A Bulk-Heterostructure Nanocomposite Electrolyte of Ce0.8Sm0.2O2-δ–SrTiO3 for Low-Temperature Solid Oxide Fuel Cells

Abstract

Since colossal ionic conductivity was detected in the planar heterostructures consisting of fluorite and perovskite, heterostructures have drawn great research interest as potential electrolytes for solid oxide fuel cells (SOFCs). However, so far, the practical uses of such promising material have failed to materialize in SOFCs due to the short circuit risk caused by SrTiO3. In this study, a series of fluorite/perovskite heterostructures made of Sm-doped CeO2 and SrTiO3 (SDC–STO) are developed in a new bulk-heterostructure form and evaluated as electrolytes. The prepared cells exhibit a peak power density of 892 mW cm−2 along with open circuit voltage of 1.1 V at 550 °C for the optimal composition of 4SDC–6STO. Further electrical studies reveal a high ionic conductivity of 0.05–0.14 S cm−1 at 450–550 °C, which shows remarkable enhancement compared to that of simplex SDC. Via AC impedance analysis, it has been shown that the small grain-boundary and electrode polarization resistances play the major roles in resulting in the superior performance. Furthermore, a Schottky junction effect is proposed by considering the work functions and electronic affinities to interpret the avoidance of short circuit in the SDC–STO cell. Our findings thus indicate a new insight to design electrolytes for low-temperature SOFCs.

Remarkable Ionic Conductivity in a LZO-SDC Composite for Low-Temperature Solid Oxide Fuel Cells

“…However, these concerns have been eliminated in our case as proved by the high OCVs, which are close to or even higher than 1 V as shown in Figure 3. This can be attributed to a Schottky junction effect based on metal-semiconductor contacts between Ni/Co (reduced NCAL) and LZO-SDC, which has been reported before with a function of blocking electron passage from anode to semiconductor electrolyte by the Schottky barrier when operating the fuel cells [14,33,34].…”

“…In Figure 3c, the performance of the 5LZO-5SDC fuel cell at various temperatures is further shown. In our previous study, the SDC electrolyte-based SOFC with the same NCAL-Ni electrodes exhibited a peak power density of 389 mW cm −2 at 550 • C [34]. Compared with simplex LZO and SDC fuel cells, the power density of 5LZO-5SDC fuel cell is remarkably improved, while the fuel cells based on other two composites reveal slightly progressive or comparable power outputs.…”

“…Due to the lower ohmic and polarization resistence, the 5LZO-5SDC cell showed higher performance. In addition, the resistance parameters (R o and R p ) of 5LZO-5SDC cell acquired from EIS were further compared to the previously reported SOFCs based on LZO, SDC, SrTiO 3 -SDC, LSCF-SCDC, NCAL-NSDC electrolytes using the same NCAL-Ni electrodes [14,22,23,34]. As summarized in Table 2, the 5LZO-5SDC cell reveals lower R o and R p than those of other five cells, implying higher ionic conductivity and higher electrode reaction activity of the 5LZO-5SDC cell.…”

High Performance Low-Temperature Solid Oxide Fuel Cells Based on Nanostructured Ceria-Based Electrolyte

“…In recent years, cerium-based oxide (CeO 2 ) has attracted extensive interests as the electrolyte in the fields of fuel cell due to the characteristic to store and release oxygen via facile Ce 4+ /Ce 3+ redox cycles [4][5][6]. However, pure CeO 2 has poor thermal stability and can be easily sintered at high temperature, which causes a rapid decrease in its oxygen storage/release capacity and catalytic activity [7,8].…”

An Interface Heterostructure of NiO and CeO2 for Using Electrolytes of Low-Temperature Solid Oxide Fuel Cells

“…The high total electrical conductivity of 0.38 S cm −1 and the corresponding power output of 718 mW cm −2 were achieved in the H 2 /air atmosphere at 550 • C. The results illustrate that interfacial ionic conduction between these two phases is a dominant factor that yields significant enhancement in proton conductivity. Very recently, Cai et al developed bulkheterostructure electrolytes based on Ce 0.8 Sm 0.2 O 2−δ and SrTiO 3 to reduce the operational temperature of SOFCs [21]. They achieved a high peak power density of 892 mW cm −2 and an open circuit voltage of 1.1 V at 550 • C. They explained that a Schottky junction is formed in the cell, which can overcome the short-circuit issue.…”