Investigation of Sr doping effect on oxygen ion de-localization in Gd2Ti2O7 pyrochlore system and its influence on charge relaxation dynamics and ionic conductivity: as electrolyte for IT-SOFCs

IF 2.4 4区 化学 Q3 CHEMISTRY, PHYSICAL
Ionics Pub Date : 2024-09-18 DOI:10.1007/s11581-024-05784-y
Arshiya A. A. Ali, Smita Acharya, Kuldip Bhongale, Shraddha Shirbhate, Shilpa Kulkarni, Shraddha Joshi
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Abstract

In the present attempt, we explore Gd2-xSrxTi2O7, pyrochlore system, where x = 0, 0.02 and 0.04, 0.06, 0.08 and 0.1 as an electrolyte for intermediate temperature (500–650 °C) solid oxide fuel cell (IT-SOFCs). Structural information is collected using X-ray diffraction and confirmed by Rietveld Refinement as an anion-deficient pyrochlore phase with Fd-3 m symmetry. Microstructural features of as-calcined and sintered samples are studied by using scanning electron microscopy (SEM); Sr existence in the GTO matrix is verified by the EDAX study. Raman spectroscopy study reveals (1) the suppression of F2g near 481 cm−1 associated with Gd-O(1) stretching vibration with increasing Sr2+ doping level and (2) the disappearance of F2g modes near 610 cm−1 associated with Gd-O(2) stretching vibration with the emergence of new vibration modes near 796 cm−1 in GSTO compositions having x ≥ 4 related to the de-localization of oxygen ion from 48f to vacant 8a site. Ionic conductivity and activation energy data are extracted through AC impedance measurement, and conductivity maximum is obtained for composition GSTO-4. The electric modulus study is explored to reveal ion hopping dynamics. Sr doping in GTO exhibits dispersion in oxygen-ion relaxation frequency. To quantify the relaxation mechanism, M″ relaxation peak and its dispersion are mapped using the Kohlrausch–Williams–Watts (KWW) fit; the stretching exponent “β” is extracted. Cooperative hopping dynamics is measured in terms of oxygen ion-vacancy interactions which is notably influenced on ionic conductivity. The optimized dopant composition of GSTO-4 exhibits the highest conductivity (σ = 4.3 × 10−3 S/cm@650 °C). Button-shape SOFCs are fabricated using GTO and GSTO-4 as electrolytes and NiO-GSTO-4 as anode and Dy0.9Sr0.1Co0.8Fe0.2O3-δ:GSTO-4 as cathode and depict maximum power densities of the cells 41, 33, and 25 mW cm−2 at 650 °C, 600 °C, and 550 °C, respectively, for the GSTO-4 system. In contrast, the pristine GTO system exhibits power densities of 32, 23, and 19 mW cm−2 at the same temperatures. The study demonstrates the potential of GSTO-4 as a prospective system for IT-SOFCs.

Abstract Image

研究掺入硒对 Gd2Ti2O7 烧绿宝石体系中氧离子去定位的影响及其对电荷弛豫动力学和离子电导率的影响:作为 IT-SOFC 的电解质
在本次尝试中,我们探索了将 Gd2-xSrxTi2O7(x = 0、0.02 和 0.04、0.06、0.08 和 0.1)热绿晶体系作为中温(500-650 °C)固体氧化物燃料电池(IT-SOFC)的电解质。利用 X 射线衍射收集了结构信息,并通过 Rietveld Refinement 确认其为具有 Fd-3 m 对称性的阴离子缺失型火成岩相。使用扫描电子显微镜(SEM)研究了煅烧和烧结样品的微观结构特征;通过 EDAX 研究验证了 GTO 基体中硒的存在。拉曼光谱研究表明:(1) 随着 Sr2+ 掺杂水平的增加,与 Gd-O(1) 伸展振动相关的 481 cm-1 附近的 F2g 模式被抑制;(2) 在 x ≥ 4 的 GSTO 成分中,与 Gd-O(2) 伸展振动相关的 610 cm-1 附近的 F2g 模式消失,而在 796 cm-1 附近出现了新的振动模式,这与氧离子从 48f 去定位到空缺的 8a 位点有关。通过交流阻抗测量提取了离子电导率和活化能数据,成分 GSTO-4 获得了最大电导率。电模量研究揭示了离子跳跃动力学。在 GTO 中掺入锶会导致氧离子弛豫频率的分散。为了量化弛豫机制,使用 Kohlrausch-Williams-Watts (KWW) 拟合法绘制了 M″ 弛豫峰及其弥散图,并提取了伸展指数 "β"。根据氧离子-空位相互作用测量了合作跳动动力学,该动力学对离子电导率有显著影响。GSTO-4 的优化掺杂成分显示出最高的电导率(σ = 4.3 × 10-3 S/cm@650°C)。利用 GTO 和 GSTO-4 作为电解质,NiO-GSTO-4 作为阳极,Dy0.9Sr0.1Co0.8Fe0.2O3-δ:GSTO-4 作为阴极,制造出了钮扣形 SOFC,在 650 ℃、600 ℃ 和 550 ℃ 时,GSTO-4 系统的电池最大功率密度分别为 41、33 和 25 mW cm-2。相比之下,原始 GTO 系统在相同温度下的功率密度分别为 32、23 和 19 mW cm-2。这项研究证明了 GSTO-4 作为 IT-SOFC 前瞻性系统的潜力。
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来源期刊
Ionics
Ionics 化学-电化学
CiteScore
5.30
自引率
7.10%
发文量
427
审稿时长
2.2 months
期刊介绍: Ionics is publishing original results in the fields of science and technology of ionic motion. This includes theoretical, experimental and practical work on electrolytes, electrode, ionic/electronic interfaces, ionic transport aspects of corrosion, galvanic cells, e.g. for thermodynamic and kinetic studies, batteries, fuel cells, sensors and electrochromics. Fast solid ionic conductors are presently providing new opportunities in view of several advantages, in addition to conventional liquid electrolytes.
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