Tailoring the Oxygen Vacancy to Achieve Fast Intrinsic Proton Transport in a Perovskite Cathode for Protonic Ceramic Fuel Cells

Abstract

Protonic ceramic fuel cells (PCFCs) are receiving increasing attention because of their high energy conversion efficiency. However, traditional mixed oxygen-ionic and electronic conductors (MOECs) show sluggish oxygen reduction kinetics when used in PCFCs because of their intrinsic low protonic conductivity. Herein, it is reported that cooperatively regulating the concentration and basicity of oxygen vacancies can result in fast proton transport in MOECs, which is demonstrated in a Zr 4+ -doped Sr 2 Fe 1.5 Mo 0.5 O 6−δ (SFMZ) perovskite. The so-obtained SFMZ perovskite renders plentiful oxygen vacancies and strong hydration ability, which can boost the formation of protonic defects. Furthermore, the chemical diffusion coefficient of protons (D H,chem ) is established first to determine the proton mobility of the cathode. The results indicate that SFMZ exhibits improved proton diffusion kinetics with a D H,chem value of 8.71 × 10 −7 cm 2 s −1 at 700 °C, comparable to the diffusion coefficient of the commonly used protonic electrolyte BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ of 1.84 × 10 −6 cm 2 s −1 . A low polarization resistance of 0.169 Ω cm 2 and a peak power density as high as 0.79 W cm −2 were achieved at 700 °C with the SFMZ cathode. Such excellent performance suggests that rationally tailoring the oxygen vacancy is a feasible strategy to promote proton diffusion in perovskite-structured electrode materials as efficient PCFC cathodes.

High-performance proton-conducting solid oxide fuel cells using the first-generation Sr-doped LaMnO3 cathode tailored with Zn ions

“…However, the encouraging performance of the LSMZ cell tackles this problem. The cell performance is even higher than or comparable to some of the recently reported high-performance H-SOFCs based on novel cathodes [5,36,[40][41][42][43][44][45][46][47]. The result indicates that the Zn-doping strategy effectively brings LSM back to the intermediate-temperature range with high performance, although LSM is the first-generation cathode that has been regarded only to perform well at high temperatures (above 800°C).…”

“…2b shows the weight change of LSM and LSMZ between the dry and wet air conditions, indicating the hydration ability of the sample. The hydration ability of the LSM and LSMZ materials was determined by cooling the materials in dry and wet atmospheres and measuring the weight difference in these two atmospheres [36]. As shown in Fig.…”

Roadmap for Sustainable Mixed Ionic‐Electronic Conducting Membranes

“…Much of this work has probed systematic, incremental changes to previously known TIECs to probe fundamental changes in material properties, using methods such as A-site and B-site deficiency [216,309,310] and simple doping strategies. [311,312] These studies build upon the early research which quantified high-performance materials in fuel-cell or electrolysis applications, while providing fundamental benchmarks for future TIECs. The main challenge associated with TIECs is limited understanding of the complex bulk transport, surface kinetics and stability relationships required for high-performance materials in advanced electrochemical applications.…”

“…TIEC stability remains a difficult challenge for fuel cell and electrolysis cell applications. TIECs have been shown to remain relatively stable across hundreds of hours under operating conditions, [206,273,311] yet fuel cells require lifetimes Table 6. List of claimed triple ionic-electronic conductors with available bulk material properties.…”

Surface and Bulk Oxygen Kinetics of BaCo0.4Fe0.4Zr0.2−XYXO3−δ Triple Conducting Electrode Materials

“…Electrical conductivity relaxation (ECR) is a prominent method which allows for relatively simple measurements to probe the oxygen reduction kinetics of cathode materials [10][11][12][13][14]. ECR has also recently been used to probe the kinetics of other surface behaviors, such as proton uptake and interactions with water [15][16][17]. Measuring ionic conductivity in TIECs, however, is more challenging, as most known materials in this class are predominantly electron conductors, due to their high doping concentration of multivalent elements, such as Co, Fe, Ni, and Mn [18][19][20].…”