The hydrogen electrode reaction for conventional solid oxide fuel cells (SOFC) has been widely studied and well understood. In comparison, electrochemical behaviors for hydrogen electrode reaction of proton conducting SOFC are often distinctly different and there are still many unknowns about the fundamental kinetics and mechanism for such reaction. For example, it is well known that the hydrogen electrodes for conventional oxide ion SOFC, which consist of oxygen ion conducting oxides and Ni, are susceptible to poisoning by even sub-ppm level hydrogen sulfide (H₂S). On the other hand, literature suggests that the hydrogen electrodes for proton conducting SOFC, which contains proton conducting oxides and Ni, show much better resistance against H₂S. By understanding the origin of differences like this, new insights of the fundamental reaction mechanism for the hydrogen electrode of proton conducting SOFC can be obtained. In this study, electrochemical tests based on the concept of “controlled poisoning”, which is to selectively poison specific parts of the hydrogen electrode using low concentration of either H₂S as a “Ni poison” or CO₂ as a “proton conducting oxide poison”, are carried out to understand the fundamentals about the hydrogen electrode reaction for proton-conducting SOFCs. In particular, anode-supported cell with the configuration of Ni-BaZe_0.1Ce_0.7Y_0.1Yb_0.1O₃ (BZCYYb)/BZCYYb/LSCF and anode symmetrical cell with the configuration of Ni-BZCYYb/BZCYYb/BZCYYb were subject to ppm-level H₂S and low percentage level CO₂, and the electrochemical responses for both types of cells are characterized. Preliminary results show that, contrary to the Ni-based hydrogen electrode for conventional SOFC, the Ni-BZCYYb hydrogen electrode for proton conducting SOFC shows much better resistance against “sulfur poisoning” while gets poisoned by CO₂ at low percentage level. Results for experiments aimed at understanding such differences will be presented and the implications on what the electrocatalytic roles of proton conducting oxides play in the hydrogen electrode reaction for proton conducting SOFC will be discussed.