BaZrxCeyY1-x-yO3.delta are recognized proton-conducting electrolyte materials for proton-conducting solid oxide fuel cells (H+-SOFCs) below 650 degrees C. Here Co cations are incorporated into the BaZr0.4Ce0.4Y0.2O3.delta (BZCY) scaffold to generate a 3D core-shell and triple-conducting (H+ /O-2-/e(-)) electrode in situ via infiltrating and reactive sintering. The core is the bulk BZCY scaffold, while the shell is composed of the cubic Ba(Zr0.4Ce0.4Y0.2)(1-x)CoxO3-delta, cubic spinel Co3O4 and cubic fluorite (Ce, Zr, Y)O-2. The obtained electrode exhibits an excellent compatibility with the BZCY electrolyte, and performs well in yielding a low and stable polarization resistance for oxygen reduction reaction for intermediate-temperature H+-SOFCs. In particular, it achieves polarization resistances as low as 0.094 and 0.198 Omega cm(2) at 650 and 600 degrees C in wet air (3% H2O) when the sintering temperature for the electrode is 900 degrees C. In addition, a symmetrical cell also exhibits operation stability of 70 hat 650 degrees C. Furthermore, a fuel cell assembled with the 3D core -shell and triple-conducting electrode delivers a peak power density of similar to 330 mW cm(-2) at 650 degrees C. The substantially improved electrochemical performance and high stability are ascribed to the unique core-shell structure and the formation of Ba(Zr0.4Ce0.4Y0.2)(1-x)CoxO3-delta in the shell.