Preparation and properties of thin Pt–Ir films deposited by dc magnetron co-sputtering

A series of Pt–Ir thin films envisaged for application as fuel cell cathodic catalysts are deposited by dc co-sputtering from pure metal targets. To achieve different metal ratios, the sputtering power applied on the iridium target (PIr) is varied in the range 0–100 W at constant power of the Pt target (PPt). The influence of the sputtering power on the film composition, morphology, and surface structure is analysed by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The catalytic activity towards oxygen reduction reaction (ORR) is evaluated in sulphuric acid solutions applying the methods of cyclic voltammetry and potentiodynamic polarization curves. The performed morphological and electrochemical investigations reveal that catalytic efficiency of the co-sputtered Pt-Ir films is superior compared to pure Pt. The ORR is most intensive on the sample deposited at power ratio PPt:PIr = 100:30 W containing 11 at.% Ir that has also the most developed active surface. The ORR current density for this film achieved at 0.825 V in acid solution (4.1 mA cm−2) is about 6 times higher than for pure Pt (0.67 mA cm−2). The improved activity of the thin co-sputtered Pt-Ir over Pt allows for essential reduction of the catalyst loading at preserved performance.

► Sputtering power affects the physical and electrochemical properties of Pt–Ir films. ► Sputtering method tends to increase the catalytic activity at reduced loadings. ► An optimal Pt–Ir metal ratio for fuel cell applications is established.