Bi-functional air electrode fabrication, performance and stability evaluation

Abstract

Abstract Perovskite Sm0.5Sr0.5CoO3-δ (SSC) based bifunctional (BF) air electrodes were fabricated by dry fibrillation mixing, wet tape processing and hot plate pressing method using Vulcan XC-72 carbon black as conductive support, polytetrafluoroethylene as binder and Ni exmet (or Ni foam) as current collector. The BF air electrodes exhibited encouraging performance and cycle-ability. Under the test condition of room temperature (20–22 °C), 6 M KOH and 50 mA/cm2, the obtained oxygen evolution reaction (OER) potential was around 0.67 V and oxygen reduction reaction (ORR) potential was around −0.20 V vs. Hg/HgO reference electrode. Number of cycle of 2 h (approximately) duration reached over 180 cycles at 20 mA/cm2 using a copper exmet as negative Zn electrode substrate. The Zn air battery prototype showed coulombic efficiency and energy efficiency around 95–98% and 50–52%, respectively. It was found that using Ni-foam reinforced BF air electrode structure further improved the stability of the electrode, especially for the OER. Performance degradation of approximately 1.5% and 15% were observed for the OER and the ORR, respectively over a test period of 300 h. The electrode performance degradation was explained due to KOH wetting-through the backing layer causing electrode flooding. Active SSC material de-binding and carbon support oxidation were also observed in this study.