Activity–Stability Relationship in Compositionally Tuned Magnetron Co-Sputtered Bimetallic Catalysts for Proton Exchange Membrane Fuel Cells

In the present study, magnetron-sputtered Pt_xM_100−x (M = Co, Cu, and Y; x = 25, 50, 75, and 100) bimetallic alloys were investigated as PEMFC cathodes. Accurate composition and layer thickness control enabled a systematic study of the correlation between the alloy composition, its activity, and stability. The catalysts underwent thorough characterization, employing a diverse portfolio of characterization techniques such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and cyclic voltammetry. The activity of all investigated alloys was tested directly in a fuel cell device, whereas stability was assessed through potentiodynamic cycling in a half-cell. The activity–stability index, considering experimental results for both activity and stability, was calculated and compared for all investigated catalysts. All alloys exhibited a volcano-type trend in the activity–stability index as a function of the concentration of the alloying element with maxima observed for Pt₅₀Co₅₀, Pt₅₀Cu₅₀, and Pt₇₅Y₂₅ for respective alloys, surpassing that of monometallic platinum. Overall, Pt₅₀Co₅₀ emerged as a catalyst with the highest activity–stability ratio.