Tailoring BaCe0.7Zr0.1(Dy0.1|Yb0.1)0.2O3−δ electrolyte through strategic Cu doping for low temperature proton conducting fuel cells: Envisioned theoretically and experimentally

This study addresses the challenge of high sintering temperatures in proton-conducting fuel cells (PCFCs) with BaCeO₃-doped electrolytes. We demonstrate that 1 mol% copper (Cu) doping at the B-site of BaCe_0.7Zr_0.1(Dy_0.1|Yb_0.1)_0.2O_3−δ (BCZDYb) improves sintering behavior, enabling densification at 1400 °C. However, Cu doping disrupts stoichiometry, creating barium vacancies and reducing proton-accepting cations, affecting overall conductivity. This mechanism is confirmed through density functional theory (DFT) calculations and various experimental techniques, including crystal structure analysis using X-ray diffraction (XRD) and morphology and elemental analysis via field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS). Electrochemical measurements are performed using the electrochemical impedance spectroscopy (EIS). The ionic conductivity of 1 mol% Cu-doped BCZDYb (BCZDYb-1) is 1.49 × 10⁻² S cm⁻¹ at 650 °C, which is ∼3.58 times higher than that of BCZDYb sintered at 1200 °C. The BCZDYb-1 exhibits ∼16 times higher grain boundary conductivity when sintered at 1400 °C, compared to undoped BCZDYb. The single cell employing BCZDYb-1 as the electrolyte achieved a power density of ∼606 mW cm⁻² at 550 °C. These results indicate that a controlled amount of Cu doping can enhance densification while maintaining high ionic conductivity, making it suitable for practical applications in PCFCs operating at lower temperatures.