by encapsulation of conductive metal-organic frameworks(MOF)of Ni3(HITP)2 on the surface via electrospinning and its further implemented post-annealing treatment.And the quality ratio between Ni₃(HITP)₂and La_0.6Sr_0.4Co_0.8Fe_0.2O₃ was adjusted to further optimize OER performance.It was also found that the obtained La_0.6Sr_0.4Co_0.8Fe_0.2O₃@Ni₃(HITP)₂-2 catalyst exhibits remarkably enhanced OER performance and long-term stability towards OER when the mass ratio between La_0.6Sr_0.4Co_0.8Fe_0.2O₃ and Ni₃(HITP)₂ was 1:1.The excellent OER activity is mainly attributable to the synergistic effect of unique 1D(dimensional)NFs structure and the coupled conductive MOF,which endows intrinsic electrical conductivity and fast charge transfer kinetics.(4)We report a new method for enhancing OER activity of La Ni O3 perovskite via encapsulating amorphous Fe OOH layers.The molar ratios between La Ni O₃ and Fe OOH was further regulation and optimization.It was found that the obtained La Ni O₃@Fe OOH-1:1 catalyst demonstrates remarkably enhanced OER performance when the molar ratios between La Ni O₃ and Fe OOH was 1:1.The excellent OER activity is attributed mainly to the optimized adsorption energy for oxygenated species(Fe OOH possess strong adsorption energy,La Ni O₃ possess low adsorption energy)and fast charge transfer kinetics.Similar enhancement effect of Fe OOH is also observed for other perovskite oxides(La Co O₃ and La Mn O₃),suggesting that the developed approach could be an effective strategy towards enhancing OER activity of perovskite catalysts.Moreover,when the La Ni O₃@Fe OOH is used as the OER catalyst in a rechargeable Zn–air battery,the overpotential of the cell is reduced while maintaining long cycling life.