Effect of additional anode sub-layer on hydrogen peroxide generation in PEMFC

In the past several decades, much attention has been focused upon the research and development of proton exchange membrane fuel cells (PEMFC) as power sources for stationary and portable application. A number of degradation mechanisms for the long-term stability were investigated. Particularly degradation studies on Nafion® membrane due to hydrogen peroxide were conducted in many research groups. There are two different mechanisms for hydrogen peroxide generation: The first mechanism is that oxygen diffuses from the cathode through the membrane to the anode and the hydrogen peroxide is formed. The second one is that oxygen reduction at the cathode proceed through a peroxide intermediate of hydrogen peroxide. Hydrogen peroxide reacts with trace metal ions to form OH? and HO2? radicals which attack membrane. A study on reduction of hydrogen peroxide generation must be investigated to prevent degradation of membrane and to obtain long-term stability of PEMFC. In this study, additional anode sub-layer (Vulcan XC72, Ru/C) between membrane and anode catalyst layer was used to reduce hydrogen peroxide generation due to oxygen cross-over to anode. Using Vulcan XC72 as anode sub-layer, oxygen reduction potential to form H2O was decreased until 0.5V (vs. NHE) and the chance for formation of hydrogen peroxide was reduced. As anode sub-layer was getting thinner, the amount of oxygen which diffused to the anode catalyst layer (Pt/C) was increased. As thickness of anode sub-layer was increased, all of oxygen from cross-over reacted with hydrogen in anode sub-layer and hydrogen peroxide generation was reduced. However, anode sub-layer plays a role of internal resistance to proton conductance. Relation between thickness of anode sub-layer and PEMFC performance was investigated to obtain optimum thickness. There was a limit to reduce thickness of anode sub-layer because of low reactivity of Vulcan XC72 with oxygen from cross-over. In addition, Ru/C was used as another anode sub-layer. In oxygen reduction reaction, Ru catalyst produced very low amount of hydrogen peroxide and reactivity compared with Vulcan XC72 was high. Low amount of Ru catalyst compared with Vulcan XC72 was possible to consume oxygen from cross-over in anodic sub-layer (Ru/C).