Enhancing densification and conductivity of BaCe0.4Zr0.4Y0.1Yb0.1O3-δ electrolytes via a dual-step NiO addition strategy

Achieving high density, large grain growth with reduced grain boundary resistance remains a critical challenge for zirconium-rich perovskite-type proton-conducting electrolytes such as BaCe 0.4 Zr 0.4 Y 0.1 Yb 0.1 O 3-δ . In this work, a dual-step NiO addition strategy is proposed to improve the sintering behavior and proton transport properties of BCZYYb4411 electrolytes without altering the concentration or introducing new sintering additives. A total of 1 wt% NiO was divided into two sequential additions, with 0.5 wt% introduced before calcination to promote perovskite phase formation and the remaining 0.5 wt% added before sintering to enhance grain boundary assisted densification. This strategy produced phase pure BCZYYb4411 after calcination at 1300 °C for 5 h and achieved 99.3% relative density with an average grain size of ∼7.6 μm after sintering at 1500 °C for 5 h. Electrochemical impedance spectroscopy confirmed a substantial reduction in grain boundary resistance and the highest total conductivity among the investigated samples. A single cell fabricated with the optimized electrolyte delivered a peak power density of 0.78 W cm −2 at 600 °C, demonstrating that this processing strategy provides a simple and effective method for optimizing the microstructure and transport properties of electrolyte material for protonic ceramic fuel cells application.