Influence of Potential and the Presence of Boric Acid on Pt1-xCox Alloy Electrodeposition and Magnetic Properties

The effects of potential and the presence of B(OH)₃ on Pt_1-xCo_x alloy electrodeposition from aqueous chloride-based solutions on Ru substrates was investigated. Films deposited at potentials more reducing than −0.65 V vs SCE were hexagonal close packed and greater than 90% Co (mole basis), and films deposited at potentials more oxidizing than −0.65 V were face centered cubic and showed a monotonic decrease in cobalt content as the potential increased. The composition and structure-potential dependences were not strongly affected by the presence of B(OH)₃. Structural change coincided with a distinct knee-like feature in the composition-potential relationship, along with a prominent narrow voltammetric peak associated with Co deposition, possibly related to nucleation and growth of the hcp phase. The presence of B(OH)₃ produced a sharp minimum in both Coulombic efficiency and deposition rate at potentials near −0.65 V and almost entirely suppressed the voltammetric feature. This may be associated with a combination of B(OH)₃-derived proton reduction and inhibition of metal deposition by adsorbed B(OH)₃ or B(OH)₃-derived species. The presence of B(OH)₃ affected the magnetic behavior of films deposited at potentials more oxidizing than −0.55 V (i.e., those with compositions less than about 40% Co) only weakly, but resulted in generally smaller maximum magnetizations for films deposited at more reducing potentials, and notably a much lower magnetization for films deposited at −0.65 V.