Pt3Ni supported on Co3O4 as a high performance electrocatalyst for ORR in alkaline fuel cells

Alkaline fuel cells as a promising energy sources have attracted remarkable interest amongst low–temperature fuel cells due to enhanced electrocatalysts stability and cell durability. Furthermore, operation in alkaline media allows use of fuels other than hydrogen, such as alcohols. Different kind of catalyst materials have been investigated as an electrocatalyst for fuel cell reaction. Platinum (Pt) is known as an affective electrocatalyst with great activity for oxygen reduction reaction (ORR), good electronic conductivity and stability. Nevertheless, high cost of Pt limits its extensive use in fuel cells. One approach to reduce the amount of Pt is to incorporate it with other transition metals such as nickel, cobalt, iron or copper. In this regard, PtNi/C has been extensively studied for various important electrochemical reactions, including ORR. Sakamoto et al. reported the ORR performance of Pt3Ni to be 10 fold higher than that of bare Pt in acid media. However, it is well-known that the rate of the electrochemical reaction is not only significantly affected by the catalytic activity of the used metal but also by the employed catalyst support. Carbon materials generally used as supports, such as Vulcan, offer high specific surface area, but have low involvement towards ORR. In this work, PtNi NPs were supported onto Co3O4 prepared by hydrothermal method. The probable synergistic phenoamena between transition metal oxide (Co3O4), Pt and Ni will be studied, in exploration of catalyst simultaneously active for ORR. The cobalt (II, III) oxide-supported platinum (Pt-Ni/Co3O4) catalyst was prepared employing a conventional impregnation method. A determined amount of Co3O4 powder was added to the Pt and Ni precursor solution and homogeneously dispersed by sonication for 40 min. The resulting suspension was then heated in a furnace at 250°C for 5 h under air atmosphere. Powdered samples. were cooled to room temperature and thoroughly mixed by grinding. The samples milled above were further sintered in an air atmosphere at 450° C for 2 h. 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 175 The catalytic inks were prepared by dispersing each electrocatalyst in 125 μL of 2% solution of polyvinylidene fluoride (PVDF, Alfa Aesar) in N-methyl-2-pyrrolidone (NMP, Sigma–Aldrich) and then ultrasonically treating them for ca. 30 min. PVDF was used to bind the electrocatalyst particles onto the conductive support in 125 μL of 2% solution of polyvinylidene fluoride (PVDF, Alfa Aesar) in N-methyl-2-pyrrolidone (NMP, Sigma–Aldrich) and then ultrasonically treating them for ca. 30 min. PVDF was used to bind the electrocatalyst particles onto the conductive support. For comparison purposes, CVs of Pt3Ni/Co3O4 and Pt/C were also recorded under the same conditions. The electrocatalytic performance of the as-prepared Pt3Ni/Co3O4 alloy catalyst, compared with commercial Pt/C, and the results are as shown in Figure 1. CVs of PtNi alloy( Figure 1) show typical Pt-like H underpotential deposition features, while the reduction peaks (∼0.86 V vs. RHE) in the cathodic scan for PtNi alloy have a positive shift compared to that of Pt/C catalyst (∼0.77 V vs. RHE). This shift can be attributed to the reduced adsorption forte of oxygenated species (−O or −OH) on alloy surfaces, and more essentially, due to the downshift of the d band center. The reduced surface coverage of oxides resulted in a a considerable improvement in the ORR catalytic performance for PtNi alloy catalyst, just as demonstrated by the positive shift (27mV) of half wave potentials in the polarization curves.