The performance of protonic ceramic electrochemical cells (PCECs) is largely restricted by the slow oxygen reactions on the oxygen electrode. Herein, an active composite oxygen electrode Ba0.5Sr0.5Co0.7Fe0.2Ni0.1O3−δ–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BSCFN–BZCYYb) with various mass ratios (6:4, 7:3, 8:2, and 9:1) is electrochemically investigated on fuel electrode-supported PCECs. BSCFN powder, with rich oxygen vacancies, shows a good chemical compatibility with BZCYYb electrolyte, as confirmed by the analyses of thermal gravimetric analysis and X-ray diffraction patterns. It is indicated that composite electrode with a ratio of 8:2 shows the best performance. For example, a peak power density (Pmax) of 1.14 W cm–2, an electrode polarization resistance (Rp) of 0.062 Ω cm2, and a reasonable durability test of 24 h at −0.5A cm–2 are delivered at 750 °C for the fuel cells with BSCFN–BZCYYb electrode with the ratio of 8:2. In addition, a stable operation (∼50 h) of cell with BSCFN–BZCYYb electrode (8:2 mass ratio) in dual modes of electrolysis and fuel cell (2 h for each mode) at ±0.5 A cm–2 is obtained, demonstrating a good reversibility.