Characteristic Thickness for a Dense La[sub 0.8]Sr[sub 0.2]MnO[sub 3] Electrode

Abstract

Dense La 0.8 Sr 0.2 MnO 3 ͑LSM͒ electrodes were patterned by photolithography and fabricated via pulsed-laser deposition on Y 2 O 3-stabalized ZrO 2 ͑YSZ͒ electrolytes. Impedance analysis shows that the interfacial polarization resistance decreases significantly as electrode thickness drops below a critical value, beyond which the top surface of the LSM becomes active for oxygen reduction. However, when the LSM electrodes become too thin, the in-plane sheet resistance of the LSM starts to limit the utilization of the electrodes along their length. Quantification of the characteristic thickness is important not only to intelligent design of practical mixed-conducting electrodes but also to electrode design for fundamental studies.

Thickness Dependence of Oxygen Reduction Reaction Kinetics on Strontium-Substituted Lanthanum Manganese Perovskite Thin-Film Microelectrodes

“…Because the contribution of surface oxygen exchange ͑LF1͒ to the total impedance is comparable to that of mixed TPB/bulk charge transfer ͑LF2͒ for microelectrode thickness of 240 nm, it is proposed that a LSM80-20 microelectrode with thickness of Ͻ240 nm can be considered as an effective mixed conductor. It should be mentioned that the critical thickness of 240 nm is lower than that ͑360 nm͒ reported previously by Koep et al 30 at 700°C. This difference might be attributed to the fact that LSM80-20 microelectrodes in this work can have different microstructure and surface chemical compositions from this previous study, which could greatly affect the surface exchange and TPB/bulk charge transfer, respectively.…”

“…[8][9][10][11] Therefore, numerous studies have employed porous, high-surface-area electrodes with nanometer-scale LSM particle sizes [12][13][14] or composite LSM-YSZ 3,15,16 to enhance overall TPB length and thus lower ORR resistance and overpotential. However, it is not apparent how LSM particle sizes alter the rate-limiting reaction of ORR and the contributions of the TPB and bulk pathway 6,17,18 as a function of temperature, which limits the efficiency optimization of porous electrodes for intermediate temperature operation.Electrodes with well-defined geometries, such as dense coneshaped pellets, 19-21 thin films, 22-25 and patterned microelectrodes, [26][27][28][29][30][31][32][33] have been used to provide simple scaling relationships between ORR impedance and electrode dimensions, such as TPB length. Mizusaki et al 6 first demonstrated that oxygen-ion diffusion can occur through dense, oxygen-over-stoichiometric LSM electrodes having thickness of 1-2 m at 700-900°C.…”

“…Brichzin et al 28,29 have subsequently utilized microelectrodes with a thickness of 100 nm to show that ORR occurs predominantly via the bulk pathway instead of the TPB pathway at 800°C. In addition, Koep et al 30 have used dense, patterned LSM electrodes of different thickness to show a critical thickness of 360 nm at 700°C, where the bulk pathway dominates having surface reactions as rate limiting for ORR. More recently, la O' et al 33 have employed microelectrodes to propose four distinct processes during ORR on LSM: ͑i͒ ion transport in 8YSZ, ͑ii͒ a surface diffusion process on LSM, ͑iii͒ at least one surface chemical process͑es͒ on LSM, and ͑iv͒ a mixed bulk/ TPB charge transfer process.…”

“…Electrodes with well-defined geometries, such as dense coneshaped pellets, [19][20][21] thin films, [22][23][24][25] and patterned microelectrodes, [26][27][28][29][30][31][32][33] have been used to provide simple scaling relationships between ORR impedance and electrode dimensions, such as TPB length. Mizusaki et al 6 first demonstrated that oxygen-ion diffusion can occur through dense, oxygen-over-stoichiometric LSM electrodes having thickness of 1-2 m at 700-900°C.…”

Geometrically asymmetric electrodes for probing electrochemical reaction kinetics: a case study of hydrogen at the Pt–CsH2PO4 interface

“…In most instances a reference electrode is retained as part of the configuration. [4][5][6][7][8][9] In contrast to this trend, Fleig and co-workers [10][11][12][13][14] have adopted a point electrode geometry that is explicitly reference-less. For dense, surface-limited electrodes, the assumption that the point geometry has effectively eliminated the contribution of the counter electrode is likely valid.…”