Uncovering The Impact Of Anionic Defects On Oxygen Evolution Reaction Activity Of Double Perovskite Oxide Electrocatalysts

In the face of the growing energy crisis,electrocatalytic technology is considered to be a promising solution for large scale conversion and storage of sustainable energy.Owing to the high efficiency and environmental friendliness,electrochemical energy conversion and storage devices,such as regenerative fuel cells,electrolysis cells and metal-air batteries,have attracted great attention.The performance of these devices are determined sensitively by the activity of electrocatalysts for several electrochemical reactions such as oxygen evolution reaction?OER?,oxygen reduction reaction?ORR?,and hydrogen evolution reaction?HER?.In particular,owing to the sluggish reaction kinetics,oxygen evolution reaction?OER?is usually the limiting process for many energy systems.The commonly used OER electrocatalysts are noble metal catalysts such as Ir O₂ and Ru O₂.Although these catalysts exhibited good catalytic performance for OER,the high cost and poor stability strongly limit their practical applications.Transition metal oxides?TMO?are expected to become a new generation of OER catalysts due to their low cost and good stability.However,the catalytic performance of transition metal oxides needs to be further improved to meet the requirement for industrial applications.Anionic defect engineering?introduce of oxygen defects and transmission of oxygen vacancy?recently emerged as a promising method to improve the electrocatalytic activity of transition metal oxides.Commonly observed in transition metal oxides,anionic defects?such as oxygen vacancies,oxygen interstitials and N/P/S doping?are found to critically affect the material properties such as electronic structure?shift of M 3d and O 2p band distance;O 2p band position relative to Fermi levels;band gap and e_g state filling?,ionic/electronic conductivity,and magnetic properties.In addition,anionic defects can significantly modify the adsorption and dissociation reactant or reaction intermediate,resulting in changes in reaction kinetics.So that the material exhibits more excellent electrocatalytic activity.However,due to the complex catalyst catalysis process and many influencing factors,the mechanism of affecting the OER activity on anion defects is still unclear.And there has been no systematic study on the correlation between the transport properties of protons and the reaction kinetics of OER.In addition,the technology to control the introduction of anion defects needs to be developed.In this paper,the double perovskite oxide Pr Ba_0.5Sr_0.5Co_1.5Fe_0.5O_5+??PBSCF?was chosen as a model system because of its outstanding OER activity,the capability to accommodate a large amount of oxygen vacancies without changing the crystal structure,and‘triple'conductivity(H⁺/O^2-/e^-).During the study,we prepared PBSCF thin film by pulse laser deposition?PLD?as a model system,combined with surface sensitive characterization techniques,first-principle calculations,and in-situ technology to study the effect mechanism of anion defects on the electrocatalytic activity of PBSCF.In addition,we improve the OER catalytic activity of the material through anion defect regulation.The specific research results include the following:1. We systematically studied the effect mechanism of the oxygen vacancy introduced by thermal annealing in H₂ and electrochemical reduction on the catalytic activity of PBSCF thin film material OER.Utilizing scanning tunneling microscopy/spectroscopy?STM/S?,X-ray photoelectron spectroscopy?XPS?,and first-principle calculations,we find that excessive oxygen defects promote OH^-affiliation and lower the theoretical energy for the formation of O*?Potential Determining Step as HO^-to O*?on the surface,thus greatly facilitating the OER kinetics.On the other hand,however,oxygen defects also increase the energy band gap and lower the O 2p band center of PBSCF,which may hinder OER kinetics.Still,careful tuning of these competing effects has resulted in enhanced OER activity for PBSCF with oxygen defects.In particular,PBSCF nanotubes after electrochemical reduction exhibit outstanding OER activity compared with the recently reported perovskite-based catalysts.2. We used Ar and H₂ plasma treat PBSCF,controllably introduce various concentrations oxygen defects into the material,and further study the effect of oxygen defects on the OER mechanism.Electrochemical tests show that the OER activity of PBSCF is significantly boosted with the addition of oxygen defects.In addition,the p H dependence test shows that oxygen defects formation in PBSCF lead to decoupled protons and electrons transfers in the OER process.The reason may be that the presence of oxygen vacancies changes the OER reaction pathway,so that the lattice oxygen sites participate in the OER,causing proton and electron transfer to occur in different reaction pathway.We also applied plasma processing to powder materials.The obtained defective PBSCF powders exhibits significantly enhanced OER performance,with much lower overpotential at high current density than commercialized Ir O₂catalysts.3. We controlled the proton electron transfer process of PBSCF by controlling different crystal orientations and proton transport,thereby further improving the OER catalytic activity of PBSCF.Using PLD technology,we prepared?100?,?110?,?111?crystal orientation PBSCF thin films on La Al O₃?LAO?.Electrochemical measurements,density functional theory?DFT?calculations,and synchrotron-based near ambient X-ray photoelectron spectroscopy showed that the order of OER activity and deprotonation speed of PBSCF follow the order:?100?>?110?>?111?.We believed that the PBSCF?100?orientation has a higher proton transfer process,which promotes the proton coupled electron transfer?PCET?in the OER reaction on its surface,making it have the highest OER catalytic activity.This result provides a novel perspective for the design and optimization of new high performance OER catalysts.