Catalytic Response and Electrode Kinetics on Noble Metal-Treated Type 304 Stainless Steel in 288°C Water

The catalytic response and electrochemical polarization behavior of O₂ and H₂ reactions on noble metal-treated Type 304 (UNS S30400) stainless steel (SS) in high-temperature water containing various amounts of Cu and Zn was investigated. The experimental data clearly demonstrated that, without catalytically active sites on Type 304 SS surface, the presence of Cu raised the Type 304 SS electrochemical corrosion potential (ECP) by as much as 300 mV in hydrogen water chemistry (HWC). The presence of Cu and Zn in the water or on the surface did not affect the ECP of noble metal-treated Type 304 SS, which showed a low ECP (–450 mV vs standard hydrogen electrode [SHE] to –500 mV_SHE) when stoichiometric excess hydrogen was present. However, ~ 10% to 20% decrease in recombination efficiency of oxygen and hydrogen reactions on the catalytic surface in the presence of Cu was measured. It also was noted that during further exposure to excess hydrogen water, the presence of noble metals on the surface promotes the transformation of hematite (α-Fe₂O₃) to a spinel magnetite (Fe₃O₄) type layer.