Design Of Doped-hexagonal Perovskite Oxides And Their Application In Electrocatalysis Of Oxygen Evolution Reaction

Developing highly active and stable oxygen evolution reaction(OER)catalysts has been a key and challenging part of sustainable energy applications.However,due to the slow kinetics of OER,considerable overpotential is required to provide the current density for practical application.Perovskite oxides,as one of the hotspots of OER catalyst research,exhibit efficient OER catalytic performance by virtue of their highly adjustable element composition and electronic structure.However,the study on perovskite OER catalysts is limited to cubic crystal phase system,the study on hexagonal perovskite is rare.In this work,a series of hexagonal perovskites were synthesized based on the noble metal doping strategy.Their performances in OER catalysis were also investigated:1.Based on parent perovskite 12H-Ba0.9Sr0.1Co0.8Fe0.2O3-?(BSCF-91),a 6H-Ba0.9Sr0.1Co0.8Fe0.1O3-?(BSCFI-91)has been successfully synthesized firstly by doping Ir into B site.A low-level Ir substitute for Fe in BSCF-91 did not change its hexagonal crystal structure,but decreased the formation temperature and significantly enhanced electrocatalytic performance towards OER.As a highly active electrocatalyst for OER,BSCFI-91 delivers a current density of 10 mA cm-2 at a low overpotential of 300 mV and the outstanding stability for 10 h in 1.0 M KOH electrolyte.Its Tafel slope(61.2 mV dec-1)and overpotential are apparently lower than that of BSCF-91 and also superior to commercial RuO2 and IrO2,benchmark cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-?(BSCF-55)and other pseudocubic perovskites reported in the literature.Combining the refined parameters from X-ray diffraction pattern(XRD)and results of X-ray photoelectron spectroscopy(XPS),it is believed that excellent OER catalytic activity of BSCFI-91 can be attributed to the reduction of the surface cobalt valence state and the increase of the relative content of O22-/O-.According to the DFT results,the O p band center close to the Fermi level can also account for the performance improvement of Ir-doped BSCF-91.2.A series of low-concentration Ir and Ru-doped hexagonal perovskite oxides were synthesized based on cubic perovskite BSCF-55 and hexagonal perovskite BSCF-91,respectively.From XRD,it can be found that the crystal structure of samples in BSCF-55 doping system is dominated by the 10H hexagonal structure,but most of them are not single phase;Different from the BSCF-55 doping system,the crystal structure of samples in BSCF-91 doping system belongs to 6H hexagonal structure and there are no obvious impurity peaks found.The electrochemical test results show that the overall OER catalytic activity of the BSCF-91 doping system is better than that of the BSCF-55 doping system.Inferred from the XPS spectrum,the catalytic activity of the catalyst increases along with the increase of relative content of O22-/O-on the sample surface.Moreover,the effects of synthetic temperature on the crystal structure and OER performance were also explored.As the temperature increasing,the number of layers in c axis of crystal unit cell correspondingly increased,and the OER activity decreased slightly.