PrNi_0.5Co_0.5O_3-δ (PNC) cathode material demonstrates total electrical conductivity on the order of ~300 S/cm at 400-600^oC in air, and the conductivity shows a slight increase as temperature increases with an activation energy (from ln(σT) vs 1/T plot) of 10.9 kJ/mol. The introduction of water vapor (H₂O) leads to a small (~0.16%) increase in total resistivity, which is reversible upon water removal and explained, tentatively, by the defect reaction of H₂O + 2O_o^x + 2h^• = 2(OH)_O^• + 0.5O₂. The thermal expansion coefficient (TEC) of PNC is measured to be 17.6×10^-6/K by dilatometry and 18.43×10^-6/K by in situ XRD up to 800^oC. On the other hand, despite bulk chemical stability for both PNC and BZCYYb4411 powders against low percentage H₂O and CO₂, a PNC cathode symmetrical cell over proton conducting BaZr_0.4Ce_0.4Y_0.1Yb_0.1O_3-δ (BZCYYb4411) electrolyte shows degradation (or increase) in interfacial resistance upon introduction of 3% moisture or 5% CO₂ into simulated air at temperature in the range of 650 to 450^oC. In comparison, oxygen ion conducting symmetrical cells with PNC cathode and Ce_0.9Gd_0.1O_2-δ (GDC) electrolyte show no change upon H₂O and CO₂ introduction. The observed sensitivity of the PNC cathode proton conducting symmetrical cell to H₂O and CO₂ is attributed to the preferred adsorption of H₂O and CO₂ molecules onto the BZCYYb4411 proton conducting electrolyte surface than on the PNC cathode, and such an explanation is supported by temperature programmed desorption (TPD) measurements for H₂O and CO₂ on both PNC and BZCYYb4411 powders.