Interest in low-temperature operation of solid oxide fuel cells is growing. Recent advances in perovskite phases have resulted in an efficient H⁺/O^2-/e^- triple-conducting electrode BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ for low-temperature fuel cells. Here, we further develop BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ for electrolyte applications by taking advantage of its high ionic conduction while suppressing its electronic conduction through constructing a BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ-ZnO p-n heterostructure. With this approach, it has been demonstrated that BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ can be applied in a fuel cell with good electrolyte functionality, achieving attractive ionic conductivity and cell performance. Further investigation confirms the hybrid H⁺/O^2- conducting capability of BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ-ZnO. An energy band alignment mechanism based on a p-n heterojunction is proposed to explain the suppression of electronic conductivity and promotion of ionic conductivity in the heterostructure. Our findings demonstrate that BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ is not only a good electrode but also a highly promising electrolyte. The approach reveals insight for developing advanced low-temperature solid oxide fuel cell electrolytes.

An SOFC using semiconductor TiO ₂ thin film as an electrolyte was designed using the energy band theory to prevent short-circuiting problem.

Semiconducting-ionic conductors have been recently described as excellent electrolyte membranes for low-temperature operation solid oxide fuel cells (LT-SOFCs). In the present work, two new functional materials based on zinc oxide (ZnO)—a legacy material in semiconductors but exceptionally novel to solid state ionics—are developed as membranes in SOFCs for the first time. The proposed ZnO and ZnO-LCP (La/Pr doped CeO₂) electrolytes are respectively sandwiched between two Ni_0.8Co_0.15Al_0.05Li-oxide (NCAL) electrodes to construct fuel cell devices. The assembled ZnO fuel cell demonstrates encouraging power outputs of 158–482 mW cm⁻² and high open circuit voltages (OCVs) of 1–1.06 V at 450–550 °C, while the ZnO-LCP cell delivers significantly enhanced performance with maximum power density of 864 mW cm⁻² and OCV of 1.07 V at 550 °C. The conductive properties of the materials are investigated. As a consequence, the ZnO electrolyte and ZnO-LCP composite exhibit extraordinary ionic conductivities of 0.09 and 0.156 S cm⁻¹ at 550 °C, respectively, and the proton conductive behavior of ZnO is verified. Furthermore, performance enhancement of the ZnO-LCP cell is studied by electrochemical impedance spectroscopy (EIS), which is found to be as a result of the significantly reduced grain boundary and electrode polarization resistances. These findings indicate that ZnO is a highly promising alternative semiconducting-ionic membrane to replace the electrolyte materials for advanced LT-SOFCs, which in turn provides a new strategic pathway for the future development of electrolytes.

The single–crystalline TiO₂ nanorod arrays with rutile phase have attracted much attention in the dye sensitized solar cells (DSSCs) applications because of their superior chemical stability, better electron transport properties, higher refractive index and low production cost. However, it suffers from a low surface area as compared with TiO₂ nanoparticle films. In order to enlarge the surface area of TiO₂ nanorod arrays, the 1D nanorods/3D nanotubes sample was synthesized using a facile two-step hydrothermal process involving hydrothermal growth 1D/3D nanorods and followed by post-etching treatment. In such bi-layer structure, the oriented TiO₂ nanorods layer could provide direct pathway for fast electron transportation, and the 3D nanotubes layer offers a higher surface area for dye loading, therefore, the 1D nanorods/3D nanotubes photoanode exhibited faster electron transport and higher surface area than either 1D or 3D nanostructures alone, and an highest efficiency of 7.68% was achieved for the DSSCs based on 1D nanorods/3D nanotubes photoanode with further TiCl₄ treatment.

Fuel cells could play an important role in the ongoing energy transition by providing clean and efficient energy conversion. Although the solid oxide fuel cell (SOFC) technology is a potential alternative for large-scale applications, its commercialization is limited by its electrolyte materials and has not yet been realized. Progress on new functional semiconductor-ionic materials (SIMs) and the fundamentals of SOFCs will provide new paths for their research and development. Herein, we discuss the nanoscale electrochemistry phenomena of SIMs in the context of new concepts for advanced SOFCs. A traditional SOFC consists of a three-layer anode/electrolyte/cathode structure, where the physically separated electrolyte layer is indispensable for ion transport to support the redox reaction and prevent the occurrence of short circuiting. A novel nano-SOFC concept is proposed to replace the traditional electrolyte by a SIM or semiconductor membrane and it can deliver superior performance, even at a lower temperature range (< 500 °C). The scientific basis and prospects of this new technological approach are presented and discussed.