The required protonic conductivity of cathodes on proton conducting electrolytes to extend the oxygen reduction reaction beyond the three phase boundary is explored. Experimental results for Ba0.5Sr0.5Fe0.8Zn0.2O3-δ (BSFZ) are discussed in this context. While for thin-film electrodes the effective rate constant kq of the surface reaction is the most important parameter, for porous thick cathodes kq and the electrode's proton conductivity are equally influential. The low activation energy of the latter quantity turns out to be particularly advantageous for the targeted lower operation temperatures.