Performance Investigation Of Oxygen Evolution Reaction Based On Strontium-Cobalt Perovskite Oxides

The perpetual growth of energy demand and the use of fossil fuel-based resources as well as the related environmental issues have stimulated the development of more sustainable energy storage and conversion technologies that rely upon renewable resources such as solar,wind,and tidal resources.The energy supply from these three resources however is subject to time and geographical location uncertainties;mostly of intermittent nature.Advanced electrochemical energy storage and conversion technologies such as water splitting,fuel cells,and metal-air batteries are considered as one of the key solutions to address this issue.Central to these technologies is an oxygen evolution reaction?OER?,which has sluggish kinetics given its complex four-electron oxidation process.It becomes essential to find an alternative lower cost catalyst that can provide high OER activity and long-term stability.At present,cobalt-based perovskite oxide catalysts have good catalytic performance.In this paper,based on previous studies,we focus on optimizing and developping excellent strontium-cobalt-based perovskite oxide for OER.These materials were systematically investigated based on the physical properties and electrochemical performance,and the relationships between them were explored.For the former one,an in-situ carbonate layer is decorated on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-??BSCF?surface,which increases the specific surface area as well as electronic conduction and leads to the improvement of catalytic performance.For the latter one,the electron state can be modilated by K and Fe doping.And it is verified that elements-doping can improve the OER activity.Therefore,the detailed researches are as following:1.Carbonate was modified on the surface of BSCF perovskite by simple heating treatment.The phase structure,morphology,performance and stability of the composite catalyst were investigated,and the reasons for the difference in catalytic activity were explained.In the atmosphere of carbon dioxide,Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-??BSCF?was sintered at temperature of 500,600 and 700?,respectively.A carbonate-modified perovskite composite,BSCF-X?X=500,600,700?electrode,was successfully prepared.BSCF-600 exhibits excellent catalytic performance,including onset overpotential of 240 mV;the overpotential is 357 mV at 10 mA cm^-2 current density,and the Tafel slope is 63 mV dec^-1.In addition,BSCF-600 exhibited the best intrinsic and mass activities,which were 5.04 mA cmcat^-2 and 74.14 A g^-1_cat,respectively.In alkaline solution,BSCF-600 electrode can maintain a potential of 1.61 V up to 800 minutes,which exceeds BSCF and noble metal oxide IrO₂.Finally,the reasons for BSCF-600 performance optimization were explored,including larger electrochemical surface area,faster charge transfer rate,larger conductivity and the increase of Co²⁺content in the crystal structure.2.By EDTA-CA method,elements-doping in SrCoO₃ perovskite oxides at A and B sites was completed.Meanwhile,their structure,morphology,properties and stability were studied.The reasons for the change of catalytic properties were also analyzed.SrCoO₃,as parent material,doped with K at A site and Fe at B site.Then,Sr_0.9K_0.1Fe_xCo_1-xO_3-?perovskite oxides?SKFC?were successfully synthesized.The intrinsic activity and mass activity of Sr_0.9K_0.1Fe_0.3Co_0.7O_3-??SKFC-37?are 7.10 mA cm^-2_cat and 43.103 A g^-1_cat,respectively,which surpass other materials of the same series.In addition,it exhibited onset overpotential of 235 mV,the overpotential is 365mV at 10 mA cm^-2,and the Tafel slope of 70 mV dec^-1.Compared with a series of SKFC catalysts and classical perovskite BSCF as well as IrO₂,the OER performance of SKFC-37 is outstanding.After that,the stability of the catalyst in alkaline solution was further studied.The stability of SKFC-37 was proved to be better by several methods,including accelerated durability test,cyclic voltammetry and chronopotentiometry.Finally,the reasons for the change of catalytic performance were comprehensively analyzed,contributing to faster ion transfer rate,larger electrochemical surface area,the formation of oxygen vacancy and the change of metal ion structure at B site.3.Using a combination of a chromatograph and an electrochemical workstation,the sampling time of the gas sample was analyzed by gas chromatography?GC?per 10 min from the start of the reaction in the potential control experiment and every 10 min from the stability test.The full solution process is controlled by an electrochemical workstation and collects relevant electrochemical data.The catalyst was supported on a 1*1 cm² carbon paper as an anode,the loading was 4 mg cm^-2,the platinum plate was used as the cathode of the complete water-releasing device,and the cathode and anode were placed in a sealed electrolysis of a 1 M KOH electrolyte solution.The pool consists of a full battery unit.The instantaneous potential method?CP?is adopted,that is,the current density is set to be constant,and the voltage and time are changed.Compared with the benchmark comparative catalyst noble metal oxide IrO₂,the hydrogen production rate of BSCF-600 and SKFC-37 catalysts increased,and the energy conversion efficiency increased by about 10%.