Extended X-ray Absorption Fine Structure and X-ray Diffraction Examination of Sputtered Nickel Carbon Binary Thin Films for Fuel Cell Applications

Abstract

Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) are used to study the structure of sputtered binary nickel carbon alloy films (5–44 atom % Ni) for use as potential electrocatalysts in acidic solutions. Three compositional regions are identified: “low” (5 atom % Ni), where the structure consists mainly of isolated Ni atoms or dimers in a carbon matrix; “medium” (11–24 atom % Ni), where the Ni–Ni nearest-neighbor coordination is increased but there is little longer-range order; and “high” (35–44 atom % Ni), where crystalline Ni 3 C is formed. This indicates a threshold concentration of Ni of between 25 and 35 at% before Ni 3 C starts to form.