Abstract
Layered Ruddlesden-Popper (RP) lanthanide nickelates, Lnn+1NinO3n+1 (Ln = La, Pr, and Nd; n = 1, 2, and 3) have generated great interest as potential cathodes for proton conducting fuel cells (PCFCs). The high-order phase (n = 3) is especially intriguing, as it possesses the property of a high and metallic-type electronic conductivity that persists to low temperatures. To provide the additional requirement of high ionic conductivity, a composite electrode is here suggested, formed by a combination of La4Ni3O10±δ with the proton conducting phase BaCe0.9Y0.1O3-δ (40 vol%). Electrochemical impedance spectroscopy (EIS) is used to analyse this composite electrode in both wet (pH2O ~ 10−2 atm) and low humidity (pH2O ~ 10−5 atm) conditions in an O2 atmosphere (400–550 °C). An extended analysis that first tests the stability of the impedance data through Kramers-Kronig and Bayesian Hilbert transform relations is outlined, that is subsequently complemented with the distribution function of relaxation times (DFRTs) methodology. In a final step, correction of the impedance data against the short-circuiting contribution from the electrolyte substrate is also performed. This work offers a detailed assessment of the La4Ni3O10±δ-BaCe0.9Y0.1O3-δ composite cathode, while providing a robust analysis methodology for other researchers working on the development of electrodes for PCFCs.
Highlights
Protonic ceramic fuel cells (PCFCs) stand out as one of the most promising technologies for energy conversion [1]
The majority of published works have focused on the use of mixed ionic electronic conductors (MIECs) as potential PCFC electrodes, where materials selection is driven by that traditionally used in solid oxide fuel cells (SOFCs), based on both oxide-ion and electron (O2−/e−) conduction [6,7,8,9,10,11,12]
According to Quarez et al [37], an enhanc3e.m1. eMnticirnosthtreuectluecretrochemical activity of RP-PCFC cathodes can be obtained for highly porous eFliegcutroed2eas.shTohwe sntohtedtoopp-veinewpomroiscirtoystrreugcitsuterreesdwiinththEiDs Swmorakppisinmg,odstenoting a well likely a result fdriosmtribthueterdelmatiixveolfyblootwh ltaenmthpaenriadteuraendusBeCdY(105p0h°aCse)s
Summary
Protonic ceramic fuel cells (PCFCs) stand out as one of the most promising technologies for energy conversion [1]. One of the key attractions of lower order nickelate phases (n = 1, 2) has been documented to suffer an abrupt depletion as the operating temperature decreases below 600 °C, in air, as a result of temperature dependent changes in crystallographic symmetry [16]. This drop in electronic conductivity below 600 °C is concerning, as it may bring into question the continued validity of these lower order nickelate materials for the intended PCFC operati2oonfa1l7 temperature range of (400–600 °C).
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