Oxygen Electrocatalysis on High-Surface Area at Non-Pt Modified Carbon Catalysts

Although a Pt/C electrocatalyst is the most widely used cathode material, there is a great interest in the development of more active catalysts for the oxygen electroreduction reaction (ORR). Promising results have been achieved by alloying Pt with non-noble metals [1]. In order to lower the cost of cathode catalysts, employing bi-metallic catalysts that combine platinum with other less expensive metals are under investigation [2,3].

The main aim of this work is to extend the previous study in order to characterize the ORR kinetics on non-Pt and Fe-Pt nanoparticles in alkaline media (0.1M KOH solution) using crystallographically and structurally different carbon supports.

The novel non-conventional micro-mesoporous carbide derived carbon powder, synthesized from molybdenum carbide (Mo₂C) at 750°C using the high-temperature chlorination method, and carbon aerogel (CAG) have been used as electrocatalyst supports for oxygen electroreduction. For comparison, the commercially available VulcanXC72^® has been used.

XRD, XRF and SEM methods were applied for structural and electronic characterization of the materials. Gas adsorption data at liquid nitrogen temperature were used for the porosity analysis of the materials under discussion (Table).

XRD patterns of the electrode materials were recorded on a Bruker D8 diffractometer (Bruker Corp.) employing CuKα radiation with a step size of 0.01° and counting time of 2 s using a position sensitive LynxEye detector. The diffraction spectrums were recorded at 25 °C.

XRD patterns of the obtained catalysts show the characteristic peaks (2q = 24.5^o) of carbon supports (presented in Figure). Analysis shows that the Fe-Pt nanoclusters have been deposited mainly as the face-centered cubic and face-centered tetragonal internal crystals at all carbon supports studied. The metal particles were distributed uniformly on the carbon supports. Both C(Mo2C) and CAG based catalysts are practically amorphous. However, there is a small amount of graphitic structure in all materials as well [4].

The RDE measurements were carried out in a three-electrode electrochemical cell. Several important reaction parameters, such as the number of electrons involved in the ORR, Tafel slopes, and the kinetic rate constant for the ORR, were obtained [5-9].

Potentials were measured against Hg|HgO|0.1M KOH reference electrode. RDE data were measured at rotation rates from 0 to 3000 rpm (v=10 mV∙s^-1) and in the region of potentials from +0.21 to -0.75 V vs. Hg|HgO|0.1M KOH. CVs were measured at potential scan rates (v mV/s) 5, 10, 20, 30, 50, 70, 100, 150 and 200, in both Ar and O₂ saturated solutions. The solutions were saturated with Ar or O₂, respectively, between measuring of each voltammogram.

Acknowledgements: This work was supported by the Estonian Centre of Excellence in Science Project TK117T "High-technology Materials for Sustainable Development", the Estonian Energy Technology Program project SLOKT 10209T, the Materials Technology project SLOKT12180T.

 

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