Abstract
Interest in low-temperature operation of solid oxide fuel cells is growing. Recent advances in perovskite phases have resulted in an efficient H+/O2-/e- triple-conducting electrode BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for low-temperature fuel cells. Here, we further develop BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for electrolyte applications by taking advantage of its high ionic conduction while suppressing its electronic conduction through constructing a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ-ZnO p-n heterostructure. With this approach, it has been demonstrated that BaCo0.4Fe0.4Zr0.1Y0.1O3-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+/O2- conducting capability of BaCo0.4Fe0.4Zr0.1Y0.1O3-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 BaCo0.4Fe0.4Zr0.1Y0.1O3-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.
Highlights
Interest in low-temperature operation of solid oxide fuel cells is growing
Practical industrial applications of SOFCs have not been successfully realized primarily due to high operational temperatures required by the predominant oxygen ion (O2-) electrolyte yttrium stabilized zirconia (YSZ), which results in high costs, performance degradation, slow start-up and shut-down cycles, as well as technological complexities[3,4]
The thin film techniques are confronted by key issues that include high cost, long production period, difficulties on scaling up and μSOFC silicon technology, while doped-ceria is subject to its well-known problem of reduction in hydrogen atmosphere, making them difficult to realize practical LT-SOFCs
Summary
Interest in low-temperature operation of solid oxide fuel cells is growing. Recent advances in perovskite phases have resulted in an efficient H+/O2-/e- triple-conducting electrode BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for low-temperature fuel cells. As a doped derivative of H+/O2− conducting BaZrxY1−xO3-δ (BZY), the cathode BCFZY gains remarkably activated electron-hole conductivity via heavy B-site doping with Co and Fe while maintaining its high ionic conductivity, leading to good catalytic activity and triple conduction[14,15] In another featured breakthrough study with respect to protonic perovskite materials, a nickelate SmNiO3 (SNO) possessing high initial ionic and electronic conductivity can be utilized as an electrolyte in a LT-SOFC, revealing a peak power output of 225 mW cm−2 at 500 °C along with sufficient open-circuit voltage (OCV) of 1.03 V16. The SNO electrolyte presented a high H+ conductivity at 300–500 °C that is comparable to the best-performing solid electrolytes while its electronic conduction was suppressed via a filling-controlled Mott transition[16] These interesting studies indicate that perovskite oxides involving H+ conduction are more capable at lower temperatures (350–550 °C) compared to conventional SOFCelectrolytes. It has been reported that H+ can transport in the perovskite structure and along interfaces of composite materials[18]
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