The blue, green, and purple circles represent the position of the oxygen vacancies in the 1st, 2nd, and 3rd layers, respectively. XPS spectra of (c) cobalt 2p orbitals and (d) oxygen 1s orbitals of the Co-NSC composite. b) Additional discharge and charge profiles are investigated at higher current density in the range from 0.5 to 2.0 mA cm-2.
Introduction
- Kinetics and mechanism of the ORR and OER
- Solid Oxide Fuel Cell (SOFC)
- Metal-Air Battery (MAB)
- Perovskite Oxide
As shown in Equation (1.2.4), ORR requires not only oxygen and electrons, but also the transport ability to transport the generated oxygen ions from the reaction site to the inside of the bulk electrolyte. The high oxygen vacancy concentration in perovskite oxides not only facilitates the migration of oxygen species on the surface but also inside the bulk of the electrode material.40 On the other hand, for MAB devices, the high performance of perovskite oxides was explained without ionic conductivity.
Conductivity-Dependent Completion of Oxygen Reduction on Oxide Catalysts
Experimental
The loading density of the catalyst and carrier agent composition was fixed at 0.8 mg cm-2. For geometry optimization, the convergence thresholds for the maximum energy change were set to be 1×10-5 eV/atom (for fixed lattice) and 5×10-.
Results and Discussions
However, the difference in value between the catalysts became smaller as the carbon content increased (Fig. However, the more conductive catalysts (LSCO and NBSCO) did not show a significant change in c with carbon content except for 0 wt% C.
Conclusion
Major role of surface area in perovskite electrocatalysts for alkaline systems
Experimental
To precipitate the metal cations, 30 ml of aqueous (NH4)2CO3 solution (10 wt%) was slowly added to the solution by a syringe pump while stirring at 700 rpm. LnSC inks were prepared by dispersing 20 mg of nanoparticles in 0.45 mL of ethanol, 0.45 mL of isopropyl alcohol, and 0.1 mL of 5 wt% nafion solution without any conductive material. The loading density of the nanoparticle-conductive agent composite was determined to be 0.8 mg cm-2.
ORR polarization curves were obtained on a disk electrode with a cathodic sweep from 0.1 V to -0.9 V (vs. Hg/HgO) at 10 mV s-1 after several CV cycles.
Results and Discussions
Interestingly, the catalytic activities of the measured samples, which have similar surface area (~30 m2 g-1), were independent of the different lanthanides in the A site. The results show that the surface area only affects the current densities, which causes drastic changes (Fig. 3.5). Also, the current densities of OER at −0.9 V (vs Hg/HgO) decreased rapidly with decreasing surface area.
Therefore, it is confirmed that the improvement of ORR and OER only comes from increasing the surface area.
Conclusion
Enhancing Bifunctional Electrocatalytic activities via Metal d-Band-Center-Lift in
Experimental
To control the oxygen depletion, the sintered sample was annealed at 800 oC for 1 hour and the sample was quenched at 25 oC (room temperature) or -196 oC (liquid nitrogen). A Brunauer–Emmett–Teller (BET, BELSORP-max, MicrotracBEL Corp.) measurement was performed for the SSC surface using N at 77 K. A voltage of 0.4 V was applied to the ring electrode to estimate the amount of peroxide formed from the disk electrode.
The dipole correction was taken into account in all the slab calculations.28 The convergence criteria for structure optimization was set to 0.02 eV Å-1.
Results and Discussions
Then ring-rotating disk electrode (RRDE) measurements were performed to check the ORR and OER catalytic activities of different SSC samples (Fig. 4.5). The closer the oxygen vacancies are to the surface, the greater the catalytic reaction. In contrast, in OER, the RDS depends on the position of the oxygen vacancy; the second step for V2-SSC and the first step for all other samples (Fig.
The free energy profile for the oxygen-mediated pathway (LOM) of OER is given in Fig.
Conclusion
Introduction
Optimization of LaxSr1-xCoO3-δ perovskite cathodes for medium temperature solid oxide fuel cells by analysis of crystal structure and electrical properties. Therefore, we optimized the effect of lanthanum doping by systematically evaluating the structural and electrochemical characteristics of the LSC cathode with respect to its application as an IT-SOFC cathode material. In this study, we report excellent electrochemical performance under operating conditions by doping La onto the A site of the Sr1-xCoO3-δ potential cathode material.
In addition, we study the structural features and electrochemical properties of LaxSr1-xCoO3-δ (x and 0.7) with respect to its application as an IT-SOFC cathode material.
Experimental
LaxSr1-xCoO3-δ and GDC powders are mixed using the ball milling process for 24 hours with the weight ratio of 6:4 to measure the cell performance. The Ni-GDC anode is produced from nickel oxide, GDC powder and starch mixture (weight ratio and ball milling with ethanol for 24 hours. The GDC electrolyte layer is made by drop coating process on the surface of Ni cermet anode - GDC.
An aluminum tube is used to place the single cell using a ceramic adhesive (Aremco, Ceramabond 553).
Results and Discussions
Thermogravimetric analysis (TGA) data describing the change in weight and oxygen content in LaxSr1-xCoO3-δ oxides upon heating to 1173 K in air are shown in the figure. The electrical conductivity of LaxSr1-xCoO3-δ cathodes is presented in the temperature range of 373~1023 K in air, as shown in the figure. Crystal structure is an important factor in the electrochemical performance of LaxSr1-xCoO3-δ oxides.
At x ≤ 0.5, LaxSr1-xCoO3-δ retains the cubic structure; however, above x = 0.5, LaxSr1-xCoO3-δ oxide structures are changed to rhombic structures.
Conclusion
In contrast, a two-electron transfer pathway is partially responsible for the ORR current; does not carry out a reaction of the ORR, but generates peroxide as an intermediate. However, their low electron transfer number (n) generates large amounts of HO2− oxidants that induce oxidation/corrosion of carbon carriers, resulting in an increase in charge/discharge overpotential.15-19 In addition, Li2CO3 is generated from the reaction between carbon and intermediates (Li2O2) during the discharge process gives rise to an increase in the resistance and degradation of the cycle performance of rechargeable solid-state Li-air batteries.20 To overcome the disadvantages of both noble metals and carbon materials, it is necessary to develop a noble metal and carbon-free catalyst material. The stoichiometric NSC is also synthesized and compared to identify the effect of the composite on microstructure and electrochemical properties.
Here, we investigate the electrochemical effect of cobalt oxide and perovskite composite electrocatalysts fabricated via an electrospinning process compared to state-of-the-art catalysts and performed in a lithium-air hybrid battery.
Experimental
A lithium foil with a thickness of 0.2 mm was obtained from Honjo Metal, and discs with a diameter of 1 cm were cut for use as the anode. 1 M lithium hexafluorophosphate (LiPF6, Sigma-Aldrich Co.) in tetraethylene glycol dimethyl ether (TEGDME, Sigma-Aldrich Co.) was used as an organic liquid electrolyte, and 0.1 M lithium hydroxide (LiOH, Sigma-Aldrich Co.) in pure water was used as the aqueous liquid electrolyte. The air electrodes were prepared by spraying the catalyst ink made with the prepared catalysts, carbon (catalyst:carbon = 4:1 wt. ratio) and PVdF-HFP binder (Sigma-Aldrich Co.) onto the gas diffusion layer (Toray TGP). -H-090).
Thus, the current density could be easily normalized with the catalyst loading density (0.8 mg cm-2).
Results and Discussions
The cobalt oxides and NSC exist separately and are uniformly distributed in the Co-NSC composite. The slice current for the ORR of the NSC and Co-NSC catalysts is shown and compared to that of a commercial Pt/C catalyst (Fig. Interestingly, the current density of the Co-NSC composition is comparable to that of Pt/C at high tension.
Even at a higher current density of 2.0 mA cm-2, the difference in charging voltage between Co-NSC and Pt/C increases to 0.33 V.
Conclusion
A highly efficient and robust cation-ordered perovskite oxide as a bifunctional catalyst for rechargeable zinc-air batteries. The demand for safe, clean and renewable energy has stimulated extensive research into rechargeable metal-air batteries. Recently, the cation-ordered perovskites have been effectively used as an electrode in high-temperature applications (600~900 oC) due to their high oxygen kinetics, electrical conductivity, and structural stability compared to ABO3-δ type perovskite oxides.23-33 Recently, these oxides have been explored as an efficient and stable oxygen catalyst for low-temperature applications.15, 19.
Moreover, it also showed remarkable charge-discharge stability even at high current density (10 mA cm-2) in Zn-air batteries37, 38.
Experimental
A zinc plate was used as the anode, which was separated by a nylon polymer membrane separator (Cell guard 3501 membrane) from the cathode, and a 6 M KOH electrolyte was filled between the cathode and the anode, and a nickel grid was used as a current collector. The only difference between the primary and the rechargeable Zn-air battery was that 0.2M zinc acetate in 6M KOH should be added as the electrolyte for the rechargeable battery. For comparison, a pristine air electrode was used, which could act as a gas diffusion layer composed of carbon and PTFE binder.
Results and Discussions
The morphology of PBSCF-NFs was tailored by varying the precursor solutions and electrospinning parameters. The OER performance of PBSCF-NF was investigated in 0.1 M KOH solution (PH=13) and compared with PBSCF-P, IrO2 and BSCF. In addition, the superior electrochemical stability of PBSCF-NF was confirmed by a long-term cycling test (5000 cycles) in 0.1 M KOH solution.
Discharge polarization curves of PBSCF-NF and Pt/C were obtained by scanning current densities up to 300 mA cm-2 as shown in Figure 1.
Conclusion
List of Publications
Changmin Kim, Ohhun Gwon, In-Yup Jeon, Youngsik Kim, Jeeyoung Shin, Young-Wan Ju*, Jong-Beom Baek* and Guntae Kim*, Cloud-like graphene nanosheets on Nd0.5Sr0.5CoO3-d nanorod as an efficient bifunctional electrocatalyst for Hybrid Li-air Batteries, J. Dong-Gue Lee†, Ohhun Gwon†, Han-Saem Park, Su Hwan Kim, Juchan Yang, Sang Kyu Kwak, Guntae Kim* and Hyun-Kon Song*, Conductivity-Dependent Termination of oxygen reduction on oxide catalysts, Angew. Ohhun Gwon, Seonyoung Yoo, Jeeyoung Shin* and Guntae Kim*, Optimization of La1- xSrxCoO3-d perovskite cathodes for intermediate temperature solid oxide fuel cells through analysis of crystal structure and electrical properties, Int.
Areum Jun, Seonyoung Yoo, Ohhun Gwon, Jeeyoung Shin and Guntae Kim*, Thermodynamic and electrical properties of Ba0.5Sr0.5Co0.8Fe0.2O3-d and La0.6Sr0.4Co0.2Fe0.8O3-d for solids at intermediate temperatures oxide fuel cells, Electrochim.
Permissions
Almond stick-type perovskite-cobalt oxide composite, doi jes). from “A highly efficient and robust cation-ordered perovskite oxide as a bifunctional catalyst for zinc-air rechargeable batteries,” 10.1021/acsnano.7b06595). Guntae Kim for his constant support of my PhD studies and research, for his patience, motivation, enthusiasm and immense knowledge. I am very grateful to him for long discussions which helped me to arrange the technical details of my research.
Above all, I would like to thank my parents, brother and my entire family for their endless love, understanding and support.
