Specific features of galvanic displacement of electrodeposited copper by palladium. Activity of Pd0(Cu) composite in FAOR

Galvanic displacement (GD) of electrodeposited (e.d.) copper by palladium in PdSO4+H2SO4 solutions in the absence (solution I) and in the presence (solution II) of copper ions Cu2+ is carried out. The resulting samples are characterized by several methods (SEM, XPS, AES-ICP, etc.). In is found that on freshly formed Pd0(Cu)-I and Pd0(Cu)-II composites, no Pd shell is formed. The copper content is shown to be 10at.% and higher in the surface layer and 22–27% in the bulk (Pd+Cu=100%). Voltammetric and XPS data allow assuming that the surface layer contains mixed oxides (such as PdCuOx) and copper ions which prevent the formation of the Pd shell. Both freshly formed Pd0(Cu) samples and those subjected to potential cycling (0.3–1.2V, RHE) demonstrate the high specific activity in formic acid electrooxidation reaction (FAOR, 1M HCOOH+0.5M H2SO4) which exceeds the activity of e.d. Pd by a factor of 3–4 at 150mV and 8–10 at 300mV. The possible reasons for the higher FAOR activity of Pd in Pd0(Cu) composites are discussed.