Advanced LT-SOFC Based on Reconstruction of the Energy Band Structure of the LiNi_0.8Co_0.15Al_0.05O₂–Sm_0.2Ce_0.8O_2-δ Heterostructure for Fast Ionic Transport

Abstract

Formation of a heterostructure of semiconductor materials is a promising method to develop an electrolyte with high ionic conductivity at low operational temperature of solid oxide fuel cells (LT-SOFCs). Herein, we develop various heterostructure composites by introducing a pure ionic conductor Sm 0.2 Ce 0.8 O 2-δ (SDC) into a semiconductor LiNi 0.8 Co 0.15 Al 0.05 O 2 (LNCA) for LT-SOFCs electrolyte. The morphology, crystal structure, elemental distribution, micro-structure, and oxidation states of the composite of LNCA−SDC are analyzed and studied via X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution-transmission electron microscopy (HR-TEM), high energy dispersive spectrometry, and X-ray photoelectron spectroscopy (XPS). Electrochemical studies found that the optimal weight ratio of 0.5 LNCA-1.5 SDC heterostructure composite exhibits relatively high ionic conductivity (0.12 S cm −1 at 520 °C), which is much higher than that of SDC. The designed composite of LNCA-SDC heterostructures with optimal weight ratio (0.5:1.5) delivers a remarkable fuel cell power output of 0.735 W cm −2 at 520 °C. The formation of the heterostructure and reconstruction of energy bands at the interface play the crucial roles in enhancing ionic conduction to improve electrochemical performance. The prepared composite heterostructure delivers a unique and insightful strategy of electrolyte in advanced LT-SOFCs.

ZnO/MgZnO heterostructure membrane with type II band alignment for ceramic fuel cells

“…The obtained ionic conductivity falls in the range of 0.10-0.03, 0.135-0.05 and 0.16-0.08 S cm -1 for ZnO, Mg-ZnO and ZnO/Mg-ZnO at 420-520 °C, respectively, as shown in Figure 3D. The attained ionic conductivity values for the composite SH are higher than for ZnO and Mg-ZnO [10,12,15] . Such reliable ionic conduction is a result of the formation of the SH and constituted BIEF at the interface, which acts as driving forces to enhance the ionic carriers.…”

“…The GB arcs tend to disappear with increasing temperature, and as a result, a single arc is shown in Figure 3A-C. Furthermore, a similar relaxation time for the grains and grain boundaries might be the reason for such behavior [5][6][7][8][9][10] . Therefore, to distinguish the grain, grain boundary and electrode contributions, the obtained EIS data for all materials were fitted using the R o (R 1 Q 1 )(R 2 Q 2 ) circuit through ZSIMPWIN software.…”

“…According to the Debye-Scherrer equation, the calculated crystalline size for ZnO is 26 nm, while for Mg-ZnO, this value is 24 nm, which might be due to the doping of Mg into the ZnO lattice. Moreover, due to the doping effect, peak shifting was noticed because of the different radii of Mg 2+ (0.57 Å) and Zn (0.60 Å) following Vegard's law [10] . The XRD analysis of the synthesized heterojunction after the fuel cell measurements was also evaluated, as displayed in Supplementary Figure 1.…”

“…The obtained fuel cell performance is higher than those in the reported literature, illustrating that the prepared SH holds excellent potential for fuel cell technology [1,12,14,15,20] . Moreover, symmetrical electrodes (anode and cathode) NCAL with better catalytic activity were used, significantly contributing to the enhanced fuel cell performance, as reported previously [5][6][7][8][9][10][11][12][13][14][15] . The comparison between the presented electrolytes regarding fuel cell performance at different temperatures is visualized in Figure 2D.…”

“…On this basis, Xia et al proposed that the doping of Li into ZnO causes a reduction in the energy bandgap, leading to enhanced fuel cell performance and better ionic conductivity [4] . Furthermore, many semiconductors have been reported to tune the energy bandgap using the doping or coating approach to improve the ionic conductivity of fuel cell devices [5][6][7][8][9][10] . Recently, the semiconductor heterostructure (SH) approach has become the most popular method and is regarded as the key to enhancing ionic conductivity without short-circuiting.…”